Evaluation of cattle sub-species and growth-promoting technology on growth performance, carcass characteristics, and enteric gas flux of steers finished in winter feedlot conditions.

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.