Effect of Late-Gestation Supplementation and Post-Partum Progestin on Probability of Culling Spring Calving Cows in the Nebraska Sandhills

A 2-yr study evaluated effects of late-gestation supplementation, and post-partum progestin administration, on culling rate of March calving cows. In yr 1, 120 crossbred beef cows (BW 479 ± 57 kg) were assigned to 1 of 4 levels of late-gestation supplementation and post-partum progestin or control in a 4 × 2 factorial arrangement of treatments in a completely random design. The four supplement (32% CP; DM) levels were: 1) 0 kg/d Dec 1 to Mar 1; 2) 0.41 kg/d DM Dec 1 to Mar 1; 3) 0.41 kg/d DM Jan 15 to Mar 1; or 4) 0.82 kg/d DM Jan 15 to Mar 1 while cows grazed dormant upland Sandhills range. Approximately 3 mo postpartum, cows from each supplement treatment either received: 1) controlled internal drug release device for 7 d; or 2) no progesterone administration. Cows were culled for 1 of 2 production reasons: 1) failure to produce a calf; or 2) failure to become pregnant. Culled cows were not replaced, but stocking rate was maintained. Previous analysis of these data demonstrated higher levels of late-gestation supplementation increased cow BW (P < 0.05) and cow BCS (P < 0.05) but did not affect (P < 0.12) reproductive measures or calf performance. Using a limited dependent variable methodology, it was determined that late-gestation supplementation decreased culling rate. Conversely, feeding no supplement from Dec 1 to Mar 1 significantly (P < 0.02) increased the probability of cows being culled. Feeding supplement from Dec 1 to Mar 1 decreased the probability of a cow being culled (P < -0.01; 7 vs. 20%; supplement vs. no supplement). Neither level of supplementation from Jan 15 to Mar 1 altered (P < -0.19) the number of cows culled compared with the Dec 1 to Mar 1 supplementation treatment. Post-partum exogenous progesterone administration did not (P < 0.60) influence the culling rate of beef cows. Supplementation for the duration of the winter grazing period decreased culling rate, however, did not influence pregnancy rate or calf performance.