means were done by using a t-test. Cumulated CH4 evolution was analysed by a repeated measures model using PROC MIXED
of SAS (2008). Sources of variation included treatment, time, and the treatment × time interaction. The random variable was
pig within treatment. Variables were analysed subjected to three covariance structures: compound symmetry, compound
symmetry heterogeneous and autoregressive order 1. Using the largest Akaike information criterion and Schwarz Bayesian
criterion, the compound symmetry was the structure that fitted the model best.