Effects of estradiol benzoate and trenbolone acetate, alone or in combination at dose levels present in Synovex Choice, on performance by feedlot heifers.

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 implants coated with a polymeric, porous film improve performance of beef steers and heifers fed in confinement for up to 200 days.

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.

Dietary zilpaterol hydrochloride. I. Feedlot performance and carcass traits of steers and heifers.

Experiments were conducted at 3 US locations (CA, ID, and TX) to determine the effects of dietary zilpaterol hydrochloride (Zilmax, Intervet Inc., Millsboro, DE) and duration of zilpaterol feeding on performance and carcass merit of finishing steers and heifers. At each site, 160 steers and 160 heifers were stratified within sex by initial BW (study d -1) and assigned randomly within BW strata to 1 of 4 treatments in a randomized complete block design (4 blocks/treatment for each sex). The 4 treatments were arranged in a 2 (no zilpaterol vs. zilpaterol) x 2 (20 or 40 d duration of zilpaterol feeding) factorial arrangement of treatments. When included in the diet, zilpaterol was supplemented at 8.3 mg/kg of DM. Each pen consisted of 10 animals. Each animal was individually weighed unshrunk on d 1, 21 or 41, and 66 of the experiment. Following d 66, cattle were slaughtered and carcass data collected. Feeding zilpaterol increased (P<0.01) final BW of steers and heifers by 11.6 and 6.7 kg, respectively. In addition, feeding zilpaterol hydrochloride increased (P or= 0.12) and KPH (P >or= 0.70) were not affected by feeding zilpaterol to steers or heifers. Feeding zilpaterol decreased (i.e., improved; P=0.02) calculated yield grade of steer and heifer carcasses. Marbling score (P=0.002) and quality grade (P=0.002) were decreased when zilpaterol hydrochloride was fed to steers, and the decrease in marbling score and quality grade tended to be greater when zilpaterol was fed for 40 compared with 20 d (zilpaterol x duration interaction, P=0.07). For heifers, marbling score tended (P=0.07) to be decreased and quality grade was decreased (P=0.05) when zilpaterol hydrochloride was fed. In general, it appears from these data that zilpaterol hydrochloride fed for 20 to 40 d at the end of the finishing period enhances growth performance and carcass muscle deposition for steers and heifers.

Comparison of ivermectin SR bolus, benzimidazole anthelmintics, and topical fenthion on productivity of stocker cattle from grazing through feedlot.

A study was conducted to determine the effect of different parasite control programs on weight gain and other measurements for stocker beef calves during the grazing season and subsequent feedlot phase of production. One hundred eighty recently weaned beef steers were purchased from a Mississippi sale barn and were allocated by restricted randomization on pretreatment weight to three treatments: (1) no anthelmintic treatment; treated only with a topical organophosphate (OP) during processing into the feedlot; (2) one benzimidazole (BZD) treatment at initiation of grazing, and a second given at the time of processing upon arrival at the feedlot, along with a topical OP; and (3) ivermectin sustained-release (SR) bolus administered at initiation of grazing, with no further treatment given at the feedlot. The cattle grazed separately by treatment for 125 days, with six replicated pastures per treatment; then were penned according to the same groupings after entry into the feedlot on day 127. Cattle were individually weighed at approximately 2-month intervals, and feed consumption was measured during the 167 days in the feedlot. Fecal nematode egg counts were individually monitored for all animals during both phases of the trial. Carcass weight, quality grade, yield grade, and the incidence of liver abscesses were recorded for each animal at slaughter. Cattle treated with the ivermectin SR bolus gained significantly (P < .05) more weight through the grazing period and from the start of grazing through the end of the feedlot phase than the controls or the cattle treated with BZD products. There were no significant differences in feed efficiency between any of the groups. Mean carcass weight for cattle treated with boluses was significantly (P < .05) greater than that of the controls and the group treated with BZD. Dressing percentage and quality grade were significantly (P < .05) higher for the BZD and bolus groups, and yield grade was slightly (but not significantly) better for each of these groups than for controls. Significantly (P < .05) fewer livers of cattle treated with boluses had abscesses at slaughter than did livers of controls or cattle treated with BZDs. During both phases of the trial, fecal egg counts were significantly (P < .05) lower for the group treated with boluses than for the untreated group or the group treated with BZD. These data indicate that treatment with boluses for parasite control at the beginning of the grazing period had beneficial effects on weight gain as compared to no anthelmintic treatment or treatment with a BZD at the start of grazing and again at the time of introduction into the feedlot. These bolus benefits were sustained through the feedlot phase of production and provided further improvements with significantly (P < .05) increased carcass weights. The bolus is a tool that can significantly increase the efficiency of production for cattle producers who retain ownership into the feedlot phase of production or feedlot operators who graze stockers before feedlot entry.

