Relationships Between Feed Efficiency and Gas Emissions in Beef Cows on Pasture
Estimating feed efficiency of beef cows on pasture is difficult due to technical challenges with measuring individual pasture intake and assessment of body weight and body composition. In addition, other measures of feed efficiency, like residual feed intake and feed conversion ratio, also may not accurately reflect efficiency in mature cows, and new measurements better characterizing metabolic efficiency are needed. However, new technologies like C-Lock Greenfeeder (C-Lock Inc., Rapid City, SD) which can individual animal gas exchange on pasture, may be a useful tool to identify metabolically efficiency animals in both dry lot and pasture systems. The purpose of this study is to determine relationships between feed efficiency, and CO2, O2, and enteric methane production, and calculated metabolizable energy intake of beef cows on dry lot and pasture. The first phase 64 pregnant multiparous beef cows were measured individual intake, Greenfeeder measurements (enteric methane and carbon dioxide production), body weight, body condition score, and back fat depth by ultrasound every 30 days for 10 weeks. In the second phase of the trial, the same cows were block by weight and calving date and randomly assigned to pasture paddock where similar performance and gas exchange measures were obtained in mid and late summer. Preliminary data suggest enteric emissions were 263±40.3 g CH4/d in dry lot, however daily enteric CH4 emissions per kg of pregnancy corrected body weight ranged from 0.26 to 0.53 g CH4/kg pcBW. On pasture, daily CH4 was shown to be 258±50.5 g CH4/d, with 0.11 to 0.56 g CH4/kg BW. This data will be used to calculate metabolizable energy intake and a model developed to better identify feed efficient mature cows, and to work towards a more sustainable future in food production.
Key words: Methane, Beef, Cow, Feed Efficiency.
Presented at the 2021 Animal Nutrition Conference of Canada. For information on the next edition, click here.
