Comparative study on the chemical composition of different bones/parts of bones in growing pigs differently supplied with inorganic phosphorus and phytase
From the veterinarian point of view, the precise assessment of the phosphorus (P) supply of pigs is of great interest, especially in cases of clinical disorders like 'leg weakness' or lameness when bone mineralisation may be disturbed. Thus, the question arises which bone is most suitable for diagnostic purposes and is reflecting changes in dietary P supply most clearly. Thirty-six growing pigs (BHZP db.Viktoria x Piétrain, about eleven weeks old, mean bw: 28.3 ± 3.44 kg) were allotted to three groups differently supplied with P by receiving a diet either supplemented with inorganic P (iP) and phytase (500 FTU/kg; controls/group C), without iP but phytase added (500 FTU/kg; group 1) or containing only endogenous phytase (group 2). The inclusion of iP resulted in total P contents in diets for group C of 4.76 and 4.23 g/kg as fed from 28 to 57 and >57 kg body weight (bw), respectively. In diets for group 1 and 2, the corresponding P contents were 3.08/2.72 g/kg as fed (group 1) and 3.08/2.88 g/kg as fed (group 2). On days 26, 47 and 82 of the dietary treatment, four pigs of each group were euthanised. Furthermore, four additional pigs were euthanised one day before starting the experiment. Standardised samples of the femur (distal part), tibia/fibula (proximal part) and os metatarsale III (MT III, in toto) were taken during dissection and submitted to chemical analysis. At all time points, pigs of group C had significantly higher ash contents in all types of bone samples compared to pigs from group 1 and 2. Relative differences between means of groups (C = 100%) were less for the ash content in MT III (reduction by up to -9.1%) compared to the distal femur and the proximal tibia/fibula (reduction by up to -23.2 resp. -22.7%). Variation coefficient (irrespective of group and time point) was lower for ash content in MT III (4.29%) compared to the distal femur and the proximal tibia/fibula (both: 11.8%). Under the conditions of this study, ash contents of the distal femur and the proximal tibia/fibula reflected the different P supply more pronounced indicating higher sensitivity compared to MT III.