Variation in rumen fermentation and the rumen wall during the transition period in dairy cows

Strong adaptive changes occur in the peri-parturient dairy cow related to a marked rise in dry matter intake and alteration in diet composition after calving. Early lactation dairy cattle are susceptible to metabolic disorders and impaired rumen function during the transition period, with detrimental effects on cow performance. For a quantitative understanding of the dietary effects on rumen function, several classes of influencing factors can be distinguished (intrinsic degradation characteristics of feed, characteristics of microbial activity, rumen fermentation conditions, rumen wall function). Interpretation of experimental results requires all these factors to be taken into consideration simultaneously. This contribution aimed to review the capacity of the rumen wall to adapt to the marked increase in feed intake by the post-parturient dairy cow. While the principle of distinct adaptations of the post-parturient rumen wall is generally accepted, literature is not always conclusive about the size of the effects. Virtually all studies on adaptation of the post-parturient rumen wall were performed post-mortem and with isolated tissue in vitro. Therefore, an in vivo trial with twelve rumen fistulated dairy cows is presented to support and discuss the various factors involved in this review. A faster (in 10 d) versus a slower (in 20 d) increment of starch-rich concentrate intake after calving was evaluated for effects on adaptive response of rumen epithelia and altered rumen functioning up to twelve weeks after calving. Results showed transient changes in rumen epithelia and suggest a different adaptive response of rumen epithelia during the first weeks of lactation due to differences in supplemental concentrate feeding. No evidence was found for any detrimental effect of a fast increment of concentrate intake on dry matter intake, rumen fermentation, and cow performance. Results in literature either confirm or contradict these findings, and they attribute either a more important role to molecular mechanisms in rumen epithelia or to cell proliferation and epithelial morphology. The different research methods adopted and the high variability of results obtained with this type of research strongly limit our understanding of the relative importance of cell metabolic changes, epithelia proliferation and rumen wall morphology. In conclusion, the ruminal epithelia in the peri-parturient cow responds in a coordinated manner to rapid dietary changes which is of high significance to maintain normal rumen functio