GROWTH-PERFORMANCE AND BRAIN NEUROTRANSMITTERS IN PIGS AS AFFECTED BYTRYPTOPHAN, PROTEIN, AND SEX

The effects of dietary levels of tryptophan (TRP) and protein on volun tary feed intake, growth performance, muscle pH, and brain indoleamine and catecholamine concentrations were studied in an experiment involv ing 48 crossbred Pietrain x White pigs (38 kg initial weight). Equal n umbers of females, intact males, and barrows were used and they were g iven ad libitum access to feed during the 28-d experiment. Four dietar y treatments were compared in a 2 x 2 factorial arrangement, with the following levels of analyzed TRP and CP: 1) .12 and .16% TRP, suboptim um and optimum for growth, respectively, 2) 12.7% CP of a diet based o n corn-soybean meal and adequately balanced for limiting essential ami no acids other than TRP; and 16.7% CP diet with additional protein fro m corn gluten meal. Dietary CP interacted with TRP on feed intake and growth, with a greater depressive effect at .12% TRP than at .16% TRP in the three genders. Norepinephrine concentration, which was the high est in the preoptic area, was higher in females than in intact or cast rated males. Serotonin concentration was increased by TRP supplementat ion in the different brain regions. Additional CP depressed serotonin concentration more at .12% TRP than at .16% TRP. The greater sensitivi ty of feed intake and growth of pigs, especially females, to TBP defic iency in the presence of additional CP may have been related to a more critical serotonergic activity, when hypothalamic serotonin concentra tion fell below a threshold level. Supplemental TRP increased muscle p H, both at 45 min and 24 h after death, in ham (adductor femoris and s emimembranosus) and loin (longissimus), suggesting a sedative effect o f TRP for reducing stress response.