Genetic parameters for fecal egg counts and their relationship with body weights in Katahdin lambs.

Reliance on anthelmintic drugs to control internal parasites in sheep is no longer sustainable because of the development of resistance to these drugs in parasite populations. Genetic selection may offer an alternative long-term solution, as differences in parasite resistance exist both within and among sheep breeds. However, selection for parasite resistance may have correlated effects on other production traits. The objectives of this study were to estimate genetic parameters for weaning (WFEC) and postweaning (PWFEC) fecal egg counts (FEC) and assess their relationship with birth (BWT), weaning (WWT), and postweaning (PWWT) BW in Katahdin lambs. The study used WFEC (n = 2,537), PWFEC (n = 3.421), BWT (n = 12,869), WWT (n = 10,961), and PWWT (n = 7,812) from 12,869 lambs measured between 2003 and 2015 in 13 flocks enrolled in the U.S. National Sheep Improvement Program. Animal and sire models were fitted to the data using the ASReml statistical package. Records were corrected for fixed effects of dam age, joint effect of type of birth and rearing, and management group (defined by joint effects of flock, sex, and birth year and season); lamb age in days at each measurement time was fitted as a covariate. Maternal additive and maternal permanent environmental effects were not significant (P > 0.05), but litter effects influenced (P < 0.01) both WFEC and PWFEC. Heritability estimates ranged from 0.18 to 0.26 for WFEC and 0.23 to 0.46 for PWFEC, depending on the model used. Heritability estimates from sire models were higher than estimates from animal models. Direct additive, litter, residual, and phenotypic correlations between WFEC and PWFEC were 0.82, 0.25, 0.15, and 0.29, respectively. Bivariate analyses revealed low to moderate correlations between BW and FEC. Moderate heritabilities for FEC in this study indicated that genetic progress for this trait can be achieved in Katahdin lambs and that selection for low FEC should have little or no effect on BW.

Variance components for direct and maternal effects on body weights of Katahdin lambs.

The aim of this study was to estimate genetic parameters for BW in Katahdin lambs. Six animal models were used to study direct and maternal effects on birth weight (BWT), weaning weight (WWT), and postweaning weight (PWWT) using 41,066 BWT, 33,980 WWT, and 22,793 PWWT records collected over 17 yr in 100 flocks. Models included fixed effects of management group, dam age, type of birth (for BWT) or birth and rearing (for WWT and PWWT), and lamb age at weighing (fitted as a covariate for WWT and PWWT; all < 0.05). Variance components for random effects were estimated in sequentially more complex models and tested for significance with likelihood-ratio tests. A model that fitted only an additive animal effect overestimated additive variance for all BW, resulting in larger estimates of direct heritability than models that included maternal effects. Maternal effects explained variation ( < 0.05) in all BW. Heritability estimates for optimal models were 0.15 ± 0.01 for BWT, 0.18 ± 0.02 for WWT, and 0.20 ± 0.02 for PWWT. Estimates of maternal heritabilities were 0.14 for BWT, 0.10 for WWT, and 0.06 for PWWT, with SE = 0.01. Permanent environmental maternal effects explained 4 to 6% (±1%) of total phenotypic variances for these BW. Litter effects included temporary environmental effects common to littermates and a proportion of the dominance genetic variance and accounted for 16 to 19% (±1%) of phenotypic variance. Correlations between additive direct and maternal genetic effects were -0.14 for BWT, -0.23 for WWT, and -0.04 for PWWT but differed from 0 ( < 0.05) only for WWT. The total heritability predicted the total response in direct and maternal genetic effects from mass selection and was 0.23 for BWT, 0.20 for WWT, and 0.23 for PWWT. Direct and maternal additive, maternal permanent environmental, residual, and phenotypic correlations between BWT and WWT were 0.53 ± 0.05, 0.58 ± 0.06, 0.51 ± 0.06, 0.39 ± 0.01, and 0.44 ± 0.01, respectively; those between BWT and PWWT were 0.45 ± 0.06, 0.58 ± 0.08, 0.36 ± 0.08, 0.33 ± 0.01, and 0.37 ± 0.01 respectively; and those between WWT and PWWT were 0.85, 0.99, 0.92, 0.77, and 0.81, respectively, with SE ≤ 0.02. Therefore, both direct and maternal effects had an important impact on BW in Katahdin lambs. Models that included both additive and permanent environmental maternal effects as well as a temporary environmental litter effect should result in more accurate estimates of breeding values and better selection decisions.

