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Trials were conducted with beef heifers at 4 sites to evaluate feedlot performance and carcass characteristics in response to implants containing 14 mg estradiol benzoate and 100 mg trenbolone acetate (EB/TBA; Synovex Choice, Zoetis LLC, New York, NY), 14 mg estradiol benzoate (EB), 100 mg trenbolone acetate (TBA), or a sham-implanted control (SC). The study design at each site was a randomized complete block with 12 blocks and 4 treatments. Blocks of cattle at each site were harvested in commercial abattoirs when masked personnel estimated at least 60% of animals would yield carcasses with USDA quality grades of Choice or Prime. Data were pooled across sites for statistical analysis. Initial BW averaged 374 kg, and days on feed ranged from 98 to 126 d (mean 112 d). Heifers implanted with EB/TBA, EB, and TBA had greater ADG and G:F (P < 0.05) than SC; ADG and G:F were greater for EB/TBA than EB or TBA (P < 0.05). Heifers treated with TBA had greater G:F than EB (P < 0.05). Feed intake was not affected by treatments. Mean HCW and LM area for EB/TBA were greater than for other treatments (P < 0.05). Mean HCW for TBA was greater than SC (P < 0.05) but not different from EB. Mean LM area for EB and TBA were greater than SC (P < 0.05) but not different from each other. There were no treatment differences (P > 0.05) for KPH, 12th-rib fat thickness, or yield grade. Dressing percent was greater for EB/TBA than SC (P < 0.05) but not different from EB or TBA. Marbling score was decreased by EB/TBA (P < 0.05) compared with other treatments, but no other differences were noted. Despite the effect of EB/TBA on marbling scores, there were no significant (P > 0.05) treatment differences on proportions of carcasses with quality grades ≥ Choice vs. < Choice. With respect to ADG and G:F, implants containing EB, TBA, or EB/TBA produced improved responses over SC. Furthermore, EB/TBA induced greater ADG and G:F responses than EB and TBA. Results confirmed that EB and TBA have additive effects, as evidenced by the observation that calves implanted with EB/TBA had significantly greater ADG and G:F than heifers implanted with either EB or TBA alone or compared with SC heifers.

Synovex Plus (SP) is a product that delivers 28 mg of estradiol benzoate (EB) and 200 mg of trenbolone acetate (TBA). We studied the impact of a polymeric, porous coating on SP implants (CSP) to prolong release of EB and TBA, and stimulate feedlot performance of feedlot cattle for an extended period. In an explant study, 30 steers were implanted with SP in one ear and CSP in the contralateral ear. Cattle (n = 6/d) were necropsied 40, 81, 120, 160, and 200 d after treatment, and remaining EB and TBA were quantified. Linear regression of EB and TBA remaining as a function of time for each treatment were computed. Rates of EB and TBA depletion from SP were -0.1980 (r(2) = 0.9994) and -1.7073 mg/d (r(2) = 0.9644), respectively, and for CSP rates of EB and TBA depletion were -0.1049 (r(2) = 0.9123) and -0.9466 mg/d (r(2) = 0.9297), respectively. The effect of treatment on depletion rates of each analyte were significant (P < 0.05). Data also showed EB and TBA were delivered from CSP at least 200 d but were delivered from SP about 120 d. Multisite trials with beef-type steers (4 sites) and heifers (4 sites) evaluated feedlot performance and carcass characteristics in response to a CSP implant or when sham implanted (SC). A randomized complete block design with 9 blocks and 2 treatments was used per site within animal gender. Across sites, steers (n = 342, BW = 297 kg) were fed finishing rations for 190 to 202 d (mean 198 d) and heifers (n = 342, BW = 289 kg) were fed finishing rations for 191 to 201 d (mean 198 d). Cattle were harvested and carcasses evaluated. Data were pooled across sites within gender for statistical analysis. Steers and heifers treated with CSP yielded greater (P ≤ 0.003) ADG, DMI, and G:F than SC steers and heifers. Mean BW differences between CSP and SC continued to increase throughout the study, indicating CSP stimulated growth of steers and heifers for 198 d. Mean carcass weights of CSP steers (P = 0.005) and heifers (P = 0.004) were greater than those of SP steers and heifers by 26.2 and 20.6 kg, respectively. The LM area was larger (P < 0.001) in CSP steers and heifers than SC cattle. Marbling decreased with CSP treatment (P ≤ 0.031), which caused reductions (P ≤ 0.006) in proportions of carcasses grading Prime or Choice. Evidence from these studies showed that a single administration of CSP increased feedlot cattle performance for at least 198 d, compared with SC, and may reduce the need to reimplant cattle.

Two studies evaluated growth promoting effects of implant pellets (IP), each containing 3.5 mg estradiol benzoate (EB) and 25 mg trenbolone acetate (TBA), to which a polymeric, porous coating was applied. Trial 1 evaluated performance of heifers (n = 70/treatment, initial BW = 188 ± 2.2 kg) and steers (n = 70/treatment, initial BW = 194 ± 2.2 kg) implanted subcutaneously in the ear with 0 (SC), 2 (2IP), 4 (4IP), or 6 (6IP) pellets that delivered EB/TBA (mg/mg) doses of 0/0, 7/50, 14/100, and 21/150, respectively, over grazing periods of 202 d (heifers) or 203 d (steers). Animals received experimental treatments on d 0 and over the grazing period were managed as single groups by sex in a rotational grazing system. When pasture forage availability became limited, cattle were supplemented with preserved forage but not concentrate supplements. Weight gains by heifers treated with 2IP, 4IP, and 6IP were greater (P < 0.05) than SC heifers but not different from each other. Weight gains by steers treated with 2IP, 4IP, and 6IP were greater than SC steers (P < 0.05), and ADG by steers treated with 6IP was greater (P < 0.05) than steers given 2IP or 4IP. Trial 2 was a multisite grazing study performed with heifers and steers to compare ADG after treatment with one 6-pellet, coated implant delivering 21 mg EB and 150 mg TBA (6IP) to sham treated negative controls (SC) over a grazing period of at least 200 d. A completely random design was used at each site, with the goal to treat 70 cattle per site, treatment, and sex; data were pooled across sites. Heifers (n = 558, initial BW = 229 ± 16 kg) and steers (n = 555, initial BW = 235 ± 20 kg) grazed in rotational programs consistent with regional practices for an average of 202 d. When necessary, cattle were supplemented with preserved forage, but no concentrate supplements were fed. Over 202 d, ADG by heifers treated with 6IP was 11.3% greater (P = 0.0035) than SC heifers (0.64 ± 0.06 kg/d), and ADG by steers treated with 6IP was 17.2% greater (P = 0.0054) than SC steers (0.66 ± 0.08 kg/d). In neither study was there evidence that concurrent therapeutic treatments or abnormal health observations were influenced by experimental treatments. These studies demonstrated that a 6-pellet implant with a polymeric, porous coating that delivers 21 mg EB and 150 mg TBA improved ADG by grazing heifers and steers for at least 200 d compared to sham-implanted negative controls.

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