Abstract
The study objectives were to evaluate the comparative growth performance, carcass characteristics, and gas flux of yearling Bos taurus indicus (BI; Brahman) and Bos taurus taurus (BT; Angus) steers managed with (GPT+) and without (GPT-) the use of growth-promoting technology (GPT) in winter conditions. One hundred BI (initial body weight [IBW] = 364 ± 22 kg) and 100 BT (IBW = 323 ± 17 kg) steers were fed for 180 d in two consecutive phases. In Phase 1, day 0-83, steers of each sub-species were blocked by IBW and randomly assigned to a treatment (10 hd/pen, 5 pens/treatment). In Phase 2, day 84-180, steers were moved to Climate Smart Research Pens, where each treatment was randomly assigned to a research pen equipped to measure individual feed intake and gas flux (50 hd/pen, 1 pen/treatment). Data were analyzed with R (R Core Team, 2021, v. 4.4.1) software to assess the fixed effects of cattle sub-species, treatment, and the sub-species × treatment interaction. In Phase 1, IBW differed (P < 0.01) by sub-species, but did not differ (P = 0.98) by treatment. Dry matter intake (DMI), average daily gain (ADG), and feed efficiency (G:F) were greater (P < 0.01) for BT, resulting in greater final body weight (FBW) for Phase 1. Within sub-species, DMI, on a total daily basis and as a percentage of body weight, did not differ (P ≥ 0.09) between treatments in Phase 1, but ADG, G:F, and FBW were greater (P ≤ 0.04) for GPT+ than GPT-. In Phase 2, G:F and DMI when represented on a total daily and as a percentage of BW basis had a sub-species × treatment interaction (P ≤ 0.04) where greater increases in G:F and DMI were observed between GPT+ and GPT- for BI than for BT. Steers managed with GPT and BT steers had greater (P ≤ 0.01) ADG and FBW. Calculated yield grade and backfat thickness were greater (P < 0.01) for BT steers, and BT had more (P < 0.01) USDA Choice and Prime quality grades than BI. Longissimus muscle area was greater (P < 0.01) for BT and GPT+ steers. Daily methane (CH4) emitted was less for BI steers; however, CH4 as a proportion of DMI and gross energy intake were less (P < 0.01) for BT steers. There was a sub-species × treatment interaction (P < 0.01) for CH4 per unit ADG, where a decrease was observed between GPT- and GPT+ for BI, while no difference was observed for BT. In conclusion, BT had greater growth performance and carcass quality, but observations differed by cattle sub-species when CH4 was reported on an absolute versus yield or intensity basis.