Enteric methane production and neutral detergent fiber plasticity: A potential indicator trait for forage utilization in dairy breeding

This study aims to evaluate the use of a reaction-norm model, with NDF concentration in the ration as an environmental gradient, and its plasticity as a candidate phenotype for identifying animals that efficiently utilize plant fiber. A dataset from a feeding trial with 40 cows fed different types of silage and concentrate with differing NDF concentrations was used. Single-visit ln-transformed methane production was analyzed using a model accounting for systematic environmental effects; among these a fixed effect of NDF concentration as a fixed effect, along with random effects for individual intercept and slope, both of which were significant. Plasticity, defined as the individual slope of the response in ln-transformed methane production to NDF concentration in the ration, was further examined in relation to underlying data structure and NDF digestibility. Underlying data structure was analyzed with an explanatory factor analysis of mean and variance for variables not included in the reaction-norm model, interpreted as either feed composition or feed intake and activity. The individual slope showed a significant positive relationship to individual NDF digestibility, suggesting that it could serve as an indicator trait to breed cows that efficiently utilize roughage. However, this finding needs to be validated in a larger dataset suitable for genetic analysis.