Dynamic of voluntary intake, feeding behaviour and rumen function in sheep fed three contrasting types of hay

The purpose of this experiment was to analyse the dynamic relationships linking intake, feeding behaviour, and rumen content in sheep fed three types of hay representing contrasting nutritional situations. Six fistulated sheep received, ad libitum in a replicated 3 x 3 Latin square design, a late-cut mixed grass hay, an early-cut cocksfoot hay and an early-cut lucerne hay. Neutral detergent Fibre content decreased from 684 to 637 and to 447 g/kg dry matter (DM), and in situ DM rate of degradation increased from 0.017 to 0.040 and to 0.092 h(-1) for mixed grass, cocksfoot and lucerne respectively. Voluntary DM intake was 1000, 1484 and 1608 g (P < 0.01) for mixed grass, cocksfoot and lucerne respectively. Differences in voluntary intake among hays were mostly related to differences in the size of the principal meals and in intake rate, especially initial intake rate at the beginning of the meal. Cocksfoot was associated with a higher number of small meals. Early-cut hays needed less mastication time per g consumed than the late-cut hay. Rumen content before the meal was lower for the early-cut hays (P < 0.05). After the principal meal wet weight of rumen content was similar for the two grass hays but remained lower for lucerne. Faster clearance rate of rumen DM with early-cut hays (P < 0.01) after the principal meal was due to the higher disappearance rate of the degradable fraction. Intake of low quality forages seems to be primarily limited by a high content of undegradable and slowly degradable material in the rumen. Studying the dynamic of intake and rumen function is promising for development of mechanistic models to predict intake.