PERIPARTURIENT CHANGES IN INTAKE, RUMINAL CAPACITY, AND DIGESTIVE CHARACTERISTICS IN BEEF-COWS CONSUMING ALFALFA HAY

Four multiparous, ruminally fistulated Angus x Hereford cows (average BW = 568 kg) were bred to the same bull and used to monitor periparturient changes in DMI, ruminal capacity, and digestion and fermentation characteristics. Cows were individually fed alfalfa hay (16.0% CP, 51.3% NDF) at 130% of the average DMI of the previous 5-d period. Ruminal capacity and DM fill were measured once every 2 wk by removing the ruminal contents from each cow and filling the empty rumen with water. Dry matter intake was measured daily. Ruminal VFA, pH, NH3, and total tract DM digestibility (DMD) were measured during three 7-d periods (average of 58 d before calving, 16 d before calving, and 25 d after calving). Ruminal capacity and DM fill varied in a quadratic manner (P < .01); both were least 6 d before calving. Forage DMI (quadratic effect; P = .02) increased moderately during the prepartum period but increased dramatically after parturition. Although postpartum (d 22) ruminal capacity was only 5% greater than at 61 d before calving, postpartum DMI was 69% greater than DMI measured 61 d before calving. Indigestible ADF (IADF) passage rate changed quadratically with period (P = .01); the greatest IADF passage rate was observed 6 d before calving. Ruminal VFA (mM) also tended to change quadratically (P = .08); the highest concentrations occurred 25 d after calving. The acetate:propionate ratio declined linearly with period (P = .01). Ruminal fluid dilution rate, pH, NH3, and DMD did not change significantly over time. In conclusion, the observed patterns and magnitude of changes in ruminal capacity and DMI are interpreted as indicating that factors other than ruminal capacity and distension, per se, play a critical role in causing intake changes during the periparturient period.