Date of this Version
Butterfield, K. M. (December, 2022). Timing of Implants Use in Backgrounding System [MAS Thesis]. University of Nebraska.
A study was conducted over two years to determine the interactions of winter rate of gain at a high gain (HG) of 0.91 kg and low gain (LG) 0.45 kg, and implant strategy in the backgrounding and subsequent effects in the finishing phases. There were three phases in this study, the winter phase (~148 days), the summer phase (~60 days) and the finishing phase (~120 days). This was a 2 x 3 factorial design. The first factor is a rate of gain at either 0.91 kg (HG) or 0.45 kg (LG). The next factor is the timing of implant where steers either receive an implant in the winter and summer phases (STRONG-IMP), an implant only in the summer phase (MED-IMP) or no implant in the winter nor summer phases (NO-IMP). Steers were either fed a HG (0.91 kg/d) of 30% MDGS, or a LG (0.45 kg/d) of 10% MDGS in smooth bromegrass hay diets, respectively. The experimental unit is the pen which consists of ten head. During the winter phase, STRONG-IMP steers were implanted with 36 milligrams (mg) of zeranol (Ralgro; Merck Animal Health) lasting around 90 days; all steers remained in the winter phase for 148 days. In the summer phase, steers grazed Smooth Bromegrass pasture and both MED-IMP and STRONG-IMP received an implanted with 40 mg of trenbolone acetate (TBA) and 8 mg of estradiol (Rev-G; Merck Animal Health) lasting 120 days. Eighty steers did not receive an implant during the winter nor summer phases (NO-IMP). Steers remain in the summer phase for approximately 56 days. In the finishing phase, all steers were given 200 mg of TBA and 40 mg of estradiol (Rev-XS) lasting approximately 200 days. The steers remained in the feedlot for approximately 115 days. In the winter phase, there was a significant difference in the ending body weight (EBW), average daily gain (ADG) and gain to feed ratio (G:F) for the main effects of winter rate of gain and implant strategy (P < 0.01), with the HG and STRONG-IMP gaining the most at 0.89 kg/d, having the largest EBW and greatest G:F of 0.109. For the summer phase, there was a statistical difference for winter rate of gain and implant strategy (P < 0.01) of EBW. High gain and STRONG-IMP resulted in the largest EBW but did not gain the most over the summer phase. When comparing the treatments of HG verses LG, the LG treatments gained more than the HG during the summer. There was a significant difference for EBW in the finishing phase for both main effects (P < 0.01) with HG and STRONG-IMP being the greatest. Hot carcass weight (HCW) followed a similar trend to EBW with a statical difference for both main effects of winter rate of gain and implant strategy (P < 0.01) and the HG and STRONG-IMP weighing 416 kg, which is numerically 44 kg greater than the LG and NO-IMP in the winter nor summer phases. Supplementing at a high rate of gain during the winter backgrounding phase and implanting in the winter, summer and finishing phases results in the greatest total system gain and HCW.
Advisor: James C. MacDonald