Animal Science 2004, 79: 41-48 © 2004 British Society of Animal Science
1357-7298/04/30350041$20·00
Genetic parameters for growth, reproductive performance, calving ease and suckling performance in beef cattle heifers F. Phocas† and J. Sapa Institut National de la Recherche Agronomique, Station de Génétique Quantitative et Appliquée, 78 352 Jouy-en-Josas Cedex, France † E-mail :
[email protected]
Abstract There is considerable concern about the consequences on fitness-related traits of using narrow breeding objectives for production traits. The aim of this study was to assess the potential consequences of selection for growth in French beef cattle breeds by estimating genetic correlations between growth, reproduction, calving and suckling traits of Charolais, Limousin and Blonde d’Aquitaine heifers. Data consisted of the records collected from 1985 to 2002 in progeny test stations that were used in the genetic evaluation of 284 Charolais, 125 Limousin and 118 Blonde d’Aquitaine AI sires. Seven traits were considered simultaneously in the analysis : weights at 18 months and after calving (for measuring heifer growth), sexual precocity and fertility (for measuring heifer reproductive performance), calving difficulty score and pelvic opening (for measuring calving ease) and milk yield (for measuring the suckling ability of the primiparous cow). REML (co)variance estimates were derived using linear multitrait sire models. Estimates of heritability were in the range of values given in the literature. They were very similar in the Charolais and Blonde d’Aquitaine breeds, and rather different for reproductive and suckling performance in the Limousin breed. Estimates were about 0·35 for heifer growth traits and about 0·15 for calving difficulty score in the three breeds. In the Charolais and Blonde d’Aquitaine breeds, estimates of heritability were 0·15 for sexual precocity and 0·05 for heifer fertility. These estimates were close to zero in the Limousin breed. Heritabilities of pelvic opening and milk yield were, respectively, 0·2 and 0·6 in the Limousin breed and around 0·3 in the other two breeds. Genetic correlations between traits concerning the same ability (as, for instance, weight at 18 months and weight at calving) were high and, in general, similar among breeds. Genetic correlations between heifer growth, reproductive traits, calving ease and suckling performance were nil or slightly favourable in the three breeds. Consequently, past selection mainly directed towards increasing growth seems not to have adversely affected the efficiency of female reproduction and the maternal abilities of French specialized beef cattle breeds. Keywords: beef cattle, calving, fertility, growth, milk production.
Introduction
these traits are of primary interest in terms of the economic efficiency of beef cattle farms (Phocas et al., 1998). In French beef cattle breeding programmes, sire selection for artificial insemination (AI) is based on individual and progeny testing on stations in order to reduce environmental variability of performance. Beef traits are recorded on the sons and female traits are recorded on the daughters of the AI candidates for selection. Recording of female traits includes the heifer growth, its sexual precocity, its fertility, its calving performance at 2 years and, eventually, its suckling performance. The objective of
For the last three decades, beef cattle breeds have been selected mainly for muscular growth. Information on genetic correlations between beef production and female traits is scarce in the literature (MacNeil et al., 1984; Smith et al., 1989; Meyer et al., 1991; Rege and Famula, 1993; Gregory et al., 1995; Splan et al., 1998; Mialon et al., 2001) but antagonism between these traits is feared mainly due to the antagonism observed between breeds. Female traits are not very well known in beef cattle breeds because they are difficult to measure on farms. However, 41
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this research was to estimate genetic parameters for these female traits, recorded in AI sire progeny testing stations in the three main French beef cattle breeds : Charolais, Limousin and Blonde d’Aquitaine.
