Relationships between rumen volatile fatty acid concentrations and milk production in dairy cows: a literature study

Data from 20 research studies with 92 treatment means were summarized from the journals of dairy science and animal science 2000-2002. All studies were conducted with Holstein cows in Latin square or simple reversal design and included serial sampling of rumen fluid via cannula. Treatments included the effects of feeding various carbohydrate sources, corn milling byproducts, particle size of forage or grain, level of non-structural carbohydrates and the source and digestibility of forages. Studies included rations based on both stored forages and pasture. Simple statistics, correlation, linear regression and mixed model analysis assessing the random effect of Study were used to describe the relationships between rumen and production parameters. Milk yield was most highly related to rumen concentrations of butyrate (r(2) = 0.47) and propionate (r(2) = 0.23). There was little or no relationship between milk yield and either rumen acetate or total VIA concentration. Milk yield was related positively to dry matter intake (r(2) = 0.69) and negatively to days in milk (r(2) = 0.25). An improvement in the regression of milk yield was obtained if the theoretical yield of ATP (to the host) per milliliter of rumen fluid was used as the independent variable in place of butyrate alone. Relationships between rumen volatile fatty acid concentrations and milk composition were moderate to weak. Content of milk fat (g/100 g) had a positive association with rumen acetate/propionate ratio (r(2) = 0.26). Milk protein (g/100 g) had a negative relationship with rumen pH (r(2) = 0.17) and a positive relation to days in milk. Rumen butyric acid concentration was positively related to dry matter intake (r(2) = 0.28). Rumen butyric acid concentration had the strongest positive association with milk production and dry matter intake in this data set. The results suggest that in lactating cows increased energy intake is channeled largely through increases in rumen production of butyric and propionic acids and their yield of ATP to the host animal. (C) 2004 Elsevier B.V. All rights reserved.