Genetic relationships between steer performance ... - CSIRO Publishing

CSIRO PUBLISHING

Animal Production Science, 2014, 54, 85–96 http://dx.doi.org/10.1071/AN13141

Genetic relationships between steer performance and female reproduction and possible impacts on whole herd productivity in two tropical beef genotypes M. L. Wolcott A,B,D, D. J. Johnston A,B, S. A. Barwick A,B, N. J. Corbet A,C and H. M. Burrow A,C A

Cooperative Research Centre for Beef Genetic Technologies, University of New England, Armidale, NSW 2351, Australia. B Animal Genetics and Breeding Unit1, University of New England, Armidale, NSW 2351, Australia. C CSIRO Livestock Industries, Rockhampton, Qld 4702, Australia. D Corresponding author. Email: [email protected]

Abstract. Steer growth and carcass composition, and female reproductive performance have been identified as key aspects of productivity by breeders of tropically adapted beef cattle in Australia. Research has also demonstrated that traits describing meat quality and feed intake and efficiency are of economic importance to Australia’s beef industry. The present study aimed to determine genetic relationships of traits describing steer growth, feed intake and efficiency, carcass composition and meat quality with female reproductive performance in two genotypes of tropically adapted beef cattle. Female reproduction traits describing outcomes of first (Mating 1) and second (Mating 2) annual matings and lifetime reproduction (averaged over 6 matings) were analysed for 1020 Brahman (BRAH) and 1117 Tropical Composite (TCOMP) females. Steer traits were available for 1007 BRAH and 1210 TCOMP half-sibs of the females evaluated for reproductive performance, and measurements of liveweight and body composition for 1025 BRAH and 1520 TCOMP bull progeny of the same females were included in the analysis. Results demonstrated that selection to increase steer carcass weight and eye muscle area and decrease carcass fat depth would have no significant unfavourable impact on female reproductive performance for both genotypes. Measures of liveweight, eye muscle area and P8 fat depth in young BRAH bulls, however, were only moderately correlated with steer carcass equivalents (rg = 0.28 to 0.55) and results showed that selection on the basis of bull measurements alone may negatively affect female lifetime annual calving rate (rg = –0.44 to –0.75) if both were not included in a multi-trait genetic evaluation and considered when making selection decisions. More favourable (lower) net feed intake in BRAH steers was genetically associated with lower Mating 1 weaning rate (rg = 0.76) and higher days to calving (rg = –0.50), although this did not significantly affect lifetime annual calving or weaning rate (rg = 0.10 and 0.29, respectively). For TCOMP, higher steer carcass P8 fat depth was unfavourably genetically associated with female Mating 2 weaning rate (rg = –0.76), although these relationships were not as strong for weaning rate at Mating 1 or when averaged over the animals lifetime (rg = 0.43 and –0.13, respectively). Lower (more favourable) shear force (a measure of tenderness) also displayed a significant genetic association with higher (less favourable) Mating 1 days to calving in TCOMP and, while standard errors were high, tended to be unfavourably associated with other measures of female reproduction evaluated for the present study. Steer growth, carcass composition, meat quality and residual feed intake and female reproduction could be improved simultaneously if measurements describing both are included in a multi-trait genetic evaluation. Results of the present study also showed that expanding female reproduction traits to include descriptors of first and second mating outcomes, as well as lifetime reproductive performance, would allow a fuller account to be taken of genetic relationships of male traits with female reproduction. Received 12 April 2013, accepted 2 August 2013, published online 8 October 2013

Introduction Steer sale weight and carcass composition and female weaning rate have been identified as key drivers of profitability for northern Australia’s beef producers (Anonymous 2010, 2011). Archer et al. (2004) also showed that economic benefit could be obtained at the industry level from evaluating and selecting for residual 1

feed intake (a measure of feed efficiency) for a range of production systems. A key component of the northern breeding project of the Beef Cooperative Research Centre (Burrow et al. 2003) was to establish whether selection could be undertaken to improve these elements of herd productivity and, importantly, whether

AGBU is a joint venture of NSW Department of Primary Industries and the University of New England.

Journal compilation CSIRO 2014

www.publish.csiro.au/journals/an

86

Animal Production Science

selection to improve male growth, feed efficiency and carcass traits could be undertaken without unfavourably affecting female reproduction in tropically adapted genotypes of beef cattle. Wolcott et al. (2009) reported that variation in traits describing carcass characteristics had a genetic basis, and that steer carcass weight and composition measures were moderately to strongly genetically associated with their live animal equivalents. Barwick et al. (2009b) demonstrated that residual feed intake (RFI) was moderately heritable in Brahman (BRAH) and Tropical Composite (TCOMP) steers and that traits describing steer liveweight and body composition measured before feedlot entry could be exploited as genetic indicators of RFI. Johnston et al. (2009, 2014a) examined the genetics of female puberty and reproductive performance at their first and second mating, and over their lifetime (lifetime reproduction traits in the present study described reproductive performance averaged over up to 6 matings). Consistent with the results of other studies (Meyer et al. 1990; Burrow 2001), those of Johnston et al. (2009, 2014a) showed that commonly measured descriptors of cow reproductive performance (days to calving, calving rate and weaning rate) were lowly to moderately heritable (h2 = 0.03 to 0.20), while biological mechanisms examined in the study which may underlie these, specifically age at puberty and lactation anoestrous interval, were more highly heritable (h2 = 0.26 to 0.57). In BRAH, steer RFI was negatively (unfavourably) genetically associated with age at puberty (rg = –0.60). Wolcott et al. (2014b) demonstrated that measures of growth and body composition in females before their first mating displayed consistently positive genetic relationships with first-mating outcomes, which were of sufficient magnitude to be exploited as genetic indicators of early reproductive performance. Studies evaluating genetic relationships between traits describing steer productivity and female reproduction are not common and are virtually absent for tropically adapted genotypes. Bourdon and Brinks (1982), MacNeil et al. (1984), Meyer et al. (1991) and Mialon et al. (2001) reported low to moderate positive genetic associations of higher male weight with female reproductive performance. Of these studies, only that of Meyer et al. (1991) included tropically adapted genotypes, for which the genetic correlation between bull liveweight and female days to calving ranged from –0.66 to –0.10. Oyama et al. (1996) reported positive genetic relationships between steer carcass fat depth and age at first calving, and negative relationships of carcass weight, eye muscle area and marble score with age at first calving in Wagyu animals. The present paper presents results from a large breeding project that examined aspects of the genetics of whole-herd profitability in northern Australia. The primary aim here was to identify any significant genetic antagonisms between steer traits and female reproduction, and to determine whether selection could be undertaken to simultaneously improve both of these in BRAH and TCOMP genotypes. Materials and methods Animals and measurements Animals used for this study were part of the northern breeding project of the Beef Cooperative Research Centre (Burrow et al.

M. L. Wolcott et al.

2003), with genotypes selected to represent the cattle populations managed in the semi-arid, subtropical and tropical environments of northern Australia. Briefly, 2159 females, 1027 BRAH and 1132 TCOMP, and 2216 steers (1007 BRAH and 1209 TCOMP) were born over a 4-year period (from 1999–2000 to 2002–2003) on eight co-operating properties, as a result of a combination of artificial insemination (AI) and natural mating, with 54 BRAH and 52 TCOMP sires represented. The TCOMP genotype comprised ~50% tropically adapted Bos indicus or African Sanga, and 50% non-adapted Bos taurus genetics. Use of AI sires ensured genetic linkage across years and breeding locations. A subset of the male progeny of the females described above (1639 BRAH and 2424 TCOMP, representing 136 sires) was retained as bulls for evaluation of male reproduction, growth and body composition traits. Cow reproduction traits, describing reproductive performance for the first and second annual matings, and averaged over six matings, and cow management over this period were described by Johnston et al. (2009, 2014a). Briefly, following weaning, female progeny were allocated to one of four research stations, with locations selected to be representative of the beef production environments of northern Australia (Barwick et al. 2009a). At each research station, heifers of a single birth year were managed in one group. Heifers were first mated to calve as 3-year olds, and every year subsequently for a total of six matings. Cows that failed to wean a calf for two consecutive years were removed from the experiment. Table 1 presents a brief description of female reproduction measurement times and traits. Reproductive outcomes of the first and second annual mating period are subsequently referred to as ‘Mating 1’ and ‘Mating 2’ traits, and those describing average reproductive performance calculated over up to six matings are subsequently referred to as ‘lifetime’ traits. Following weaning each year, steer progeny were transported to one of five grow-out properties where they were managed in a single group under pasture conditions, until they reached a group mean liveweight of 400 kg. Steers were then transported to a feedlot for finishing on a high-energy ration for an average of 119 days, with the aim of slaughtering animals at 540 kg to produce a 300-kg carcass. A subset of the steers (700 BRAH and 787 TCOMP) was allocated for feed-intake measurement to allow estimation of residual feed intake. Body composition and weight measurements collected in steers from weaning to feedlot exit were described by Barwick et al. (2009b), and those analysed for this experiment are described briefly in Table 1. Once steer groups achieved the designated average feedlot exit weight, they were transported, in complete management groups or allocated subsets thereof, to slaughter at one of two processing locations. Slaughter and meat-quality evaluation protocols were described by Perry and Thompson (2005) and carcass and meat-quality traits by Wolcott et al. (2009), with traits analysed for the present study being described in Table 1. Bull progeny of the females evaluated for reproductive performance were born over 7 years, from 2003 to 2009. Following weaning bulls were transported to one of two evaluation stations, with allocations to bull-research stations designed to maintain genetic linkage and genotype representation at both locations. At evaluation stations, bulls born in the same year were managed as a single contemporary

