Submitted to: Western Section of Animal Science Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 4/1/2013
Publication Date: 6/1/2013
Publication URL: www.asas.org/docs/default-source/western-section/proceedings.pdf?sfvrsn=0
Citation: Kirschten, D.P., Notter, D.R., Lewis, G.S. 2013. Genetic evaluation of the probability of lambing in yearling Targhee ewes. Western Section of Animal Science Proceedings. 64:161-164. Interpretive Summary: Modern genetic technologies can be used to enhance the inherent abilities of ewe lambs to conceive as lambs and produce lambs at one year of age. Enhancing these inherent abilities would allow producers to conserve feed and natural resources, increase the rate of genetic selection, and increase the efficiency of producing human foods. Thus, genetics studies are underway at the USDA, Agricultural Research Service, U.S. Sheep Experiment Station to characterize the effects of selecting ewe lambs to lamb at one year of age. Recent results from these studies indicate that sire has important effects on the ability of a ewe lamb to lamb at one year of age, and that genetic variation exists among ewe lambs in their ability to lamb at one year of age. Sheep producers can use this information to select sires to make significant improvements in their economic returns and simultaneously improve the efficiency of producing human foods.
Technical Abstract: The objective of this study was to determine the additive genetic control of lambing percentage in yearling Targhee ewes. The records of 3,103 ewe lambs born from 1989 to 2011 and mated at approximately 7.5 mo of age were analyzed. Records included sire, dam, weaning weight, breeding pen, age of dam, and lambing data. Lambing data were recorded as a binomial trait. Live or stillborn, full-term lambs were recorded as a lambing success (i.e., 1) for a yearling ewe; failure to produce a full-term lamb by a ewe was indicated in the data with a 0. The 314 sires of the ewe lambs had an average of 9.6 daughters/sire; 146 sires had = 5 daughters, and 36 sires had = 20 daughters. The 1,770 dams of the ewe lambs had an average of 1.85 daughters/ewe, with a range from 1 to 8. Yearling lambing percentage (n lambed/n mated) varied from 26 to 79% across years and averaged 49.6%. Lambing percentage of yearling ewes varied among sires from 0 to 100%, and values for sires with = 20 daughters ranged from 23 to 88%. Lambing was analyzed as a threshold trait with an underlying continuous distribution. The genetic model included fixed effects of year, breeding pen, and age of dam, with weaning weight as a covariate. The relationship matrix included 6,877 animals and included a minimum of 4 generations of pedigree information, with correspondingly more generations included for later-recorded animals. The heritability of lambing percentage on the underlying scale was 0.18 ± 0.04. The EBV for lambing percentage of sires of ewe lambs on the observed scale ranged from -37 to 36% and averaged -1%. The 10th and 90th percentiles of sire EBV were -20 and 17%, respectively, which indicated that sires in the 90th percentile would be expected to produce daughters with an 18.5% greater likelihood of lambing at 1 yr of age than sires with EBV in the 10th percentile.