Material and methods Animals In French progeny testing programmes for AI beef sires, daughters of the test sires enter the progeny testing station of their breed selection unit as weaned heifers. Although the testing stations belong to the selection units, data are recorded by technicians from the ‘Institut de l’Elevage’ which is a national technical institute independent of the selection units. Heifers, born within a restricted season, are bought from commercial herds to be a representative sample of the purebred daughters of the AI candidate sires. As these heifers originate from commercial herds, no information is available on their dam or maternal grandsire identification. The unique relationship among these heifers is therefore provided by the tested sires. Selection of AI bulls is a multistage process run by breeding units : the first step is the selection on their on-farm birth and weaning traits, the second step is the selection on their post-weaning growth, muscular development and food efficiency, recorded in individual test stations, and the third step is the selection on beef traits of male progeny and on female traits of female progeny, both being recorded in test stations (Phocas et al., 1995). Across year comparisons of candidates for selection are possible through the use of reference sires in progeny test stations and existing relationships among sires. Measures are recorded from the weaning of the heifers to the weaning of their calves. Heifers are inseminated during a fixed 10-week period in order to get a first calving at 2 years of age. Only two
purebred mating bulls are used each year. They are used for several years in order to correct for their effect on heifer fertility and on calf performance. Table 1 summarizes the quantity of data available for each of the three breeds. Data before 1985 (1987 for the Limousin breed) were excluded from the analyses because important changes in performance recording were introduced in those years. Breeding programmes for the Limousin and Blonde d’Aquitaine breed are very similar in terms of size (the number of sires progeny tested each year is 6 or 7 and the number of daughters recorded per sire ranges from 25 to 30). The Charolais breeding programme is actually larger (the number of sires progeny tested each year ranges from 16 to 19 and the number of daughters recorded per sire ranges from 20 to 25). Data The female traits analysed were the heifer’s weight at 18 months (W18 m) and its weight after calving (WC) for measuring heifer growth, the observation of oestrus at 15 months for measuring its sexual precocity (SP; 0 or 1), the observation of calving success after a fixed insemination period (74 days) for measuring its fertility (FE; 0 or 1), the calving difficulty score (CS; 0 for no or easy assistance, 1 for hard pull or caesarean) and the pelvic opening (PO, measured by the product of the pelvic height and the pelvic width) for measuring calving ability, and the milk yield (MY, derived by the calf-weigh-suckleweigh technique) for measuring suckling ability. Analysis models Analyses were performed for each trait i using a sire linear model: yi = Xiβ + Zis + ε where yi is the vector of observations, β is the vector of fixed effects, s is the vector of random effects of the heifer’s sire, ε is the vector of random residual
Table 1 Summary of the data sets Breed Charolais Years of evaluation 1985 – 2002 No. of heifer growth records 6448 No. of heifer fertility records 6425 No. of calvings 4681 No. of lactations 4396 No. of sires recorded on daughters’ growth and fertility 284 No. of sires recorded on daughters’ calving and suckling abilities 284 No. of sires in the pedigree 1731
Limousin
Blonde d’Aquitaine
1987 – 2002 3394 3310 1845 1733 125 101 906
1985 – 2002 3435 3433 2451 2260 118 118 441
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Genetic parameters for female traits in beef cattle Table 2 Phenotypic means and standard deviations of heifer traits within breed Breed Charolais
Weight at 18 months (W18m, kg) Weight after first calving (WC, kg) Sexual precocity at 15 months (SP,%) Calving success (FE,%) Calving difficulty score (CS,%) Pelvic opening (PO, cm2) Milk yield (MY, kg/day)
Limousin
Blonde d’Aquitaine
Mean
s. d.
Mean
s. d.
Mean
s. d.
