Tibiotarsus bone characteristics and tibial dyschondroplasia incidence of broilers fed diets supplemented with leucine and valine
Leucine restriction in rats has shown to reduce proliferation and differentiation of chondrocytes in the growth plate (Kim et al., 2009). Similarly, Phornphutkul, Wu, Auyeung, Chen, and Gruppuso (2008) reported that the metatarsal cells of mice with rapamycin resulted to a decrease in bone length by inhibition of the mechanistic target of rapamycin (mTOR), suggesting that mTOR is an important protein to modulate bone growth. Leucine is the most effective nutrient to activate mTOR (Kimball & Jefferson, 2006). Therefore, the restriction of this amino acid can impair bone development, as it blocks the mTOR signalling pathway (Kim et al., 2009). In addition to leucine, valine may also influence bone metabolism. Farran and Thomas (1992) reported a reduction in bone calcium and ash concentrations and lower bone weight of birds fed a valine‐deficient diet, suggesting a decrease in osteoblast activity by the low levels of this amino acid. The role of BCAA on bone metabolism has been seldom studied and it is unclear whether the leucine and valine interaction may interfere with bone development in birds as well as their mechanism of action. Therefore, two experiments were conducted in this study to determine the effect of leucine and valine supplementation on tibiotarsus bone characteristics and tibial dyschondroplasia incidence and also to ascertain whether leucine and valine amino acids are important for reducing the hypertrophic cartilage zone of the proximal tibiotarsus growth plate from day 1 to 21 (Experiment I) and day 21 to 42 (Experiment II) post‐hatch.