Bone metabolism in poultry - Doug Korver

Hello gerard huyghebaert :

Yes, I agree with this approach, but I think that we need to re-evaluate the absolute levels of Ca and aP that we feed to layers. We recently completed a long-term study (to 74 weeks of age), and found that our negative control diet, with a moderate reduction in ca and aP from the management guide recommendations, actually had greater structural bone reserves at the end of the study than the positive control diet. Also, we typically do not see a phytase response (multiple studies, multiple products) when our negative control diets have the Ca and aP reduced by the matrix value of the phytase. Phytases are effective when re further reduce the Ca and aP levels, so it is a matter of the PC diets providing well in excess of what the birds require. Richard Miles did some nice work in the past showing that excess aP in layer diets reduces shell quality, so as we look at an industry shifting to longer and longer production cycles, we will see more stress placed on the skeletal system and subsequently on shell quality. I think that for these reasons, we need to re-evaluate the recommended levels of Ca and aP in the diets of layers, to better address what the birds actually require, because of the consequences of excess Ca and aP, and to more effectively use phytase.

Hello Sayed Mohammad Mortazavi :

There are several approaches that should be used. First, body weight management is critical. Birds that enter lay at too light a weight will necessarily have smaller frames, and therefore less calcium reserves. Body weight should be kept on target throughout the rearing phase, rather than trying to get the birds to gain a lot of weight close to the onset of lay - -this can result in birds that still have small frames, but have more body fat. If pullets are under weight at the desired age of photostimulation, it is better for long-term productivity to delay photostimulation until birds reach target weight. Feeding appropriate amounts of Ca and aP during the pullet phase is also critical. although the primary breeder management guide recommendations for these minerals are, in my opinion, higher than is necessary, the recommendations for pullets are generally fairly good. A pre-lay diet may be used, but only to prepare the bird for lay -- not as a last-ditch effort to add body weight. Once the flock starts to lay, the hens NEED additional Ca, and must be switched to a start-lay type diet. Excessive amounts of time on a pre-lay diet after the flock starts production will force the birds to mobilize excessive bone reserves early in lay. Good flock uniformity and management will ensure that the entire flock starts to lay at very close to the smae time, and dietary changes can be managed to reflect the needs of each individual bird in the flock as closely as possible.

Hello Hiren Pancholi:

Certainly. Several trace minerals are essential in the formation of the organic matrix of bone, particularly during the rearing phase. Vitamin D activity is also extremely important in bone formation. As the hens progress through the laying cycle, structural bone can be mobilized, but is no longer formed. However, there is a daily turnover (mobilzation, formation) of medullary bone as long as the hens are in lay.