THE EFFECTS OF GRASS PRESERVATION ON INTAKE, APPARENT DIGESTIBILITY AND RUMEN DEGRADATION CHARACTERISTICS

A study was carried out to examine the effects of method of grass conservation on intake and apparent digestibility by sheep and rate of degradation in the rumen of cattle. Thirty-six hoggets were arranged in a three-period partial change-over design involving nine treatments. The treatments consisted of fresh herbage or herbage from the same pasture which was ensiled for 2, 4, 7, 10, 20 and 41 days in round bales or herbage from the same pasture conserved as hay or ensiled in a bunker silo for 51 days. In addition the rate of dry-matter disappearance in the rumen for each treatment was determined using three rumen fistulated steers. The flesh and ensiled treatments had been frozen prior to feeding. Results from the study showed that the dry-matter intakes, corrected for losses of volatile compounds, of material ensiled in round bales, was increasingly depressed with period of ensiling up to 20 days after ensiling. Intakes of digestible energy followed a similar trend. Regression analysis indicated that reductions in intake with ensiling were mainly due to increases in ammonia N and n-butyric acid concentration, while changes in pH, water-soluble carbohydrate and acetic acid concentration also influenced intake. The differences in intakes of dry matter and digestible energy between fresh herbage and herbage from the bunker silo were not significant. The ensiling of herbage in round bales had little effect on organic matter apparent digestibility but led to an increase in nitrogen apparent digestibility and effective degradability when calculated at rumen outflow rates of 0.05 per h and 0.08 per h. Conservation of grass as hay led to a reduction in the intake, apparent digestibility and effective degradability of dry matter.