Genetics of whole-herd productivity


87

Table 1. Description of measurement times and trait definitions Parameter

Description

Measurement time Male body composition Measured when steers were removed from their dams (6.5 months). WeaningA Designated measurement time after steers were relocated to grow-out location (9 months). Post-weaningA Measurements collected on bull progeny at ~15 months of age. BullC Measurements collected on steers at feedlot entry (22 months). Feedlot entryA Measurements collected on steers at feedlot exit (25.5 months). Feedlot exitA Measurements collected on steers at slaughter (26 months). CarcassD Mating 1B Mating 2B LifetimeB

Female reproduction Measurements on females, describing the outcomes of their first annual 3-month mating period (27 months). Measurements on females, describing the outcomes of their second annual 3-month mating period (39 months). Lifetime reproduction traits calculated as averages of reproductive outcomes for up to six annual matings (36–95 months). Trait definition

Cow reproductionB PREG DC WEAN LAI

Pregnancy assessed by ultrasound pregnancy test (1 = pregnant, 0 = non-pregnant). Days from start of specified mating to subsequent calving, with cows which failed to calve assigned a penalty record. Cow weaning rate (1 = weaned a calf, 0 = failed to wean a calf). Interval between start of the second annual mating period and the estimated date (by ultrasound scanning to identify a corpus luteum) of first subsequent ovulation, in lactating cows only (days). WP Pregnant and weaned a calf (= 1) or not (= 0), assessed at mating 2 pregnancy testing for all cows. LACR Total number of calves born from Mating 1 and up to Mating 6, divided by the number of matings experienced (Meyer et al. 1990) for all cows from the start of Mating 1. LAWR Total number of calves weaned from Mating 1 and up to Mating 6, divided by the number of matings experienced for all cows from the start of Mating 1. SteerA and bullC growth and body composition WT Liveweight at specified measurement time measured using electronic weigh scales (kg). ADG Individual animal regression of steer liveweight on days over the period from weaning to feedlot entry (average of 9.0 liveweight records per animal), or on days while in the feedlot (average of 8.4 liveweight records per animal) (kg/day). EMA Real-time ultrasound-scanned area of the eye muscle (M. longissimus thoracis et lumborum (LTL)) between the 12th and 13th rib (cm2). P8 Real-time ultrasound-scanned subcutaneous fat depth at the P8 site on the rump (at the intersection of a line parallel to the spine from the tuber ischium and a line perpendicular to it from the spinous process of the third sacral vertebra) (mm). BCS Subjective body condition score on a 1–5 scale with plus and minus increments. Converted to a numeric variable such that 0.66 (1–) = very poor, 5.33 (5+) = very fat. HH Height of the animal at the hook, when standing squarely on a level surface (cm). IGF-I Concentration of insulin-like growth factor-I in serum (ng/mL). Steer feed intakeA DFI Electronically recorded average individual daily feed intake over an ~70-day test period (kg/day). RFI Residual feed intake calculated as daily feed intake less daily feed requirements based on growth and maintenance requirements (kg/day). Steer carcass and meat quality traitsD Carcass WT AUSMEAT standard hot carcass weight (kg) (AUSMEAT 1998). Carcass EMA EMA measured at the quartering site by Meat Standard Australia (MSA)-certified graders (cm2). Carcass P8 Cold P8 fat depth assessed on left sides after 12 h in a chiller by trained technicians (mm). RBY Retail beef yield measured as percentage of saleable product from a carcass fabricated to 17 boneless retail cuts trimmed to 4-mm external fat (%). HMP Hump height assessed by MSA-certified graders: measured as the greatest height of hump from the spinal column (mm). OSS Ossification score assesses age, as the degree of conversion of cartilage to bone at the sacral, lumbar and thoracic vertebrae: 50-point subjective score measured from 100 (young ~9 months) to 590 (old ~96 months or older). Assessed by MSA-certified graders. IMF Percentage of intramuscular fat measured by near infrared spectrophotometry from a sample of the eye muscle (%). MS Marble score assessed on a 100-point 1.0–10.0 scale by MSA grader. SF Average shear force for six samples of the LTL muscle measured using a 4-mm flat blade pulled upward through cooked samples at 100 mm/min at right angles to the fibre direction (kg). CMP Average compression measured as the product of hardness and cohesiveness for six samples of the cooked LTL. A blunt, cylindrical metal rod (6.3 mm in diameter) was forced through a cooked sample at 50 mm/min, twice in the same position (kg). LOSS Cooking loss measured as percentage difference in weight between a cooked and pre-cooked sample of the LTL. Cooking was for 60 min in a 70C water bath, followed by a 30-min cooling period (%). A

Adapted from Barwick et al. (2009b). Adapted from Johnston et al. (2014a). C Adapted from Corbet et al. (2013). D Adapted from Wolcott et al. (2009). B

88


group under pasture conditions. Bull measures were collected when contemporary groups averaged 15 months of age (447 and 472 days for BRAH and TCOMP, respectively), and included measurements of liveweight, ultrasound-scanned fat depth and eye muscle area, hip height, subjective body condition score and flight time. Burns et al. (2013) provided details of bull management and growth and body composition traits, and a brief description of traits analysed for the current study is presented in Table 1 (henceforth, the trait acronyms used are as per Table 1). Statistical analyses Modelling for each trait has been described in previous publications reporting the results of genetic analyses of female Mating 1, Mating 2 and lifetime reproduction (Johnston et al. 2014a), steer post-weaning to feedlot exit traits, which included steer feed intake and efficiency (Barwick et al. 2009b), steer carcass and meat-quality traits Wolcott et al. (2009) and bull growth and body composition traits (Corbet et al. 2013). Significant fixed effects for each trait, within genotype, were determined using PROC MIXED in SAS (SAS Institute, Cary, NC, USA), by considering main effects and first-order interactions, with sire fitted as random. Initial models for all traits included design variables describing the property of origin, location, year, month of birth and age of dam in years. For female reproduction traits describing outcomes of Mating 1 and Mating 2, fixed effects also included mating groups (i.e. the annual multisire mating group to which animals were allocated). For Mating 2 reproduction traits, previous mating group and lactation status at Mating 2 were also fitted, as well as terms describing the sex and age (in months) of their calf from Mating 1. Cows not calving from Mating 1 were allocated an additional level of the fixed effect describing previous calf effects. For LACR and LAWR, a ‘lifetime mating group’ was built which described all previous mating groups. For steer post-weaning IGF-I, a term was included which described the batch and plate associated with different runs of the enzyme-linked immunosorbent assay test, as described by Moore et al. (2005). Models for steer feedlot entry traits initially tested a term describing any splitting of year/location contemporaries (i.e. paddock allocations) that had occurred during the backgrounding phase. Models for feedlot exit traits tested feedlot pen allocations, which also identified whether animals were part of the subset allocated to feed intake testing. For carcass traits, date of kill was included in the initial models. For TCOMP, terms that described the genotype of their sire and dam were also tested. For each trait, models were stepped down by sequentially removing non-significant effects (P > 0.05) to yield final models, within genotype. For bivariate analyses, final models contained significant fixed effects, with animal and, where significant, the dam permanent environment effect fitted as random. Bivariate analyses were performed separately for BRAH and TCOMP. Following Johnston et al. (2014b), categorical female reproduction traits (PREG, WEAN and WP) were analysed assuming a normal distribution for the bivariate analyses. No selection was practiced that affected the female reproduction records available on cows. Although females that failed to wean a calf in consecutive years were removed from the


