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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #147416
Title: RISK FACTORS ASSOCIATED WITH CULLING FEMALES IN A COMPOSITE BEEF HERD

Author
item ROGERS, P - WA STATE UNIV PULLMAN
item GASKINS, C - WA STATE UNIV PULLMAN
item JOHNSON, K - WA STATE UNIV PULLMAN
item Macneil, Michael

Submitted to: Western Section of Animal Science Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 4/1/2003
Publication Date: 6/1/2003
Citation: ROGERS, P.L., GASKINS, C.T., JOHNSON, K.A., MACNEIL, M.D. RISK FACTORS ASSOCIATED WITH CULLING FEMALES IN A COMPOSITE BEEF HERD. WESTERN SECTION OF ANIMAL SCIENCE PROCEEDINGS. 2003. V, 54. P. 68-71.

Interpretive Summary: In beef production systems, longevity of breeding stock has substantial impact on economic efficiency. Females remaining in production beyond their breakeven age must compensate for females culled earlier. The goal of this research was to identify factors placing beef females at risk of being culled before they could reach their breakeven age. Specific objectives were to evaluate genetic and phenotypic variables that potentially affected 1) the probability of a heifer calving as a 2-yr-old, and 2) the subsequent survival of the cow. Data were from a composite population collected over the period 1982-2001. Heifers born later in the calving season and those with heavier birth weights were more likely to calve as 2-yr-olds. Conversely, probability of calving at two years of age tended to decrease as 200 d pre-weaning gain and BV for mature weight increased Heifers reared by mature cows (5+ years old) were more likely to calve at two than heifers reared by younger cows. Relationships of age at culling with breeding values and first calving measurements of females were assessed in separate survival analyses. As breeding value (BV) for mature weight increased, risk of being culled decreased. On average, as direct and maternal BV for pre-weaning gain increased so did the risk of being culled. Phenotypes for age at first calving, birth weight, and 200 d pre-weaning gain of a heifer's first calf did not influence age at culling. Heifers experiencing dystocia were at 36% greater risk of being culled than heifers that did not. Cows having a genetic profile consistent with nutritional resources were at less risk of being culled than those with greater genetic potential for production.

Technical Abstract: Our goal was to identify factors affecting probability of a heifer calving as a two-yr-old and factors affecting risk of a beef female being culled. Data were from the CGC composite herd (1/2 Red Angus, 1/4 Charolais, 1/4 Tarentaise) at Miles City, MT in which heifers were exposed to bulls as yearlings. Logistic regression was used to assess the effect that heifer (n = 1,756) phenotypes and breeding values (BV) had on the probability of calving as a 2-yr-old (P(C2)). Heifers born later in the calving season (P < 0.05) and those with heavier birth weights (P < 0.1) had an increased P(C2). Conversely, P(C2) tended to decrease as 200 d pre-weaning gain and BV for mature weight increased (P < 0.05). Heifers reared by mature cows (5+ years old) were more likely to calve at two than heifers reared by younger cows (P < 0.05). Neither direct nor maternal BV for pre-weaning gain affected P(C2) (P > 0.10). Relationships of age at culling with breeding values (n = 1,382) and first calving measurements (n = 1,254) of females were assessed in separate survival analyses using Cox regression. Independent variables were coded into evenly spaced categories. Records from pregnant cows that were sold and from cows in the herd in 2001 were treated as censored (33%). As BV for mature weight increased, risk of being culled decreased (P < 0.01). On average, as direct and maternal BV for pre-weaning gain increased so did the risk of being culled (P < 0.1). Phenotypes for age at first calving, birth weight, and 200 d pre-weaning gain of a heifer's first calf did not influence age at culling (P > 0.10), but heifers experiencing dystocia were at 36% greater risk of being culled than cohorts that did not (P < 0.01). Heifers with genetic potential to become larger cows were less likely to calve at two years of age. Heifers experiencing dystocia when calving at two years of age were at substantially greater risk of being culled than heifers that calved without assistance. Additionally, a genetic profile consistent with nutritional resources will reduce the risk of a cow being culled before her breakeven age.