481·3 557·6 59·9 79·1 15·4 296·8 6·1
34·34 43·97 44·97 40·35 35·55 25·39 1·58
420·1 488·8 30·1 76·5 25·8 260·7 4·7
29·68 39·69 42·05 41·93 41·30 38·39 1·33
472·7 530·4 65·2 76·3 23·6 286·1 5·3
38·78 46·63 44·73 42·07 40·57 23·54 1·43
effects, and X, and Z are the corresponding incidence matrices. The discrete nature of some reproductive and calving performance traits was ignored because the genetic evaluation is based on a linear model and because this type of model can perform evenly or better than a threshold model when the incidence of the observed trait is intermediate (25 to 75%) (Meijering and Gianola, 1985) or the amount of information per sire or fixed effect level is low (Moreno et al., 1997; Phocas and Laloë, 2003). Moreover, estimates of genetic correlations are not affected by the statistical treatment (linear or threshold model) of the categorical trait (Kadarmideen et al., 2003). The fixed effects considered for W18 m, WC and SP were the birth region of France (five levels in the Blonde d’Aquitaine breed, six levels in the Charolais breed and eight levels in the Limousin breed), the birth year-period of the heifers (six periods per year for the Charolais breed and four periods for the other breeds) and the calving parity of their dam (1 to 4 and over 4). The fixed effects for FE were the same as for W18 m, WC and SP plus the mating bull effect (six levels for Charolais, five for Limousin and three for Blonde d’Aquitaine). With respect to calving performance traits, the calving period within year (three levels) and the calf sex were added to the previous model. For MY, the suckling batch within year (five levels) was included in the model instead of the calving period within year and the calving difficulty score (two levels : easy calving and hard pull or caesarean section) was added to the model. The age at calving (in days) was also fitted as a covariable for calving and suckling traits. Estimation procedure of genetic parameters The software ASREML developed by Gilmour et al. (2000) was used for the estimation of genetic parameters within breed. It maximized the REML
log-likelihood function using the average information algorithm (Gilmour et al., 1995). The seven traits were analysed simultaneously. Convergence of the REML log-likelihood was reached with the ASREML criterion of changes less than 0·002 times the current iteration value.
Results and discussion Estimation of phenotypic means and variances Table 2 shows the phenotypic means and standard deviations (after correction for the fixed effects) for the seven traits analysed. The three breeds had quite different performance levels for heifers calving at 2 years (25 months, more precisely). In general, the Blonde d’Aquitaine had intermediate performance levels between the heavy Charolais heifer (480 kg at 18 months) and the light Limousin heifer (420 kg at 18 months). The Limousin heifer had the latest sexual precocity with 30% showing oestrus at 15 months (compared with 60% and higher for the other breeds) and the lowest milk yield with a mean below 5 kg/day (compared with values around 6 kg/day for the other breeds). Mean average calving difficulty score was lower in the Charolais breed (15%) than in the other breeds (about 25%), probably because only Charolais mating bulls were chosen on their calvingease ability. The phenotypic coefficients of variation were higher than 7% for all traits and breeds. The lowest coefficients of variation were found for heifer growth and pelvic opening and the highest coefficients of variation (over 50%) were found for the binary traits (SP, FE and CS). Estimation of heritabilities Table 3a, b and c show the parameters estimated for the Charolais, Limousin and Blonde d’Aquitaine breeds, respectively. As expected, heifer growth and milk yield were the most heritable traits across all breeds. Estimates of heritability for heifer growth were similar for the three breeds. They were around
