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 i ncrease growth hormone (GH) secretion and antibody production in preru minant calves was tested. Sixteen newborn calves were randomly assigne d to either Arg+ or Arg- treatment groups. Both groups were fed a sing le dose of Colostrx(R) within 6 h after birth followed by milk replace r twice daily until weaning. Beginning with the Colostrx feeding, calv es in the Arg+ group were supplemented with L-arginine at 500 mg kg.BW -1.d(-1), and the Arg- roup received equivalent, but unsup plemented, diets. All calves were immunized against keyhole limpet hemocyanin (KL H) on d 4 and received a booster vaccination on d 14. The Arg+ treatme nt increased (P < .05) plasma L-Arg and urea concentrations an average of 2.8-fold and 26%, respectively, during the 4-wk supplementation pe riod. 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 decre ase (P <.01) in circulating leukocyte numbers. Differential counts rev ealed that the decrease in circulating leukocyte numbers was due to de creases in absolute numbers of lymphocytes, monocytes, and neutrophils . The Arg+ diet did not affect mean plasma GH concentrations during th e first 3 wk of life, but GH mean concentrations were decreased(P <.01 ) during wk 4 due to depressed (P < .10) pulse amplitudes. The decreas e 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 circulat ing leukocyte populations in preruminant calves.