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

Energy content is an important criterion for evaluation in lucerne breeding . The in sacco method was used to investigate the phenotypic variation in t he kinetics of degradation of dry matter and fibre for 15 lucerne cultivars grown in one location, and to compare these kinetic parameters with labora tory analyses of dry matter solubility, fibre content (NDF, neutral deterge nt fibre), and fibre solubility. Bags containing forage samples were incuba ted for 2, 4, 8, 12, 24, 48, and 72 h in 3 fistulated Holstein cows. Dry ma tter and NDF degradation curves were modelled with a sigmoid curve with 3 p arameters. Phenotypic variations were observed for dry matter and NDF disap pearance at each time interval, and for the parameters of the degradation k inetics. For both dry matter and NDF, the totally degraded fraction was cor related with the solubility measured by wet chemistry, but the rate of degr adation of the slowly degraded fraction was not correlated with chemical an alyses. The effect of the variations in the parameters of dry matter and fi bre degradation on ruminant performance needs to be studied further.