Predictions of enteric methane emissions for various summer pasture and winter feeding strategies for cow calf production

Mechanistic (COWPOLL and MOLLY) and empirical (IPCC Tier 2 and ELLIS) models were used to predict enteric CH4 emissions from 2 summer pasture systems and 4 winter feeding strategies for cow calf production in the Western Canadian Parkland. The models used average values for nutrient composition of diets, body weight and body condition score of multi- and primiparous cows to predict 90d emissions for each strategy. Average values were determined from data collected over 5 production years with British-Continental crossbred cows assigned to each strategy for life. Each production year began in June with summer grazing of cow calf pairs (n=288/yr including 76 primiparous cows) assigned to either alfalfa-grass (AG) or grass (G) pastures until weaning in September. November post weaning, pregnant cows (n=240/yr) were assigned to either extended grazing (EG) of dormant regrowth of perennial pastures and swathed annual crops, or one of 3 diets fed in a drylot: hay (HY), straw/barley (SB; 700 oat straw:300 steam-rolled barley grain dry matter (DM)), or silage/straw (SS; 400 barley silage:600 oat straw DM). Cows were fed common diets between weaning and wintering, and pre-calving and grazing of summer pastures. Differences in prediction of enteric CH4 emissions were much bigger among models (26-35%) than among systems (3-5%). For suckled beef cows, the mechanistic and empirical models predicted similar enteric CH4 between AG and G summer pasture groups. The COWPOLL, MOLLY and ELLIS models predicted enteric CH4 emissions from dry pregnant cows to be higher for EG and HY than SB and SS winter feeding strategy groups. In contrast, IPCC Tier 2 predictions were lowest for EG. Enteric CH4 emissions from cow calf production can be lowered in the winter by feeding dry pregnant cows conserved feeds containing straw combined with barley silage or grain, rather than hay alone. A more comprehensive assessment is required to determine the net contribution of extended grazing or drylot feeding programs to greenhouse gas mitigation strategies for beef production. Finally, the substantially higher differences in the prediction of enteric CH4 emissions among models than among production systems preclude their use for regulatory purposes in their current form. This article is part of the special issue entitled: Greenhouse Gases in Animal Agriculture - Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors; K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson. © 2011 Elsevier B.V.