New Approaches to Control of Ruminal Acidosis in Dairy Cattle

Eighty Holstein-Friesian cows were randomly assigned to four treatment groups of 20. The four groups of twenty cows were fed on diets that were designed to place cows at some degree of risk of ruminal and metabolic acidosis. The cows were fed either 10 kg of pellet and ate pasture, or a subgroup of six cows per group was fed 10 kg of pellet with ad lib forage in a Calan gate facility. Cows in Group 1 were fed the basal diet that contained no feed additives (C); Group 2 were fed the basal diet and 20 mg of Tylosin (T) per kg of feed; Group 3 were fed the basal diet and 20 mg of Tylosin and 20 mg of monensin (TM) per kg of feed, and Group 4 were fed the basal diet and 30 mg of Virginiamycin (VM) per kg of feed. The TM group had significantly lower rumen pH than the Tylosin group or the VM group. Volatile fatty acid concentrations in rumen fluid were consistently higher for the TM group. Cows in the VM group and control cows also had significantly higher mean blood glucose concentrations than the TM group. Mean blood glucose concentrations significantly decreased over time, but concentrations for the TM group were significantly less variable than for other groups. There was a tendency for blood urea nitrogen concentrations to be higher in the TM group. Concentrations in this group increased markedly over time, though pattern of increase was not significantly different from the other groups. Plasma urea concentrations increased significantly over time. The TM group maintained a higher level of milk production over the period than any of the other groups and did not decline as much over the trial as did the other groups. There were marked differences in rumen metabolism, blood concentrations of metabolites and milk production that suggest that controlling rumen fermentation to reduce lactic acid production may be a useful means of reducing health risks from acidosis.