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Genetic and economic analysis of introgression the B allele of the FecB (Booroola) gene into the Awassi and Assaf dairy breeds
Livestock Production Science 71 (2001) 49–58 www.elsevier.com / locate / livprodsci
Genetic and economic analysis of introgression the B allele of the FecB (Booroola) gene into the Awassi and Assaf dairy breeds a, a a a a b E. Gootwine *, A. Zenu , A. Bor , S. Yossafi , A. Rosov , G.E. Pollott a
The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel Imperial College at Wye, Ashford, Kent TN25 5 AH, UK
b
Abstract Selection for yield and the adoption of an intensive management system underpins the high milk production of the Improved Awassi and the Assaf dairy flocks in Israel. However, lamb production, which contributes some 40% of the income, remains relatively low at 1.2 and 1.6 lambs born / ewe lambing (LB / EL) for the Awassi and the Assaf, respectively. To increase the profitability, through improved lamb production, a breeding scheme was initiated in 1986 to introduce the B allele of the FecB (Booroola) gene to the Awassi and Assaf breeds. This led to the formation of the Afec–Awassi and Afec–Assaf strains with prolificacy of about 2.0 LB / EL. A marker assisted selection approach and the use of induced ovulation rate as selection criteria were incorporated into the breeding programs. The Awassi is the main type of sheep in the Middle East where about 80 million sheep of this breed and other related fat tail breeds are present. Distribution of the BB Afec semen or rams in those flocks, through regional breeding programs, can improve their productivity and their economics, facilitating the transition into a more intensive production system. The economic justification for launching such a breeding program depends mainly on the local lamb price. 2001 Elsevier Science B.V. All rights reserved. Keywords: Awassi; Assaf; Booroola; Afec; Dairy sheep; Economic analysis
1. Introduction The Awassi, the main type of sheep in the Middle East is kept under a wide range of production systems: from nomadic flocks relying on natural pasture in semi-arid areas where lamb production is the primary product, to intensive dairy flocks where *Corresponding author. Tel.: 1972-3-9683-752; fax: 1972-39603-678. E-mail addresses: [email protected] (E. Gootwine), [email protected] (G.E. Pollott).
milk and lambs contribute almost equally to the flock gross income (Epstein, 1985). The Awassi is known for its hardiness and adaptability and in the case of the Improved Awassi, also for its high milk production. Yet, prolificacy of the Awassi is low; about 1.2 lambs born per ewe lambing (LB / EL) (Epstein, 1985). As lamb production is an important source of income in all Awassi flocks, increasing fecundity of the Awassi has always been an important breeding goal. Indeed, Finn and Romanov crosses with the Awassi had a prolificacy of about 2.0 (Goot et al., 1980). However, those crosses were not widely
0301-6226 / 01 / $ – see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S0301-6226( 01 )00240-8
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accepted by the industry, mainly because of the preference for the traditional fat tail phenotype by both breeders and consumers. Crossing the Awassi with the East Friesian breed resulted in the formation of the Assaf breed (Gootwine and Goot, 1996) which has become the main dairy breed in Israel and has been integrated into sheep production systems in other Mediterranean countries, such as Spain and Portugal (Ugarte et al., 2000). The prolificacy of the Assaf is higher than that of the Awassi at about 1.6 LB / EL (Epstein, 1985). However, this semi-fat tail breed is less adaptable to local conditions than the Awassi. The FecB gene is a major gene that affects ovulation rate in sheep. 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 et al., 1985). In 1986, breeding schemes were initiated in Israel to introduce the B allele into the Awassi and Assaf breeds. Production of the F1 generation was achieved through crossing local sheep with four BB homozygous Booroola Merino rams obtained from the Invermay Agriculture Center, New Zealand. The first backcross (BC1) populations were produced by mating eight F1 Booroola–Awassi and six F1 Booroola–Assaf rams with Awassi and Assaf ewes, respectively. This was followed by several backcrossing steps, along with selection of ewes carrying the B allele using a marker assisted selection approach (Gootwine et al., 1998), and a final intercross phase. As the available markers for the FecB gene were found to be informative only in the case of the Booroola–Awassi crosses, induced ovulation rate at 5 months of age, natural ovulation rate monitored in cycling ewes and litter size were the criteria for selection of B 1 ewes in the Booroola–Assaf crosses (Gootwine et al., 1993). Altogether, 127 Booroola–Awassi BC1, 95 Booroola–Assaf BC1, 181 Booroola–Awassi BC2 and 159 Booroola–Assaf BC2 ewes were produced through the crossbreeding work. Once BB homozygous nucleus populations have been established, BB rams will be distributed to intensive or semi-intensive commercial Awassi or Assaf flocks. First results of the effect of the Booroola Merino inheritance on lamb and milk production in the F1
and the BC1 generations were described by Gootwine et al. (1993) and Gootwine (1995). High prolificacy as a result of carrying the B allele and relatively low milk yield due to the presence of other Merino genes were the main observations. The economic aspects of increasing lamb production in semi-intensive non-dairy Awassi flocks by introducing the B allele were investigated taking into consideration different breeding methods for handling the Booroola gene and different economic environments (Spharim and Gootwine, 1997). It was found that under the range of economic parameters tested, this operation would be profitable in most scenarios and the higher the ratio between lamb price and feed costs, the greater the benefit from the use of the Booroola gene. The aims of the present communication are to analyze prolificacy and milk production characteristics in advanced Booroola Awassi backcross generations and to provide economic analyses which will define at what stage homozygous crossbred BB Awassi or Assaf rams may be profitably introduced into commercial dairy flocks.
2. Materials and methods
2.1. Ein Harod management The intensive management system of the Ein Harod Improved Awassi flock, where the crossbreeding programme has been taking place, was described by Gootwine et al. (1995) and Gootwine and Pollott (2000). Briefly, the flock comprised about 1200 ewes, was kept indoors all year round and ewes were fed to meet their nutritional requirements according to their level of production. Reproductive management included four 34-day breeding periods in the year when ewes were handmated following heat detection. Hoggets were first exposed to the ram at about 9 months of age, following oestrus synchronization. All lambs were identified at lambing and were moved to an artificial rearing unit. Ewes were milked twice daily from the day of lambing until their milk yield dropped to about 0.5 l / day or until they had to be dried off before lambing. Milk yield was recorded on the 15th day of each month and
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total milk yield throughout the lactation (TMY) was calculated as described by Pollott and Gootwine (2000a). Test day milking records were validated and stored using the on-farm ‘Ewe and Me’ software (Gootwine and Zenou, 1997).
