Plasma concentrations of prolactin, glucose, insulin, urea nitrogen, and total amino acids in stallions after ingestion of feed or gastric administration of feed components.

Concentrations of prolactin, glucose, insulin, urea N, and total amino acids in plasma of stallions after ingestion of pelleted feed were compared to those after direct gastric administration of water, NaCl, egg albumin, or corn starch (Exp. 1) or water, egg albumin, hydrolyzed casein (Amicase), or a mixture of indispensable amino acids (Exp. 2). Stallions were fed once daily (75% pellet and 25% hay) at 1500 for 30 d. On d 22, 24, 26, 28, and 30, blood samples were collected every 30 min from 1 h before through 4 h after treatment, which occurred at 1100. In Exp. 1, there was a positive secretory response for prolactin (P = .013) only after the meal. Positive glucose and insulin responses were observed after the meal (P < .055) and after gastric administration of corn starch (P < .001). Total amino acids increased (P = .008) only after the meal. In Exp. 2, a positive prolactin response (P < .001) occurred after the meal and a negative response (P = .023) after administration of water; administration of Amicase increased (P = .061) prolactin concentrations after a 2.5-h delay. Positive responses were observed for glucose, insulin, and total amino acids after the meal (P < .001) and after administration of Amicase or the amino acid mixture (P < .026). Positive urea N responses were observed after administration of Amicase and the amino acid mixture (P < .001).(ABSTRACT TRUNCATED AT 250 WORDS)