In the experiment, four grass (tall fescue hay and Italian rye grass hay, harvested in March and May) and four legume (lucerne hay, harvested in March and May; and red clover hay, harvested in March and April) forages were used. Duplicate samples were incubated in sacco in the rumens of three fistulated mature cows for 2, 4, 8,16, 2i, 48 and 72 h and the degradabilities of dry matter (DM), nitrogen, neutral-detergent fibre (NDF), cellulose and hemicellulose were measured. The maximum degradation rate (MDR) and time of maximum degradation rate (TMDR) were calculated from the first and second derivatives of a Gompertz equation.
The MDR differed between chemical components and was generally higher for cellulose (from 2·31 to 6·95% per h) and nitrogen (from 2·06 to 6·75% per h) in all forages studied. Lignin content of forages was found to be well correlated with the MDR of the fibre components (r = -0·74 for NDF, -0·72 for cellulose and -0·84 for hemicellulose).
The TMDR values were much shorter for DM and nitrogen (< 4·2 h) than for the fibre fractions (from 6·8 to 14·0 h). Furthermore, in grasses, hemicellulose TMDR occurred before those of cellulose, while in legumes the order of TMDR was less clear. Elevated positive correlation coefficients between the fibre components and their TMDR possibly indicate that the structural arrangement and types of linkages within and between these components regulate their fermentation process.
The possibility of using the Gompertz first and second derivatives to study the synchrony of the release of nitrogen and organic matter into the rumen was examined.