The effects of dietary phosphorus and calcium, and phytase supplementation on production, eggshell and bone quality in laying hens from 55 to 74 weeks of age

Hello Alvaro:

In this study, we made the decision to use an available P level that would be based on a consistent standard - the breed management guide. Arguments can be made (and I make this argument on a regular basis) that in general, management guides recommend available P well in excess of the actual hen requirements. However, the guide is a consistent standard or point of reference. In our current layer studies, we typically include a second negative control, with a much lower level of available P. In the future, we will probably use this second, lower available P negative control treatment rather than both.

With respect to the effect on egg size, the NC diet was reduced in Ca, available P and Na only. No reductions were made in dietary energy or digestible amino acid levels. Although an extraphosphoric effect, particularly of the highest dose of phytase may explain some of the increase, I agree that the scale of the increase for the NC + 1200 units of phytase seems quite large. I will confirm the calculations and get back to you. It is interesting to note, however, that the diets containing any level of phytase had greater egg mass than both the PC and the NC diets.

Hi, Alvaro, interesting topic. I have heard of a similar scenario, if pullets were fed a deficient in methionine, they responded better to methionine in the layer phase, and also if overfed methionine, they then became refractory in the layer phase, did not respond to increased levels of methionine. I would like to see more research, like reduced protein in the later stage of the pullets diets to see how they perform in the layer barn.

Body phosphorus homeostasis network allows laying hens to adapt to wide range of changes in dietary phosphorus levels. Phytase hydrolyzes phytate rendering phosphorus and reduces the laying hens' requirements for inorganic phosphate rock. Hence there is no need to keep large safety margins in dietary phosphorus when hens are fed with phytase.

Hi, Doug, interesting findings. I have another question: Would an increase in fiber in layer and pullet diets increase the calcium and phos digestible, due to longer retention time? Any studies done on this?

Thanks, Mike.