Prediction of enteric methane emissions from Holstein dairy cows fed various forage sources.
Rico, D.E., Chouinard, P.Y., Hassanat, F., Benchaar, C., and Gervais, R. (2016). "Prediction of enteric methane emissions from Holstein dairy cows fed various forage sources.", Animal, 10(2), pp. 203-211. doi : 10.1017/S1751731115001949 Access to full text
Milk fatty acid (FA) profile has been previously used as a predictor of enteric CH4 output in dairy cows fed diets supplemented with plant oils. The objective of this study was to investigate the relationships between milk FA and enteric CH4 emissions in lactating dairy cows fed different types of forage. A total of 81 observations from 3 separate 3×3 Latin square design (with 32-d periods) experiments using a total of 27 lactating cows (96 ± 27 DIM; Mean ± SD) were used. In all experiments, dietary forages were included at 60% of ration DM and were: 1) 100% corn silage 2) 100% alfalfa silage 3) 100% barley silage 4) 100% timothy silage 5) 50:50 mix of corn and alfalfa silages, 6) 50:50 mix of barley and corn silages, and 7) 50:50 mix of timothy and alfalfa silages. Enteric CH4 was measured in individual air-flow controlled chambers during 3 consecutive days. Milk was sampled during the 6 d of each period and analyzed for components and FA profile. Test variables included DMI (kg/d), dietary NDF (%), dietary EE (%), milk yield (kg/d), milk components (%), and individual milk FA (% of total FA). Associations between test variables and CH4 were analyzed using the CORR procedure of SAS. The GLMSELECT procedure was used to identify a set of candidate models using the LASSO and LARS methods. Data were then fitted into a random regression using the MIXED procedure including the random effects of cow and period. The VC and UN covariance structures provided best fit for the random and repeated statements, respectively. Denominator degrees of freedom were calculated by the Satterhwaite equation. A positive association was observed between CH4 and DMI (r = 0.59, P < 0.001), whereas negative associations were observed between CH4 and c9-17:1 (r = -0.58, P < 0.001), and t8, c13-18:2 (r = -0.51, P < 0.001). The selected model predicted observations with a coefficient of determination of 0.92 and was: CH4 (g/d) = 357.1 + 15.2 × DMI – 56.9 × 15:0 – 81.7 × c9-17:1 – t10-18:1 × 41.0 – c11-18:1 × 53.3 – t8, c12-18:2 × 243.0 – t8, c13-18:2 × 563.7.0 – t11, c15-18:2 × 242.9. Milk FA profile and DMI can be used to predict CH4 emissions in dairy cows across a range of dietary forage sources.
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