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Table 3 Estimated genetic parameters in (a) Charolais, (b) Limousin and (c) Blonde d’Aquitaine heifer traits: heritabilities on the diagonal, genetic correlations above the diagonal (standard errors in brackets) and environmental correlations below the diagonal† Weight at 18 Weight at months (W18m) calving (WC)
Sexual precocity (SP)
Calving success (FE)
Calving difficulty (CS)
Pelvic opening (PO)
Milk yield (MY)
0·47 (0·26) 0·46 (0·26) 0·68 (0·30) 0·02 (0·02) 0·20 –0·11 0·09
0·10 (0·13) –0·04 (0·12) –0·03 (0·15) –0·07 (0·30) 0·15 (0·03) –0·15 0·00
0·41 (0·09) 0·50 (0·08) 0·09 (0·12) –0·11 (0·24) –0·61 (0·11) 0·33 (0·05) 0·06
0·21 (0·10) 0·19 (0·10) 0·14 (0·12) 0·11 (0·24) 0·04 (0·13) 0·19 (0·11) 0·36 (0·05)
–0·07 (0·23) –0·08 (0·25) 0·72 (0·70) – 0·12 (0·06) –0·10 –0·25
0·80 (0·16) 0·90 (0·20) –0·94 (0·67) – –0·18 (0·28) 0·19 (0·06) 0·03
0·27 (0·15) 0·42 (0·15) –0·37 (0·44) – –0·33 (0·21) 0·35 (0·18) 0·60 (0·11)
0·13 (0·19) 0·18 (0·19) –0·18 (0·21) –0·10 (0·27) 0·18 (0·06) –0·26 0·04
0·53 (0·13) 0·48 (0·13) 0·52 (0·16) 0·17 (0·24) 0·08 (0·21) 0·26 (0·07) 0·21
0·00 (0·17) 0·10 (0·16) –0·01 (0·19) 0·29 (0·23) –0·07 (0·20) 0·05 (0·18) 0·31 (0·07)
(a) W18m WC SP FE CS PO MY
0·37 (0·05) 0·76 0·18 0·01 –0·01 0·37 0·03
0·89 (0·03) 0·46 (0·05) 0·11 –0·01 –0·11 0·61 0·10
0·01 (0·11) 0·13 (0·11) 0·15 (0·03) 0·07 –0·02 0·08 0·02
(b) W18m WC SP FE CS PO MY
0·33 (0·06) 0·76 0·18 – 0·03 0·12 0·08
0·92 (0·08) 0·26 (0·06) 0·13 – –0·11 0·17 0·20
–0·27 (0·38) –0·73 (0·58) 0·02 (0·02) – –0·02 0·07 0·08
(c) W18m WC SP FE CS PO MY
0·34 (0·07) 0·80 0·24 0·13 0·01 0·41 0·18
0·95 (0·02) 0·38 (0·07) 0·19 0·15 –0·14 0·67 0·20
0·02 (0·17) –0·02 (0·17) 0·17 (0·05) 0·06 0·04 0·04 0·02
– – – 0·00 – – – 0·09 (0·22) 0·02 (0·22) 0·76 (0·17) 0·08 (0·04) 0·08 –0·07 0·00
† Standard errors for environmental correlations in Charolais, Limousin and Blonde d’Aquitaine traits were always in the range 0·02 to 0·07, 0·03 to 0·11 and 0·02 to 0·10, respectively.
0·35, varying from 0·33 to 0·37 for W18 m and from 0·26 to 0·46 for WC. For MY, the higher estimate for the Limousin breed (0·60) was probably due to the co-existence of two different sub-populations in this breed : one selected for suckling ability and veal production and the other one selected for growth and beef production. This variability in the dam sample used for testing sires certainly increased the genetic variability of MY. Since the sampling was done in unrecorded herds without any indication about the production system, a correction factor for this production system could not be fitted in the model. Traits related to calving ease had low to moderate heritabilities which were similar across breeds. The heritability of CS was around 0·15 for all the breeds, varying from 0·12 to 0·18. The heritability of pelvic opening was about 0·25, varying from 0·19 (Limousin) to 0·33 (Charolais). Heritabilities of reproduction traits were rather different across breeds. Concerning sexual precocity, the estimates were around 0·15 for the Charolais and
Blonde d’Aquitaine breeds and 0·02 for the Limousin breed. Estimates for FE were lower : 0·08 for the Blonde d’Aquitaine, 0·02 for the Charolais and 0·00 for the Limousin heifer. The complete absence of genetic variability for Limousin fertility was probably due to the elimination of the progeny of the worst sires for this trait. This elimination (not performed in the other breeds) was motivated by the lack of space in the Limousin station. The two Limousin sires whose daughters’ have the worst fertility on average are eliminated from the sire evaluation after their daughters’ breeding season, because these sires do not have enough daughters’ calving and suckling performances to give accurate estimated breeding values. The estimates of heritability of female traits in this study agree with those described in the literature (Koots et al., 1994). In particular, the low estimates of heritability of female reproductive performance were expected. As is also established in the literature, environmental correlations were quite moderate, with estimates below 0·3 in absolute value, except for traits related to heifer growth (PO, W18 m and WC).
