102 Pooled analysis of six large-pen feedlot studies: Non-coated initial and a non-coated terminal implant compared with a single initial and delayed release implant at arrival in feedlot heifers

Abstract

Abstract Randomized complete block design experiments (n = 6 experiments) were conducted in large-pen feedlot research facilities between 2015 and 2018 comparing an 80 mg trenbolone acetate (TBA) and 8 mg estradiol-17β (E2) initial implant and re-implant with 200 mg TBA and 20 mg E2 protocol (IH/200) to a single 80 mg TBA and 8 mg E2 uncoated; 120 mg TBA and 12 mg E2 coated implant at arrival (XH) on growth and carcass responses in finishing heifers. Experiments occurred in Nebraska, Oklahoma, Washington, and Texas. Similar arrival processing was used across experiments where 17,675 heifers [initial BW = 333 kg SEM (4.1)] were enrolled into 180 pens (90 pens/treatment with 65 to 240 heifers/pen) and fed for 152 to 214 d. Only IH/200 heifers were removed from their pen at re-implant. Diets contained monensin and tylosin, consisted of ingredients common to each region, and contained greater than 90% concentrate. Ractopamine hydrochloride was fed for a minimum of 28 d prior to harvest. Linear mixed-models were used for all analyses; model-adjusted means for each implant group and the corresponding SEM were generated. Distributions of USDA quality (QG) and yield grade (YG) were analyzed for ordinal outcomes. No differences (P ≥ 0.11) were detected for any performance parameters except DMI, where XH had greater (P = 0.02) DMI (9.48 vs. 9.38 ± 0.127 kg) compared with IH/200. Heifers implanted with IH/200 had greater (P ≤ 0.02) HCW by 1.3%, caused by greater dressing percentage, and ribeye area; lesser (P ≤ 0.01) back fat by and calculated YG, while marbling scores were similar (P = 0.74) compared with XH heifers. Distributions of USDA YG and QG were impacted (P ≤ 0.03) by treatment, IH/200 had fewer USDA Prime and YG 4 and 5 carcasses. These data indicate that heifer growth performance did not differ between implants, but HCW and muscling did; IH/200 is suited for grid marketing and XH is suited for heifers sold on a live basis.