Abstract The present study was conducted to evaluate the adequacy of applying heat treatment and methionine (Met) supplementation to improve the use of bitter vetch (BV) as a feed ingredient in the growth diet of broilers. A total of 540 Ross-308 chicks were fed various BV-supplemented diets between the ages of 35 and 49 days. The chicks were assigned randomly to one of nine experimental treatments,including raw and cooked bitter vetch seeds at two levels (100 and 200 g/kg) with or without Met (210 mg/kg) supplement and a corn–soybean-based diet as control. Results showed that feeding the 200-g/kg raw BV decreased feed intake by 52% in relation to the control diet (P<0.05). Cooking the BV did not improve the feed intake. Met supplementation of 100 g/kg raw or cooked BV and 200 g/kg cooked BV resulted to a similar feed intake in the control group. Chicks fed with the 200 g/kg raw BV had an average depressed body weight gain of 90% in comparison to the birds fed with the control diet. The combination of cooking and Met supplementation of this diet resulted to a similar body weight gain to the control diet. Feeding 100 g/kg of raw or cooked BV also reduced (P<0.05) body weight gain, and Met supplementation of these diets resulted in a body weight gain similar to the control group. Chicks fed with 100 g/kg of raw or cooked BV supplemented with Met or 200 g/kg of cooked BV plus Met has similar feed conversion ratio to the control group. In conclusion, heating BV seeds is not sufficient to overcome the limiting effects of BV seeds on feed intake and weight gain, and that Met supplementation does provide some improvement. The combination of cooking and Met supplementation was more efficient
