Effect of methionine hydroxy analog-free acid on growth performance and chemical composition of liver of broiler chicks fed a corn-soybean based diet from 0 to 6 weeks of age

The experiment was carried out to determine the effects of liquid DL-methionine hydroxy analog-free acid (LMA) and dry DL-methionine (DLM) on growth performance, carcass quality and chemical composition of the livers of broiler chicks during 0-6 weeks of age. Four hundred and fifty male commercial broiler chicks (Ross strain) were used. The chicks were divided into three groups, and each group consisted of six replicates of 25 chicks each. The chicks were kept in floor pens, and water and feed were supplied ad libitum throughout the experiment. Three experimental diets were provided as follows: (i) corn-soybean-based diet deficient in methionine; (ii) methionine-deficient corn-soybean-based diet supplemented with DLM to meet the methionine requirements of broiler chicks; and (iii) methionine-deficient corn-soybean-based diet supplemented with LMA(1.25-fold (w/w) the amount of DLM supplied to the second group, given an assumption that 100 units of liquid LMA can be replaced by 80 units DLM to give similar performance results). During the starter period, the weight gains of chicks fed LMA or DLM were significantly greater than those in chicks receiving the methionine-deficient diet (P0.05), and the addition of LMA significantly improved weight gain compared with the addition of DLM. Adding DLM or LMA significantly improved the feed conversion ratio (FCR) and percentage of uniformity (P0.05). No significant differences between the effects of DLM and LMA on these parameters were found. During the grower period (3-6 weeks of age), weight gain, FCR, uniformity and feed intake of chicks that received diet supplemented with DLM, or LMA were superior to those of the methionine-deficient group (P0.05). Chicks fed LMA had the same bodyweight gain and uniformity as those fed DLM. However, adding LMA resulted in a significant increase of FCR resulting from excess feed consumption. Outer breast meat yields were significantly improved and abdominal fat was significantly decreased when methionine sources were added (P0.05), and adding LMA tended to promote edible meat growth better than did adding DLM. Although no significant effects of methionine sources on the chemical composition of the liver were seen, adding methionine sources tended to increase liver fat content. In conclusion, it seems that the bioefficacy of LMA relative to DLM is not less than 80%. Therefore, chicks fed with diet supplemented with 1.25-fold (w/w) as much LMA as DLM might exceed requirements for growth performance, while meeting requirements for meat production. Moreover, the relative bioefficacies of LMA and DLM between the starter and grower periods may perhaps be different.