Reproductive performance and milk production of the ...

0003-3561/95/33400109$20-00

Animal Science 1995,60: 109-115 © 1995 British Socictv of Anim.il Science

Reproductive performance and milk production of the improved Awassi breed as compared with its crosses with the Booroola Merino E. Gootwine, A. Bor, R. Braw-Tal and A. Zenou Institute of Animal Science, Agricultural Research Organization, The Volcani Center, FOB 6, Bet Dagan 50250, Israel

Abstract Ovulation rate, embryo survival, lamb production, lamb survival and milk production of Awassi and BooroolaAwassi crossbred ewes, kept indoors, were compared. Awassi were non-carriers while Booroola X Awassi (F,) and about half of 3/4 Awassi-1/4 Booroola (BQ) ewes were heterozygous at the FecB gene. Mean ovulation rate increased by 1-5 to 1-6 corpora lutea per ewe ovulating and prolificacy by 0-7 lambs born per ewe lambing in Fj and BC} (B+) ewes as compared with Awassi. Embryo survival rates in BCj ewes with two, three and four ovulations were 0-83, 0-68 and 0-71, respectively. Lamb survival rates at 1 day of age were 0-93, 0-90 and 0-77 and average birth weight was 4-9, 4-0 and 3-0 kg for lambs born as singles, twins and triplets, respectively. Average milk production of the Awassi was 506 I per ewe per lactation. F1 and BC: ewes produced respectively, proportionately 0-48 and 0-63 of the Awassi milk production and there was no significant difference in milk production between BC,(B+) and BC-I(++) ewes. The relatively low milk production of the Booroola Awassi crosses suggests that heterosis and recombination effects on milk production were negative. It is concluded that incorporation of the B allele per se can increase lamb production in the Awassi without affecting its milk production. Keywords: Awassi, Booroola, milk production, reproductive performance.

Introduction

prolificacy of the Awassi — about 1 -2 lambs born per ewe lambing. To increase lamb production of the Improved Awassi without affecting its superiority in adaptability and milk production, a scheme was initiated to introduce into this breed the B allele of the FecB gene (Gootwine, 1985). The FecB is a major gene that affects ovulation rate in sheep and on average, one copy of the B allele increases ovulation rate by 1-2 ova shed per ewe ovulating and lambing rate by 0-6 lambs born per ewe lambing (Piper, Bindon and Davis, 1985). Production of F] generation through crossing with BB homozygous Booroola Merino rams followed by several backcrossing steps along with selection of ewes carrying the B allele, and a final intercross phase, are the main outlines of the proposed breeding programme.

Attempts to improve lamb production of low-prolific fat-tailed sheep in the Mediterranean basin through crossbreeding with exotic non-fat-tailed prolific breeds had only a marginal impact on sheep production in the region (Aboul-Ela and AboulNaga, 1987). This has been due mainly to the low adaptability of the exotic breeds and their crosses to the local environment and to the preference for the traditional fat-tailed phenotype by the local consumers. The Awassi is the main type of sheep in the Middle East, raised for meat, milk and wool. Awassi sheep are run under a wide range of systems of production from nomadic systems with reliance on pasture in semi-arid areas, to dairying systems where the Improved Awassi type is kept in intensive indoor units (Epstein, 1985). The management in those intensive units is such that the ewes are supervised most of the day, especially at lambing time, and all lambs are raised in artificial rearing units. This type of management is suitable for dealing successfully with prolificacy which is higher than the present

Higher embryonic losses (Hanrahan, 1987; Kleemann, Walker, Walkley, Smith, Grimson and Seamark, 1990a) and increased lamb mortality (Hinch, Crosbie, Kelly, Owens and Davis, 1985; Kleemann, Walker, Walkley, Smith, Ponzoni and Seamark, 1990b) were reported in Booroola crosses. These factors may reduce the beneficial effect of the 109