2.2. Identifying carriers of the B allele of the FecB ( Booroola) locus Booroola Awassi crossbred ewes and rams were identified as B-allele carriers using the AE101 (Montgomery et al., 1993) and the BM1329 (Lord et al., 1998) microsatellites that flank the FecB locus (Lord et al., 1998, Gootwine et al., 1998). These markers were found to be informative in some of the Booroola Awassi families. The lambing rates of different backcrosses were compared by Chi Square analysis.
2.3. Milk records analysis Two milk yield data sets were analyzed in this study. The first data set included TMY records for 9385 lactations from ewes that lambed between 1980 and 2000. The distribution of the lactation records according to ewe genotype and the respective litter size is presented in Table 1, where BC1–4 was the first to the fourth backcross to the pure Awassi. The following model was fitted to TMY using least-squares analysis for unbalanced data [GLM procedure of the Statistical Analysis Systems (SAS) Institute, 1997]:
Table 1 The number of Awassi TMY records analyzed according to ewe genotype and litter size Genotype
Litter size
Total
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TMY ijklnp 5 m 1 E i 1 LN j 1 LS k 1 Ml 1 Gn 1 e ijklnp where TMY ijklnp is the TMY of the ith ewe (E) in its jth lactation (LN), LS k is the litter size born to the ewe at the respective lambing, Ml is the month when the ewe lambed, Gn the ewe genotype (Awassi, BC1, BC2, BC3 and BC4) and e ijklnp is the randomly distributed error term. To see if the effect of LS differed between genotypes the interaction of LS and genotype was also fitted. Litter sizes greater than three were grouped into one category. Least-squares means, within an effect, were compared and the paired differences between levels within an effect were tested against a two-tailed t distribution. The second milk yield data set consisted of 3740 complete lactations with 5–10 test-day records from 1360 Awassi, BC2, BC3 and BC4 ewes. A lactation was assumed to be completed when its last daily milk yield record reached 0.6 l / day. This data set included TMY and other calculated lactation parameters (see Pollott and Gootwine, 2000a) namely: lactation length (LL), lambing interval (LINT), day of peak yield (DP), peak yield (PY), maximum secretion potential (MS), relative growth rate in milk production (GR), relative decline rate in milk production (DR), daily increase in milk production midway between lambing and peak (GM) and daily loss of milk production midway between peak and end of lactation (DM). Lactation curve parameters for each complete lactation were calculated using the Pollott Multiplicative model (Pollott, 2000) using an iterative least-squares non-linear curve fitting procedure (Procedure NLIN in SAS). The ‘best fit’ curve was obtained for each lactation when there was a less than 10 26 difference between the error sums of squares in successive iterations. The following model was fitted to the various lactation parameters using the GLM procedure of SAS: Pijklnp 5 m 1 E i 1 LN j 1 LS k 1 Ml 1 Gn
1
2
31
Awassi BC4 BC3 BC2 BC1
5625 195 186 322 55
2178 81 126 240 165
25 22 42 84 39
7828 298 354 646 259
Total
6383
2790
212
9385
1 (Gn 3 LS k ) 1 ei jklnp where Pijklnp is a lactation parameter of the ith ewe in its jth lactation, LS k is the number of lambs born to the ewe at the start of the lactation, Ml is the month when the ewe lambed, Gn is the ewe genotype (Awassi, BC2, BC3, BC4), Gn 3LS k is the
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genotype3litter size interaction and ei jklnp is the randomly distributed error term. Ewes were absorbed in the analyses in order to reduce the size of the matrix of fixed effects and all results quoted are from Type III analyses (SAS Institute, 1997). Least-squares means were computed by fitting the above model to the data using the REML option in the SAS MIXED procedure and including ewe as a random effect. Least-squares means, within an effect, were compared and the paired differences between levels within an effect were tested against a twotailed t distribution.
2.4. Estimation of genetic parameters The transmitted (gI), heterosis (hI) and recombination (rI) effects for TMY were estimated for the Booroola Awassi crosses by equating their expected relative values as defined in Table 2 (Dickerson, 1969) with the least-squares means of TMY estimates for the different genotypes derived from the RAML analysis and presented in Table 6. Pure Booroola Merino ewes were never present in the Ein Harod flock and Booroola–Awassi F1 ewes were not included in the present study. To obtain the genetic estimates, it was postulated that TMY of Booroola Merino ewe performing under the Ein Harod management was 70 l, and that TMY of F1 ewes was 252 l – the result obtained in previous study (Gootwine et al., 1995).
Table 2 Expected relative performance for different crosses between the Booroola Merino and the Awassi breeds Genotype
Awassi Booroola–Merino a Booroola3Awassi (F1) F13Awassi (BC1) Awassi3BC1 (BC2) Awassi3BC2 (BC3) Awassi3BC3 (BC4)
Crossbreeding coefficients gI
hI
rI
1 0 1/2 3/4 7/8 15 / 16 31 / 32
0 0 1 1/2 1/4 1/8 1 / 16
0 0 0 1/4 1/8 1 / 16 1 / 32
Coefficients for transmitted (gI), heterosis (hI) and recombination (rI), effects relative to the pure Booroola Merino and the Awassi performances. a Not available from these data.
2.5. Economic analysis The net present value (NPV) of transforming a pure Awassi or Assaf flock into a flock where all ewes are heterozygous for the B allele over an 8-year period was investigated. The B1 flock was constructed by inseminating, once a year for 4 years, all 1 1 ewes in the flock with BB rams and recruiting their B1 female progeny as the sole replacements Rams with Awassi /Assaf levels of 87.5% (BC2) or more were considered. In the fifth year of the project, 3 / 4 of the flock consists of B1 ewes and in the sixth year all ewes are B1. Those B1 ewes are bred to non-carrier 1 1 males and their B1 ewe lambs were selected as replacements from the fifth year based on genotyping for markers linked to the FecB gene. In this economic analysis, a flock of 1000 breeding ewes was considered, the yearly replacement rate was 25%, hoggets lambed for the first time at the age of 2 years and ewes were culled after their fourth lactation. It was assumed that increasing prolificacy did not affect the reproductive activity of the flock. Other parameters that were used in the economic analysis are listed in Table 3.
