Authors : D. K. Lunt , F. T. McCollum and K. S. Barling
Abstract: Two trials were conducted to compare weight gain and feed efficiency of calves in response to estrogen-only, androgen-only and androgen + estrogen combination implants administered during a limit feeding growing program. Four implant treatments were evaluated: Nonimplanted controls, estrogen implant (Synovex-S?), trenbolone acetate implant (Finaplix-S?), and trenbolone acetate + estrogen combination implant (Revalor-S?). All cattle in both trials were managed under limit-feeding conditions during an 85-day growing period. Daily feed intake was restricted and formulated to produce 1.0 kg daily weight gain. Average daily gain for all treatment groups was similar to the target gain. An implant treatment effect was detected (P < 0.05) for average daily gain in Trial 1 (the group-fed steers). Preplanned orthogonal contrasts indicated that the combination of estrogen and androgen (Revalor-S?) produced a greater average daily gain than androgen-only or non-implanted control. Average daily gain for the steers receiving the combination implant also tended (P = 0.085) to be greater than that of estrogen-only. In Trial 2, however, where difference in feed bunk behavior was eliminated by individually feeding the steers, no treatment effect was detected for either rate or efficiency of weight gain. Feed to gain ratio was inversely proportional to rate of weight gain in all treatment groups, but large within treatment variation precluded detection of a significant difference among treatments. These data seem to indicate that the superior gains for the combination implant observed in Trial 1 may have been due to an increase in feed consumption rather than increased efficiency of growth.
D. K. Lunt , F. T. McCollum and K. S. Barling , 2004. Rate of Gain and Efficiency of Growth in Steer Calves That Have Been Implanted and Limit-Fed Individually or in Groups . Journal of Animal and Veterinary Advances, 3: 652-655.