Genetic parameters for female traits in beef cattle Genetic correlations between heifer growth and reproductive performance Weight at 18 months was always highly correlated (about 0·9) with weight after calving. Consequently, both traits related in a similar manner to other heifer abilities. Genetic correlations between heifer growth and SP were not significantly different from zero in the Charolais and Blonde d’Aquitaine breeds. An unfavourable genetic correlation was estimated in the Limousin breed, but its standard error was very high. Genetic correlations between growth and FE were close to zero in Blonde d’Aquitaine heifers and around 0·45 in Charolais heifers. These results disagree with the results from Phocas et al. (2002) who found a large negative genetic correlation between heifer calving success and yearling weight in an experimental herd of Charolais heifers undergoing a divergent selection for lean growth rate (Phocas et al., 2002). They also disagree with earlier papers describing negatively correlated responses in reproduction of cows selected for growth rate (Scholtz and Roux, 1984; Luesakul-Reodecha et al., 1986). However, our results confirm a more recent tendency observed in the literature that there seems to be little, if any, favourable genetic correlation between growth and fertility, even in harsh environments (e.g. Mercadante et al., 2003). The genetic correlation between FE and WC was found to be moderately favourable (0·3) in Holstein primiparous cows (Moore et al., 1990). In beef cattle, low favourable genetic correlations were shown between weaning or yearling growth and female fertility measured by calving date in Hereford, Angus and Nelore cows (Smith et al., 1989; Meyer et al., 1991; Rege and Famula, 1993; Johnston and Bunter, 1996; Mercadante et al., 2003) and between growth (weaning or yearling weights, weight at calving for females and weight at slaughter for males) and ovarian activity measured by age at puberty or length of post-partum anoestrus in Hereford and Charolais cows (Bourdon and Brinks, 1982; Smith et al., 1989; Gregory et al., 1995; Mialon et al., 1999 and 2000; Bennett and Gregory, 2001). Previous results concerned mainly British breeds whose growth rate and mature size are smaller than those observed in the French specialized beef breeds (Simm et al., 1990). However, these biological differences across breeds do not affect the genetic correlations among growth and reproduction traits within breed. Genetic correlations between heifer growth and calving performance If calving difficulty scores were analysed as a trait of the calf, the effect of the heifer sires would
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correspond to one-quarter of their direct genetic effect transmitted to their grand-progeny plus half of their maternal genetic effect transmitted to their daughters, without any possibility of separation between the two genetic effects. In this research, CS was only considered as a trait of the dam. Thus the effect considered was the direct calving-ease ability of the dam whereas the birth ability of its calf was ignored. Genetic correlations between heifer growth and CS were not significantly different from zero across the three breeds. In contrast, genetic correlations between heifer growth and PO varied considerably from one breed to another : the correlations were moderate (0·4 to 0·5) in the Charolais and Blonde d’Aquitaine breeds and highly positive (0·8 to 0·9) in the Limousin breed. Genetic correlations between the two indicators of calving ease ability (i.e. CS and PO) varied also greatly across breeds. The genetic correlation between CS and PO ranged from zero for the Blonde d’Aquitaine to –0·6 for the Charolais breed. The favourable genetic association between CS and PO (i.e. the higher PO was the lower CS was) was expected in Charolais and Limousin cows. The surprising nil relationship encountered in Blonde d’Aquitaine cows may be related to the following facts : (1) the Blonde d’Aquitaine calves were the heaviest at birth with an average weight of 41 kg (compared with 38 kg and 34 kg at birth for Charolais and Limousin calves, respectively); (2) CS was almost totally explained by calf birth weight (unpublished results from this data set) and this breed had the highest direct (0·7) and maternal (0·6) genetic correlations between CS and birth weight (F. Phocas and D. Laloë, unpublished results from a different data set). Furthermore, Bennett and Gregory (2001) found a slightly positive average estimate (0·1) for the genetic correlation between direct effects on CS and PO from 12 experimental beef cattle populations. Genetic correlations between heifer growth and suckling performance Genetic correlations between heifer growth and MY were close to zero for the Blonde d’Aquitaine and moderately favourable in the Charolais (about 0·2) and Limousin (about 0·35) breeds. There is little information available on genetic correlations between MY and growth traits for beef cattle. Meyer et al. (1994) estimated genetic correlations between MY and weaning weight for a herd of Polled Herefords and a herd of a multibreed synthetic. They confirmed that MY represented the main component of maternal genetic effect on weaning weight and found no direct additive genetic or phenotypic association between the two traits. A lack of genetic association between MY and WC was also reported in dairy cattle (Lee et al., 1992). Otherwise, there is an