3. Results and discussion
3.1. Prolificacy assessment of different Booroola– Awassi crosses The genotype at the FecB locus was identified, using molecular markers, for 20, 32 and 63% of the BC2, BC3 and BC4 ewes, respectively. For the other ewes, the markers were not informative. Chi Square analysis showed that genotype and parity had a highly significant effect (P,0.005) on prolificacy whereas the effect of the backcrossing stage was not significant (P.0.6). Overall, the average prolificacy in the first four parities for B1 and 1 1 ewes was, respectively, 1.88 and 1.22 lambs born / ewe lambing. The prolificacy of the different genotypes according to parity is presented in Table 4. The difference of 0.66 lambs born / ewe lambing between B1 and 1 1 ewe in this study is in agreement with similar difference found in previous work in the Booroola Assaf and the Booroola Awassi
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Table 3 Parameters used in the economic analysis Parameter
Awassi
Assaf a
Percent of ewes lambing / year No. lambings / ewe / year Prolificacy of 1 1 ewes (LB / EL)b 1st parity 2nd parity 3rd parity 4th parity Prolificacy of B1 ewes 1st parity 2nd parity 3rd parity 4th parity Lamb mortality rate For 1 1 ewes For B1 ewes Milk production of a ewe in the 4th lactation (l) Milk production of crosbred ewe relative to Awassi ewe Milk production / lactation relative to the 4th lactation c 1st lactation 2nd lactation 3rd lactation Price / kg live lamb at the farm gate ($) Lamb weight at marketing (kg) Price / kg milk at the farm gate ($) Price / kg feed ($) Kg of feed / ewe / year Cost of producing marginal kg milk ($) Cost of raising a lamb d ($) Price for BB semen ($) Price for genotyping a ewe lamb entering the flock ($) Interest rate (%)
90 1.0
1.2
1.13 1.21 1.33 1.31
1.40 1.51 1.60 1.60
1.66 2.01 1.89 2.10
1.80 2.01 2.10 2.30
0.04 0.15 520
320 0.88
0.76 1.06 1.05 3.5 50 0.7 0.27 500 0.11 72.5 4.8 22 7
a
Only values that differ from the Awassi model are presented. Based on results of the present study. c Based on the 1999 Israeli Flock Book. d Costs include rearing in an artificial rearing unit, weaning at 1 month and fattening on ad lib concentrates and 0.1 kg hay / day / head until marketing. b
F1 and BC1 generations (Gootwine et al., 1993, 1995) and in line with the estimated effect of one copy of the B allele on prolificacy found in other breeds (Piper et al., 1985).
3.2. Milk production A summary of the tests of significance from the REML analysis for the effects of the various factors
on TMY is presented in Table 5. Lactation, crossbreeding level, interaction of crossbreeding level and litter size, month of lambing and ewe all had a significant effect (P,0.01) on TMY. Leastsquares means for the effect of crossbreeding level on TMY are shown in Table 6 by litter size. Generally, TMY increased as upgrading to the Awassi progressed. However, the increase in average TMY lagged behind the proportion of the Awassi in
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Table 4 Prolificacy (lambs born / ewe lambing) up to the 4th parity of Booroola–Awassi BC2, BC3 and BC4 ewes identified as carriers (B1) or non carriers (1 1) using markers linked to the FecB gene Backcross
n
Prolificacy of non-carrier 1 1 ewes BC2 BC3 BC4 Overall Prolificacy of carrier B1 ewes BC2 BC3 BC4 Overall
Parity 1
2
3
4
39 41 69
1.15 1.05 1.15
1.12 1.20 1.27
1.29 1.25 1.40
1.33 1.37 1.24
149
1.66
2.01
1.89
2.10
26 19 54
1.61 1.58 1.73
1.97 1.58 1.73
1.97 1.84 1.82
2.18 2.10 1.91
99
1.13
1.21
1.33
1.31
Table 5 Significance levels for the effects included in the analysis of total milk yield (l)
3.3. Estimation of genetic parameters for TMY in the Booroola– Awassi crosses
Factor
DF
F
P
Lactation No. Litter size Cross Cross3LS Month of lambing
9 3 4 12 125
135.7 2.5 46.2 25.3 25.3
*** 0.08 ** ** ***
Estimates of TMY for the Awassi, BC2, BC3 and BC4 genotypes are shown in Table 6. The estimate used for the F1 generation was 252 l (Gootwine et al., 1995). The transmitted, heterosis and recombinant effect in the Booroola Awassi crosses was calculated to be 436610 l (P,0.005), 236610 l (P,0.04) and 2211642 l (P,0.01), respectively. Investigating a range of values (40–150 l) for pure Booroola Merino TMY did not change the results very markedly. The negative value for the heterosis effect suggests that dominant genes for low milk production may be present in the Booroola Merino, as anticipated by Gootwine et al. (1995). The
**P,0.01; ***P,0.001.
the cross. In this study, the TMY of BC1 ewes was 0.64 of the pure Awassi. A similar result for BC1 TMY of 0.63 was obtained by Gootwine et al. (1995) when the TMY of the pure Awassi was 506 l.
Table 6 Least-squares mean values for TMY (l) for Awassi, BC1, BC2, BC3 and BC4 ewes by litter size Genotype
Awassi (%)
Litter size 1
2
3
520 a 504 a 461 a 424 a 314 b
526 a 475 a 438 a 405 a 279 b
Overall mean
TMY relative to Awassi
516 z 485 zy 450 zy 413 y 331 x
1.00 0.94 0.87 0.80 0.64
Total milk yield Awassi BC4 BC3 BC2 BC1 ab
100.0 96.9 93.7 87.5 75.0
513 a 477 a 452 a 413 a 402 a
Within a genotype row, litter size means followed by different superscripts differ significantly. xzyWithin the ‘Overall mean’ column, means followed by different superscripts differ significantly.
E. Gootwine et al. / Livestock Production Science 71 (2001) 49 – 58
relatively high recombination loss for TMY indicates that epistatic gene-effects can explain part of the Awassi’s high milk producing ability. A similar conclusion on the genetics behind the Awassi’s high milk production was reached by Pollott and Gootwine (2000b) from a within-Awassi breed analysis and the implication of that result on further selection for high milk production in the Awassi has been discussed.
3.4. Effect of crossbreeding on lactation parameters In order to study the crossbreeding effect on lactation parameters, records from complete lactations were investigated. The results from the analysis show that ewe, litter size, lactation number, month of lambing, month of conception and ewe genotype all had significant effects on the different lactation parameters. Those results are in line with results from a similar analysis of pure Awassi records reported by Gootwine and Pollott (2000), except for the fact that in this analysis, LS has become a significant effect on DP, GR and DR and has increased its level of significance for TMY, MS, GM and DM. Also, month of conception affected PY and GM and has become a greater influence on DR. Type of Booroola–Awassi cross affected all traits except DP and GR but there was no significant interaction between LS and type of cross. Least-squares means for the different traits, where the effect of the type of cross was significant, are presented in Table 7. Pure Awassi ewes had a higher milk yield, longer lactations, longer lambing intervals, a higher peak yield, a higher maximum secretion potential, a slower rate of loss in milk secretion potential, secreted more milk mid-way between parturition and peak and were less persistent than most of the backcrosses.
