Mineral status, bone characterisitics, carcass characteristics, and performance of feedlot lambs implanted with zeranol

Abstract

Fifty-four Rambouillet (avg wt, 34.6 kg) wether lambs were used to determine the effects of zeranol of p and N excretion, animal performance, carcass characteristics, and bone characteristics. Lambs were blocked by sire, randomly allotted to pens of 3 to 4 in an open sided barn and assigned to either an implant (1) or non-implant (NI) treatment group . Lambs had ad libitum access to a high concentrate diet containing 38% TDN and 16% CP or 67 d. Lambs were fed for 21 d prior lo implanting. At 14 d intervals post implanting, pens were thoroughly cleaned and excreta allowed to accumulate for 2 d. Excreta was collected and analyzed for P and N content. Lambs were slaughtered on d 67 and carcass characteristics were determined. Phosphorus excretion expressed as a percentage of P intake for I vs NI treatment groups at 4, 28, 42, and 56 d post implanting was 55.7 vs 61.4% (P=.32) 45.4 vs 55.8% (P=.04)1 50.5 vs 53.5/'o (P = .67) and 78.9 vs 80.7% (P =-.85), respectively. This resulted in an increase (P<. 05) in P retention for 1 lambs (2.56 g/d vs 3.19 g/d) on d 28. The percentage difference appears to follow the pay-Out, curve of the zeranol implant. There was no effect (P> . 1O) of zeranol oil N excretion in this study. Implanted lambs had a 26.3% greater (P =.0009) ADG and 16.8% improvement (P=.02) in feed efficiency compared with NI lambs. implanting treatment did not affect carcass characteristics" however, implanted lambs did have thicker hides (P < . 0 1) and larger livers (P < 10). Bone breaking load was increased (P <.05) in I lambs compared to NI lambs. However, there were no other differences in physical characteristics of the metacarpal bones. Results of this study indicate that zeranol improved P utilization, feed efficiency, and ADG in feedlot lambs. Zeranol treatment also altered metacarpal bone characteristics and increased hide thickness and liver weights.