Phenotypic variation for in sacco dry matter and fibre degradation kinetics in lucerne

Abstract

Energy content is an important criterion for evaluation in lucerne breeding. The in sacco method was used to investigate the phenotypic variation in the kinetics of degradation of dry matter and fibre for 15 lucerne cultivars grown in one location, and to compare these kinetic parameters with laboratory analyses of dry matter solubility, fibre content (NDF, neutral detergent fibre), and fibre solubility. Bags containing forage samples were incubated for 2, 4, 8, 12, 24, 48, and 72 h in 3 fistulated Holstein cows. Dry matter and NDF degradation curves were modelled with a sigmoid curve with 3 parameters. Phenotypic variations were observed for dry matter and NDF disappearance at each time interval, and for the parameters of the degradation kinetics. For both dry matter and NDF, the totally degraded fraction was correlated with the solubility measured by wet chemistry, but the rate of degradation of the slowly degraded fraction was not correlated with chemical analyses. The effect of the variations in the parameters of dry matter and fibre degradation on ruminant performance needs to be studied further.