Are dairy cow rumen pH levels affected by herbage mass and daily herbage allowance?

PALLADINO R. A., O´DONOVAN M., KENNY, D. A., MC EVOY, M.

Suecia

Congreso; 22nd General Meeting of the European Grassland Federation; 2008

European Grassland Federation

The objective of this study was to characterize the rumen pH of dairy cows grazing ryegrass pastures with two different levels of pre grazing herbage mass and daily herbage allowance (DHA). Eight cannulated cows were allocated to four grazing treatments. High and low herbage mass (2200 and 1500 kg DM ha-1 respectively), at two DHA (16 and 20 kg cow-1 day-1) were compared. Rumen pH was measured at four periods (between June and August) at 700, 1100, 1500 and 2000 h. Milk production and composition were collected weekly during each period as well as herbage measurements. The mean rumen pH for all the treatments was 5.87 with a maximun of 7.00 and a minimun of 5.35. Rumen pH tended to be lower at low herbage mass (5.82 vs 5.88 in the high herbage mass treatment; P=0.09) and was significantly different for the treatment low herbage mass and low DHA (pH = 5.77; P<0.05). Milk yield was higher for high DHA. In conclusion, sward characteristics (herbage mass) affect rumen pH levels and cows grazing such swards had low rumen pH levels (< 6.00) for long periods of the day.