Variation of Rumen Bacterial Diversity in Steers after the Beginning of Grazing

Holstein heifers before or after puberty often are herded on public pastures in Japan. The herbage intake and rumen fermentation of grazing heifers that are not adapted for fresh herbage decreases due to a change of feed from stall-fed dried forage to fresh herbage. This limits their performance during the first several weeks on pasture. Thus, the feeding program such as supplementation before and after the beginning of grazing is important. An increase in ammonia concentration and a decline in fibre degradation in the rumen of a heifer (both of which occur simultaneously with low herbage intake and rumen fermentation) would be caused by the reduced capacity of various bacteria to produce peptides and degrade fibre (Oshio and Tahata 1981). This suggests that variation in rumen bacterial diversity plays an important role in herbage intake and rumen fermentation. However, less information is available on how bacterial diversity in heifers varies during the first few weeks of grazing. This information will provide the basis for designing nutritional management programs for heifers before and after the beginning of grazing. The objective of this study was to determine how herbage intake, digestibility, and rumen bacterial diversity vary in steers that have started grazing without adaptation for fresh herbage during the first 4 weeks after the beginning of grazing