experiment, records for LACR and LAWR were available for all cows. To avoid very high standard errors being associated with estimates, the results reported were limited to female reproduction traits with heritability greater than 0.05 (LACR in TCOMP: h2 = 0.04), and to male traits with heritability greater than 0.10 In response to apparent differences in the genetic relationships of steer carcass and bull growth and body composition traits with female reproduction, genetic correlations were also estimated, within WT, P8 and EMA traits, between steer carcass and bull measures at 15 months of age. To provide additional insight into the genetic relationship of steer carcass P8 with aspects of TCOMP female reproduction, an analysis was performed to estimate the correlation of the maternal genetic component of weaning weight (an estimate of genetic milk production) with steer carcass P8 for that genotype. Details of weaning-weight data analysed and modelling for the trait are provided by Wolcott et al. (2014a). Genetic correlations were estimated using pairwise bivariate analyses in ASReml (Gilmour et al. 2009) for BRAH and TCOMP separately, with relationships between animals described by a pedigree of up to three generations. Results Genetic relationships of steer carcass traits and measurements of weight and body composition in young bulls with female reproduction are presented below. Measurements on young bulls represent the major source of growth and carcass composition data submitted for genetic evaluation in Australia for tropically adapted beef breeds (Anonymous 2012) and it is for this reason, that genetic relationships with bull traits are reported here. Relationships of male traits with female reproduction in Brahmans Tables 2–4 present genetic correlations of BRAH steer and bull traits with female reproduction. Genetic relationships of BRAH steer carcass WT with female reproduction were low to moderate and universally not significantly different from zero (Table 2). Steer feedlot exit and entry WT and HH, and both measures of ADG, followed this trend, although there was a moderate negative genetic relationship of steer feedlot entry WT with Mating 2 PREG (rg = –0.46) which was reflected by the negative correlation of –0.40 between steer feedlot entry WT and LACR. WT measured in bulls at 15 months of age displayed a negative genetic relationship with LACR (rg = –0.74) which was supported by negative relationship of LACR with bull EMA, P8 and BCS (rg = –0.52, –0.44 and –0.37, respectively). These results were consistent with only moderate genetic relationships of steer carcass and bull measures of LWT, EMA and P8 (rg = 0.28 0.27, 0.55 0.29 and 0.43 0.28, respectively) observed for BRAH (results not tabulated). There was a trend for relationships of male weights with LAWR to be of lower magnitude than those observed for LACR, and only negative for male weight measures for steers at feedlot entry and in bulls at 15 months of age (rg = –0.19 and –0.35, respectively). Male EMA in BRAH, with the exception of the trait measured in bulls at 15 months, displayed consistently moderate and positive genetic associations with female Mating 1 PREG and WEAN (rg = 0.38 to 0.75), and negative (favourable) correlations with Mating 1 DC (rg = –0.29


Table 2.


89

Genetic correlations of Brahman male growth, hip height and eye muscle area with female reproduction traits (þs.e. in parentheses) See Table 1 for a description of steer and bull traits and female reproduction traits

Steer and bull trait

Mating 1 reproduction PREG DC WEAN

Bull 15 months

–0.18 (0.16) 0.02 (0.28) –0.06 (0.24) –0.03 (0.23)

0.09 (0.19) –0.20 (0.31) –0.13 (0.27) –0.13 (0.26)

0.03 (0.27) –0.04 (0.38) 0.24 (0.33) 0.21 (0.32)

–0.12 (0.15) 0.11 (0.27) –0.21 (0.22) –0.11 (0.22)

WT –0.06 (0.18) –0.46 (0.24) –0.21 (0.24) –0.23 (0.23)

0.10 (0.22) 0.30 (0.29) –0.11 (0.27) –0.08 (0.26)

–0.17 (0.23) –0.34 (0.31) –0.03 (0.28) –0.06 (0.28)

–0.01 (0.15) –0.23 (0.26) –0.02 (0.23) –0.10 (0.22)

–0.74 (0.26) –0.40 (0.31) –0.15 (0.29) –0.16 (0.28)

–0.35 (0.27) –0.19 (0.35) 0.09 (0.31) 0.04 (0.30)

–0.26 (0.21) –0.22 (0.28)

0.08 (0.25) 0.05 (0.32)

0.21 (0.32) –0.48 (0.36)

–0.08 (0.22) 0.07 (0.28)

ADG –0.15 (0.23) –0.23 (0.28)

–0.10 (0.26) 0.17 (0.31)

–0.05 (0.27) –0.15 (0.33)

0.01 (0.23) –0.36 (0.26)

–0.07 (0.28) –0.30 (0.33)

0.16 (0.29) –0.40 (0.35)

0.15 (0.14) 0.13 (0.24) –0.12 (0.23)

–0.33 (0.18) –0.11 (0.28) 0.16 (0.26)

0.44 (0.29) 0.25 (0.33) 0.20 (0.32)

–0.16 (0.13) –0.47 (0.20) –0.26 (0.21)

0.08 (0.15) 0.18 (0.24) –0.05 (0.23)

–0.01 (0.019) –0.24 (0.26) –0.06 (0.26)

–0.10 (0.20) 0.24 (0.28) 0.03 (0.28)

0.16 (0.13) 0.30 (0.23) 0.05 (0.22)

–0.10 (0.26) 0.11 (0.30) –0.27 (0.26)

0.03 (0.30) 0.19 (0.30) 0.08 (0.30)

0.08 (0.16) 0.45 (0.25) 0.38 (0.37) 0.43 (0.25)

0.01 (0.19) –0.50 (0.27) –0.53 (0.51) –0.29 (0.31)

0.55 (0.35) 0.75 (0.32) 0.51 (0.50) 0.52 (0.36)

–0.24 (0.16) –0.11 (0.26) –0.01 (0.37) 0.26 (0.27)

EMA 0.06 (0.18) –0.07 (0.27) –0.44 (0.35) –0.35 (0.26)

–0.03 (0.21) 0.21 (0.3) 0.18 (0.48) 0.14 (0.31)

–0.05 (0.23) –0.15 (0.31) –0.24 (0.43) –0.28 (0.32)

0.15 (0.16) 0.13 (0.26) –0.03 (0.36) –0.33 (0.26)

–0.52 (0.26) –0.01 (0.33) –0.17 (0.45) –0.13 (0.34)

–0.10 (0.28) –0.01 (0.34) –0.30 (0.46) –0.14 (0.36)

Feedlot entry Feedlot exit Carcass

Wean to entry Entry to exit

LAI


WP

Lifetime reproduction LACR LAWR

HH Bull 15 months Feedlot entry Feedlot exit

Bull 15 months Feedlot entry Feedlot exit Carcass

to –0.50), although there was a slight trend for steer feedlot exit and carcass EMA to be negatively genetically related to Mating 2 PREG and WEAN (rg = –0.28 to –0.44). Brahman steer BCS at feedlot exit showed clear genetic antagonisms with female Mating 2 reproduction, being negatively correlated with PREG, WEAN and WP (rg = –0.77, –0.92 and –0.69, respectively) and positively correlated with LAI and DC (rg = 0.57 and 0.60). This was reflected in a negative genetic relationship of steer feedlot exit BCS with LACR (rg = –0.43), though there was no relationship with LAWR (rg = –0.09). Genetic relationships of BRAH steer P8 (Table 3), a key component of subjectively assessed BCS, with female Mating 2 reproduction reflected the unfavourable relationships observed for BCS though were not as strong (rg = -0.28 to -0.57 for steer feedlot exit and carcass P8 with Mating 2 WEAN and PREG). Some reflection of the results for BCS can also be seen in the relationships of feedlot exit and carcass EMA with cow Mating 2 performance, though these were not as strong. Measures of blood IGF-I concentration in young steers, at post-weaning and feedlot entry, displayed favourable genetic relationships with female Mating 1 reproduction, being positive with PREG and WEAN (rg = 0.41–0.60) and negative with DC (rg = –0.48 and –0.32 respectively).

