EFFECTS OF ENSILAGE OF GRASS ON PERFORMANCE AND NUTRIENT UTILIZATION BY DAIRY-CATTLE .2. NUTRIENT METABOLISM AND RUMEN FERMENTATION

A study seas carried out to examine the effects of ensiling and pattern of silage fermentation on nitrogen and energy utilization, rumen fermentation and rumen degradation characteristics of forage by lactating dairy cows. Six non-fistulated dairy cows and three rumen fistulated dairy cows were offered fresh grass (G) or grass silage produced from the same sward which had undergone either an extensive (E) or restricted (R) fermentation. Animals offered extensively fermented silage had higher urinary nitrogen (N) outputs (expressed as a proportion of N intake) than those offered fresh grass (P < 0.05). Corresponding values for animals offered restricted fermented silage were intermediate between those offered grass and extensively fermented silage. Animals offered fresh grass and restricted fermented silage also had higher methane energy losses (P < 0.05), than those offered extensively fermented silage. The ensiling of grass had little effect on metabolizable energy (ME) intake or on the efficiency of utilization of ME for lactation (k(1)). Animals offered extensively fermented silage had higher proportions of propionate and lower proportions of acetate than those offered fresh grass or restricted fermented silage (P < 0.001). Ensiling resulted in an increase in the soluble (a) fraction and a reduction in the potentially degradable (b) fraction of N.