105. Evaluation of Administering a Suckling Implant to Angus Crossbred Steer Calves Reared in a Western Rangeland Environment.

Abstract Administering an implant in beef calves prior to weaning can be a useful tool in maximizing weaning weights and later growth performance, as well as optimizing forage utilization in drought conditions. The objectives of this study were to better understand the impact of administering suckling implants on weaning weight, growth performance, and growth composition during the receiving phase, and to evaluate the effect of dam age on pre-weaning growth performance in Angus crossbred steers reared in a Western rangeland environment. Suckling beef steer calves from the SDSU Cottonwood Research Station in western South Dakota [n = 57; initial body weight (BW) 68 to 113 kg] were utilized in a suckling and receiving study. The treatment groups were determined utilizing calf birth weight (BW = 39 ± 0.5 kg) and dam age (< 4 years and ≥ 4 years of age) with equal representation of dam age in each treatment: 1) no implant administered at branding (NI), or 2) implant (Synovex-C; 100 mg progesterone and 10 mg estradiol benzoate) administered at time of branding (IMP). Steers were weighed at branding, pre-conditioning (25 d prior to weaning) and at weaning (upon arrival at feedlot), as well as d 14, 28, and 49 post-weaning. Carcass ultrasonography was performed and recorded on d 1 and d 49 to understand the impact of suckling implants on the composition of carcass growth. Treatment (NI vs IMP) was the fixed effect, and block within the feedlot was the random effect. Steer BW at the time of implantation was included as a covariate for growth performance measures pre-weaning. Steers were all fed a common diet upon arrival to the feedlot. No significant differences (P ≥ 0.29) in BW or average daily gain (ADG) were observed between treatment groups from the time of implantation to weaning. The lack of differences during this stage may be a result of above average precipitation in western South Dakota, leading to inadequate grass composition for implanted steers to gain as predicted. An analysis of the effect of dam age (< 4 years and ≥ 4 years of age) on weaning weight by treatment found no significant differences (P ≥ 0.31) in weaning weight between dam ages for both treatment groups. From weaning (d 1) to d 49 in the feedlot, no differences (P ≥ 0.07) in performance measures were observed between treatment groups. No differences in carcass composition measured via ultrasound were noted on d 1 (P ≥ 0.12) or d 49 (P ≥ 0.28) between treatment groups. Overall, implantation at branding did not affect growth performance or composition under the conditions of this experiment. Further investigation is warranted to account for background variations.