Measures of DFI and RFI were significantly and positively genetically associated with female Mating 1 WEAN (rg = 0.68 and 0.76 respectively), and negatively associated with Mating 1 DC (rg = –0.34 and –0.50 respectively). These trends were reversed and relationships were of lower magnitude for Mating 2 reproduction, with a low to moderate and consistently nonsignificant relationship of DFI and RFI with LACR and LAWR (rg = 0.10 to 0.39). The genetic relationships of meat-quality traits (IMF, MARB, SF and CMP) with Mating 1 female reproduction (Table 4) were positive with PREG and WEAN (rg = 0.00 to 0.61) and negative with DC (rg = –0.40 to –0.13), and relationships with LACR and LAWR were low to moderate and positive (rg = 0.00 to –0.38). For Mating 2, relationships were of lower magnitude and the consistency of sign within female reproduction traits observed for Mating 1 and lifetime correlations was not present (rg = –0.39 to 0.27). Relationships of male traits with female reproduction in TCOMP Tables 5–7 present genetic correlations of TCOMP steer and bull traits with female reproduction. Genetic correlations of TCOMP steer carcass WT and EMA (Table 5) with female reproductive

90



Table 3. Genetic correlations of Brahman male fat depth, body condition score, blood IGF-I concentration, flight time and feed intake with female reproduction traits (þs.e. in parentheses) See Table 1 for a description of steer and bull traits and female reproduction traits Steer and bull trait

Bull 15 months Feedlot exit Carcass

Bull 15 months Feedlot exit

Post-weaning Feedlot entry Feedlot exit

Post-weaning Bull 15 months

DFI RFI


LAI


WP

Lifetime reproduction LACR LAWR

–0.29 (0.16) –0.15 (0.24) 0.09 (0.23)

0.34 (0.20) 0.07 (0.26) 0.02 (0.26)

–0.42 (0.29) –0.19 (0.33) –0.23 (0.33)

P8 fat –0.19 0.06 (0.16) (0.18) 0.53 –0.57 (0.21) (0.20) 0.47 –0.35 (0.21) (0.23)

–0.19 (0.21) 0.42 (0.25) 0.33 (0.25)

0.08 (0.23) –0.41 (0.26) –0.28 (0.27)

–0.01 (0.16) –0.53 (0.21) –0.56 (0.20)

–0.44 (0.25) –0.28 (0.29) –0.09 (0.29)

–0.18 (0.28) 0.02 (0.30) –0.03 (0.30)

–0.18 (0.17) –0.09 (0.32)

0.23 (0.20) –0.05 (0.36)

–0.42 (0.26) –0.20 (0.44)

BCS –0.13 (0.16) 0.57 (0.29)

0.05 (0.19) –0.77 (0.33)

–0.19 (0.21) 0.60 (0.40)

0.23 (0.22) –0.92 (0.36)

–0.11 (0.16) –0.69 (0.32)

–0.37 (0.30) –0.43 (0.41)

–0.06 (0.29) –0.09 (0.32)

0.47 (0.22) 0.41 (0.23) –0.13 (0.28)

–0.48 (0.25) –0.32 (0.27) 0.12 (0.32)

0.44 (0.31) 0.60 (0.33) 0.50 (0.39)

IGF-I –0.56 0.33 (0.20) (0.24) –0.31 0.11 (0.25) (0.26) –0.10 –0.16 (0.27) (0.27)

–0.25 (0.28) –0.09 (0.29) 0.02 (0.32)

0.34 (0.28) 0.16 (0.30) 0.01 (0.33)

0.45 (0.21) 0.16 (0.24) –0.09 (0.27)

0.37 (0.30) 0.32 (0.30) 0.26 (0.34)

0.32 (0.31) 0.07 (0.32) 0.24 (0.36)

0.48 (0.36) –0.10 (0.17)

–0.39 (0.39) 0.28 (0.22)

0.57 (0.47) –0.49 (0.30)

Flight time 0.11 0.02 (0.40) (0.41) –0.10 0.25 (0.16) (0.017)

–0.10 (0.45) –0.28 (0.21)

0.43 (0.47) 0.25 (0.22)

0.13 (0.38) –0.01 (0.15)

0.47 (0.46) –0.19 (0.26)

0.45 (0.47) 0.19 (0.29)

0.06 (0.24) 0.36 (0.29)

–0.34 (0.27) –0.50 (0.33)

0.68 (0.33) 0.76 (0.38)

Feed test –0.11 –0.19 (0.24) (0.25) 0.23 –0.28 (0.29) (0.30)

–0.06 (0.28) 0.56 (0.32)

–0.11 (0.29) –0.43 (0.33)

0.09 (0.24) –0.03 (0.29)

0.15 (0.30) 0.10 (0.36)

0.39 (0.29) 0.29 (0.37)

Table 4. Genetic correlations of Brahman steer carcass and meat-quality traits with female reproduction (þs.e. in parentheses) See Table 1 for a description of steer carcass and female reproduction traits Steer carcass trait RBY HMP OSS IMF MARB SF CMP


LAI

–0.64 (0.29) –0.26 (0.29) –0.36 (0.22) –0.28 (0.30) –0.13 (0.29) –0.27 (0.26) –0.40 (0.28)

0.51 (0.30) 0.24 (0.26) –0.39 (0.20) –0.27 (0.24) 0.02 (0.25) –0.23 (0.23) –0.39 (0.29)

0.63 (0.26) 0.14 (0.26) 0.16 (0.21) 0.35 (0.26) 0.20 (0.25) 0.00 (0.23) 0.34 (0.26)

0.25 (0.47) 0.31 (0.35) 0.41 (0.27) 0.07 (0.37) 0.21 (0.36) 0.39 (0.32) 0.61 (0.32)

performance were consistently low to moderate and described no significantly unfavourable relationships (rg = –0.35 to 0.46). Measures of WT, ADG and EMA in live steers and bulls followed

Mating 2 reproduction PREG DC WEAN –0.30 (0.37) –0.16 (0.26) 0.22 (0.22) –0.17 (0.26) –0.15 (0.26) 0.05 (0.24) –0.02 (0.28)

0.38 (0.40) –0.08 (0.30) –0.12 (0.25) –0.19 (0.30) –0.15 (0.29) –0.01 (0.26) 0.02 (0.31)

–0.56 (0.38) 0.20 (0.31) 0.29 (0.25) –0.09 (0.31) 0.02 (0.30) 0.17 (0.27) 0.16 (0.33)

WP –0.45 (0.31) –0.22 (0.24) 0.24 (0.20) –0.13 (0.25) –0.20 (0.24) 0.15 (0.22) 0.21 (0.27)

Lifetime reproduction LACR LAWR 0.32 (0.42) 0.28 (0.32) 0.13 (0.27) 0.26 (0.34) 0.17 (0.32) 0.04 (0.29) 0.00 (0.34)

–0.71 (0.44) 0.56 (0.30) 0.23 (0.28) 0.14 (0.34) 0.16 (0.33) 0.27 (0.28) 0.38 (0.33)

these trends. Higher steer HH at feedlot exit in TCOMP tended to be associated with lower female Mating 1 PREG and higher DC (rg = –0.64 and 0.37, respectively), although this was not as


Table 5.

