Chemical composition of bone tissue in broiler chickens intended for slaughter

Selected parameters characterizing the chemical composition of bones were determined in 60 male and 60 female hybrid Ross 308 chickens aged 40 days at the end of the fattening period. The chickens received a complete feed mixture intended for pre-feeding (starter) in a period from the start of the experiment until Day 10, followed by the feed mixture intended for fattening until Day 30 (grower), and the feed mixture for the third phase of fattening, i.e. until Day 40 (finisher). The feed mixtures and drinking water were provided <I>ad libitum</I>. At the end of the experiment, chickens were slaughtered and the femur and the tibiotarsus from the right pelvic limb were collected and the following parameters were determined in wet tissue: dry matter (DM), crude protein (CP) (N × 6.25), fat, ash, calcium (Ca), phosphorus (P) and magnesium (Mg); the content of organic matter was calculated. The resultant values were recalculated to 100% of DM. Differences between males and females in the chemical composition of retrieved bones were investigated. The content of CP in wet tissue from both bones ranged from 354.0 ± 11.8 to 365.1 ± 14.3 g/kg being significantly lower (<I>P</I> < 0.01) in the tibiotarsus. Differences between sexes were very small. The content of fat in the bones ranged from 16.12 ± 8.71 to 16.17 ± 8.85 g/kg, with higher levels of fat being detected in female chickens (17.16 ± 8.53 to 17.24 ± 8.28 g/kg) as compared to male chickens (15.01 ± 9.05 to 15.19 ± 9.12 g/kg). No statistically significant differences between the femur and the tibiotarsus were detected. The levels of ash ranged from 472.2 ± 13.1 to 480.1 ± 10.83 g/kg, being statistically higher in the tibiotarsus in both male and female chickens (<I>P</I> < 0.01; <I>P</I> < 0.001). The levels of Ca ranged from 180.4 ± 8.57 to 181.6 ± 12.32 g/kg, showing higher values in both bones from female chickens (181.7 ± 9.17 to 183.8 ± 14.71 g/kg), as compared to male chickens (179.2 ± 7.8 to 179.3 ± 8.91 g/kg). No statistically significant changes were found. The levels of P ranged from 83.17 ± 9.82 to 83.29 ± 7.42 g/kg, with higher levels being observed in female chickens (84.1 ± 9.21 to 89.8 ± 7.47 g/kg), as compared to male chickens (76.5 ± 6.93 to 82.5 ± 5.00 g/kg). The levels of P were significantly higher in the femur (<I>P</I> < 0.001) in female chickens and in the tibiotarsus (<I>P</I> < 0.001) in male chickens. The Ca:P ratios for both analysed bones was greater in males (femur 2.20, tibiotarsus 2.21), as compared to females (femur 1.98, tibiotarsus 2.09). The mean weight of male and female broiler chickens on Day 40 was 2 694 ± 32.6 g and 2 345 ± 23.9 g, respectively. In comparison with the expected performance parameters of ROSS 308 hybrid chickens, the weight increased in both male and female chickens by 8.2% and 10.6%, respectively. Although the chickens grew very quickly, no clinical signs indicating pathological changes in the bone system were found.