Dietary supplements of methionine increase breast meat yield and decrease abdominal fat in growing broiler chickens

The response of male broiler chickens to graded amounts of an essential amino acid (methionine) or an amino acid analogue (methionine hydroxy analogue free acid, MHA-FA) was examined in this experiment. The effects of each supplement on food intake, food conversion and the masses of a demand tissue (breast meat) and an indicator of body fat (abdominal fat pad) were measured. Birds grew significantly faster, ate more and had a lower food conversion ratio when there was more DL-methionine or MHA-FA in the diet. After standardising the differences in food intake between treatments, there were still highly significant differences in liveweight between diets. After removing the variation due to treatment differences in body mass, the data showed that adding either DL-methionine or MHA-FA to the diet increased the mass of breast meat and reduced the size of the abdominal fat pad. Exponential equations fitted to the body mass and feed conversion ratio data indicate that, in an equimolar comparison, MHA-FA is 78 and 70% as potent as DL-methionine for growth and feed conversion ratio respectively. Similar equations fitted to the carcass data show that MHA-FA is only 71% as potent as DL-methionine in depositing breast tissue. Increasing amounts of DL-methionine reduced the variability in liveweight and carcass, breast and abdominal fat pad weights. Adding 0.05% MHA-FA reduced variability in these traits compared with the basal ration but higher amounts of MHA-FA had no additional effect.