Dietary DL-methionine replacement by a novel DL-methionyl-DL-methionine dipeptide increases milk protein synthesis in breeding pigeons and improves the growth performance of squabs

Abstract

The purpose of this study was to explore the effects of parental dietary supplementation with DL-methionine (DL-Met) and DL-methionyl-DL-methionine (DL-Met-Met) on milk protein synthesis in breeding pigeons and on the growth performance of squabs. A total of 324 pairs of breeding pigeons and 1296 one-day-old squabs were selected and allotted to 9 dietary treatments in a completely randomized design, and the experiment lasted for 45 days. The diets included a basal diet (BD, crude protein = 15%, Met = 0.25%) and BD + 0.15%, 0.30%, 0.45%, or 0.60% DL-Met or DL-Met-Met. After the experiment, the average daily feed intake (ADFI) and weight loss of breeding pigeons, casein content of crop milk and average daily gain (ADG) and mortality of squabs were measured respectively. Compared with the BD group, parental dietary supplementation with DL-Met or DL-Met-Met (especially at the dose of 0.30%) effectively increased the average daily feed intake and decreased the weight loss of breeding pigeons, as well as increased the αS1-casein, αS2-casein, and β-casein contents in their crop milk (P < 0.05). In addition, the average daily gain (ADG) of squabs was increased and the mortality of young squabs was decreased after DL-Met or DL-Met-Met supplementation (P < 0.05). The bioavailability values of DL-Met-Met relative to DL-Met were 211% and 346% based on the weight loss of breeding pigeons and the ADG of squabs, respectively (P < 0.001). Therefore, DL-Met-Met was more effective than DL-Met at decreasing the weight loss of pigeons and improving the growth performance of young squabs (P < 0.05). As a novel source of Met, DL-Met-Met, rather than DL-Met, was more beneficial to young squabs.