Effect of parity and day on nutrient intake by foals and nutrient demand on mares during the first month of lactation.

Arabian mares, three primiparous (P) and three multiparous (M), were used to estimate milk and nutrient intake by foals and nutrient demand on mares. Milk intake was estimated on d 10, 20 and 30 of lactation by weigh-suckle-weigh. Milk was collected on d 11, 21 and 31. Digestible energy (DE) requirements (Mcal/d) were estimated based on milk E content derived from milk lactose, protein and fat concentrations and a conversion coefficient (CC) of 0.72. Digestible protein (DP) requirements (g/d) were estimated based on daily true milk protein (TP) and a CC of 0.65. Data were analyzed as repeated measures over d of lactation and relationships between d of lactation and response variables determined by linear and quadratic orthogonal contrasts. Milk yield (kg) did not change with d of lactation in P mares but tended to increase in M mares (linear, P = 0.12) (12.98, 12.86, and 12.85 vs 12.66, 14.62, and 14.31 ± 1.43, respectively). As a percentage of BW, milk yield over d of lactation was 3.05 and 3.40 for P and M mares, respectively. Concentrations of TP decreased (linear, P = 0.05) and lactose and total solids increased (linear, P = 0.05 and P ≤ 0.001, respectively) in P mares, but did not change in M mares. Milk fat of M mares decreased (linear, P ≤ 0.05) with d of lactation (3.2 to 1.7 %) but did not change in P mares (2.05 to 2.39 %). Fat and TP yield did not differ between parities, but lactose yield was higher (P ≤ 0.05 on d 30) in M compared to P mares. Day of lactation increased (linear, P ≤ 0.01) lactose yield in M mares. Estimates of DP (g/d) requirements in P mares decreased (linear, P ≤ 0.05) with d of lactation (625, 579 and 503 for d 10, 20 and 30, respectively), but did not change in M mares (564, 527 and 633 for d 10, 20, and 30, respectively). Estimates of DE (Mcal/d) did not differ between P and M mares or between d of lactation (26.8, 26.3 and 27.2 vs 29.5, 30.0, and 31.8 ± 3.3, respectively). Results suggest that decreasing milk TP yield with d of lactation and lower milk lactose yield in P mares may limit foal protein and carbohydrate intake compared to that of M mares. [ABSTRACT FROM AUTHOR]