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Effect of Excess Methionine and Methionine Hydroxy Analogue on Growth Performance and Plasma Homocysteine of Growing Pekin Ducks

M. Xie^*,, S. S. Hou^*,,1, W. Huang^*, and H. P. Fan^*,

^* Institute of Animal Science, Chinese Academy of Agricultural Sciences, Beijing, China 100094; and State Key Laboratory of Animal Nutrition, Beijing, China 100094

¹ Corresponding author: houss{at}263.net

One experiment was conducted to study the effect of excess DL-methionine (DLM) and DL-2-hydroxy-4-methylthiobutanoic acid free acid (DL-HMB-FA) on duck growth. One-day-old male white Pekin ducklings were fed common starter diets from hatch to 21 d of age and then fed the experimental diets from 21 to 42 d of age. Three hundred twenty 21-d-old birds were allotted to 40 raised wire-floor pens with 8 birds per pen according to similar pen weight. There were 5 dietary treatments that included a methionine-adequate control diet and control diets supplemented with 2 levels of dry DLM (1 or 2%) or 2 equimolar levels of liquid DL-HMB-FA (1.13 or 2.26%). Each dietary treatment was replicated 8 times. At 42 d of age, weight gain, feed intake, and gain/feed were measured and plasma was collected to analyze homocysteine. Compared with ducks fed control diets, excess DLM or DL-HMB-FA supplementation reduced weight gain and feed intake of birds significantly. However, on the equimolar basis, at 1 or 2% supplemental methionine activity, DL-HMB-FA was less growth-depressing than DLM. According to the growth response to excess methionine, the tolerable upper limit of dietary methionine for growing ducks may be less than 1.38% when the methionine level of the control diet (0.38%) was considered. On the other hand, plasma homocysteine was elevated markedly when 2% DLM or 2.26% DL-HMB-FA was added to control diets, but plasma homocysteine of ducks fed 2.26% DL-HMB-FA supplemented diets was lower significantly than birds fed equimolar DLM-supplemented diets, which indicated the toxicity of excess methionine sources and less toxicity of DL-HMB-FA relative to DLM.

Key Words: methionine • methionine hydroxy analogue • duck • toxicity