Relationships of residual feed intake and residual average daily gain with carcass traits and growth of Brahman steers

Abstract

The objectives of this study were (a) to quantify residual feed intake (RFI), residual average daily gain (RADG), and G:F efficiencies for yearling Brahman bulls; and (b) to ascertain the relationships of these ef- ficiency groupings with subsequent growth, feedlot per- formance, and carcass characteristics of Brahman steers. For each of 3 years, yearling (380 d of age) Brahman bulls (n = 56, 47, and 34 head) were fed for 70 d using Calan gates (American Calan Inc.), with 5 to 6 head per pen. After feeding, efficiency mea- sures of RFI, RADG, and G:F were calculated for each bull. For each efficiency measure, bulls were classified into 4 efficiency groups based on 0.5 standard deviation from the means. In early July after Calan gates, bulls were stocked on bermudagrass pastures. At completion of stocking (19 mo, 400 kg) steers were shipped 700 km to a South Texas feedlot. After feeding, steers were transported 65 km to a commercial abattoir. In year 3, steaks from the 13th rib were dissected, vacuum-packed, and frozen for Warner–Bratzler (WB) shear force measurement. During the 70-d period, 3-yr means for daily feed intake, ADG, and G:F were simi- lar for RFI groups. For RADG and G:F groups, feed in- take was similar, but ADG and G:F differed (P < 0.0001) among groupings. Feedlot ADG was similar for all efficien-cy groupings, at approximately 1.5 kg/d. From yearling through feedlot, the most efficient RADG group (group 1) reached harvest earlier than the least efficient RADG group (group 4). Hot carcass weights were greater for the most efficient compared with the least efficient RADG grouping. Internal fat (KPH) was greater (P = 0.04) for the RFI efficiency group 1 compared with group 4. The WB measurement showed that the most tender steaks were from the most efficient groupings and the least ten- der from the least efficient groupings of RADG and G:F. Growth rate from yearling to harvest of the most efficient RADG group has significant economic implications for Brahman bulls– steers. Steak tenderness in the 4 RADG groupings showed the most direct alignment for most efficient compared with the least efficient Brahman steers.