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Gootwine, Bor, Braw-Tal and Zenou

Booroola gene in the Awassi. In addition, the Booroola Merino is a non-dairy breed and therefore, the FecB gene or other Merino genes may have undesirable effects on the Awassi milk production. On the other hand, increasing litter size in the Awassi may improve its milk production, since a positive correlation between number of foetuses carried by the ewe and her post-partum milk production has been demonstrated in sheep and goats (Hayden, Thomas and Forsyth, 1979; Butler, Fullenkamp, Cappiello and Handwerger, 1981). The aim of the work reported in the present communication was to compare embryo survival, lamb production, lamb survival and milk production in Booroola-Awassi (Fj) ewes and in ++ and B+ 3/4 Awassi-1/4 Booroola (BQ) ewes with those of their contemporary pure Awassi ewes.

Material and methods Animals and management

The crossbreeding programme was conducted in the Kibbutz Ein Harod flock which included some 1200 Improved Awassi ewes. Thirteen Booroola-Awassi Fj ram lambs and 21 Fj ewe lambs were produced in 1986 following insemination of Awassi ewes with semen taken by electroejaculation from four homozygous BB Booroola Merino rams obtained from the Invermay Agricultural Centre, New Zealand. The BC] generation was produced twice: in 1987 and in 1988, by mating eight F, rams, progeny of all four Booroola sires, with Awassi ewes. F, and BC] ewes were mated with Awassi rams to produce respectively, BCj lambs that were not kept for breeding, and BC2 lambs. Contemporary groups of Awassi ewes were run with the Booroola crosses and altogether 136 Awassiewes, daughters of 10 Awassi sires, 19 F, ewes, 44 BC](++) and 51 6^(8+) ewes were included in the study. Out of the 19 Fj ewes milk production was recorded for 12 ewes. Reproductive performance and milk production were studied up to the third parity and no selection was done during that time in the experimental groups except for culling due to health problems. The flock at Ein Harod was kept indoors all year round and given food according to the Israeli Ministry of Agriculture recommendations (Landau and Leibovich, 1992). Foods included concentrates, barley grains, cotton seeds, rye grass, vetch hay and corn silage. In the spring, the ewes grazed for about 2 h/day on natural or artificial pasture. Ovulation rate

Ovulation rate (number of corpora lutea (CL) per ewe ovulating) was determined by laparoscopy 3 to 8 days following heat detection in 2- to 3-year-old cycling ewes. Animals were fasted for 12 h before

laparoscopy, which was carried out under sedation with 0-2 to 0-3 ml Rompun solution (2% w/v xylazine, Bayer, Munich, Germany) administered intravenously. CL on both ovaries were counted. Mating and lambing

During four 34-day periods (May to June; August to September; October to November; December to January), ewes were checked daily for oestrus and those ewes in heat were hand mated. All hoggets were mated for the first time at approximately 8 to 10 months of age, after being treated with progestagen intravaginal sponge and 600 i.u. pregnant mare serum gonadotropin (Chronogest, Intervat, Boxmeer, The Netherlands). Forty-nine percent of the hoggets conceived following that hormonal treatment. The other hoggets conceived in the following naturally occurring cycles. During the lambing periods, ewes were inspected for 18 h/day and assistance with difficult lambings was given at this time. Early lamb mortality included stillbirths and deaths during the first 24 h. On the day of lambing, all lambs were weighed and moved to an artificial rearing unit, where commercial milk replacer was offered ad libitum until weaning at about 1 month of age. Milk production

Ewes were milked twice daily from the day of lambing until their milk yield dropped to about 0-5 I/day or when they had to be dried off before lambing. Milk yield was recorded monthly and the data used to estimate milk production in the first 90 days of the lactation using the first 3-monthly records (90 day milk) and total milk yield during the lactation (total milk). Embryo survival rate

