Relation of Dietary Acetic and Butyric Acids to Intake, Digestibility, Lactation Performance, and Ruminal and Blood Levels of Certain Metabolites

The hypothesis was tested that acetic and butyric acids are related to the lower dry matter intake and superior efficiency which usually results froi~ feeding lactating cows silage rations compared to hay.Voluntary intake of dry matter was not affected by 2% acetic, 1% butyric, or a combination of these acids added to a hayconcentrate ration.However, a mixture of 4% acetic and 2% butyric acidsappeared to cause nasal irritation and reduced intake.Milk yield and nfilk fat content were not appreciably affected by treatments.Although acetic acid increased energy digestibility, none of the treatments improved efficiency of energy utilization.Rumen concentration of acetic and butyric acids was higher, and propionic acid lower, for the supplemented rations.Blood acetic and butyric adds were elevated by the acetic and the acetic-butyric acid supplements.These results generally did not support the hypothesis that acetic and butyric acids increased effÉciency of dry matter utilization.Voluntary consumption of dry matter from weli-fermented silage is generMly lower than that for hay from the same source.However, cows fed these forages usually produce similar daily yields of fat-corrected milk (FCM), resulting in superior efficiency in utilization of dry matter from the silage rations.The factor(s) responsible for the poor consumption of silage and its more efficient utilization have not been determined.Since a major difference between hay and silage dry matter is the content of fernlentation products, various of these substances have been examined in previous studies for effects on intake.Intrarunfinal administration of silage effluent (26) and dietary supplementation with various combinations of silage acids and acid