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
Published:August 22, 2023
Summary
Summary This study was conducted to test the efficacy of phytase in low phosphorus and calcium diets in the late production cycle for maintaining the productivity, eggshell and bone quality of hens fed low phosphorus and calcium. Problem Exogenous phytase supplementation has become a standard practice for poultry diets to liberate available phosphorus and reduce excretion of phosphorus in ...
Dear authors. Called my attention the very high level of avP in the control diet making the negative control still sufficient. Literature is prodigal in papers showing that laying hens produce quite well with levels around 0.20%. Why this particular choice? Also funny that egg mass increased so much (almost 20%) but egg production is said no to be affected significantly. Did egg weight increased so much? There's no mention to it in the text.
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.
Thank you for the clarifications, Dr. Korver. Maybe the good and old NRC might have been a better standard, even after all the modifications genetics has introduced in current layers.
Indeed, the phytase effect was very large. Something to be better investigated. Kind regards.
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?
Dear All, coming back to egg mass. Good to see increases, but any thoughts on why positive control was so low? At 74 weeks, Nick Chick would be expecting about 63 - 64 g egg mass, not the 51 recorded...? MPS
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.
Dear Dr. Vermana. Safety margins are a common practice in animal nutrition basically as a way to ensure birds receive 100% of the time (or close to that) the nutrients they need to keep high standards of performance. In that regard, use of phytase (which itself is another source of variability) does not eliminate the use of safety margins. Our job is to try to reduce them as much as we can (precision nutrition) for both economical and ecological reasons.
On the other hand, I totally agree with your comment about hens ability to adapt to different situations. In my MsC thesis work, I substituted deffated rice bran for dicalcium phosphate on a total P basis, until completely eliminating the use of DCP. After 4 weeks, the hens showed a decrease in production parameters and tibia ash. But after 12 weeks, performance and bone ash were the same. I can't say if there was an improvement in the use of vegetable P (no phytase available at that time) or an improvement in the use of absorbed P but they sure found a way to adapt to a situation of P shortage.
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.