Crossbreeding in tropical sheep: incidence of dystocia and parturition losses.

Studies were carried out on the incidence of dystocia and parturition losses during a crossbreeding experiment involving 96 West African Dwarf (WAD) ewes mated with rams of 4 breeds--WAD, Ouda, Permer and Yankassa. Results obtained indicated 8 (5.7%) cases of dystocia and 20 (10.64%) cases of stillbirths or death of lambs at birth. The WAD sires were not associated with dystocia or stillbirths but other sire groups were involved in both. All the difficult parturitions occurred during the rainy season while all stillbirths not associated with dystocia occurred during the dry season. The sires used and the level of feeding the ewes during pregnancy may be associated with the dystocia cases and parturition losses recorded. Eighty per cent of the dystocias involved ram lambs. The mean gestation period of the ewes that lambed during the dry season was significantly (P < 0.01) longer than that of the rainy season group. Application of traction and Caesarean operation were used in the treatment of dystocia cases.

Response of Nigerian zebu cattle to zeranol implants.

The effect of Zeranol, an anabolic agent, on the weight gains of Nigerian zebu fattening bulls was investigated over a period of 16 weeks. Implanted Sokoto Gudali and White Fulani bulls showed average daily weight gains of 0.5 and 0.49 kg respectively as compared to 0.47 and 0.41 kg by non-implanted counterparts. The anabolic effect of Zeranol was evident up to 8 to 9 weeks after implantation, after which there was no significant difference in weight gains of implanted and control animals.

Crossbreeding of exotic and indigenous cattle in Nigeria--haematological correlates.

The blood values of the German Brown, N'Dama and their three-quarter, half and quarter hybrids were studied to ascertain if and how some haematological parameters changed with crossbreeding. It was found that the red blood cell (RBC) and white blood cell (WBC) count and packed cell volume percentage (PCV) were significantly higher (P less than 0.01) in the N'Dama than in the German Brown; the crosses had values which were intermediate as compared to the two parent breeds. Generally, the changes in the mean blood values paralleled changes in the expected genotypes resulting from crossbreeding of the two parent breeds. The tendency of the blood values to change in direct proportion to the degree of N'Dama contribution was strongest for the WBC, followed by the PCV and RBC, respectively. A small random sample for leucocyte differential count did not reveal any differences amongst the genotypic groups.

Mitochondrial genetic variation in European, African and Indian cattle populations.

Mitochondrial DNA from representative animals of 13 different cattle breeds was assayed for restriction fragment length polymorphisms (RFLP) to determine phylogenetic relationships and levels of variation among breeds; 16 different mitotypes were found, described by 20 polymorphisms. Within these 16 mitotypes two major lineages were apparent: an Afro-European and an Asian type. These were found to differ at over 2.3% of sites surveyed. None of the mitotypes found in the Asian lineage was detectable in the Afro-European lineage and vice versa. Within each of the major mitotypes there were no further significant differences within or among breeds. Using rates of mitochondrial evolution estimated from other species, the two lineages were estimated to have diverged between 575,000 and 1,150,000 years ago; well outside the 10,000 years bp timeframe postulated by a single domestication hypothesis. The results presented are concordant with those generated in other studies and provide strong evidence for an independent domestication of Asian Bos indicus. Furthermore, the grouping of all African indicine populations within the clade containing all Bos taurus lineages points to the hybrid origins of the humped cattle of that continent.