Evaluating the effects of dietary glutamine on bone geometry, mechanical properties, and mineral composition in laying quail

This study investigated the effect of dietary L-glutamine (Gln) supplementation on tibial quality in Japanese quail (Coturnix japonica) during the early and peak laying periods. A total of 288 female quail were assigned to four dietary treatments with Gln added at 0 %, 0.5 %, 1.0 %, or 1.5 % of the diet. Birds were euthanized at 6 and 12 weeks of lay, and tibiae were collected for morphometric, densitometric, mechanical, and mineral composition analyses, as well as X-ray diffraction measurements. Dietary Gln supplementation affected several bone parameters in a Gln level- and age-dependent manner, including a significant increase in bone calcium content (P < 0.001). However, these changes did not consistently translate into improvements in mechanical strength. Bone breaking strength showed no significant main effect of Gln or age, although a significant Gln level × age interaction was observed (P < 0.05), indicating that the response to Gln varied with the stage of lay. The absence of consistent improvement in bone strength despite enhanced mineralization may reflect differences in the distribution or type of mineralized tissue, as medullary bone contributes little to biomechanical performance in laying birds. Overall, these findings suggest that dietary Gln supplementation improves mineralization-related parameters but does not substantially enhance tibial mechanical strength in laying quail. Glutamine may therefore support skeletal calcium buffering during lay without markedly improving resistance of the tibia to mechanical loading.