Voluntary intake, milk production and plasma metabolites in nursing mares fed two different diets

Voluntary food intake, milk yield and composition, and blood metabolites were measured during the first 2 mo of lactation in draft broodmares fed diets containing either 95% hay and 5% concentrates (Diet F) or 50% hay and 50% concentrates (Diet C). Voluntary food intake was higher for mares fed Diet C than for those fed Diet F (22.9 vs. 21.4 kg dry matter in wk 4). Both diets, especially Diet C, were eaten in amounts exceeding the energy requirements. Daily milk yield in wk 4 was 26.4 kg and 23.4 kg for mares fed Diets C and F, respectively. Milk fat and protein concentrations were higher (P less than 0.01) for mares fed Diet F than for those fed Diet C and decreased (P less than 0.01) from colostrum (48 +/- 12 h after foaling to wk 8); lactose concentration was higher (P less than 0.05) for mares fed Diet C than for those fed Diet F and increased (P less than 0.01) from colostrum to wk 8. Minerals varied mainly with lactation stage. Milk fat was higher in linolenic acid and lower in linoleic acid for mares fed Diet F than for those fed Diet C. Glucose concentration was higher in plasma of mares fed Diet C; 3-hydroxybutyrate and acetate concentrations were higher in plasma of mares fed Diet F.