Age- and sex-related differences of morphometric, densitometric and geometric parameters of tibiotarsal bone in Ross broiler chickens.

For the first time computed tomography has been used to analyze densitometric and geometric parameters in proximal metaphyses and the mid-diaphyses of tibiotarsal bones in broiler chickens in posthatching development as influenced by age and sex. The research was conducted on 60 tibial bones of 2-, 4- and 6-week-old broiler chickens (Ross 308) (10 males and 10 females in each age group). Statistical analysis has been conducted with the use of one-way ANOVA and Fisher's exact test. Calculations have been performed separately for each sex, with age as a differentiation variable and separately for each of the developmental stages, with sex as a differentiation factor. Pearson's correlation coefficient have been calculated. Also, relative bone density has been determined. It was observed that volumetric bone mineral density (vBMD) in the diaphyses was two times higher (app. 550 cm3) than in the proximal metaphyses (app. 230 cm ) of the tibiae in broiler chickens. In the proximal metaphyses of the tibiotarsal bones, densitometric and geometrical parameters increased with age of the birds. Densitometric parameters (vBMD, BMC) in 6-week-old males displayed (slightly) higher values than in females. It is worth emphasising that in both sexes bone mineral content (BMC) was higher in the tibial proximal metaphyses than in the diaphyses. At the mid-diaphysis, most of the densitometric and geometrical parameters, i.e. bone mineral content (BMC), Strength-Strain Index (SSI), periosteal circumference (PERI_C), endosteal circumference (ENDO_C), cortical area(CRT_A), trabecular area (TRAB_A) and bone area (TOT_A), tended to grow with the birds' age. vBMD (volumetric bone mineral density in situ) is the only parameter that did not grow with age. It was also observed that in males in 4 wk, vBMD in the proximal metaphyses displayed the lowest values during posthatching development (217.47 cm3). Also between 2 and 4 wk of the development, vBMD in the diaphyses decreased from 637.64 cm3 to 539.12 cm3, (P < or = 0.05). What is important is that vBMD and BMC are parameters that play a key role in bone mineralization. However, there was no correlation observed between them. Analysis of Pearson's correlation coefficient showed that BMC in both bone sections displayed positive correlation with all the geometric and densitometric parameters (except for vBMD). It may be concluded that vBMD is independent ofother parameters. The strongest correlations were observed between BMC and TRAB_A, and TOT_A in the proximal metaphysis, they were (r = 0.98) and (r = 0.98) respectively, P < or = 0.01, and between BMC and CRT_A at the mid-diaphysis (r = 0.99), P < or = 0.05. It was demonstrated that in the group of males, decreasing vBMD in the proximal metaphyses between 2 and 4 wk and in the diaphyses from 2 to 6 wk during posthatching development, as well as decreasing relative bone weight, from 1.03% to 0.79%, led to deformities and breaks of the tibiae, which may have a negative effect on the productivity of the broiler chickens flock.