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extensive literature about direct and maternal genetic effects on weaning weight in beef cattle (Koots et al., 1994). In general, direct-maternal genetic correlations are reported to be negative for weaning weight, but some arguments related to data structures and models exist that could explain negative estimates without a truly genetic association between growth and milk production (Robinson, 1996a and b). Genetic correlations between sexual precocity and other traits Correlations between SP and other traits were different between the Limousin breed and the two other breeds. This could be linked to the very low phenotypic sexual precocity of the Limousin (30% v. 60% for the other breeds) and to its low heritability (0·02 v. 0·15 for the other breeds) which is probably related to the elimination of the Limousin sires that were worst in terms of the daugthers’ fertility. SP was always unfavourably correlated to other traits in the Limousin breed, but the standard errors of the estimates of correlations were very large (0·4 to 0·7). The genetic correlation between SP and FE was quite favourable (around 0·7) in the Charolais and Blonde d’Aquitaine breeds. This estimate was higher than that previously reported for an experimental herd of Charolais heifers (Phocas et al., 2002). This correlation was not estimated for the Limousin breed because no genetic variation was found for FE. In Charolais and Blonde d’Aquitaine breeds, genetic correlations between SP and most of the other heifer abilities were not significantly different from zero. The only exception was a moderate genetic correlation estimated between SP and PO in Blonde d’Aquitaine heifers (around 0·5). However, heifer fertility was genetically uncorrelated to the two indicators of calving ease (PO and CS) in both breeds. Genetic correlations between calving ease and suckling performance A tendency towards favourable genetic associations between MY and both indicators of calving ease was observed. The Limousin cows exhibited the highest genetic correlations with estimates around 0·3 in absolute values, while no genetic associations were observed for Blonde d’Aquitaine cows. In Charolais cows, a slightly favourable genetic correlation between PO and MY was observed, whereas the genetic correlation between CS and MY was zero. Genetic correlations between reproductive and suckling performance A slightly favourable genetic correlation was estimated between FE and MY in Charolais and
Blonde d’Aquitaine breeds. This correlation was however not significantly different from zero. In beef cattle, there is no information available of genetic correlations between MY and fertility traits. Estimates of genetic correlations between MY and FE in dairy cows range from zero (Raheja et al., 1989) to moderately unfavourable (Oltenacu et al., 1991; Dematawewa and Berger, 1998; Roman and Wilcox, 2000). Since energy requirements for milk production are much lower for beef than for dairy cows, these results can not be extrapolated to beef cows whose body tissue mobilization during lactation is not as important as it is in dairy cows. Body condition score (used as a measure of energy status) was shown to be phenotypically and genetically antagonistic with reproductive performance in Holstein cows (Veerkamp et al., 2001). Dechow et al. (2002) showed that a higher loss in body condition score (i.e. more negative energy balance) in early lactation was genetically related to the delay in the onset of first oestrus. However, some studies (e.g. , Masilo et al., 1992) supported the conclusion that selection for higher milk yield has no detrimental effects on cow reproduction, at least when cows were given adequate food. De Rouen et al. (1994) showed that body condition of primiparous beef cows at calving was a reliable indicator of subsequent reproductive performance. Their results suggest the existence of a threshold in the energy balance at calving above which there is no negative effect on reproductive performance. Thereby, relationships between MY and FE could be nil in beef cows, at least for cows with sufficient food around calving. Implications The results of this research question the traditionally held belief of a genetic antagonism between growth and female traits in beef cattle breeds. It was shown that few, and then may be even favourable, genetic correlations exist between heifer growth, reproductive performance, calving ease and suckling performance of the primiparous beef cow. Consequently, simultaneous genetic improvement of the different components of female productivity may be achieved in beef cattle breeds. Selecting for heifer growth will lead to an indirect slight improvement of its suckling performance and will have no genetic effects on heifer reproduction or calving ease. Selection for suckling ability would not cause the reproductive performance of beef cows to deteriorate, at least not under high nutritional and management conditions.
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