3.5. An economic analysis of the introgression of the Booroola gene into Awassi or Assaf populations According to the analysis, a flock of 1000 Awassi or Assaf ewes produce annually 1076 and 1581 lambs and 503 000 and 310 000 l of milk, respectively. Inseminating all ewes in such flocks with BC2
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Table 7 Least-squares means for TMY and other lactation parameters for Awassi, BC2, BC3 and BC4 ewes Trait
Genotype Awassi
BC4
BC3
BC2
477 204b 371 b 3.42 a 3.91 a 0.0220 b 67.3 a 17.1 ab
443 202 b 368 b 3.22 3.71 0.0225 b 63.5 a 16.6 b
Parameter values TMY (l) LL (day) LINT (day) PY (l) MS (l) DR GM (g / day) DM (g / day)
533 a 214 a 388 a 3.68 4.22 0.0211 a 71.0 18.0 a
514 a 214 a 388 a 3.44 a 3.95 a 0.0208 a 65.7 a 16.0 b
Within traits, values followed by the same superscript are not significantly different (P,0.05).
homozygous BB rams will result, over the 8 years of the simulated project, in the development of prolific BC3 B1 flocks with a milk production performance equal to 87% of the respective pure breed, as presented in Table 6. Through the time course of the project, annual changes in lamb and milk production were first observed in the third year and came into full expression in the sixth year of the project (Fig. 1). The net present values for developing an Awassi flock into a B1 flock, under different combinations of milk and meat prices, are presented in Table 8. Interestingly, while introgression of the Booroola gene into non-dairy Awassi flocks was found to have positive NPV in most cases (Spharim and Gootwine, 1997), in dairy Awassi flocks under most conditions, such a project has a negative NPV when homozygous BC2 rams are used. Only when the meat price was high (4.0 US$ / kg), was the project marginally profitable. The same analysis for the Assaf showed that even for the case of the highest lamb price and the lowest milk price, the project had a negative NPV of US$254 000. The analysis in Table 8 was carried out for BC3 ewes at 87% of the Awassi milk production level (Table 6). The effect of the Awassi proportion on the project NPV has been further investigated, as shown in Table 9. The results in Table 9 show that under a situation where the milk price was 0.7 US$ / l and the live
E. Gootwine et al. / Livestock Production Science 71 (2001) 49 – 58
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Fig. 1. Change over time in lamb and milk production following introgression of the B allele of the FecB gene to a flock of 1000 Awassi or Assaf ewes.
Table 8 Net present values (NPV) of a simulated project where the Booroola gene is introgressed into a dairy Awassi flock
Table 9 NPV for different Awassi contributions in a simulated project where the Booroola gene was introgressed into an Awassi flock
Milk price (US$ / l)
Milk production (l) at the 4th lactation
Lamb meat price (kg live weight, US$) 2.5
3.0
3.5
4.0
211 215 220 224 228
17 13 9 4 0
NPV (31000 US$) 0.65 0.60 0.70 0.72 0.75
268 272 276 280 285
239 244 248 252 256
% Awassi 88
90
94
97
100
32 32 33 33 34
58 58 59 59 59
84 84 84 84 84
NPV (31000 US$)
lamb price was 3.5 US$ / kg (Table 3), profitability from introducing the B allele into an Awassi dairy flock was achieved only when ewes had over 90% Awassi genes. In order to achieve that, rams belonging to the BC3, or a more advanced backcross, need to be used.
550 520 490 460 430
221 220 219 218 217
23 22 21 0 0
A comparable analysis carried out for an Assaf flock (Table 10) showed that under similar conditions, profitability will only be achieved when the new B1 ewes have at least 97% Assaf genes, implying that inseminations should be started only when BC4 BB rams are available. As the prolificacy
E. Gootwine et al. / Livestock Production Science 71 (2001) 49 – 58 Table 10 NPV for a project where the Booroola gene is introgressed into an Assaf flock Milk production (l) at the 4th lactation
the economy of the breed. Increasing prolificacy on the other hand proves to be an effective way to increase profitability.
% Assaf 88
90
94
97
100
Acknowledgements
NPV (31000 US$) 350 320 290 260 230
57
234 233 232 231 230
223 222 221 220 220
22 22 21 0 0
14 14 14 15 15
31 31 31 31 31
of the Assaf was higher than that of the Awassi, even under optimal conditions, the NPV of the project was less than that for the Awassi. The genotyping of ewe lambs, daughters of B1 ewes and 1 1 rams, is required in order to identify and select B1 ewe lambs as replacements in the last 3 years of the 8-year project and on average, two ewe lambs have to be typed for every ewe lamb selected. The genotyping price has an effect on the economics of the project and doubling the genotyping price from 22 to 44 US$ / ewe entering the flock will reduce profitability by 33, 18 and 13% for flocks where milk production of the crossbreds is 94, 97 and 100% of the Awassi, respectively.
4. Conclusions Introgression of the Booroola gene into the Awassi and the Assaf dairy breeds is a unique situation as in most other cases the Booroola gene has been introgressed into meat or wool–meat dual purpose breeds. In non-dairy breeds, where lamb production is the main source of income, the economic contribution of the Booroola gene can be appreciated as early as in the first-cross generation. However, as the Merino genes have an adverse effect on Awassi and Assaf milk production, a careful breeding design has to be undertaken to benefit from the Booroola gene in those dairy breeds. The results of the present study indicate that nonadditive genetic effects play an important role in determining the high milk production of the Awassi. If so, selection for higher milk production in the Awassi may have a limited contribution to improve
The authors express their thanks to the Invermay Agricultural Research Center, New Zealand for supplying Booroola rams, to the team of the Ein Harod Awassi flock for continuous collaboration and to Mr. Geel Eilat for help with the economic analysis.
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on Genetics Applied to Livestock Production, Vol. 27. University of New England, Armidale, pp. 19–21. Montgomery, G.W., Crawford, A.M., Penty, J.M., Dodds, K.G., Ede, A.J., Henry, H.M., Pierson, C.A., Lord, E.A., Galloway, S.M., Schmack, A.E., Sise, J.A., Swarbrick, P.A., Hanrahan, V., Buchanan, F.C., Hill, D.F., 1993. The ovine Booroola fecundity gene (FecB) is linked to markers from a region of human chromosome 4q. Nat. Genet. 4, 410–414. Piper, L.R., Bindon, B.M., Davis, G.H., 1985. The single gene inheritance of the high litter size of the Booroola Merino. In: Land, R.B., Robinson, D.W. (Eds.), Genetics of Reproduction in Sheep. Butterworths, London, pp. 115–125. Pollott, G.E., 2000. A biological approach to lactation curve analysis. J. Dairy Sci. 83, 2448–2458. Pollott, G.E., Gootwine, E., 2000a. Appropriate mathematical models for describing the lactation of dairy sheep. Anim. Sci. 71, 197–207.