91

Genetic correlations of Tropical Composite male growth, hip height and eye muscle area with female reproduction traits (þs.e. in parentheses) See Table 1 for a description of steer and bull traits and female reproduction traits

Steer and bull trait


Wean to entry Entry to exit

Bull 15 months Feedlot entry Feedlot exit




LAI


WP

Lifetime reproduction LAWR

–0.20 (0.22) –0.31 (0.27) –0.06 (0.27) –0.35 (0.30)

–0.02 (0.19) 0.03 (0.28) –0.10 (0.26) 0.16 (0.29)

0.12 (0.24) –0.27 (0.32) 0.08 (0.31) 0.16 (0.34)

WT 0.04 (0.16) 0.24 (0.26) 0.12 (0.24) 0.10 (0.26)

–0.28 (0.26) –0.04 (0.40) –0.12 (0.37) –0.03 (0.39)

–0.05 (0.19) 0.01 (0.29) –0.01 (0.26) –0.22 (0.27)

–0.09 (0.26) 0.27 (0.36) 0.10 (0.34) 0.21 (0.36)

–0.14 (0.19) –0.24 (0.24) –0.06 (0.23) –0.01 (0.27)

–0.17 (0.26) –0.25 (0.33) –0.06 (0.42) 0.08 (0.35)

–0.32 (0.30) 0.09 (0.28)

0.19 (0.29) –0.09 (0.27)

0.01 (0.35) 0.30 (0.32)

ADG 0.32 (0.25) 0.01 (0.26)

–0.25 (0.40) 0.04 (0.38)

0.05 (0.29) –0.15 (0.27)

0.16 (0.39) 0.15 (0.35)

–0.11 (0.27) 0.14 (0.24)

–0.19 (0.35) –0.17 (0.43)

–0.17 (0.19) –0.34 (0.30) –0.64 (0.25)

0.15 (0.17) 0.06 (0.30) 0.37 (0.28)

–0.01 (0.22) –0.27 (0.35) –0.20 (0.35)

HH 0.12 (0.14) –0.16 (0.27) –0.16 (0.28)

–0.08 (0.25) 0.00 (0.41) 0.14 (0.42)

–0.04 (0.18) –0.26 (0.28) –0.39 (0.29)

0.10 (0.27) 0.24 (0.37) 0.45 (0.39)

–0.10 (0.17) –0.14 (0.28) –0.04 (0.28)

–0.27 (0.22) –0.38 (0.36) –0.36 (0.35)

–0.07 (0.21) 0.03 (0.28) –0.13 (028) 0.43 (0.25)

0.09 (0.20) 0.03 (0.27) 0.24 (0.26) 0.03 (0.30)

–0.20 (0.25) –0.06 (0.32) –0.19 (0.32) –0.07 (0.36)

EMA 0.05 (0.16) 0.41 (0.23) 0.47 (0.25) 0.46 (0.28)

0.07 (0.28) 0.14 (0.37) –0.12 (0.39) 0.02 (0.42)

–0.15 (0.19) 0.07 (0.26) 0.05 (0.27) –0.16 (0.30)

0.23 (0.28) 0.05 (0.35) –0.05 (0.36) 0.26 (0.38)

–0.13 (0.18) –0.11 (0.25) –0.22 (0.24) –0.12 (0.28)

–0.26 (0.27) –0.13 (0.33) –0.21 (0.34) –0.10 (0.37)

strong for Mating 1 WEAN, LARC or LAWR (rg = –0.38 to –0.20), and standard errors for these relationships were high. There were significant genetic relationships for TCOMP between steer carcass P8 and female Mating 2 reproduction, being negative with Mating 2 PREG, WEAN and WP (rg = –0.73, –0.76 and –0.16, respectively) and positive with LAI and DC (rg = 0.78 and 0.57, respectively). In contrast, there tended to be a favourable genetic relationship of lower carcass P8 measures with female Mating 1 reproduction, and a ‘net’ relationship of P8 with LAWR, which was consistently not significantly different from zero. For TCOMP, there was a moderate and positive correlation between the maternal genetic component of weaning weight (genetic milk) and steer carcass P8 (rg = 0.39 0.17, results not tabulated), which may provide some insight into the genetic relationship of higher steer carcass P8 with Mating 2 reproduction observed for this genotype. For TCOMP, the similarity between genetic relationships of steer and bull measures with female reproduction were consistent with positive and moderate to high genetic correlations of steer carcass WT, P8 and EMA with corresponding bull traits (rg = 0.84 0.16, 0.72 0.36 and 0.43 0.18, respectively) (results not tabulated). BCS in TCOMP tended to follow the trends of P8, although relationships were not as strong as those observed for P8. Higher steer IGF-I

was consistently genetically associated with higher Mating 1 and 2 PREG and WEAN, WP and lifetime annual weaning rates (rg = 0.29 to 0.73), and lower Mating 1 and 2 DC, and LAI (rg = –0.10 to –0.50). Measures of DFI and RFI (Table 6) displayed low to moderate genetic relationships with female reproduction, which were consistently not significantly different from zero (rg = –0.14 to 0.48). Relationships between female reproduction and steer meatquality traits for TCOMP (Table 7), which included cooking loss for this genotype, tended to be of higher magnitude than those for BRAH. For TCOMP, CMP and LOSS displayed almost no relationship with Mating 1 traits (rg = –0.21 to 0.15), but correlations were of higher magnitude with Mating 2 female reproduction, where they were positively associated with DC (rg = 0.31 and 0.96, respectively) and negatively associated with PREG, WEAN and WP (rg = –0.05 to –1.00). LOSS also displayed a moderate negative genetic association with LACR (rg = –0.49) for this genotype. While for TCOMP, there were some strong genetic relationships of steer meat-quality traits with female reproductive performance (particularly at Mating 2), standard errors were also high and care is recommended in the interpretation of these relationships. In contrast, IMF, MARB and SF were all positively genetically associated with Mating 1

92



Table 6. Genetic correlations of Tropical Composite male fat depth, body condition score, blood IGF-I concentration, flight time and feed intake with female reproduction traits (þs.e. in parentheses) See Table 1 for a description of steer and bull traits and female reproduction traits Steer and bull trait

Bull 15 months Feedlot exit Carcass

Bull 15 months Feedlot exit

Feedlot entry Feedlot exit

Post-weaning Bull 15 months

DFI RFI



LAI

WP


0.25 (0.32) 0.08 (0.27) 0.20 (0.29)

–0.18 (0.31) –0.41 (0.23) –0.58 (0.23)

0.34 (0.41) 0.35 (0.31) 0.43 (0.33)

P8 fat 0.19 –0.72 (0.29) (0.48) 0.24 –0.40 (0.30) (0.40) 0.78 –0.73 (0.20) (0.46)

0.70 (0.26) 0.05 (0.26) 0.57 (0.24)

–0.50 (0.43) –0.16 (0.35) –0.76 (0.33)

–0.22 (0.31) 0.03 (0.24) –0.16 (0.26)

–0.59 (0.46) –0.19 (0.32) –0.14 (0.36)

0.10 (0.28) –0.39 (0.30)

–0.19 (0.26) –0.12 (0.31)

0.04 (0.31) 0.19 (0.37)

BCS 0.39 (0.27) 0.28 (0.27)

–0.29 (0.42) –0.42 (0.43)

0.28 (0.26) 0.16 (0.30)

–0.39 (0.38) –0.44 (0.38)

–0.32 (0.28) –0.11 (0.28)

–0.11 (0.40) –0.34 (0.35)

0.42 (0.38) 0.36 (0.34)

–0.50 (0.35) –0.10 (0.33)

0.36 (0.43) 0.33 (0.37)

IGF-I –0.48 (0.32) –0.24 (0.29)

0.36 (0.50) 0.29 (0.42)

–0.22 (0.36) –0.24 (0.31)

0.60 (0.52) 0.67 (0.29)

0.47 (0.32) 0.45 (0.27)

0.73 (0.49) 0.37 (0.39)

–0.11 (0.40) 0.11 (0.27)

–0.03 (0.39) –0.14 (0.25)

0.34 (0.46) 0.08 (0.31)

Flight time 0.35 0.43 (0.35) (0.49) –0.03 –0.26 (0.19) (0.33)

–0.26 (0.38) 0.18 (0.21)

0.48 (0.45) –0.32 (0.30)

0.03 (0.39) –0.17 (0.21)

0.26 (0.46) 0.21 (0.35)

0.09 (0.29) –0.09 (0.33)

–0.30 (0.26) –0.11 (0.30)

0.22 (0.32) 0.09 (0.36)

Feed test –0.03 (0.27) 0.04 (0.29)

–0.20 (0.28) –0.12 (0.31)

–0.03 (0.38) –0.34 (0.41)

0.12 (0.25) 0.10 (0.27)

0.04 (0.35) –0.07 (0.38)

–0.02 (0.40) –0.13 (0.42)

Table 7. Genetic correlations of Tropical Composite steer carcass and meat-quality traits with female reproduction (þs.e. in parentheses) See Table 1 for a description of steer carcass and female reproduction traits Steer carcass trait RBY OSS IMF MARB SF CMP LOSS

Mating 1 reproduction PREG DC WEAN 0.05 (0.41) 0.13 (0.28) 0.20 (0.29) 0.20 (0.29) 0.38 (0.29) –0.08 (0.34) 0.04 (0.32)

