RESUMEN
Skeletal problems are common in both young and old poultry and are often related to bone weakness. They affect mortality on the farm and condemnations within processing plant and thus raise both welfare and economic concerns. To understand the basis of bone strength, the metaphyseal histology, composition, and the biomechanical properties of tibiae from 7- and 72-wk-old male and female broiler breeder chickens were compared. The biochemical constituents included ash, collagen, proteoglycan, transforming growth factor-beta (TGF-beta), pyridinium crosslinks, and the organic matrix-associated fluorescence. Blood variables were measured to determine the metabolic status of these birds as related to bone physiology. Although there were no differences in blood chemistry of 7-wk-old males and females, there were several differences between young and old birds. The levels of calcium, triglyceride, and iron were higher in older females than in older males. The collagen content was reduced, and the proteoglycan content increased in 72-wk-old hens. The TGF-beta content of bones from 7-wk-old females was higher than that of other groups of birds. Bone strength and stiffness, measured using loads at break and Young's modulus, respectively, were higher in older birds. The presence of medullary bones in 72-wk-old hens did not affect their bone strength, although it reduced strain values and increased Young's modulus. Compared to other groups, the 72-wk-old hens had a higher content of an inorganic matrix. The levels of hydroxylysylpyridinoline (HP) and lysylpyridinoline (LP) and the collagenase-extractable fluorescence of the organic matrix from older birds was higher. The decalcified bone matrix from older birds also showed higher susceptibility to bacterial collagenase than their younger counterparts. Bone strength showed positive correlations with its ash content, density, pyridinium crosslinks, and the fluorescence of the matrix. However, the correlation was strong with both pyridinium crosslinks and the fluorescence of the organic matrix. These results suggest that bone strength is influenced by the content of its collagen crosslinks.
Asunto(s)
Desarrollo Óseo , Matriz Ósea/crecimiento & desarrollo , Pollos/crecimiento & desarrollo , Tibia/fisiología , Bienestar del Animal , Animales , Fenómenos Biomecánicos , Colágeno/metabolismo , Colagenasas/metabolismo , Femenino , Masculino , Compuestos de Piridinio/metabolismo , Tibia/químicaRESUMEN
The growth of an animal part (y) relative to the whole (x), is expressed in terms of an exponential equation, y = alpha x beta, where alpha and beta are growth constants. For the present study x is body weight and y is shank length determined for 10 lines of chickens at 20 weeks of age. The derived values of alpha and beta, assumed to be limiting relative growth constants for bone, were estimated by least squares of the log-transformed (linear) exponential equation. From the means of alpha and beta, calculated for each of seven Leghorn and three Fayoumi lines, individual values of alpha i and beta i were calculated for more than 24,000 pedigreed birds included in 9 years of records. The individual values (i) were calculated as: (formula; see text) If the initial growth constant, alpha, is the primary hereditary growth parameter governing conformation, then the parameter, beta, should not be as highly heritable as alpha. To test this hypothesis, the heritability (h2) of both alpha and beta were calculated for each of the 10 lines. For alpha sire component h2 values ranged from .12 +/- .05 to .45 +/- .10 and for beta from .05 to .41. The pooled h2 estimate of alpha over lines (.31 +/- .02) was not significantly different from that for beta (.31 +/- .02). Compared with the original data on body weight and shank length, the transformation significantly reduced the heritability estimated. We conclude that the parameters, alpha and beta, are useful only in describing phenotypic and not genetic differences in relative growth.