Adaptation to High Concentrate Diets by Beef Cattle. II. Effect of Ruminal pH Alteration on Rumen Ferementation and Voluntary Intake of Wheat Diets

Abstract

An in vivo and in vitro fermentation study was conducted in conjunction with a feed intake trial to study the effect of controlling rumen pH on feed intake and rumen microbial fermentation patterns in steers fed a 90% concentrate wheat diet. Rumen pH was supported by direct rumen infusion of an equal molar mixture of sodium and potassium hydroxide. Total feed intake was greater (P<.1) for hydroxide (9.87 kg) infused than for the control steers (8.39 kg). Higher period intakes were observed for the infused steers at all times with the exception of hour 2. Rumen pH values were significantly lower (P<.01) for the control steers (5.39 vs 5.88). These data indicate a possible relationship between low rumen pH and cessation of voluntary feed intake. Small differences in in vivo lactate occurred between these two treatments, possibly because of rumen microbial adaptation to a high concentrate diet at the time the study was conducted. However, higher (P<.01) in vitro lactate concentrations were observed in incubations where ruminal fluid source was from the hydroxide infused steers. Differences in volatile fatty acids (VFA) concentrations due to treatment were not large with the exception of valerate, which was appreciably higher (P<.05) in the control animals. Moles/100 moles of acetate and isovalerate were significantly greater and valerate lower in the hydroxide infused versus control steers.