Lactation in the Horse: Milk Composition and Intake by Foals

Milk samples averaging 500 ml were collected weekly from 10 to 54 days postpartum from five lactating mares. Samples were obtained by hand milking after oxytocin administration and while the foal nursed. Dry matter, protein and gross energy were higher in samples obtained at 10 and 17 days postpartum than those obtained during the midlactation period of 24-54 days. Midlactation samples averaged 10.5% dry matter, 1.29% fat, 1.93% protein, 6.91% sugar and 50.6 kcal/100 g. Protein comprised 22% of milk energy. Milk intake was estimated in five foals from deuterium oxide (D2O) turnover to be 16, 15 and 18 kg/day at 11, 25 and 39 days postpartum. Milk intake differed significantly among foals and at the various postpartum ages, whether intake was expressed as a daily amount, as a percent of foal body weight, per kilogram0.75 or per gram of foal body weight gain. Milk production was equivalent to 3.1% of the mare's body weight at 11 days postpartum, 2.9% at 25 days and 3.4% at 39 days. On the basis of metabolic body size milk output by the mare was 149 g/kg0.75, 139 g/kg0.75 and 163 g/kg0.75 at 11, 25 and 39 days postpartum, respectively. Nutrient intakes by foals were calculated from milk composition and intake data. At 11, 25 and 39 days postpartum, respectively, dry matter intake equaled 3.1, 2.1 and 2.0% of foal body weight, and daily gross energy intake was 9380, 7590 and 8910 kcal. For each gram of body weight gain, foals ingested 0.37 g protein and 8.3 kcal at 11 days, 0.26 g protein and 6.7 kcal at 25 days, and 0.30 g protein and 7.8 kcal at 39 days of age.