Response of broilers to varying dietary calcium and phosphorus

This is the authors' abstract. We don't add key points for this paper.

) of four diets. During each experimental phase (0 to 9 d, 10 to 21 d, and 22 to 35 d), broilers were fed either a low Ca and digestible P diet (L), a moderate diet (M), or a high diet (H), the latter formulated to maximise bone mineralisation based on a mechanistic requirement model. Bone mineral content (BMC), body lean mass, and fat mass were measured by dual-energy X-ray absorptiometry on one bird per cage. Allometric regression predicted tissue growth in relation to BW. Growth performance, lean and fat masses were not modified by dietary treatments at 9 d; BW tended to increase (Lin, P = 0.086), and BMC tended to decrease (+39% in L vs H diet; P = 0.082). Birds fed both deficient diets (L and M) had reduced BMC (-20% and -14%, respectively; Lin, P = 0.003) compared with those fed the H diet at 35 d. Daily BMC deposition did not differ between birds fed L and M diets and tended to be higher for those fed the H diet (10 to 21 d, Quad, P = 0.081; 22 to 35 d, Lin, P = 0.037). Similarly, the allometric slope of whole-body BMC for birds fed the H diet did not deviate from 1, whereas in birds fed L and M diets, the slopes were 17% (L vs H) and 19% (M vs H) lower, respectively. Bone mineral content relative to protein deposition declined progressively with lower Ca and P diets. These findings suggest that bone mineralisation was more sensitive to diet than lean tissue growth in birds fed lower Ca and P diets, while both parameters increased proportionally to BW when birds were fed adequately. This implies that Ca and P deposition into bone is not strictly related to body protein.