Pollott, G.E., Gootwine, E., 2000b. The genetics of dairy production from the complete lactations of Improved Awassi sheep. In: Proceedings of 51st Annual Meeting of the European Association for Animal Production. Wageningen Pers, Wageningen, p. 291. Statistical Analysis Systems Institute, 1997. SAS User’s Guide. SAS Institute, Cary, NC. Spharim, I., Gootwine, E., 1997. Economic evaluation of breeding ´ ´ for higher prolificacy in Awassi flocks. Options Mediterraneennes 33, 157–161. Ugarte, E., Ruiz, R., Beltran de Heredia, I., 2000. Impact and influence of foreign breeds on the Spanish breeds of dairy sheep. In: Proceedings of the 51th Annual Meeting of the European Association For Animal Production. Wageningen Pers, Wageningen, p. 297.
Genetic and economic analysis of introgression the B allele of the FecB (Booroola) gene into the Awassi and Assaf dairy breeds a, a a a a b E. Gootwine *, A. Zenu , A. Bor , S. Yossafi , A. Rosov , G.E. Pollott a
The Volcani Center, P.O. Box 6, Bet Dagan 50250, Israel Imperial College at Wye, Ashford, Kent TN25 5 AH, UK
b
Abstract Selection for yield and the adoption of an intensive management system underpins the high milk production of the Improved Awassi and the Assaf dairy flocks in Israel. However, lamb production, which contributes some 40% of the income, remains relatively low at 1.2 and 1.6 lambs born / ewe lambing (LB / EL) for the Awassi and the Assaf, respectively. To increase the profitability, through improved lamb production, a breeding scheme was initiated in 1986 to introduce the B allele of the FecB (Booroola) gene to the Awassi and Assaf breeds. This led to the formation of the Afec–Awassi and Afec–Assaf strains with prolificacy of about 2.0 LB / EL. A marker assisted selection approach and the use of induced ovulation rate as selection criteria were incorporated into the breeding programs. The Awassi is the main type of sheep in the Middle East where about 80 million sheep of this breed and other related fat tail breeds are present. Distribution of the BB Afec semen or rams in those flocks, through regional breeding programs, can improve their productivity and their economics, facilitating the transition into a more intensive production system. The economic justification for launching such a breeding program depends mainly on the local lamb price. 2001 Elsevier Science B.V. All rights reserved. Keywords: Awassi; Assaf; Booroola; Afec; Dairy sheep; Economic analysis
1. Introduction The Awassi, the main type of sheep in the Middle East is kept under a wide range of production systems: from nomadic flocks relying on natural pasture in semi-arid areas where lamb production is the primary product, to intensive dairy flocks where *Corresponding author. Tel.: 1972-3-9683-752; fax: 1972-39603-678. E-mail addresses: [email protected] (E. Gootwine), [email protected] (G.E. Pollott).
milk and lambs contribute almost equally to the flock gross income (Epstein, 1985). The Awassi is known for its hardiness and adaptability and in the case of the Improved Awassi, also for its high milk production. Yet, prolificacy of the Awassi is low; about 1.2 lambs born per ewe lambing (LB / EL) (Epstein, 1985). As lamb production is an important source of income in all Awassi flocks, increasing fecundity of the Awassi has always been an important breeding goal. Indeed, Finn and Romanov crosses with the Awassi had a prolificacy of about 2.0 (Goot et al., 1980). However, those crosses were not widely
0301-6226 / 01 / $ – see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S0301-6226( 01 )00240-8
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E. Gootwine et al. / Livestock Production Science 71 (2001) 49 – 58
accepted by the industry, mainly because of the preference for the traditional fat tail phenotype by both breeders and consumers. Crossing the Awassi with the East Friesian breed resulted in the formation of the Assaf breed (Gootwine and Goot, 1996) which has become the main dairy breed in Israel and has been integrated into sheep production systems in other Mediterranean countries, such as Spain and Portugal (Ugarte et al., 2000). The prolificacy of the Assaf is higher than that of the Awassi at about 1.6 LB / EL (Epstein, 1985). However, this semi-fat tail breed is less adaptable to local conditions than the Awassi. The FecB gene is a major gene that affects ovulation rate in sheep. 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 et al., 1985). In 1986, breeding schemes were initiated in Israel to introduce the B allele into the Awassi and Assaf breeds. Production of the F1 generation was achieved through crossing local sheep with four BB homozygous Booroola Merino rams obtained from the Invermay Agriculture Center, New Zealand. The first backcross (BC1) populations were produced by mating eight F1 Booroola–Awassi and six F1 Booroola–Assaf rams with Awassi and Assaf ewes, respectively. This was followed by several backcrossing steps, along with selection of ewes carrying the B allele using a marker assisted selection approach (Gootwine et al., 1998), and a final intercross phase. As the available markers for the FecB gene were found to be informative only in the case of the Booroola–Awassi crosses, induced ovulation rate at 5 months of age, natural ovulation rate monitored in cycling ewes and litter size were the criteria for selection of B 1 ewes in the Booroola–Assaf crosses (Gootwine et al., 1993). Altogether, 127 Booroola–Awassi BC1, 95 Booroola–Assaf BC1, 181 Booroola–Awassi BC2 and 159 Booroola–Assaf BC2 ewes were produced through the crossbreeding work. Once BB homozygous nucleus populations have been established, BB rams will be distributed to intensive or semi-intensive commercial Awassi or Assaf flocks. First results of the effect of the Booroola Merino inheritance on lamb and milk production in the F1
and the BC1 generations were described by Gootwine et al. (1993) and Gootwine (1995). High prolificacy as a result of carrying the B allele and relatively low milk yield due to the presence of other Merino genes were the main observations. The economic aspects of increasing lamb production in semi-intensive non-dairy Awassi flocks by introducing the B allele were investigated taking into consideration different breeding methods for handling the Booroola gene and different economic environments (Spharim and Gootwine, 1997). It was found that under the range of economic parameters tested, this operation would be profitable in most scenarios and the higher the ratio between lamb price and feed costs, the greater the benefit from the use of the Booroola gene. The aims of the present communication are to analyze prolificacy and milk production characteristics in advanced Booroola Awassi backcross generations and to provide economic analyses which will define at what stage homozygous crossbred BB Awassi or Assaf rams may be profitably introduced into commercial dairy flocks.