Litter size for BQ ewe was related to ovulation rate at the oestrus of conception. Embryo survival rate and embryo loss rate were calculated using Hanrahan's equations (Hanrahan, 1980). In all cases litter size was smaller than the respective ovulation rate. Assigning ewes as ++ or B+

All the Awassi ewes were ++ and all the F, ewes were B+ according to their origin. Genotyping of BQ ewes was based on four to five records comprising lambing records up to the third lambing (Table 1) and one to two ovulation records. Nine BC,(B+) ewes had only lambing records. BQ ewes that had litter size or ovulation rate record of three or more were classified as B+ (Davis, Montgomery, Allison, Kelly and Bray, 1982). Other BC, ewes were assigned as ++. For 21 out of 22 BCj ewes, all progeny of the same sire, the assigned genotype was in agreement with that determined by the OarAElOl genetic markers (Montgomery, Crawford, Penty, Dodds, Ede, Henry,

Performance of Awassi ewes and crosses

111

Table 1 Number of ewes lambing according to genotype, year of birth, lambing number, and ewe's age at first parity (months) Genotype BC,(B+)

Awassi

Year of birth

Age at first parity

Parity no. 1

2

Age at first parity

Parity no.

Age at first parity

Parity no.

3

Mean

s.e.

1

2 3

Mean

s.e.

1986 25 23 21 1987 57 56 53 1988 54 50 44

17-1 17-0 17-1

10 0-7 0-7

19 18 18

16-0

1-5

1

2

Age at first parity

Parity no.

3

Mean

s.e.

1

2

3

Mean

s.e.

20 19 16 24 24 18

17-7 15-5

1-0 0-5

23 23 21 28 28 26

17-0 16-3

0-7 0-9

Table 2 Ovulation rate in Awassi, F,,BCl(++)andBC ,(B+) ewes Proportion of records with CL number of:

No. of: Genotype Awassi F,

BC,(++) BC,(B+) n,b

Ewes 34 16 44 42

Records 34 26 60 88

1

0-82 0-15 0-63 0-14

2

3

Ovulation rate >3

018

0-12 0-37 0-24

0-50

0-23

0-46

0-16

Mean

s.e.

a

0-1 01 01 0-1

l-20 2-80b l-37a 2-67b

Proportion of ewes with record of three CL or more 0-'

0-88b

0a

0-71b

Within columns, means followed by different superscripts differ significantly (P< 0-05).

Pierson, Lord, Galloway, Schmack, Sise, Swarbrick, Hanrahan, Buchanan and Hill, 1993; Gootwine, Bor, Braw-Tal, Ofir, Yossefi, Zenou, van Stijn, Penty and Montgomery, 1994). The Oar AE101 marker was not informative for BQ ewes from other sire families. Statistical analysis

sire within genotype. The last effect was included in the GLM model as a random effect. Least-squares means and standard errors were calculated from models that included significant main effects and interactions only. Factors affecting ovulation rate and embryo survival were tested using %2. Differences of P < 0-05 were considered significant.

Birth weight, 90-day milk, total milk, lactation length and lambing intervals were analysed using the general linear model (GLM) procedure in the SAS Results computer package (Statistical Analysis Systems; SAS Number of ewes and age at lambing Institute, 1985). Litter size and lamb survival were Number of ewes from the different genotypes in the analysed by the CATMOD procedure of SAS for various age groups and mean age at first parity are categorical data modelling using the generalized presented in Table 1. On average, first parity logit model to obtain significance tests. Least-squares occurred at 16-8 (s.e. 1-0) months of age. Second and means for litter size and lamb survival were obtained third parities occurred after 124 (s.e. 0-2) and 11-3 by the GLM procedure for presentation. The main (s.e. 0-2) months, respectively. Lambing intervals in fixed effects included in the models in both the GLM Awassi and F, ewes were similar and significantly and CATMOD procedures for the different variables, as longer by 1-3 months than lambing intervals of BC, indicated in Table 3 were: genotype (Awassi, F ]; BC,(++), BC,(B+), year of birth (1986, 1987, 1988), genotype X year of birth, parity number, genotype X Ovulation rate, and prolificacy parity number, sex of lamb and litter size within Means and distributions of ovulation rate of Awassi, breed with three classes: singles, twins and triplets or F,, BQ(++) and BC1(B+) ewes are shown in Table 2. more. The models contained also age at lambing Mean ovulation rate was similar in Awassi and within parity which was included as a covariant, and BC,(++) ewes being 1-20 and 1-37 CL per ewe

