348 An aggressive implant strategy altered non-carcass components in long-fed Jersey steers

Abstract Jersey cattle are recognized for superior marbling, however, feeding Jerseys to market potential is typically uneconomical due to slow-maturation and excessive internal fat accretion. Growth-promoting agents have been used to improve growth and may improve the efficiency of Jersey steers. Our study was designed to evaluate by-product yields of Jersey steers in response to an aggressive implant program. Jersey steers (n = 12) were fed over a 420-d period and were randomly allocated to one of two treatments in a completely randomized design; control (CON) or implant (IMP). Control steers received no implant, whereas IMP steers received a Revalor-200 (200mg trenbolone acetate/20mg estradiol) implant in alternating ears every 70 d, totaling 6 implants per animal. Non-carcass components were weighed during harvest and results were analyzed using an independent t-test. A 19 and 30% reduction (P ≤ 0.02) in total internal fat (66.41 vs 81.66 kg) and cod fat (4.01 vs 5.70 kg) was observed for IMP vs CON steers. Aggressive implanting increased (P < 0.01) penis weight by 51% (0.71 vs 0.35 kg) and decreased (P < 0.05) skull thickness (12.06 vs 20.96 mm) and tail switch (0.36 vs 0.49 kg) of steers. When expressed on an empty body weight basis (g/kg EBW), cod fat and KPH decreased (P ≤ 0.05) from 11.09 and 50.88 g/kg EBW in CON to 7.70 and 37.74 g/kg EBW in IMP steers, and a 20% reduction (P ≤ 0.01, 126.60 vs 158.90 g/kg EBW) of total internal fat was observed for IMP vs CON steers. Implantation also increased (P ≤ 0.01; 0.67 to 1.35 g/kg EBW) penis and decreased (P = 0.04; 0.96 vs 0.67 g/kg EBW) tail switch weight on an EBW basis. These results suggest a shift in energy partitioning away from internal fat accumulation in aggressively implanted Jersey steers.