2. Materials and methods
2.1. Ein Harod management The intensive management system of the Ein Harod Improved Awassi flock, where the crossbreeding programme has been taking place, was described by Gootwine et al. (1995) and Gootwine and Pollott (2000). Briefly, the flock comprised about 1200 ewes, was kept indoors all year round and ewes were fed to meet their nutritional requirements according to their level of production. Reproductive management included four 34-day breeding periods in the year when ewes were handmated following heat detection. Hoggets were first exposed to the ram at about 9 months of age, following oestrus synchronization. All lambs were identified at lambing and were moved to an artificial rearing unit. Ewes were milked twice daily from the day of lambing until their milk yield dropped to about 0.5 l / day or until they had to be dried off before lambing. Milk yield was recorded on the 15th day of each month and
E. Gootwine et al. / Livestock Production Science 71 (2001) 49 – 58
total milk yield throughout the lactation (TMY) was calculated as described by Pollott and Gootwine (2000a). Test day milking records were validated and stored using the on-farm ‘Ewe and Me’ software (Gootwine and Zenou, 1997).
2.2. Identifying carriers of the B allele of the FecB ( Booroola) locus Booroola Awassi crossbred ewes and rams were identified as B-allele carriers using the AE101 (Montgomery et al., 1993) and the BM1329 (Lord et al., 1998) microsatellites that flank the FecB locus (Lord et al., 1998, Gootwine et al., 1998). These markers were found to be informative in some of the Booroola Awassi families. The lambing rates of different backcrosses were compared by Chi Square analysis.
2.3. Milk records analysis Two milk yield data sets were analyzed in this study. The first data set included TMY records for 9385 lactations from ewes that lambed between 1980 and 2000. The distribution of the lactation records according to ewe genotype and the respective litter size is presented in Table 1, where BC1–4 was the first to the fourth backcross to the pure Awassi. The following model was fitted to TMY using least-squares analysis for unbalanced data [GLM procedure of the Statistical Analysis Systems (SAS) Institute, 1997]:
Table 1 The number of Awassi TMY records analyzed according to ewe genotype and litter size Genotype
Litter size
Total
51
TMY ijklnp 5 m 1 E i 1 LN j 1 LS k 1 Ml 1 Gn 1 e ijklnp where TMY ijklnp is the TMY of the ith ewe (E) in its jth lactation (LN), LS k is the litter size born to the ewe at the respective lambing, Ml is the month when the ewe lambed, Gn the ewe genotype (Awassi, BC1, BC2, BC3 and BC4) and e ijklnp is the randomly distributed error term. To see if the effect of LS differed between genotypes the interaction of LS and genotype was also fitted. Litter sizes greater than three were grouped into one category. Least-squares means, within an effect, were compared and the paired differences between levels within an effect were tested against a two-tailed t distribution. The second milk yield data set consisted of 3740 complete lactations with 5–10 test-day records from 1360 Awassi, BC2, BC3 and BC4 ewes. A lactation was assumed to be completed when its last daily milk yield record reached 0.6 l / day. This data set included TMY and other calculated lactation parameters (see Pollott and Gootwine, 2000a) namely: lactation length (LL), lambing interval (LINT), day of peak yield (DP), peak yield (PY), maximum secretion potential (MS), relative growth rate in milk production (GR), relative decline rate in milk production (DR), daily increase in milk production midway between lambing and peak (GM) and daily loss of milk production midway between peak and end of lactation (DM). Lactation curve parameters for each complete lactation were calculated using the Pollott Multiplicative model (Pollott, 2000) using an iterative least-squares non-linear curve fitting procedure (Procedure NLIN in SAS). The ‘best fit’ curve was obtained for each lactation when there was a less than 10 26 difference between the error sums of squares in successive iterations. The following model was fitted to the various lactation parameters using the GLM procedure of SAS: Pijklnp 5 m 1 E i 1 LN j 1 LS k 1 Ml 1 Gn
1
2
31
Awassi BC4 BC3 BC2 BC1
5625 195 186 322 55
2178 81 126 240 165
25 22 42 84 39
7828 298 354 646 259
Total
6383
2790
212
9385
1 (Gn 3 LS k ) 1 ei jklnp where Pijklnp is a lactation parameter of the ith ewe in its jth lactation, LS k is the number of lambs born to the ewe at the start of the lactation, Ml is the month when the ewe lambed, Gn is the ewe genotype (Awassi, BC2, BC3, BC4), Gn 3LS k is the
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genotype3litter size interaction and ei jklnp is the randomly distributed error term. Ewes were absorbed in the analyses in order to reduce the size of the matrix of fixed effects and all results quoted are from Type III analyses (SAS Institute, 1997). Least-squares means were computed by fitting the above model to the data using the REML option in the SAS MIXED procedure and including ewe as a random effect. Least-squares means, within an effect, were compared and the paired differences between levels within an effect were tested against a twotailed t distribution.
2.4. Estimation of genetic parameters The transmitted (gI), heterosis (hI) and recombination (rI) effects for TMY were estimated for the Booroola Awassi crosses by equating their expected relative values as defined in Table 2 (Dickerson, 1969) with the least-squares means of TMY estimates for the different genotypes derived from the RAML analysis and presented in Table 6. Pure Booroola Merino ewes were never present in the Ein Harod flock and Booroola–Awassi F1 ewes were not included in the present study. To obtain the genetic estimates, it was postulated that TMY of Booroola Merino ewe performing under the Ein Harod management was 70 l, and that TMY of F1 ewes was 252 l – the result obtained in previous study (Gootwine et al., 1995).
Table 2 Expected relative performance for different crosses between the Booroola Merino and the Awassi breeds Genotype
Awassi Booroola–Merino a Booroola3Awassi (F1) F13Awassi (BC1) Awassi3BC1 (BC2) Awassi3BC2 (BC3) Awassi3BC3 (BC4)
Crossbreeding coefficients gI
hI
rI
1 0 1/2 3/4 7/8 15 / 16 31 / 32
0 0 1 1/2 1/4 1/8 1 / 16
0 0 0 1/4 1/8 1 / 16 1 / 32
Coefficients for transmitted (gI), heterosis (hI) and recombination (rI), effects relative to the pure Booroola Merino and the Awassi performances. a Not available from these data.
2.5. Economic analysis The net present value (NPV) of transforming a pure Awassi or Assaf flock into a flock where all ewes are heterozygous for the B allele over an 8-year period was investigated. The B1 flock was constructed by inseminating, once a year for 4 years, all 1 1 ewes in the flock with BB rams and recruiting their B1 female progeny as the sole replacements Rams with Awassi /Assaf levels of 87.5% (BC2) or more were considered. In the fifth year of the project, 3 / 4 of the flock consists of B1 ewes and in the sixth year all ewes are B1. Those B1 ewes are bred to non-carrier 1 1 males and their B1 ewe lambs were selected as replacements from the fifth year based on genotyping for markers linked to the FecB gene. In this economic analysis, a flock of 1000 breeding ewes was considered, the yearly replacement rate was 25%, hoggets lambed for the first time at the age of 2 years and ewes were culled after their fourth lactation. It was assumed that increasing prolificacy did not affect the reproductive activity of the flock. Other parameters that were used in the economic analysis are listed in Table 3.
