Submitted to: World Congress of Genetics Applied in Livestock Production
Publication Type: Proceedings
Publication Acceptance Date: 3/13/2002
Publication Date: 8/19/2002
Citation: Southey, B.R., Rodriguez-Zas, S.L., Leymaster, K.A. 2002. Analysis of lamb mortality using competing risks. Proceedings of the 7th World Congress of Genetics Applied in Livestock Production. CD-ROM Communication No. 02-03. Montpellier, France. Interpretive Summary: Lamb survival is an important factor that influences profitability of sheep production. Seedstock producers have not used selection to improve survival due to the low heritability, typically reported about 10%. But lambs die due to numerous reasons and some causes of mortality may be under greater genetic control than other causes. Heritability estimates indicated that mortality caused by disease and external (injury and weather related) factors were less heritable than deaths due to dam, pneumonia, and other causes. Accounting for causes of mortality could allow producers to select more effectively for improved lamb survival.
Technical Abstract: A competing risks model was used to describe lamb mortality up to four weeks of age in a composite sheep flock with 8,642 lamb records. Discrete survival methods were applied using sire and animal models. The results indicated that substantial variation exists in the risk of lambs dying from different causes including disease, pneumonia and dam related effects such as dystocia. Estimates of heritability typically ranged between 10 and 20% and depended on the cause of mortality. These results indicate that ignoring the causes of mortality and longevity may hide important genetic differences. Therefore, breeding programs are likely to be ineffective when multiple causes such as mortality and longevity are ignored.