0.20 (0.39) –0.01 (0.27) –0.33 (0.26) –0.11 (0.28) –0.56 (0.25) 0.15 (0.33) 0.00 (0.31)

0.22 (0.47) –0.04 (0.33) 0.50 (0.34) 0.42 (0.32) 0.47 (0.34) –0.21 (0.38) 0.02 (0.37)

LAI 0.13 (0.38) –0.38 (0.24) –0.23 (0.23) –0.34 (0.25) –0.09 (0.28) –0.12 (0.32) 0.39 (0.27)

and 2 PREG, and WEAN, as well as WP and LAWR (rg = 0.19 to 0.53), and negatively correlated with Mating 1 and 2 DC and LAI (rg = –0.56 to –0.09). For TCOMP, genetic relationships

Mating 2 reproduction PREG DC WEAN 0.08 (0.55) –0.26 (0.40) 0.38 (0.33) 0.25 (0.40) 0.50 (0.41) –0.43 (0.45) –0.85 (0.39)

0.02 (0.39) 0.17 (0.28) –0.32 (0.24) –0.20 (0.29) –0.36 (0.28) 0.31 (0.32) 0.96 (0.20)

0.23 (0.52) –0.16 (0.37) 0.33 (0.34) 0.19 (0.37) 0.52 (0.36) –0.32 (0.43) –1.00 (0.37)

WP


0.02 (0.36) 0.09 (0.24) 0.53 (0.22) 0.49 (0.23) 0.50 (0.23) –0.05 (0.30) –0.32 (0.26)

0.70 (0.45) –0.34 (0.35) 0.32 (0.34) 0.26 (0.35) 0.33 (0.33) –0.08 (0.41) –0.49 (0.35)

between female reproduction and steer RBY were generally of lower magnitudes than those observed for BRAH, and universally positive (rg = 0.02 to 0.70), with high standard errors.


Discussion Genetic relationships of male growth and body composition with female reproduction Genetic relationships of steer carcass WT and EMA with female reproduction in both genotypes suggest that selection for these could be undertaken without significant unfavourable consequences for female reproductive performance. Meyer et al. (1991) reported no genetic antagonism of bull 400- and 600-day weights with days to calving evaluated over multiple parities, in genotypes similar to the TCOMP examined for the present study (rg = –0.10 to –0.66), which supported the results for Mating 1 and 2 DC in the current study. Mialon et al. (2001) reported low and negative genetic relationships of Charolais cow lactation anoestrous interval with bull weight (rg = –0.14), which was also consistent with the results presented here for BRAH (rg = –0.12). While standard errors were high, there was a difference in the genetic relationship of steer carcass P8 with female reproductive performance in BRAH and TCOMP. For BRAH and TCOMP, selection to reduce steer carcass P8 will be genetically associated with higher female Mating 2 reproduction. For TCOMP, this may be genetically associated with lower Mating 1 performance, where for BRAH results suggested that Mating 1 reproduction would not be impacted by selection to change steer carcass P8. The non-significant relationships of steer carcass P8 with LAWR, however, suggests that, overall, selection to reduce steer carcass fatness could be undertaken without significantly affecting lifetime female reproduction for either genotype. In TCOMP, there was a moderate and positive relationship of the maternal genetic component of weaning weight (genetic milk) with steer carcass P8 (rg = 0.39 0.17, results not tabulated), and higher maternal weaning weight was shown by Wolcott et al. (2014b) to be unfavourably genetically related to female Mating 2 reproductive performance in TCOMP (rg = 0.40, –0.72, 0.45 and –0.58 with Mating 2 LAI, PREG, DC and WEAN, respectively, and –0.26 with LAWR). The consistency of these relationships with those presented for steer carcass P8 in the present study, in association with the moderate and significant genetic relationship of the trait with maternal weaning weight for this genotype, may indicate that steer carcass P8 is acting as a genetic indicator of maternal weaning weight in this instance. Mialon et al. (2001) reported a low and negative genetic relationship of Charolais bull carcass fat percentage with cow lactation anoestrous interval (rg = –0.13), which was consistent with the results for bull P8 from the current study. Meyer and Johnston (2003) reported low and negative genetic relationships between days to calving (over multiple parities) and ultrasound measured fat depth in young Hereford bulls and heifers (rg = –0.04 to –0.08), which were in contrast to the generally stronger relationships of steer and bull P8 with Mating 1 and 2 DC observed for the tropical genotypes examined in the current study. The trend for WT, EMA, P8 and BCS measures in BRAH bulls at 15 months of age, to be negatively genetically related to cow lifetime reproduction (particularly LACR) was less apparent for Mating 1 and 2 reproductive performance, suggesting that unfavourable reproductive outcomes associated with bull traits must have primarily affected the outcomes of Matings 3–6. The genetic relationships of bull traits with the corresponding steer


93

carcass WT, EMA and P8 (rg = 0.28 0.29, 0.55 0.29 and 0.43 0.28, respectively) in BRAH (results not tabulated) suggest that measures of these in young bulls can be treated as only moderately correlated with their steer carcass equivalents in a multi-trait genetic evaluation. These results were lower than those reported by Devitt and Wilton (2001) for genetic correlations of age-constant bull scanned P8 fat depth and eye muscle area with steer carcass equivalents (rg = 0.88 and 0.66, respectively) in animals of diverse genotypes. Reverter et al. (2000) reported strong genetic relationships of bull ultrasound P8 with steer carcass P8 in Angus and Herefords (rg = 0.82 for both breeds), but more variable correlations for EMA (rg = 0.29 and 0.94 for Angus and Herefords, respectively). Because measurements in young bulls are the dominant source of weight and carcass information submitted to Australia’s national genetic evaluation (BREEDPLAN), this is an important result, and shows that selection to increase these traits may have negative genetic implications for female lifetime reproduction. Subsequent research will examine the genetics of mature cow weight and body composition, and their relationship with female reproductive performance, which may improve our understanding of these relationships. For TCOMP, results suggest that selection to increase male HH may result in lower female Mating 1 and lifetime reproductive performance (although only the correlation of steer feedlot exit HH with Mating 1 PREG was different from zero). Wolcott et al. (2014b) reported a negative genetic relationship between female Mating 1 reproduction and HH measured in the TCOMP females evaluated for the present study before their first mating, which was consistent with the results seen here for steers. Gargantini et al. (2005) reported a negative genetic correlation (rg = –0.48) between HH measured in yearling bulls of diverse genotypes and Mating 1 pregnancy rate, which was consistent with the results of the current study for TCOMP. For BRAH, increased male HH displayed no significant genetic antagonisms with female reproduction. The strongest relationships between BRAH male HH and female reproduction were with LAI, where selection to increase male HH, particularly in steers at feedlot entry, was genetically associated with lower (more favourable) LAI. Future research will examine the genetics of mature cow growth and body composition traits (including HH), and the relationship of these with female reproductive performance, which may provide additional insight into the different relationship of HH with female reproduction observed in BRAH and TCOMP. For both genotypes, higher (more desirable) steer postweaning FT was favourably genetically associated female reproduction. These results suggest that selection to improve temperament, by increasing flight time, could be undertaken in both genotypes with little risk of unfavourable genetic consequences for female reproduction. Genetic relationships of male IGF-I and feed intake with female reproduction With the exception of measurements in BRAH steers at feedlot exit, genetically higher IGF-I in steers was associated with higher Mating 1, Mating 2 and lifetime female reproduction in BRAH and TCOMP. For both genotypes, the results were consistent with those obtained for measures of IGF-I in the females evaluated for

