Voluntary Intake, Milk Production and Plasma Metabolites in Nursing Mares Fed Two Different Diets

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Abstract
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 < 0.01) for mares fed Diet F than for those fed Diet C and decreased (P < 0.01) from colostrum (48 ± 12 h after foaling to wk 8); lactose concentration was higher (P < 0.05) for mares fed Diet C than for those fed Diet F and increased (P < 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.