84. An Initial Assessment of the SizeR Technology and the Relationships Between Morphometric Measurements and Enteric Methane Emissions from Grazing Heifers

Abstract The SizeR (Geissler Corp., Plymouth, MN) is a new technology that has been developed for the passive measurement of morphometric data from cattle. To date, this technology has not been assessed in growing cattle in pasture. Accordingly, the objectives of this preliminary investigation was to provide an initial assessment of the SizeR estimated morphological measurements of cattle collected from the SizeR and to also investigate their relationship with body weight (BW), average daily gain (ADG), heat production (HP), and enteric methane (CH4) emissions. Heifers (n = 30; initial BW = 322 ± 19 kg) were adapted to an in-pasture GreenFeed emission monitoring system (GEM) for three weeks in confinement, followed by three weeks in pasture. Cattle grazed in coastal Bermudagrass (Cynodon dactylon) pasture with an average forage allowance of 4.68 kg of dry matter/kg of BW. Cattle were weighed and scanned by the SizeR weekly for 56 days. Results show that the log-log slopes of surface area (SA; m2) against volume in L (slope = 0.62, P < 0.01, R² = 0.95), SA against BW (slope = 0.73, P < 0.01, R² = 0.66), HP against BW (slope = 0.83, P < 0.01, R² = 0.56), and HP against SA (slope = 0.63, P < 0.01, R² = 0.27) were not different from expectations, which were 0.67 (P = 0.10), 0.67 (P = 0.55), 0.75 (P = 0.58) and 0.67 (P = 0.85), respectively. Body weight increased (P < 0.01, R2 = 0.35) by 14.0 kg, and ADG increased (P = 0.05, R2 = 0.13) by 0.11 kg/d per 1 unit increase in SizeR estimated frame score (FS). Body weight by itself explained 25% of the variation in CH4, as expected, and as BW increased, CH4 emissions increased (P < 0.01). Including both BW and FS as predictor variables explained 31% of the variation in enteric CH4. Enteric CH4 was determined to increase (P < 0.01) by 0.49 g/d per kg of BW and was reduced (P = 0.05) by -6.27 g/d per 1 unit increase in FS. We conclude that morphological measurements using the SizeR technology are promising and reveal relationships that are consistent with expectations based on previous understandings. Further, these results suggest that morphological traits of cattle are related to enteric CH4 emissions of grazing cattle.