94


the present study as heifers (Wolcott et al. 2014b), where, for example, the genetic relationship of Mating 1 and Mating 2 weaning rate with heifer IGF-1 measured at the end of their first post-weaning wet season was moderate and positive (rg = 0.43 and 0.40 for BRAH and 0.28 and 0.48 for TCOMP, respectively). These results were also consistent with the negative genetic relationship observed between BRAH heifer measures of IGF-I and age at puberty reported by Johnston et al. (2009) (rg = –0.70 and –0.43 for IGF-I measured at the end of their first post-weaning wet season and second post-weaning dry season, respectively). Garcia-Garcia (2012) demonstrated that lower IGF-I concentrations could be associated with low energy balance and play an inhibitory role in regulating the onset of puberty, which may provide some insight into the relationships observed in the current study. Barwick et al. (2014) examined the expectations for genetic progress in BRAH female reproductive performance on the basis of multi-trait selection that incorporated the genetic relationships presented in this and associated studies (Corbet et al. 2013; Johnston et al. 2014a, 2014b; Wolcott et al. 2014a, 2014b). The results showed that IGF-I measured in BRAH bulls at weaning (6 months of age) and in heifers at the end of their first post-weaning wet season (18 months of age) could be useful indicators of female age at puberty in a multi-trait analysis but less so for later measures of female reproduction, which was consistent with the results presented here for steers. Lower (more favourable) steer RFI was genetically associated with lower female Mating 1 reproductive performance, a tendency towards higher Mating 2 female reproduction and had little impact on lifetime reproduction (although standard errors were high). The unfavourable genetic associations of lower BRAH steer RFI with Mating 1 reproduction were consistent with the significant genetic relationship of lower steer RFI with higher heifer age at puberty (rg = –0.60) reported for these same animals by Johnston et al. (2009), given that higher age at puberty was significantly genetically related to lower Mating 1 reproduction for this genotype (Johnston et al. 2014b). These results were also consistent with those of Crowley et al. (2011) who reported a genetic correlation of –0.29 between RFI measured in young Bos taurus bulls and age at first calving in related females. Pitchford (2004), in reviewing genetic relationships of female reproduction with feed efficiency in non-bovine species, also concluded that there was evidence for an unfavourable genetic relationship between these traits. For BRAH, the genetic association of female EMA with steer RFI may provide some insight into the relationship observed between steer RFI and female mating 1 reproductive performance. Barwick et al. (2009a) showed that lower steer RFI was genetically associated with lower female EMA measured at the end of their first post-weaning wet season and second post-weaning dry season (rg = 0.75 and 0.66, respectively), and Wolcott et al. (2014b) demonstrated that lower EMA in heifers at the end of their first post-weaning wet season was genetically correlated with lower Mating 1 reproductive performance in BRAH (rg = 0.44, –0.35 and 0.58 with Mating 1 PREG, DC and WEAN, respectively). Barwick et al. (2009a) suggested that the negative genetic association of RFI with female EMA could reflect negative energy balance and be deleterious to female performance. The possible inhibitory role of low energy


balance in regulating the onset of puberty has been recognised by (Garcia-Garcia 2012). Selection to improve BRAH steer feed efficiency (reduce RFI) may, therefore, produce females that are genetically predisposed to a delayed onset of puberty due to lower energy balance at this stage of their development, which has a correlated and unfavourable genetic impact on Mating 1 reproductive performance. For both genotypes, DFI showed relationships with female reproductive performance that tended to mirror the magnitude and direction of those reported for RFI, and were consistent with the positive genetic correlation of DFI with RFI (rg = 0.59) reported by Barwick et al. (2009b). For TCOMP, genetic relationships of DFI and RFI with female reproductive performance were of lower magnitude than those observed for BRAH, and suggested that selection to improve steer feed efficiency (reduce RFI) would have no significant impact on reproductive performance for females of that genotype. This was consistent with the results of Arthur et al. (2005) where there were no significant differences in female pregnancy, calving or weaning rates between Bos taurus (Angus) lines divergently selected for net feed intake. Genetic relationships of male carcass and meat-quality traits with female reproduction For TCOMP, consistent genetic relationships of higher steer IMF and MARB with higher female Mating 1, Mating 2 and lifetime reproduction suggested that selection to improve steer marbling would have no unfavourable genetic consequences for female reproduction. Oyama et al. (1996), in examining the genetics of female reproduction and steer meat quality in Wagyu cattle, reported moderate and negative genetic relationships between female age at first calving and steer marble score (rg = –0.39), which was consistent with the results observed here for TCOMP. For BRAH, these relationships were of lower magnitude, suggesting that selection to improve steer marbling could be undertaken with no correlated change in female reproduction. For BRAH, genetic correlations of steer SF and CMP with female reproduction tended to be positive (unfavourable), although were universally not different from zero. Oyama et al. (2004) reported no genetic relationships between Wagyu shear force and early female reproductive performance (measured as age at first calving: rg = –0.03), which was consistent with the present results for BRAH. For TCOMP, there was a trend for lower (more favourable) SF to be genetically associated with less favourable female reproductive performance at all stages, although with the exception of Mating 1 DTC (rg = –0.56); these relationships were also not different from zero. Conversely, in TCOMP, selection to improve CMP and LOSS could be undertaken with the expectation that female reproduction may be improved as a consequence. For these relationships, standard errors were particularly high (s.e. = 0.20–0.45), and correlations would have to be confirmed before considering their applications. For BRAH, higher steer RBY was genetically associated with more favourable female Mating 1 reproductive performance but unfavourably correlated with some Mating 2 traits and LAWR. Wolcott et al. (2009) showed a positive genetic relationship between steer carcass EMA and RBY in these


animals and, while standard errors for RBY relationships in the current study were high, the consistency with carcass EMA results provided some confidence in the direction of these relationships for BRAH. For TCOMP, relationships of steer RBY with female reproduction tended to be of lower magnitude, with the exception of the positive genetic relationship with LAWR, which suggested that selection to increase steer RBY may be associated with higher female lifetime reproductive performance. Conclusions The results of this study demonstrated that selection to increase steer carcass weight and eye muscle area while reducing carcass fatness could be undertaken without significant unfavourable genetic consequences for female reproduction in both of the tropically adapted genotypes examined. Genetic correlations suggested, however, that measures of weight and body composition traits in young Brahman bulls were only moderately correlated with their steer carcass equivalents and that selection on the basis of bull measurements alone may negatively affect female reproductive performance. With these exceptions, significant relationships of male traits with female reproduction were not common, although genetic correlations suggested that selection to increase steer carcass P8 fat depth may have consequences for early female reproductive performance (favourable for first-mating in TCOMP and unfavourable for second-mating outcomes in both genotypes). Other male traits, including temperament (measured as flight time), marbling and blood IGF-I concentration, showed no significant unfavourable genetic relationships with female reproductive performance, and in some cases, displayed moderate to strong favourable correlations. Steer growth and carcass composition and cow reproductive performance have been identified as key drivers of profitability by breeders of tropically adapted beef cattle. The results of the present study indicated that if traits describing these were measured, included in a multi-trait genetic evaluation and identified as selection criteria, genetic gains could be simultaneously achieved for both of these components of herd productivity. Australia’s current genetic evaluation treats female reproduction over a cow’s life (expressed as days to calving) as a single trait. These results also suggested that if the trait was expanded to describe the results of the first and second matings, as well as lifetime reproductive performance, there would be a greater opportunity to describe significant genetic relationships in the evaluation for tropically adapted genotypes. Acknowledgements The authors acknowledge the Cooperative Research Centre for Beef Genetic Technologies and its core partners (The University of New England, NSW DPI, CSIRO and Queensland DPI), and the financial support of Meat and Livestock Australia. We also acknowledge the contributions of the Australian Agricultural Co., C. & R. Briggs, Consolidated Pastoral Co., North Australian Pastoral Co., MDH Pty Ltd, J. &S. Halberstater and G. & J. McCamley, as well as Primegro® for IGF-I analyses. We acknowledge also all Beef CRC participants, including scientists, and technical and support staff, who contributed to cattle management, data collection and data handling for female reproduction (Johnston et al. (2014a), steer growth and body composition (Barwick et al. 2009b), bull growth and body composition


95

(Corbet et al. 2013) and steer carcass- and meat-quality (Wolcott et al. 2009) studies acknowledged in previous papers.

