Influence of Maternal Plane of Nutrition and Arginine Supplementation on Mares and Their Foals: Glucose and Insulin Dynamics

Thirty-two Quarter horse mares (468 to 668 kg BW; 3 to 19 yr) were utilized in a randomized complete block design. Animals were blocked by expected foaling date and randomly assigned to treatments within block. Treatments began 110 d prior to expected foaling date and were arranged as a 2 x 2 factorial consisting of two planes of nutrition, moderate (Mod; 0.5% BW as fed grain/d) or high (High; 1% BW as fed grain/d) and two levels of L-arginine supplementation, 0.21 g/kg BW/d (Arg) or no supplemental Arg (Con; L-alanine to maintain isonitrogenous diets). Mares were housed by block, allowed ad libitum access to water and coastal bermudagrass (Cynodon dactylon) hay, and fed commercial grain twice daily in individual stalls.

A modified frequent sampling i.v. glucose tolerance test (FSIGT) was performed on mares during the 11th month gestation and on foals at 5 and 30 d of age. Jugular catheters were placed 1 h before FSIGT, and horses were allowed ad libitum access to bermudagrass hay and water throughout. After a baseline plasma sample was collected, a glucose bolus of 0.3 g/kg BW was administered. Blood samples were collected at 1, 2, 3, 4, 5, 6, 7, 8, 10, 12, 14, 16, and 19 min. At minute 20, an insulin bolus of 30 mU/kg BW was administered. Blood samples continued to be collected at 22, 23, 24, 25, 27, 30, 35, 40, 50, 60, 70, 80, 90, 100, 120, 150, and 180 min. Samples were placed into tubes containing sodium heparin, immediately placed on ice, and centrifuged within 20 min. Plasma was then collected, placed in microtubes and frozen at -20 degrees C for later analysis.

Glucose concentrations were analyzed using a colorimetric assay and insulin concentrations determined using a commercial RIA kit. There was no influence of dietary treatment on mare glucose area under the curve (AUCg) or peak glucose (PG) and insulin (PI) concentrations (P >= 0.55). Mare insulin area under the curve (AUCi) tended to be influenced by the interaction between nutritional plane and ARG supplementation (P <= 0.06) with HighCon mares having greater AUCi than ModCon (P <= 0.05), and HighCon mares having greater AUCi than mares fed HighArg (P <= 0.05). Foal AUCg, AUCi, and PI were not influenced by maternal diet. However, PG concentration in foals tended to be influenced by mare AA supplementation with foals from Con mares having higher concentrations compared to Arg (P <= 0.09) An influence of age was observed on foal AUCg and AUCi. Foal AUCg was greater at 5 d compared to 30 d (P <= 0.003). Foal AUCi tended to be greater at 30 d compared to 5 d (P <= 0.08). Data suggest maternal plane of nutrition and arginine supplementation can alter mare and foal glucose and insulin dynamics.