Arginine supplementation increases weight gain, depresses antibody production, and alters circulating leukocyte profiles in preruminant calves without affecting plasma growth hormone concentrations.

The hypothesis that dietary L-arginine (L-Arg) supplementation would increase growth hormone (GH) secretion and antibody production in preruminant calves was tested. Sixteen newborn calves were randomly assigned to either Arg+ or Arg- treatment groups. Both groups were fed a single dose of Colostrx within 6 h after birth followed by milk replacer twice daily until weaning. Beginning with the Colostrx feeding, calves in the Arg+ group were supplemented with L-arginine at 500 mg kg x BW(-1) x d(-1), and the Arg- group received equivalent, but unsupplemented, diets. All calves were immunized against keyhole limpet hemocyanin (KLH) on d 4 and received a booster vaccination on d 14. The Arg+ treatment increased (P < .05) plasma L-Arg and urea concentrations an average of 2.8-fold and 26%, respectively, during the 4-wk supplementation period. Average daily gain (ADG) of Arg+ calves was increased (P < .10) during wk 1, 3, and 5 of life. The Arg+ treatment depressed (P < .05) total and KLH-specific IgG concentrations in plasma and caused a decrease (P < .01) in circulating leukocyte numbers. Differential counts revealed that the decrease in circulating leukocyte numbers was due to decreases in absolute numbers of lymphocytes, monocytes, and neutrophils. The Arg+ diet did not affect mean plasma GH concentrations during the first 3 wk of life, but GH mean concentrations were decreased (P < .01) during wk 4 due to depressed (P < .10) pulse amplitudes. The decrease in GH mean concentrations during wk 4 was paralleled by lower (P < .10) plasma IGF binding protein-3 concentrations. These data show that supplementary L-Arg does not increase plasma GH concentrations, but it increases ADG, depresses KLH antibody production, and alters circulating leukocyte populations in preruminant calves.