References Anonymous (2010) ‘BREEDPLAN tips: Australian Belmont selection indexes.’ Available at http://breedplan.une.edu.au/tips/Interpreting% 20Australian%20Belmont%20Red%20Selection%20Indexes.pdf [Verified 30 January 2013] Anonymous (2011) ‘BREEDPLAN tips: Australian Brahman selection indexes.’ Available at http://breedplan.une.edu.au/tips/Interpreting% 20Australian%20Brahman%20Selection%20Indexes.pdf [Verified 30 January 2013] Anonymous (2012) ‘A guide to recording performance information.’ Available at http://breedplan.une.edu.au/booklets/A%20Guide%20to% 20Recording%20Performance%20(Complete).pdf [Verified 30 January 2013] Archer JA, Barwick SB, Graser HU (2004) Economic analysis of beef cattle breeding schemes incorporating performance testing of young bulls for feed intake. Australian Journal of Experimental Agriculture 44, 393–404. doi:10.1071/EA02054 Arthur PF, Herd RM, Wilkins JF, Archer JA (2005) Maternal productivity of angus cows divergently selected for post-weaning residual feed intake. Australian Journal of Experimental Agriculture 45, 985–993. doi:10.1071/EA05052 AUSMEAT (1998) ‘Handbook of Australian meat.’ (AUSMEAT: Brisbane) Barwick SA, Johnston DJ, Burrow HM, Holroyd RG, Fordyce G, Wolcott ML, Sim WD, Sullivan MT (2009a) Genetics of heifer performance in ‘wet’ and ‘dry’ seasons and their relationships with steer performance in two tropical beef genotypes. Animal Production Science 49, 367–382. doi:10.1071/EA08273 Barwick SA, Wolcott ML, Johnston DJ, Burrow HM, Sullivan MT (2009b) Genetics of steer daily feed intake and residual feed intake in tropical beef genotypes and relations among intake, body composition, growth and other post weaning measures. Animal Production Science 49, 351–366. doi:10.1071/EA08249 Barwick SB, Johnston DJ, Holroyd RG, Walkley JR, Burrow HM (2014) Multi-trait assessment of early-in-life female, male and genomic measures for use in genetic selection to improve female reproductive performance of Brahman cattle. Animal Production Science 54, 97–109. doi:10.1071/ AN13134 Bourdon RM, Brinks JS (1982) Genetic, environmental and phenotypic relationships among gestation length, birth weight, growth traits and age at first calving in beef cattle. Journal of Animal Science 55, 543–553. Burns BM, Corbet NJ, Corbet DH, Li Y, Crisp JM, Venus BK, Johnston DJ, McGowan MR, Holroyd RG (2013) Male traits and herd reproductive capability in tropical beef cattle. 1. Experimental design and animal measures. Animal Production Science 53, 87–100. doi:10.1071/AN12162 Burrow HM (2001) Variances and covariances between productive and adaptive traits and temperament in a composite breed of tropical beef cattle. Livestock Production Science 70, 213–233. doi:10.1016/S03016226(01)00178-6 Burrow HM, Johnston DJ, Barwick SA, Holroyd RG, Barendse W, Thompson JM, Griffith GR, Sullivan M (2003) Relationships between carcass and beef quality and components of herd profitability in northern Australia. Proceedings of the Association for the Advancement of Animal Breeding and Genetics 15, 359–362. Corbet NJ, Burns BM, Johnston DJ, Wolcott ML, Corbet DH, Venus BK, McGowan MR, Holroyd RG (2013) Male traits and herd reproductive capability in tropical beef cattle 2. Genetic parameters of bull traits. Animal Production Science 53, 101–112. doi:10.1071/AN12163 Crowley JJ, Evans RD, Mc Hugh N, Kenny DA, McGee M, Crews DH, Berry DP (2011) Genetic relationships between feed efficiency in growing males and beef cow performance. Journal of Animal Science 89, 3372–3381. doi:10.2527/jas.2011-3835

96



Devitt CJB, Wilton JW (2001) Genetic correlation estimates between ultrasound measurements on yearling bulls and carcass measurements on finished steers. Journal of Animal Science 79, 2790–2797. Garcia-Garcia RM (2012) Integrative control of energy balance and reproduction in females. ISRN Veterinary Science 2012, 121389. Available at http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3671732/ [Verified 23 June 2013] Gargantini G, Cundiff LV, Lunstra DD, Van Vleck LD (2005) Genetic relationships between male and female reproductive traits in beef cattle. The Professional Animal Scientist 21, 195–199. Gilmour AR, Gogel BJ, Cullis BR, Thompson R (2009) ‘ASREML users guide release 3.’ (VSN International: Hemel Hempstead, UK) Johnston DJ, Barwick SA, Holroyd RG, Fordyce G, Wolcott ML, Burrow HM (2009) Genetics of heifer puberty in two tropical beef genotypes in northern Australia and associations with heifer and steer production traits. Animal Production Science 49, 399–412. doi:10.1071/EA08276 Johnston DJ, Barwick SA, Fordyce G, Holroyd RG, Williams PJ, Corbet NJ, Grant T (2014a) Genetics of early and lifetime annual reproductive performance in cows of two tropical beef genotypes in northern Australia. Animal Production Science 54, 1–15. doi:10.1071/AN13043 Johnston DJ, Corbet NJ, Barwick SA, Wolcott ML, Holroyd RG (2014b) Genetic correlations of young bull reproductive traits and heifer puberty traits with female reproductive performance in two tropical beef genotypes in northern Australia. Animal Production Science 54, 74–84. doi:10.1071/ AN13044 MacNeil MD, Cundiff LV, Dinkel CA, Koch RM (1984) Genetic correlations of reproductive and maternal traits with growth and carcass traits in beef cattle. Paper 49. Beef research program: Roman L. Hruska. US Meat Animal Research Center. Available at http://digitalcommons.unl.edu/ hruskareports/49 [Verified 27 August 2013] Meyer K, Johnston DJ (2003) Estimates of genetic correlations between live ultrasound scan traits and days to calving in Hereford cattle. Proceedings of the Association for the Advancement of Animal Breeding and Genetics 15, 387–390. Meyer K, Hammond K, Parnell PF, Mackinnon MJ, Sivarajasingam S (1990) Estimates of heritabilities and repeatabilities for reproductive traits in Australian beef cattle. Livestock Production Science 25, 15–30. doi:10.1016/0301-6226(90)90038-8

Meyer K, Hammond K, Mackinnon MJ, Parnell PF (1991) Estimates of covariances between reproduction and growth in Australian beef cattle. Journal of Animal Science 69, 3533–3543. Mialon MM, Renand G, Krauss D, Ménissier F (2001) Genetic relationship between cyclic ovarian activity in heifers and cows and beef traits in males. Genetics, Selection, Evolution. 33, 273–287. doi:10.1186/1297-9686-333-273 Moore KL, Johnston DJ, Graser H-U, Herd R (2005) Genetic and phenotypic relationships between insulin-like growth factor-I (IGF-I) and net feed intake, fat, and growth traits in Angus beef cattle. Australian Journal of Agricultural Research 56, 211–218. doi:10.1071/AR04248 Oyama K, Mukai F, Yoshimura T (1996) Genetic relationships among traits recorded at registry, judgement, reproductive traits of breeding females and carcass traits of fattening animals in Japanese Black cattle. Animal Science and Technology (Japan) 67, 511–518. Oyama K, Katsuta T, Anada K, Mukai F (2004) Genetic parameters for reproductive performance of breeding cows and carcass traits of fattening animals in Japanese Black (Wagyu) cattle. Animal Science 78, 195–201. Perry D, Thompson JM (2005) The effect of growth during backgrounding and finishing on meat quality traits in beef cattle. Meat Science 69, 691–702. doi:10.1016/j.meatsci.2004.10.020 Pitchford WS (2004) Genetic improvement of feed efficiency of beef cattle: what lessons can be learnt from other species? Australian Journal of Experimental Agriculture 44, 371–382. doi:10.1071/EA02111 Reverter A, Johnston DJ, Graser HU, Wolcott ML, Upton WH (2000) Genetic analyses of live-animal ultrasound and abattoir carcass traits in Australian Angus and Hereford cattle. Journal of Animal Science 78, 1786–1795. Wolcott ML, Johnston DJ, Barwick SA, Iker CL, Thompson JM, Burrow HM (2009) Genetics of meat quality and carcass traits and the impact of tenderstretching in two tropical beef genotypes. Animal Production Science 49, 383–398. doi:10.1071/EA08275 Wolcott ML, Johnston DJ, Barwick SB, Corbet NJ, Williams PJ (2014a) The genetics of cow growth and body composition at first calving in two tropical beef genotypes. Animal Production Science 54, 37–49. doi:10.1071/AN12427 Wolcott ML, Johnston DJ, Barwick SB (2014b) Genetic relationships of female reproduction with growth, body composition, maternal weaning weight and tropical adaptation in two tropical beef genotypes. Animal Production Science 54, 60–73. doi:10.1071/AN13012

www.publish.csiro.au/journals/an