VOLUNTARY INTAKE, MILK-PRODUCTION AND PLASMA METABOLITES IN NURSING MARES FED 2 DIFFERENT DIETS

Voluntary food intake, milk yield and composition, and blood metabolit es were measured during the first 2 mo of lactation in draft broodmare s fed diets containing either 95% hay and 5% concentrates (Diet F) or 50% hay and 50% concentrates (Diet C). Voluntary food intake was highe r 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 th an 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 s tage. 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 aceta te concentrations were higher in plasma of mares fed Diet F. J. Nutr. 122: 992-999, 1992.