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Gootwine, Bor, Braw-Tal and Zenou

Table 3 Significance levels of the effects included in the statistical analysis models

Litter size

Effect

Lamb survival

Birth weight

90-day milk

Total milk

Lactation length

Lambing interval

Genotype (G) Sire Year of birth (Y) GXY

Parity no. (P) GXP Litter size Age at lambing Sex of lamb —, not included in the model. Table 4 Prolificacy (lamb born per ewe lambing, LB) and proportion of lambs born alive (LBL) in Aivassi, F, and BC, ewes, according to parity number

First parity

Genotype Awassi F, BC[(B+)

No. 136 19 44 51

LB 1-19" l-63 b 1-26° l-75 b

Secc>nd parity LBL 0-95 0-93 0-92 0-85

No. 128 18 43 51

LB

LBL 1

1-23' l-89 b 1-17" l-73 b

0-95 0-71 0-90 0-84

Overall mean

Third parity

LB

No. 115 18 33 47

1

1-412-12b 1-36'1 2-29b

LBL

LB

LBL

0-98 0-91 0-96 0-76

1 -28-' l-95 h 1-25'1 1.99b

0-96 0-85 0-92 0-82

Proportion of ewes with litter size three or more 0-02'1 0-53b . 0-0" 0-63b

••>.b Within parity, means followed by different superscripts differ significantly (P< 005).

ovulating respectively. In the Fj and BC,(B+) ewes, mean ovulation rate increased by 1-60 and 147 CL per ewe ovulated respectively, as compared with Awassi ewes and the maximal record was six ovulations. Tests of significance for the analysis of variance on litter size, lamb survival and birth weight are presented in Table 3. Genotype, parity number and litter size had significant effects on the traits under investigation. Lambing performance of Awassi, F,, BG](++) and BCj(B+) ewes in the first three parities is shown in Table 4. The hormonal treatment of the hoggets did not seem to increase lambing rate in the first parity over the natural lambing rate as genotype by parity and age within parity interactions were not significant. Awassi and BC1(++) ewes did not differ significantly in their overall prolificacy which was relatively low: 1-28 and 1-25 lamb born per ewe lambing, respectively. Prolificacy of F, and BC,(B+) ewes was higher than that of Awassi by 0-67 and 0-71 lamb born per ewe lambing, respectively. Lamb survival

Survival rate of lambs around lambing time according to genotype of the dam is presented in

Table 4. In the Awassi, lamb survival was the highest being proportionately 0-96 on average. The increase of about 0-55 lambs born to the Fj and the BC^(B+) ewes, over the Awassi and the BC|(++) ewes, was accompanied by increasing mortality giving altogether about 0-45 extra live lamb per ewe. Singles and twins had significantly higher survival rates and higher birth weights than triplets. Thus for singles, twins and triplets born to BC, ewes survival rates were 0-93, 0-90 and 0-77 respectively and birth weight was 4-8, 3-8 and 3-0 kg, respectively. Embryo survival rate

Embryo survival rates and embryo loss rates in BC, ewes as a function of ovulation rate are presented in Table 5. On average, proportionately 0-55 of the BC] ewes conceived following mating and conception rate did not differ significantly between ewes with different ovulation rates. Embryo survival rates for ewes with three and four ovulations were lower than those for ewes with two ovulations. Milk production

