Development of an equation to estimate the enteric methane emissions from Holstein dairy cows in Canada

The aim of this study was to use dietary factors, including the type of fats, and animal characteristics, to predict enteric methane (CH4) emissions from dairy cows under Canadian conditions. For this purpose, 193 individual observations from six different trials assessing the impact of dietary modification on enteric CH4 production were analyzed. Animal [milk yield (MY), milk fat content, milk protein content, days in milk, body weight (BW), and dry matter intake (DMI)] and dietary variables [organic matter, crude protein, neutral detergent fiber (NDF), acid detergent fiber (ADF), starch, ether extract (EE), rumen-inert fat, and unprotected fat (EE – rumen-inert fat)] were tested. A 5-fold cross validation was used to obtain the following equation: CH4 (g d-1) = -1260.4 + 1.9 × MY (kg d-1) + 62.8 × milk fat (%) –18.4 × milk protein (%) + 11.0 × DMI (kg d-1) + 0.3 × BW (kg) + 58.3 × NDF (% of DM) - 0.8 × NDF2 (% of DM) + 1.9 × starch (% of DM) - 2.5 × EE – rumen-inert fat (% of DM). The mean estimate from the proposed equation (474 g CH4 cow-1 d-1; r = 0.83, RMSE = 40.0) was close to the observed mean emission (476 g CH4 cow-1 d-1). The proposed model has a higher precision to predict CH4 emission from cows fed typical Canadian diets than other models, and it can be used to evaluate CH4 mitigation strategies.