PS11-13. The Shape of Efficiency: Linking Morphometrics to Growth, Feed Utilization, and Gas Flux of Receiving Beef Cattle.

Abstract The beef industry must improve efficiency while also addressing environmental concerns related to greenhouse gas emissions. With climate neutrality goals for the beef sector, advancements in technology may facilitate the selection of cattle with enhanced growth performance and lower emissions. Our objective was to identify morphometric differences in receiving cattle using the SizeR (Geissler Corp., Plymouth, MN) and assess associations with growth and emission traits. Crossbred beef heifers [n = 28; initial body weight (BW) = 369 ± 21 kg] were adapted for 14 d to Vytelle SENSE™ feed intake measurement bunks (Vytelle LLC, Lenexa, KS) and had been acclimated to a GreenFeed emission monitoring system (C-Lock Inc., Rapid City, SD) for the measurement of methane (CH4) and carbon dioxide emissions and oxygen consumption in a previous experiment. These gas fluxes were then used to calculate heat production (HP). Cattle were fed a sorghum silage-based grower ration (1.46 Mcal NEm/kg) for 42 d, then transitioned to a corn silage-based grower ration (1.63 Mcal NEm/kg) for the final 14 d of data collection. Cattle were weighed and scanned with the SizeR weekly. Results show that heavier cattle consumed more DMI (r = 0.73; P < 0.01), had a more efficient gain to feed (r = 0.57; P < 0.01), and produced more enteric methane (r = 0.76; P < 0.01). When assessing morphometrics, log surface area vs. log body weight (slope = 0.66; R2 = 0.89) resulted in a slope consistent with Meeh’s formula, so that as BW increases, surface area increases to the 2/3 power. Relationships between morphometrics also show that volume and surface area have stronger correlations with economically important traits than frame score and length. Specifically, comparing volume to average daily gain, gain to feed, and emission intensity results in Pearson’s correlations of 0.70 (P < 0.01), 0.61 (P < 0.01), and -0.54 (P < 0.01), where frame score correlations were 0.35 (P = 0.07), 0.33 (P = 0.09), and -0.20 (P = 0.31), respectively. This signifies that efficiency could be more closely related to abdominal dimension rather than just linear height. We conclude that morphological measurements using the SizeR technology reveal relationships that are consistent with expectations based on previous understandings. Further, these results suggest that morphological characteristics of cattle are related to economically important traits to producers. These results demonstrate promise for the SizeR, and future research should investigate if the SizeR technology can be used when allocating cattle pens to increase uniformity and ultimately producer profitability.