Significance levels of the effects on 90-day milk, total milk and lactation length from the analysis of

Performance of Awassi ewes and crosses

113

Table 5 Embryo survival rate as a function of ovulation rate in BC, ewes

Eives with litter size of:

Ewes lambed

Mean

Embryo

Embryo

4

size

rate

rate

3

1-65 2-05 2-83

0-83 0-68 0-71

0-20 0-35 0-30

NIrt nf

rate 1 2 3 4

ewes

No

Proportion

1

34 37 34 13

18 20 21 6

0-53 0-54 0-62 0-46

18 7 6 1

2

3

13

8 2

7 0

Table 6 Least-square means of 90-day milk production and total milk production of Awassi, Fl; BC{(++) and BCi (B+) ewes

Second lactation

First lactation No.

Mean

Milk production (1) in 90 days 135 233'1 Awassi 142b 12 F, 174b 44 BC,(++) 169b 51 BC,(B+) Total milk production during lactation (1) Awassi 133 429.1 11 224b F, 44 BC,(++) 271" BC,(B+) 51 252b

Third lactation

Overall

s.e.

No.

Mean

s.e.

No.

Mean

s.e.

Mean

s.e.

7 20 12 11

127 12 40 49

321* 159 b 227C 225C

7 20 12 11

114 11 30 41

327 a 180 b 240 c 220 c

7 21 14 12

293 a 160 b 213C 204 c

4 12 8 8

14 44 24 24

125 12 40 49

559 a 259 b 360 c 344C

14 42 25 24

108 10 28 39

529 a 245 b 364C 322C

15 47 30 26

506 a 242 b 332C 306 c

9 25 17 17

'i'bc Within trait and lactation number, means followed by different superscripts differ significantly (P< 0-001).

variance are shown in Table 3. Genotype, parity number and genotype by year-of-birth interaction had a significant effect for the three variables. Litter size and age at lambing within parity had no significant effect on any of the variables. Significant sire and year of birth effects were found only for 90day milk production.

On the other hand, milk production of Booroola Awassi ewes was lower than that of Awassi ewes. Since BC1(++) and BC^B-t-) had similar milk yield, the B allele appears not to have an effect per se on milk production and, therefore, it can be anticipated that further upgrading to the Awassi might increase milk yield whilst retaining the B allele.

The average lactation lengths of F], BC1(++) and BC,(B+) ewes were similar: 168 (s.e. 8), 176 (s.e. 5) and 169 (s.e. 5) days, respectively, and were significantly shorter than that of the Awassi, which was 206 (s.e. 3) days. Estimates for 90-day milk and total milk are presented in Table 6. Awassi ewes had the highest milk production, with averages of 293 and 505 1 for 90-day milk and total milk, respectively. Milk production in the Fj ewe was the lowest, being half that of the Awassi. BC,(++) and BC,(B+) milk production was similar and intermediate: on the average 0-72 and 0-63 for 90-day milk and total milk of the Awassi, respectively.

Ovulation rate and lambing rate of Fj BooroolaAwassi heterozygous B+ ewes were on average higher by 1-6 CL per ewe ovulating and 0-67 lambs born per ewe lambing than the Awassi (Tables 2 and 4). Similar effects of carrying one copy of the B allele on ovulation rate and prolificacy have been reported in other Booroola crosses (Piper et al., 1985), and also in the Booroola-Assaf (Awassi X East Friesian) cross (Gootwine, Braw-Tal, Shalhevet, Bor and Zenou, 1993).

Discussion Our results show that lamb production of BooroolaAwassi ewes carrying the B allele was higher by about 045 lambs born alive than that of Awassi ewes.

