The effect of abrupt or gradual introduction to pasture after calving and supplementation with Saccharomyces cerevisiae (Strain 1026) on ruminal pH and fermentation in early lactation dairy cows

The aim of this study was to investigate the effect of an abrupt or a gradual introduction to pasture after calving and supplementation with live yeast culture (YC) on ruminal pH and fermentation in early lactation dairy cows. Eight multiparous rumen-cannulated Holstein/Friesian dairy cows were randomly allocated to a 2 × 2 factorial arrangement of treatments prior to calving. Treatments were: nutritional management (NM), abrupt introduction to pasture on the day of calving (AP) or gradual introduction to pasture after the transition period had passed (GP); and supplementation with YC (2.5 × 109 colony forming units, cfu, of Saccharomyces cerevisiae 1026) (Y) or control (C). Ruminal fluid was harvested on d 8–10 and 22–24 post-partum (PP) to assess pH, volatile fatty acid (VFA), lactate, NH3–N and protozoal count. Ruminal pH in the first measuring period (d 8–10 PP) was not affected by YC supplementation while feeding management had an effect with higher (P<0.01) pH in GP than AP groups averaging 6.15 vs 5.96 ± 0.03, respectively. During the second measuring period (d 22–24 PP) ruminal pH was greater in Y than C groups averaging 6.10 vs 5.95 ± 0.04, respectively, and in GP than AP groups averaging 6.11 vs 5.94 ± 0.04, respectively. Consistently, rumen lactic acid concentration was higher (P<0.01) in the AP than the GP group during both measuring periods. Rumen lactic acid concentration was lower in the second period for cows in the Y treatment, with no effect of YC feeding in period one. Cows in AP and C groups were at a greater risk of developing ruminal acidosis than GP and Y groups because the hours spent at ruminal pH below 5.8 was greater in AP than GP groups during both measuring periods and greater in C than Y groups during the second measuring period. Total volatile fatty acid (tVFA) concentration was greater in Y than C groups during both measuring periods. Protozoal count was greater in the GP than the AP group during the first measuring period with no effect in the second measuring period. Results suggest that dietary supplementation with YC during early lactation increased the ruminal pH and tVFA and reduced lactic acid while the abrupt introduction to pasture after calving reduced the ruminal pH and increased lactic acid concentration with no effect on rumen volatile fatty acids.