Evaluation of Performance and Estimation of Genetic Parameters for Milk Yield and Some Reproductive Traits in Sheep Breeds and Crosses in the West Bank

This study was conducted to evaluate sheep productivity in the West Bank, and estimate genetic parameters (heritability and repeatability) for milk yield and prolificacy traits. The data included a total of 1711 milk records from 1243 ewes and a total of 3682 lambing records from 1837 ewes of the Awassi breed (AW), two Awassi-derived-lines (Improved Awassi, IA and Afec Awassi, AA), Assaf breed (AF) and Awassi x Assaf crosses (XB). The data were from the demonstration farms of the Small Ruminant Middle East Regional Program in the West Bank, collected during the years 2003 to 2010. Milk traits included total milk yield (TMY), total milk yield to 120 days of lactation (TMY120), and total milk yield to 150 days of lactation (TMY150) with number of ewes (n) and number of records (l) as follows: n=287, l=435 for AW; n=138, l=224 for IA; n=24, l=40 for AA; n=254, l= 339 for AF, and n=564, l= 758 for XB. Reproductive traits included number of lambs born per ewe lambing (NLB), number of lambs born alive per ewe lambing (NLBA), and lambing interval (LI): n=153, l=431 for IA; n=448, l=778 for AW; n=26, l=56 for AA; n=433, l= 968 for AF, and n=803, l= 1505 for XB). The data were analyzed using two linear models: a fixed-effects model for testing breed differences and other fixed environmental effects, and a mixed-model for estimation of genetic parameters. Genetic parameters were estimated using REML procedure. The fixed effects investigated for milk traits were: location-breed (LB), parity (PR), year-season of lambing (YS), treatment for induction of estrus (TRT: natural or PMSG sponges), number of lambs born per ewe lambing (NLB), number of milking tests (NMT), and lactation length (LL). For prolificacy traits, the fixed effects were: LB, PR, YS, and TRT. The results of milk traits showed that LB, PR, and YS had high significant effects on all milk traits (P < 0.001), while the effect of NLB was not significant (P > 0.05) for any milk trait. The effect of LL was highly significant (P < 0.001) on TMY, while NMT was not significant (p > 0.05). For prolificacy traits, LB, PR, and YS had significant effects (P < 0.05) for all studied traits, while TRT was significant for NLBA only. The least squares means for total milk yield (kg) per ewe over 150 days of lactation were: 185.5±8.7 for AA (experimental station of Betqad in Jenin)), 171.4 ±3.7 for IA (experimental station of Betqad), 123.6±4.1 (Jerusalem) to 212.0±7.1 (Hebron) for AW, 184.7±5.2 (Qalqilia) to 274.9±8 (Jenin) for AF, and 174.8±3.5 (Dora) to 328.3±7 (Nablus) for XB. The AA line, which carries the Booroola fecundity (FecB) gene, had the highest reproductive performance while AW and IA had the lowest performance. The least squares means of number of lambs born alive per ewe lambing were 1.47±0.06 for AA, 1.15±0.02 for IA, 1.11±0.02 (Jerusalem) and 1.19±0.04 (Hebron) for AW, ranged from 1.16±0.05 (Jenin) to 1.31±0.02 (Qalqilia) for AF, and ranged from 1.11±0.03 (Bethlehem) to 1.30±0.06 (Jerusalem) for XB. The least squares means of lambing interval (in days) were 338±14 for AA, 355±5 for IA, 361±6 (Jerusalem) and 429±14 (Hebron) for AW, ranged from 276±11 (Jenin) to 356±16 (Hebron) for AF, and ranged from 269±9 (Jerusalem) to 390±10 (Jerusalem) for XB. Estimates of heritability (h²) of TMY ranged from 0 in XB to 0.11 in AW. For TMY120 and TMY150, heritability ranged from 0 in XB to 0.16 in AW. Estimates of h² of NLB varied form 0 in XB to 0.09 in AW, and for NLBA it ranged from 0 in XB to 0.15 in AW. For LI it was 0.03 in AW and 0 for other breeds and crosses. The results of this study indicate that Assaf and Awassi x Assaf sheep are the recommended breeds for raising in the Northern areas of the West Bank (Nablus and Jenin). The study also emphasizes the need for full recording of performance and pedigree data in sheep farms as part of good management practice which should be part of a national recoding system.