Dietary glycine: its importance in growth and development of the budgerigar (Melopsittacus undulatus)

Birds have a high demand for the amino acid glycine due to its involvement in uric acid biosynthesis. Because the ability to synthesize glycine may be limited in the immature liver of young birds, glycine is usually considered to be semiessential in the diet of newly hatched chicks. This study investigated the effects of supplementary dietary glycine on growth and development in budgerigar chicks. Eighteen pairs of breeding budgerigars were randomly assigned to one of three dietary treatment groups. Each pair of birds was offered a seed-based diet and a rearing food that was used as the supplementation medium. One group received an unsupplemented rearing diet (2.7 g glycine/kg), whereas the remaining groups received diets supplemented with 15.0 and 30.0 g glycine/kg, respectively. Sixty-seven chicks were reared with records kept of growth and survival rates. A dietary glycine supplement tended to enhance the growth rate of budgerigar chicks, although this was not significant. There was no influence of diet on the rate of feather growth or the number of chicks that survived to adulthood. Follow-up measurements, conducted 1 y later, indicated that a dietary glycine supplement during development had long-term morphological effects. Bodyweight, tarsus length and beak width were all significantly greater in adult budgerigars that had received the highest level of glycine supplementation as chicks.