Complete replacement of supplemental dl-methionine by betaine affects meat quality and amino acid contents in broilers

This study was conducted to investigate the effects of dl-methionine (dl-Met) replacement with betaine on growth performance, carcass characteristics, meat quality, muscle oxidative status and amino acid contents of broilers. A total of 192 one-day-old Arbor Acres broiler chicks were randomly divided into four groups with six replicates of eight chicks, receiving a control basal diet containing 1.4 and 0.8 g/kg dl-Met (total Met: 5.0 and 4.2 g/kg during 1−21 and 22−42 days, respectively), or one of the test diets supplemented with betaine to replace dl-Met at 25% (B25), 50% (B50) and 100% (B100) level, respectively. There were no differences in growth performance or carcass characteristics of broilers among groups. Compared with the control, B100 diet resulted in lower (p < 0.05) glutathione peroxidase activity, pH value and water holding capacity of breast muscle (p < 0.05). Lysine and aspartic acid contents in breast muscle were reduced (p < 0.05) by all betaine groups. The B25 and B100 diet decreased phenylalanine content, and B50 and B100 diet decreased leucine and total amino acid contents (p < 0.05). The B100 diet also decreased (p < 0.05) the contents of threonine and serine. In addition, the B25 and B50 diet increased (p < 0.05) cysteine content compared with the control and B100 diet. It was concluded that replacement of dl-Met by betaine had no effect on growth performance or carcass characteristics, but decreased meat quality and some muscle amino acid contents in a dose-dependent manner, especially at 100% level.