|NGERE, LAURETTA - Oak Ridge Institute For Science And Education (ORISE)|
|MORGAN, JAMES - Katahdin Hair Sheep International|
|MILLER, JAMES - Louisiana State University|
|NOTTER, DAVID - Virginia Tech|
Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2017
Publication Date: 5/4/2018
Citation: Ngere, L., Burke, J.M., Morgan, J.L., Miller, J.E., Notter, D.R. 2018. Genetic parameters for fecal egg counts and their relationship with body weights in Katahdin lambs. Journal of Animal Science. 96(5):1590-1599. https://doi.org/10.1093/jas/sky064.
Interpretive Summary: Selection for parasite resistance in sheep allows farmers to minimize the need for parasite control and dewormers. However, sometimes selection for one trait (ie.,parasite resistance) leads to poorer performance in another, such as body weight. Scientists from the Oakridge Institute for Science and Education, the Agricultural Research Service - Booneville, AR, Virginia Tech, Louisiana State University and Katahdin Hair Sheep International determined that while there were low to moderate correlations between fecal egg counts and body weights in Katahdin lambs, moderate heritabilities for fecal egg counts indicated that genetic progress for this trait can be achieved and that selection for low fecal egg counts (parasite resistance) should have little or no effect on body weight. This information is important to sheep producers, scientists, veterinarians, and extension specialists aiming to improve genetic parameters in sheep.
Technical Abstract: Reliance on anthelminthic 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, type of birth and rearing, and management group (defined by joint effects of flock, sex, and birth year and season), and lamb age in days at each measurement time was fitted as a covariate. Additive maternal and maternal permanent environmental effects were not significant (P > 0.05), but litter effects influenced (P < 0.01) both WFEC and PWFEC. Heritability estimates from animal models 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. Genetic, 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.