DIFFERENTIAL-EFFECTS OF PLANE OF PROTEIN OR ENERGY NUTRITION ON VISCERAL ORGANS AND HORMONES IN LAMBS

Modulation of somatotrophic and homeorhetic hormones, along with chang es in visceral mass and metabolic activity, were measured in growing l ambs restricted in energy(ER) or metabolizable protein (PR) to maintai n BW for 7 wk and then repleted for 2 wk. Control lambs were fed an ad equate diet for 9 wk. Serum IGF-I decreased more rapidly in PR; but bo th ER and PR were 70% of controls by wk 7 of restriction (P < .05) and increased above controls by d 14 of repletion. Somatotropin, increase d by PR, returned to control levels upon repletion (P < .05). Insulin was decreased by PR (P < .02) but was transiently elevated above contr ols by repletion in ER and PR at d 2 (P < .01). Serum triiodothyronine , reduced to 70% of controls by PR and ER, returned to control levels after d 6 of repletion (P < .05). Thyroxine declined gradually to 65% of controls in ER and PR (P < .07) but did not respond to repletion. B y wk 7 of restriction, liver mass in ER and PR was decreased to 50% of controls (P < .05). Return of liver mass, on an empty body weight bas is, occurred by d 2 of repletion (P < .01). In vitro O-2 consumption p er gram of liver tissue was increased to 125% of controls by ER and PR (P < .05). Calculated whole liver O-2 consumption in ER and PR was 68 % of controls at wk 7 of restriction (P < .10). Protein restriction ha d a more immediate impact on hormones but not on visceral mass or acti vity compared with energy restriction. Elevated IGF-I levels, as obser ved in previously restricted lambs, may mediate compensatory growth in ruminants.