3. Results and discussion
3.1. Prolificacy assessment of different Booroola– Awassi crosses The genotype at the FecB locus was identified, using molecular markers, for 20, 32 and 63% of the BC2, BC3 and BC4 ewes, respectively. For the other ewes, the markers were not informative. Chi Square analysis showed that genotype and parity had a highly significant effect (P,0.005) on prolificacy whereas the effect of the backcrossing stage was not significant (P.0.6). Overall, the average prolificacy in the first four parities for B1 and 1 1 ewes was, respectively, 1.88 and 1.22 lambs born / ewe lambing. The prolificacy of the different genotypes according to parity is presented in Table 4. The difference of 0.66 lambs born / ewe lambing between B1 and 1 1 ewe in this study is in agreement with similar difference found in previous work in the Booroola Assaf and the Booroola Awassi
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Table 3 Parameters used in the economic analysis Parameter
Awassi
Assaf a
Percent of ewes lambing / year No. lambings / ewe / year Prolificacy of 1 1 ewes (LB / EL)b 1st parity 2nd parity 3rd parity 4th parity Prolificacy of B1 ewes 1st parity 2nd parity 3rd parity 4th parity Lamb mortality rate For 1 1 ewes For B1 ewes Milk production of a ewe in the 4th lactation (l) Milk production of crosbred ewe relative to Awassi ewe Milk production / lactation relative to the 4th lactation c 1st lactation 2nd lactation 3rd lactation Price / kg live lamb at the farm gate ($) Lamb weight at marketing (kg) Price / kg milk at the farm gate ($) Price / kg feed ($) Kg of feed / ewe / year Cost of producing marginal kg milk ($) Cost of raising a lamb d ($) Price for BB semen ($) Price for genotyping a ewe lamb entering the flock ($) Interest rate (%)
90 1.0
1.2
1.13 1.21 1.33 1.31
1.40 1.51 1.60 1.60
1.66 2.01 1.89 2.10
1.80 2.01 2.10 2.30
0.04 0.15 520
320 0.88
0.76 1.06 1.05 3.5 50 0.7 0.27 500 0.11 72.5 4.8 22 7
a
Only values that differ from the Awassi model are presented. Based on results of the present study. c Based on the 1999 Israeli Flock Book. d Costs include rearing in an artificial rearing unit, weaning at 1 month and fattening on ad lib concentrates and 0.1 kg hay / day / head until marketing. b
F1 and BC1 generations (Gootwine et al., 1993, 1995) and in line with the estimated effect of one copy of the B allele on prolificacy found in other breeds (Piper et al., 1985).
3.2. Milk production A summary of the tests of significance from the REML analysis for the effects of the various factors
on TMY is presented in Table 5. Lactation, crossbreeding level, interaction of crossbreeding level and litter size, month of lambing and ewe all had a significant effect (P,0.01) on TMY. Leastsquares means for the effect of crossbreeding level on TMY are shown in Table 6 by litter size. Generally, TMY increased as upgrading to the Awassi progressed. However, the increase in average TMY lagged behind the proportion of the Awassi in
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Table 4 Prolificacy (lambs born / ewe lambing) up to the 4th parity of Booroola–Awassi BC2, BC3 and BC4 ewes identified as carriers (B1) or non carriers (1 1) using markers linked to the FecB gene Backcross
n
Prolificacy of non-carrier 1 1 ewes BC2 BC3 BC4 Overall Prolificacy of carrier B1 ewes BC2 BC3 BC4 Overall
Parity 1
2
3
4
39 41 69
1.15 1.05 1.15
1.12 1.20 1.27
1.29 1.25 1.40
1.33 1.37 1.24
149
1.66
2.01
1.89
2.10
26 19 54
1.61 1.58 1.73
1.97 1.58 1.73
1.97 1.84 1.82
2.18 2.10 1.91
99
1.13
1.21
1.33
1.31
Table 5 Significance levels for the effects included in the analysis of total milk yield (l)
3.3. Estimation of genetic parameters for TMY in the Booroola– Awassi crosses
Factor
DF
F
P
Lactation No. Litter size Cross Cross3LS Month of lambing
9 3 4 12 125
135.7 2.5 46.2 25.3 25.3
*** 0.08 ** ** ***
Estimates of TMY for the Awassi, BC2, BC3 and BC4 genotypes are shown in Table 6. The estimate used for the F1 generation was 252 l (Gootwine et al., 1995). The transmitted, heterosis and recombinant effect in the Booroola Awassi crosses was calculated to be 436610 l (P,0.005), 236610 l (P,0.04) and 2211642 l (P,0.01), respectively. Investigating a range of values (40–150 l) for pure Booroola Merino TMY did not change the results very markedly. The negative value for the heterosis effect suggests that dominant genes for low milk production may be present in the Booroola Merino, as anticipated by Gootwine et al. (1995). The
**P,0.01; ***P,0.001.
the cross. In this study, the TMY of BC1 ewes was 0.64 of the pure Awassi. A similar result for BC1 TMY of 0.63 was obtained by Gootwine et al. (1995) when the TMY of the pure Awassi was 506 l.
Table 6 Least-squares mean values for TMY (l) for Awassi, BC1, BC2, BC3 and BC4 ewes by litter size Genotype
Awassi (%)
Litter size 1
2
3
520 a 504 a 461 a 424 a 314 b
526 a 475 a 438 a 405 a 279 b
Overall mean
TMY relative to Awassi
516 z 485 zy 450 zy 413 y 331 x
1.00 0.94 0.87 0.80 0.64
Total milk yield Awassi BC4 BC3 BC2 BC1 ab
100.0 96.9 93.7 87.5 75.0
513 a 477 a 452 a 413 a 402 a
Within a genotype row, litter size means followed by different superscripts differ significantly. xzyWithin the ‘Overall mean’ column, means followed by different superscripts differ significantly.
E. Gootwine et al. / Livestock Production Science 71 (2001) 49 – 58
relatively high recombination loss for TMY indicates that epistatic gene-effects can explain part of the Awassi’s high milk producing ability. A similar conclusion on the genetics behind the Awassi’s high milk production was reached by Pollott and Gootwine (2000b) from a within-Awassi breed analysis and the implication of that result on further selection for high milk production in the Awassi has been discussed.
