307. Award Talk: Lactation, Neonate Foal Health, and Maternal and Offspring Metabolism in Broodmares with Moderate Body Condition.

Abstract Body condition of broodmares during gestation impacts lactation and metabolism of mare and offspring, which may influence foal health and subsequent development. Although most mares have a moderate body condition score (BCS), much of the research focuses on mares with extreme BCS. We hypothesized that moderate differences in maternal body condition would influence maternal glucose and insulin metabolism, leptin, and adiponectin concentrations but would not influence gestation length, milk composition or foal metabolism in the early post- partum period. Light breed mares (n = 14) were divided into moderately obese (MO; n = 8) or lean (LN; n = 6) groups according to their BCS and cresty neck score (CNS) at day 315 of gestation. Mares underwent intravenous (i.v.) glucose tolerance tests at 315 days gestation and days 59 and 119 postpartum (pp). Mares were administered dextrose i.v. (0.3 g/kg BW) followed by an i.v. insulin infusion (0.3 mU/kg BW) 20 minutes later. Jugular blood samples were collected -30, -15, 0, 2, 5, 10, 15, 20, 25, 30, 45, 60, and 120 min relative to dextrose infusion for measurement of glucose and insulin concentrations. Circulating leptin and adiponectin concentrations were measured in mares at parturition and days 58 and 118 pp, and in foals on days 1, 7, 14, 28, 58, and 118. Immunoglobulin G (IgG) was measured in colostrum at parturition and in foals at 18 hours after birth. Fat and protein percentages were determined in colostrum at parturition and in milk at days 7, 58, and 118 pp. Data were analyzed using ANOVA in R Studio where P ≤ 0.05 was considered significant and 0.05 < P ≤ 0.10 considered a tendency. Moderately obese mares had greater BCS (LN: 4.1; MO: 5.9; P = 0.003) and CNS (LN: 0.9; MO: 2.8; P = 0.08) than LN mares. Gestation length was shorter in MO mares than LN mares (LN: 349 d; MO: 340 d; P = 0.04). Mare glucose and insulin peak, average and area under curve in mares (P > 0.24), and foal glucose concentrations were not influenced by group (P > 0.24). Moderately obese mares had greater leptin concentrations than LN mares (P = 0.0008), but foal leptin concentrations were not different (P = 0.36). Mare and foal adiponectin were not influenced by group (P > 0.31). Group did not influence IgG concentrations in colostrum or foal serum (P > 0.37). Protein and fat percentages in colostrum and milk were similar across groups (P > 0.33). Given the similarities in glucose metabolism among mares and foals, leptin and adiponectin in foals, and milk composition throughout lactation, our study validates the current management practice of maintaining broodmares at a moderate BCS.