Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/28/2003
Publication Date: 3/1/2004
Citation: Rogers, P.L., Gaskins, C.T., Johnson, K.A., Macneil, M.D. 2004. Evaluating longevity of composite beef females using survival analysis techniques. Journal of Animal Science 82:860-866. Interpretive Summary: Increasing longevity of females reduces annual production costs associated with raising replacement heifers, increases the number of high producing mature cows, and reduces the number of cows that are culled involuntarily. In this research we sought to 1) identify risk factors affecting longevity of beef females, 2) evaluate utility of measures collected early in life in predicting longevity, and 3) estimate the heritability of longevity, when females were culled primarily as a result of their not being pregnant following a 45-d breeding season. The relatively low heritability and lack of early in life indicators of longevity found in this study suggest genetic improvement of longevity may continue to be difficult due to prolonged generation intervals and relatively little response per unit of selection applied. Matching genetic potential of cows to the production environment, such that rebreeding performance is not compromised by concurrent lactation, appears to be a consideration in retaining beef females when open cows are culled. Calving difficulty appears to be an important risk factor contributing to early culling of beef females and management may seek to reduce its frequency or mitigate its effects. These results are useful to beef producers and their advisors in planning profitable breeding programs.
Technical Abstract: Objectives were to: 1) identify risk factors affecting longevity of beef females, 2) evaluate utility of measures collected early in life in predicting longevity, and 3) estimate heritability of longevity when females were culled primarily for not being pregnant following a 45-d breeding season. Data were from 1,379 Composite Gene Combination (CGC) (½ Red Angus, ¼ Charolais, ¼ Tarentaise) cows born from 1982 through 1999 at USDA-ARS, Fort Keogh Livestock and Range Research Laboratory, Miles City, MT and first calving at approximately two years of age. Length of productive life was modeled using Cox regression to identify factors affecting longevity of beef females. Age at first calving and progeny birth weight did not significantly influence longevity (P>0.05). Cows that experienced dystocia were at significantly greater risk of being culled than those that calved without assistance (P<0.01). On average, as breeding value for cow weight increased, risk of being culled decreased (P<0.01) whereas risk of being culled increased with increasing maternal breeding values for pre-weaning gain (P<0.05). Traits measured before one year of age did not explain significant variation in subsequent longevity of cows (P>0.20). Heritability of functional longevity was estimated to be 0.14. Relatively low heritability and lack of early in life indicators of longevity suggest genetic improvement of longevity will be difficult. Matching genetic potential of cows for size and milk production to the production environment such that rebreeding performance is not compromised by concurrent lactation appears to be a consideration in retaining beef females when open cows are culled.