Effects of weaning-period length on growth and health of preconditioned, spring-born beef calves originating from the Great Plains. II. Early weaning1

Angus × Hereford calves (n = 409; initial BW = 163 ± 31 kg) were weaned early (~ 130 d of age) and assigned randomly to treatments that corresponded to a length of time (d) between separation from their dam and transport to a feedlot: 0 (i.e., nonweaned), 15, 30, 45, or 60 d. Weaning date varied by treatment; transport occurred on a common date and at a common age (160 ± 19 d) for all treatments. Calves were vaccinated against common diseases 14 d before maternal separation and again on the day of maternal separation. Calves were transported < 20 km to a ranch-of-origin weaning facility following separation from dams and penned according to treatment. Calves were fed a complete diet (16.9% CP, 1.21 Mcal of NEg/kg) ad libitum. On a common date, all calves were transported 4 h to a commercial auction market and held for 14 h. They were transported subsequently 1 h to a feedlot. Calf BW at transport was not different between weaned and nonweaned calves (P = 0.13) but decreased linearly (P = 0.01) as the length of the ranch-of-origin weaning period increased. Pre-transport morbidity increased linearly (P = 0.05) as length of the weaning period increased. Calves not weaned before feedlot placement tended to have lesser (P = 0.08) ADG during receiving than weaned calves; moreover, ADG increased linearly (P = 0.02) as length of the ranch-of-origin weaning period increased. There were no treatment differences (P ≥ 0.24) in morbidity during receiving. In addition, finishing ADG, days on feed, slaughter BW, and carcass characteristics were not different (P ≥ 0.11) between weaned and nonweaned calves. Cow BCS change from 60 d before to 60 d after transport of calves increased linearly (P = 0.01) as weaning-period length increased. Cows with calves assigned to the 0-d pretransport weaning treatment had lesser (P = 0.03) pregnancy rates than cows with calves weaned before transport; moreover, pregnancy rate increased linearly (P = 0.03) with successively earlier weaning dates. Under the conditions of this experiment, ranch-of-origin weaning periods ≥ 15 d improved ADG of early-weaned calves during feedlot receiving but had minimal effects on health, finishing performance, or carcass characteristics.