3.4. Effect of crossbreeding on lactation parameters In order to study the crossbreeding effect on lactation parameters, records from complete lactations were investigated. The results from the analysis show that ewe, litter size, lactation number, month of lambing, month of conception and ewe genotype all had significant effects on the different lactation parameters. Those results are in line with results from a similar analysis of pure Awassi records reported by Gootwine and Pollott (2000), except for the fact that in this analysis, LS has become a significant effect on DP, GR and DR and has increased its level of significance for TMY, MS, GM and DM. Also, month of conception affected PY and GM and has become a greater influence on DR. Type of Booroola–Awassi cross affected all traits except DP and GR but there was no significant interaction between LS and type of cross. Least-squares means for the different traits, where the effect of the type of cross was significant, are presented in Table 7. Pure Awassi ewes had a higher milk yield, longer lactations, longer lambing intervals, a higher peak yield, a higher maximum secretion potential, a slower rate of loss in milk secretion potential, secreted more milk mid-way between parturition and peak and were less persistent than most of the backcrosses.
3.5. An economic analysis of the introgression of the Booroola gene into Awassi or Assaf populations According to the analysis, a flock of 1000 Awassi or Assaf ewes produce annually 1076 and 1581 lambs and 503 000 and 310 000 l of milk, respectively. Inseminating all ewes in such flocks with BC2
55
Table 7 Least-squares means for TMY and other lactation parameters for Awassi, BC2, BC3 and BC4 ewes Trait
Genotype Awassi
BC4
BC3
BC2
477 204b 371 b 3.42 a 3.91 a 0.0220 b 67.3 a 17.1 ab
443 202 b 368 b 3.22 3.71 0.0225 b 63.5 a 16.6 b
Parameter values TMY (l) LL (day) LINT (day) PY (l) MS (l) DR GM (g / day) DM (g / day)
533 a 214 a 388 a 3.68 4.22 0.0211 a 71.0 18.0 a
514 a 214 a 388 a 3.44 a 3.95 a 0.0208 a 65.7 a 16.0 b
Within traits, values followed by the same superscript are not significantly different (P,0.05).
homozygous BB rams will result, over the 8 years of the simulated project, in the development of prolific BC3 B1 flocks with a milk production performance equal to 87% of the respective pure breed, as presented in Table 6. Through the time course of the project, annual changes in lamb and milk production were first observed in the third year and came into full expression in the sixth year of the project (Fig. 1). The net present values for developing an Awassi flock into a B1 flock, under different combinations of milk and meat prices, are presented in Table 8. Interestingly, while introgression of the Booroola gene into non-dairy Awassi flocks was found to have positive NPV in most cases (Spharim and Gootwine, 1997), in dairy Awassi flocks under most conditions, such a project has a negative NPV when homozygous BC2 rams are used. Only when the meat price was high (4.0 US$ / kg), was the project marginally profitable. The same analysis for the Assaf showed that even for the case of the highest lamb price and the lowest milk price, the project had a negative NPV of US$254 000. The analysis in Table 8 was carried out for BC3 ewes at 87% of the Awassi milk production level (Table 6). The effect of the Awassi proportion on the project NPV has been further investigated, as shown in Table 9. The results in Table 9 show that under a situation where the milk price was 0.7 US$ / l and the live
E. Gootwine et al. / Livestock Production Science 71 (2001) 49 – 58
56
Fig. 1. Change over time in lamb and milk production following introgression of the B allele of the FecB gene to a flock of 1000 Awassi or Assaf ewes.
Table 8 Net present values (NPV) of a simulated project where the Booroola gene is introgressed into a dairy Awassi flock
Table 9 NPV for different Awassi contributions in a simulated project where the Booroola gene was introgressed into an Awassi flock
Milk price (US$ / l)
Milk production (l) at the 4th lactation
Lamb meat price (kg live weight, US$) 2.5
3.0
3.5
4.0
211 215 220 224 228
17 13 9 4 0
NPV (31000 US$) 0.65 0.60 0.70 0.72 0.75
268 272 276 280 285
239 244 248 252 256
% Awassi 88
90
94
97
100
32 32 33 33 34
58 58 59 59 59
84 84 84 84 84
NPV (31000 US$)
lamb price was 3.5 US$ / kg (Table 3), profitability from introducing the B allele into an Awassi dairy flock was achieved only when ewes had over 90% Awassi genes. In order to achieve that, rams belonging to the BC3, or a more advanced backcross, need to be used.
550 520 490 460 430
221 220 219 218 217
23 22 21 0 0
A comparable analysis carried out for an Assaf flock (Table 10) showed that under similar conditions, profitability will only be achieved when the new B1 ewes have at least 97% Assaf genes, implying that inseminations should be started only when BC4 BB rams are available. As the prolificacy
E. Gootwine et al. / Livestock Production Science 71 (2001) 49 – 58 Table 10 NPV for a project where the Booroola gene is introgressed into an Assaf flock Milk production (l) at the 4th lactation
the economy of the breed. Increasing prolificacy on the other hand proves to be an effective way to increase profitability.
% Assaf 88
90
94
97
100
Acknowledgements
NPV (31000 US$) 350 320 290 260 230
57
234 233 232 231 230
223 222 221 220 220
22 22 21 0 0
14 14 14 15 15
31 31 31 31 31
of the Assaf was higher than that of the Awassi, even under optimal conditions, the NPV of the project was less than that for the Awassi. The genotyping of ewe lambs, daughters of B1 ewes and 1 1 rams, is required in order to identify and select B1 ewe lambs as replacements in the last 3 years of the 8-year project and on average, two ewe lambs have to be typed for every ewe lamb selected. The genotyping price has an effect on the economics of the project and doubling the genotyping price from 22 to 44 US$ / ewe entering the flock will reduce profitability by 33, 18 and 13% for flocks where milk production of the crossbreds is 94, 97 and 100% of the Awassi, respectively.
4. Conclusions Introgression of the Booroola gene into the Awassi and the Assaf dairy breeds is a unique situation as in most other cases the Booroola gene has been introgressed into meat or wool–meat dual purpose breeds. In non-dairy breeds, where lamb production is the main source of income, the economic contribution of the Booroola gene can be appreciated as early as in the first-cross generation. However, as the Merino genes have an adverse effect on Awassi and Assaf milk production, a careful breeding design has to be undertaken to benefit from the Booroola gene in those dairy breeds. The results of the present study indicate that nonadditive genetic effects play an important role in determining the high milk production of the Awassi. If so, selection for higher milk production in the Awassi may have a limited contribution to improve
The authors express their thanks to the Invermay Agricultural Research Center, New Zealand for supplying Booroola rams, to the team of the Ein Harod Awassi flock for continuous collaboration and to Mr. Geel Eilat for help with the economic analysis.
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