Above photos show a longitudinal section of the head of the tibia bone (tibia). The white border just above the arrows is the articular cartilage. The gray layer underneath is the growth plate (where bone formation takes place). If bone formation is disturbed, this layer will become thicker. Below this layer are the bone bars which mark the start of the actual bone. In the photo on the left the arrow points to a slightly widened growth plate, while the photo on the right shows a strongly widened growth plate which – according to the study – results from a lack of phosphate.

starter feed. All the data were then analysed using a statistical model.

Hens have better bone formation The results (see Table 1) showed that some parameters are strongly related to the quality of bone formation. One of these parameters is the sex of the chick. Hens have better bone formation than males (independent of body weight). It is striking that hens also have a higher phosphate level in the blood. A higher phosphate level (regardless of gender) ap- pears to be significantly (p <0.005) correlated with better bone formation and with higher body weight. Roosters gen- erally have a lower level of phosphate in the blood as well as poorer bone quality. However, a higher calcium level in the blood had less influence on better bone formation in both males and females. What was also striking in this study is that a higher pH in the stomach was associated with a higher

32 ▶ POULTRY WORLD | No. 3, 2021

calcium level in the blood, yet it was not associated with a higher phosphate level in the blood.

Phosphate ‘promotes’ bone formation The research led to a number of surprising insights. It was ex- pected that hens would have better bone quality. But the fact that this was related to higher blood phosphate levels and less to higher blood calcium levels was a surprise. Further- more, it appeared that a higher pH in the stomach was asso- ciated with higher calcium levels in the blood, but this had less effect on bone quality. Higher phosphate levels were positively correlated with body weight, although a causal re- lationship could not be established in this study. In conclu- sion, it appears that it is not the calcium, but the phosphate level which is a more important factor to take into account when optimising broiler feed, in particular, to ensure proper bone formation.


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