Enhancing steer growth and efficiency through growth promoting technologies

Angus-cross (216; 292 ± 22 kg) steers were used to understand the implications of growth promoting technologies on measures of cattle growth, serum metabolites, and nitrogen excretion. Steers were blocked by BW into heavy (16 pens) and light (20 pens), with 6 steers per pen. One of four treatments was applied to each pen. Treatments (TRT) consisted of (i) no implant or β-adrenergic agonist (β-AA; CON), (ii) implants (IMP: Synovex Choice: 100 mg trenbolone acetate, 14 mg estradiol benzoate [d 0]; Synovex Plus: 200 mg trenbolone acetate, 28 mg estradiol benzoate [d 69]), (iii) IMP + β3-agonist lubabegron fumarate (LUB: 36 mg/steer daily for 53 d, 4-d withdrawal), (iv) IMP + β1-agonist ractopamine hydrochloride (RAC: 300 mg/steer daily for 31 d). From terminal implant onwards, study days were held consistent to days relative to harvest for each block. Body weights were recorded and blood was collected on 1 steer per pen on days -1, 0, 69, 98, 116, 141, and 172. Serum urea nitrogen (SUN), glucose, insulin, and non-esterified fatty acids (NEFA) were analyzed. Insulin sensitivity and urinary nitrogen excretion was estimated. Carcass data were collected following a 48-h chill. Proc Mixed (SAS) was used to analyze data using treatment and block as fixed effects, serum metabolite data were analyzed as repeated measures (day as repeated). Final body weight, average daily gain, dry matter intake, and gain: feed were greater with the use of growth promoting technologies (P < 0.01). Net return tended to be greater in LUB than RAC and CON, IMP was not different from other treatments (P = 0.07). Hot carcass weight was greatest in LUB, less in IMP and RAC and least in CON (P < 0.01). Marbling was least in LUB with CON and IMP being greatest and RAC being not different from other treatments (P < 0.01). Urinary nitrogen output decreased per unit of carcass adjusted ADG with the use of growth promoting technologies (P < 0.01). Serum urea nitrogen had a TRT × Day effect (P < 0.01) where CON cattle were generally greater than other treatments until d 172, indicating SUN was less in RAC and IMP, and least in LUB during the LUB feeding period. Insulin sensitivity index values were generally lesser in CON compared to all other treatments and increased greatly in LUB during the β-AA feeding period (TRT × Day; P < 0.01). Growth-promoting technologies reduce the beef industry's environmental footprint and enhance carcass value by improving feed efficiency.