288 Impact of Brahman genetics on feed efficiency and methane emissions of heifers with implications for the Florida cow-calf producers.

Abstract Feed efficiency is one of the most important traits for livestock selection. While Bos taurus cattle often exhibit superior performance and higher-quality products than Bos indicus, they are more susceptible to harsh environmental conditions. Consequently, Florida beef cattle producers and a critical proportion of beef production systems rely on genetics adapted to the southeastern U.S. region, characterized by severe warm and humid climatic conditions during a significant period of the year. The University of Florida has been developing an adapted multibreed beef herd through years of research, incorporating varying degrees of Brahman and Angus genetics to identify the most suitable genotypes for the region. The objective of this study was to evaluate how Brahman genetics influence feed efficiency in growing heifers with different Brahman percentages, with the aim of developing a future selection tool. The experiment was conducted in two years with a total of 221 replacement heifers (276 ± 41 kg). The heifers were genotyped and divided into six breed compositions: B1 = 90% Angus (10% Brahman), B2 = 68% Angus (32% Brahman), B3 = 50% Angus (50% Brahman), B4 = 35% Angus (65% Brahman), B5 = 10% Angus (90% Brahman), B6 = 100% Brahman. Each breed representative was randomly allocated to four pens. Data were analyzed as a randomized complete block design. The model included breed and pen nested within year as a fixed effect. A 56-d feed efficiency test measured dry matter intake using Vytelle Sense feedbunks (Vytelle LLC, Lenexa, KS) and body weight every 14 d. Carcass ultrasound was evaluated at the end of the 56-d experimental period. After the feed efficiency test, methane (CH4) emissions were measured using the GreenFeed System (C-Lock Inc., Rapid City, SD), where each pen had 9 d of measurement. Average daily gain (ADG) was lower in B6 compared to all other groups (0.93 vs. 1.34 kg/d; P < 0.01). Dry matter intake (DMI) expressed as a percentage of body weight was also lower for B6 compared to the other groups (3.08% vs 3.50%; P < 0.01). Methane yield (g CH₄/kg DM) was unaffected by breed composition (P > 0.05), whereas methane intensity (g CH₄/kg ADG) tended to be different (P = 0.05). In conclusion, incorporating up to 90 % of Brahman genetics had no detrimental effects on performance and tended to reduce CH₄ intensity. These findings suggest that selecting cattle with high Brahman influence has the potential to maintain productivity and enhance sustainability in cow-calf systems in the southeastern U.S.