Impact of dietary manipulation of rumen pH on health and productivity in dairy cows

Abstract

Current feeding strategies for dairy cows focus on meeting the energy requirements for high levels of milk production. However a major concern is the effect that these feeding regimes might have on rumen pH, which can have harmful effects on the cow and rumen microbial population. Several interventions have been used to counteract the effects of low rumen pH such as the use of probiotics e.g. yeast (Saccharomyces cerevisiae). However benefits have been inconclusive due to large individual animal variation in responses to treatment observed. The use of novel monitoring technologies can help assess the effect that different dietary interventions have on performance, rumen pH and rumen health. Data from three on-farm dairy cow trials (Trial 1 standard diet plus yeast; Trial 2 standard diet plus acidotic challenge plus yeast; Trial 3 cows grazing grass plus yeast) was used to evaluate the use of rumination collars (RC), rumen pH boluses, a whole cow dynamic mechanistic simulation model (SM) and the effect that different feeding strategies have on performance rumen pH dynamics and rumination time. No statistically significant differences between Control (no yeast) and Treatment (addition of yeast) diets were observed on any of the parameters measured. The lack of animal response to yeast supplementation observed in the three feeding Trials could be attributed to the stage of lactation, as the cows were passed peak lactation. Comparison of rumination time obtained with the RC and visual observations (obtained directly and from video recordings) suggest that the RC can be used to determine rumination time in housed cows. However its poor performance in grazing environments makes its use not advisable in cows outside at grass. The rumen pH boluses provided detailed and accurate data on circadian rumen pH. Highly varied individual responses to the feeding strategies were observed. This resulted in a diverse degree of risk of individual cows which experienced sub-acute rumen acidosis. The SM was able to accurately predict circadian pH, compared against the data obtained from Trials 1 and 2. The model provided pH values that were in agreement with those obtained with the rumen boluses. The use of new technologies to monitor cows individually could aid in whole-herd management, for example by setting thresholds for rumen pH and rumination time related to individual cow status, and then trigger appropriate interventions.