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Excess Levels of Cysteine and Homocysteine Induce Tibial Dyschondroplasia in Broiler Chicks^1,2,

^* Department of Nutritional ^** Department of Poultry Sciences, University of Wisconsin-Madison, Madison, WI 53706

The effect of excessive levels of cysteine and homocysteine on tibial dyschondroplasia (TD) in broiler chicks was studied. In the first experiment, graded levels of L-cysteine as well as one level of L-homocysteine were supplemented to a cornsoybean-based diet adequate in sulfur amino acids. Levels equal to or above 0.5% supplemental cysteine increased the incidence of TD, and levels equal to or above 0.75% supplemental cysteine increased the severity of TD above that found in chicks fed the basal diet. Also, L-homocysteine at 0.5% induced TD. In the second experiment, graded levels of DL-homocystine were added to the basal diet to determine the threshold value of homocystine needed to induce TD, and a level of ammonium sulfate isosulfurous to 0.45% homocystine was added to a basal diet. The results showed that 0.45% DL-homocystine was the lowest level that increased the severity of TD above that found in chicks fed the basal diet and that sulfate did not induce TD. In the third experiment, a 2 x 2 factorial design was used to investigate the interaction between DL-homocystine and copper. Copper supplementation lessened the severity of TD caused by DL-homocystine. Copper supplementation also tended to improve growth, especially in birds fed DL-homocystine.

KEY WORDS: • cysteine • homocysteine • tibial dyschondroplasia • chickens

¹ Partially supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison, WI.

² Presented in part at the 1989 Poultry Science Association meeting, Madison, WI [Zeytun, I. H., Orth, M. W., Bai, Y. & Cook, M. E. (1989) Effect of excess methionine and its metabolites on the incidence and severity of tibial dyschondroplasia (TD) in broiler chicks. Poult. Sci. 68 (Suppl. 1): 163 (abs.).]

³ Currently resides in Avcilar-Istanbul, Turkey.

Manuscript received 22 October 1990. Revision accepted 22 August 1991.