Genetic evaluation of weaning weight and probability of lambing at 1 year of age in Targhee lambs

Authors: Kirschten, David; NOTTER, DAVID - Virginia Polytechnic Institution & State University; GILMOUR, ARTHUR - New South Wales Agriculture; Lewis, Gregory; Taylor, Joshua - Bret

Submitted to: Sheep and Goat Research Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/1/2015
Publication Date: 6/1/2015
Publication URL: d1cqrq366w3ike.cloudfront.net/http/DOCUMENT/SheepUSA/SGRJ_V30_1-5_Notter_6-15.pdf
Citation: Kirschten, D.P., Notter, D.R., Gilmour, A.R., Lewis, G.S., Taylor, J.B. 2015. Genetic evaluation of weaning weight and probability of lambing at 1 year of age in Targhee lambs. Sheep and Goat Research Journal. 30:1-5.

Interpretive Summary: Results from this study indicate that genetic variation exists among ewe lambs in weaning weight and in their ability to lamb at 1 yr of age. Ewe lambs with larger weaning weights were predicted to be more likely to lamb at 1 yr of age. This positive association was primarily environmental, indicating that management practices that increase weaning weight would be expected to increase the probability of lambing. By contrast, a small negative-genetic relationship was observed between the two traits, but the relatively low magnitude of the correlation indicates that multiple-trait selection using estimated breeding values would permit concurrent improvement in both weaning weight and the probability of lambing at 1 yr of age.

Technical Abstract: The objective of this study was to investigate genetic control of 120-day weaning weight and the probability of lambing at 1 year of age in Targhee ewe lambs. Records of 5,967 ewe lambs born from 1989 to 2012 and first exposed to rams for breeding at approximately 7 months of age were analyzed. Records included lamb birth dates, sire, dam, type of birth and rearing, dam age, and weaning weight and, for ewe lambs, the breeding pen and subsequent lambing data. Weaning weight was evaluated as a continuous variable, and lambing data were recorded as a binomial trait, but both traits were analyzed as continuous variables. Full-term lambs (either born alive or stillborn) were recorded as a lambing success (i.e., 1); failure to produce a full-term lamb was indicated with a 0. The relationship matrix included 14,041 animals and at least four generations of pedigree information, with more generations included for animals born in later years of the study. Heritability estimates were 0.14 ± 0.02 for 120-day weaning weight and 0.15 ± 0.04 for probability of lambing. Phenotypic and genetic correlations between the two traits were 0.18 ± 0.02 and -0.23 ± 0.18, respectively. Weaning weight and the probability of lambing at 1 year of age are thus expected to respond to selection. Ewe lambs with heavier weaning weights were more likely to lamb at 1 year of age, but this is an environmental, rather than genetic relationship, and selection for ability to lamb at 1 year of age may result in a small decrease in genetic merit for weaning weight.