Peripheral factors associated with early response in feeding to lysine-free diet in growing chickens

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The objective of this project was to determine what peripheral factors were related to early reduction in food intake by chickens on lysine-free diet and which way conveyed the change of factors to the central nervous system.Three week-old male layer-type chickens were used. Experimental diets were purified-control (lysine. HCL11.9 g/kg) and lysine-free (no lysine. HCL) diets with same nitrogen and ME content.One hour after the lysine-free diet were presented, plasma concentration of lysine started to decrease to third of the control, and continued to decrease up to the fourth hours. Other amino acids than lysine did not change with dietary lysine level. Food intake by chickens on lysine-free diet started to decrease 5 or 6 hours after the diet was presented. This result suggests that plasma concentration of free amino acids triggered the response of feeding to lysine-free diet. Free amino acids concentration ini the pre-piriform cortex or hypothalamus, which was known to be involved in regulation of feeding, after feeding the lysine-free diet decreased half of the control, but similar changes were observed in the cortex. Therefore, tit is unlikely that amino acid in the brain did not relate to the response.Fos immunohistochemistry with medulla oblongata shows that the number of Fos immunoreactive cells observed at nucleus tractus solitarius(NTS) was larger in the lysine-free than control groups at three hours after presenting the diet. Two hours later Fos immunoreactive cells appeared at the nucleus accumbens (Ac) in the lysine-free group. These results suggest that peripheral information of plasma concentration of amino acid was conveyed thorough the NTS and got to the Ac.In conclusion, early reduction of food intake by chickens on lysine-free diet occurs after change in plasma concentration of lysine that is conveyed through the NTS and gets to the Ac.