Predicting CO2 Production from Lactating Dairy Cows Based on an International Dataset

Samenvatting

Large scale quantitative measurement of enteric CH4 production from cattle is difficult, time consuming and costly with respect to equipment needed. However, combining measured breath CO2:CH4 concentration ratio and predicted CO2 production is a potential proxy for CH4 production. In the current study, predictions of CO2 production were developed using an international data set of 1502 individual lactating cow observations of CO2 production and associated traits. Production of CO2 was recorded using either GreenFeed or respiration chambers, but method was confounded with research location, and therefore, no distinction was made. Variables for model development were as follows; continuous variables were dry matter intake (DMI), energy corrected milk yield (ECM), body weight (BW) and days in milk (DIM). Parity was a categorical variable. Stepwise regression with CO2 production as the dependent variable was used to identify which variables contributed the most to the variation in CO2 production. Based on the results from stepwise regression, retained variables were used in a mixed model with research location as random effect. The resulting equation: CO2 (L/day) = – 0.30×DIM + 23.6×BW (kg)0.75 + 176×DMI(kg/day) + b, where b is – 106, – 39.8, – 26.0 for 1 st, 2 nd and greater than 2 nd parity cows, respectively (R 2marginal= 0.59, R 2adjusted = 0.76). Simultaneously a model that can be used at farm level was developed, with predicting variables reasonable for a farmer to obtain: CO2 (L/day) = 0.92×DIM + 62.2×ECM (kg/day) + 35.4×BW (kg)0.75 + b, where b is – 171, 11.8 and – 33.7 for 1st , 2 nd and greater than 2 nd
parity cows, respectively (R 2marginal = 0.41, R 2adjusted = 0.68). In conclusion, DMI described most of the variation in CO2 production; however, farmers typically do not have this information. Therefore, metabolic body weight, ECM, DIM and parity are more practical variables for predicting individual CO2 and potentially CH4 production from lactating dairy cows on commercial farms.