Effects of a Subacute Ruminal Acidosis Model on the Diet Selection of Dairy Cows

Two experiments were conducted to study the effects of a subacute ruminal acidosis (SARA) model on diet choice in dairy cows. In the first experiment, 25% of the ad libitum dry matter intake (DMI) of the total mixed ration (TMR) was replaced with wheat-barley pellets (WBP, 50% ground wheat, 50% ground barley). Rumen pH was measured continuously via in-dwelling probes in 4 mid to late lactation cows. This diet change reduced rumen pH by 0.14±0.02 pH units (mean±SE) and increased time below pH 6.0, from 319±36min-1 to 641±36min-1. Hence, the nutritional model successfully induced SARA. The second experiment determined if inducing SARA increases the feed preference for long alfalfa hay compared with alfalfa pellets. The 2 wk of inducing SARA were separated by 1 control wk. Four cows on either SARA and control diets were given a choice of 2 feeds, 2 times per d, for 30min. The preference ratios (PR = Amount of Hay consumed/Amount of Hay+Pellets consumed) for alfalfa hay during two SARA weeks was greater (0.85±0.03) compared with the control week (0.60±0.03). In SARA weeks, average rumen pH was 0.23±0.03 units lower, and time below pH 6.0 and 5.6 was higher compared to control. These results suggest that when given a choice of feeds, dairy cows alter their diet selection to attempt to attenuate SARA.