Effects of abomasal or intravenous administration of arginine on milk production, milk composition, and concentrations of somatotropin and insulin in plasma of dairy cows.

Holstein cows just past peak lactation were used in a 3 x 3 Latin square design to determine the effects of arginine infusion on concentrations of somatotropin and insulin in plasma, milk production, and milk composition. Treatments were: 1) control; 2) arginine injection into jugular vein, and 3) arginine infusion into abomasum. Concentrations of arginine and ornithine in plasma were increased by injection of arginine into the jugular vein compared with the control. The concentration of ornithine in plasma was increased shortly after injection of arginine into the jugular vein, and both arginine and ornithine concentrations in plasma decreased rapidly. Abomasal infusion of arginine significantly increased concentrations of arginine, ornithine, and urea in plasma compared with concentrations in the control treatment. Injection of arginine into the jugular vein increased concentrations of somatotropin and insulin in plasma, but the increase did not persist for more than 30 min. A secondary peak in plasma somatotropin concentration occurred approximately 1 h after the initial peak. Arginine infusion into the abomasum did not alter plasma concentrations of either somatotropin or insulin. Dry matter intake, milk production, and milk composition were not affected by treatments. Lack of changes in milk production and milk composition suggest that acute increases in somatotropin with concomitant increases in insulin are not sufficient to stimulate synthesis of milk and milk components by cows during established lactation.