Estimation of Genetic and Maternal Effects in Crossbred Cattle of Angus, Charolais and Hereford Parentage. I. Birth and Weaning Weights

Seventy-two crossbred steer calves, averaging 61.6 kg in weight and 75 days of age, were divided into two pasture groups. Six calves in each pasture group received one of six estradiol 17β impregnated silastic rubber implant treatments. Steers receiving treatment 1 were administered a 2.54 cm nonmedicated implant; treatment 2, a 2.54 cm solid; treatment 3, a .64 cm coated; treatment 4, a 1.27 cm coated, treatment 5, a 2.54 cm coated; treatment 6, a 3.81 cm coated implant. Solid refers to estradiol being evenly distributed throughout the implant and coated refers to estradiol being evenly distributed throughout the outer .5 mm of the implant. Subsequent performance of the steer calves was measured during a 169-day suckling phase, a 215-day postweaning growing phase and an 84-day finishing phase. The average calculated estradiol 17β release per day during the 468 days was 37.06 µg, 9.01 µg, 16.96 µg, 33.04 µg and 49.73 µg for treatments 2 through 6, respectively. During the suckling phase, average daily gains were not different (P>.05) due to treatment. Average daily gains during the growing phase were greater (P<.05) for steers implanted with 2.54 cm solid implants compared to the control and .64 cm implant treated steers. Average growth response, feed intake and carcass characteristics were similar (P>.05) for steers on all treatments during the finishing phase.