Efficacy of sustained release needle-less ceftiofur sodium implants in treating calves with bovine respiratory disease.

Three experiments were conducted to determine preliminary efficacy of sustained release needle-less implants in effecting cure in calves with bovine respiratory disease. One hundred and twenty beef calves with a rectal temperature > or = 40 degrees C and shallow or labored respiration and coughing were used in these experiments. Four groups (1-ceftiofur sodium injections [days 1, 2, and 3], 2-ceftiofur sodium needle-less implants [days 1, 2, and 3], 3-ceftiofur sodium needle-less implants [days 1 and 3], and 4-ceftiofur sodium needle-less implants [day 1] were included. All treatments contained 250 mg of ceftiofur sodium and were administered intramuscularly in the neck after diagnosis of bovine respiratory disease. Experiment 1 included 20 calves (group 1-10 calves and group 3-10 calves; 213 to 255 kg) and calves were monitored for clinical efficacy. Experiment 2 included five calves per group (all four groups; 164 to 192 kg) and calves were bled frequently after treatment for desfuroylceftiofur (the primary ceftiofur metabolite) concentrations. Experiment 3 included 20 calves per group (all four groups; 160 to 205 kg) and calves were monitored for clinical efficacy. Blood desfuroylceftiofur concentrations remained above the minimum inhibitory concentration for Pasteurella haemolytica, Pasteurella multocida, and Haemophilus somnus for 24 hours after injection and 72 hours after implantation (P < 0.05). Mortalities and the number of calves with a positive response and relapse response were similar (P < 0.25) among the four groups. In summary, the administration of one-250 mg ceftiofur sodium needle-less sustained release implant was as efficacious in treating bovine respiratory disease as three daily 250 mg injections of ceftiofur sodium.

Effects of dietary virginiamycin on performance and liver abscess incidence in feedlot cattle.

The effects of dietary virginiamycin level on performance and liver abscesses in feedlot cattle were evaluated in seven dose-response studies. Steers and heifers were fed finishing diets ranging in energy content from 1.34 to 1.51 Mcal of NEg/kg of DM. In all studies, virginiamycin added to the diet improved average daily gain and(or) feed conversion, with no substantial effect on dry matter intake. Pooled analyses of four studies providing virginiamycin at 11.0, 19.3, and 27.6 mg/kg of DM in the complete diet indicated that growth and feed conversion were linearly improved (P < .05); feeding 19.3 mg/kg improved these measurements by 3.0 and 3.8%, respectively. Overall incidence (score 0 vs score 1, 2, and 3) and severity (score 0, 1, and 2 vs score 3) of liver abscesses were reduced (P < .01) by feeding virginiamycin at either 19.3 or 27.6 mg/kg. Linear plateau modeling indicated that the effective dose range for virginiamycin in feedlot diets (DM basis) was 19.3 to 27.3 mg/kg for increasing average daily gain, 13.2 to 19.3 mg/kg for improving feed conversion, and 16.5 to 19.3 mg/kg for reducing liver abscess incidence.

Problems and practice in mass medication of beef cattle.

Mass medication is a health management tool that, when used appropriately, results in cost savings and sound economic return to the food animal producer. Careful planning and consideration should precede the implementation of a mass treatment program, clearly defining the goal to be achieved and a detailed plan of execution. For economic as well as professional reasons, indiscriminate administration of antimicrobials to large groups of food animals should be avoided.