Combining information on lambing and ovulations and using the threshold of three ovulations (Davis et al., 1982) or triplets born for distinguishing ++ from B+ ewes, 51 out of the 95 BCj ewes were classified as B+ and their ovulation rate and prolificacy were respectively higher by 1 -3 CL per ewe ovulating and 0-74 lambs born per ewe lambing than in BCT(++) ewes. According to this classification, all F, ewes

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Gootwine, Bor, Braw-Tal and Zenou

were classified as B+ and proportionately 0-98 of 136 Awassi ewes were classified as ++. The three misclassified Awassi ewes had triplets. Those three sets of triplets were born in a total of 379 Awassi lambings, similar to the frequency for triplets that was reported before for the Awassi breed (Epstein, 1985). Increased ovulation rate was followed by decreased embryo survival. Embryo survival rates for BC](B+) and BC1(++) ewes with two, three or four CL per ewe ovulating were 0-83, 0-68 and 0-71, respectively (Table 5). These values are in good agreement with estimates for embryo survival rates obtained for other breeds and crosses (Hanrahan, 1980; Kleemann et al., 1990a). Increasing ovulation rate did not affect proportion of ewes lambing (Table 5), supporting the observation in Booroola Merino crosses that fertilization failure was independent of ovulation rate (Kleemann et al, 1990a). Relatively low lamb survival in Booroola crosses has been considered to be a major concern which may hamper the commercial use of the Booroola gene (Davis, Elsen, Bodin, Fahmy, Castonguay, Gootwine, Bor, Braw-Tal, Greeff, Lengyel, Paszthy and Cummins, 1990). Indeed, in our study mortality among lambs out of F-j and BC1(B+) ewes was higher than that in litters out of Awassi or BCj(++) ewes. However, the net result was that F, and BC,(B+) ewes produced on average 045 more live lambs than Awassi ewes (Table 4). Taking into consideration that with the use of artificial rearing units, lamb mortality until marketing in intensive dairy flocks is rather low, being proportionately about 0-05 only (unpublished data), utilization of the Booroola gene in those flocks can be beneficial. Average milk production of Awassi ewes in the first three lactations was 506 1 per lactation with average lactation length of 206 days. This is in accordance with previous estimates of milk production in the Ein Harod flock (Epstein, 1985). As might be expected from a cross with a non-dairy breed, lactation length of F-, Booroola Awassi ewes was shorter (proportionately 0-83) and total milk yield was proportionately only 0-48 that of the Awassi. The milk production of Booroola Merino-ewes under the management of Ein Harod was not estimated in the present study. However, if milk production is inherited in an additive way, milk production of the F, ewes should be higher than half the milk production of the Awassi. This was not the case and therefore, our results suggest negative heterosis for milk production. This result is unexpected since only zero or weak positive heterosis for milk production has been found in other Awassi crosses (Epstein, 1985).

Upgrading to the Awassi resulted in significantly higher milk production in the BC, than in the Fj generation. However, it did not reach the mid value between the Awassi and the F,. This deviation from additivity suggests the presence of a negative recombination effect. Interestingly, a negative recombination effect on milk production was found also in crosses between dairy and non-dairy cattle breeds (Cunningham and Syrstad, 1987). Estimates of the crossbreeding parameters in this study are based on production records from a limited number of F, ewes and therefore, further designed trials are necessary to support our observations. Finally, it was suggested that udder development and milk production in sheep and goats are affected by the number of foetuses carried by the dam (Hayden et al., 1979; Butler et al., 1981). Our results do not support this notion, as litter size did not affect significantly 90-day milk or total milk, and BC1(B+) and BC|(++) ewes were similar in their milk production despite the big difference in litter size.

Acknowledgements The authors express their thanks to the Invermay Agricultural Research Centre, New Zealand, for supplying Booroola rams, to Dr A. Genizi for the help with the statistical analysis and to the devoted team of the Ein Harod flock. This research was supported by grants from the United States-Israel Binational Agricultural Research and Development Fund (BARD) and from the Israel Academy of Science. Contribution no. 1211-E, 1993 series, from the Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel.

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