PHOTO: HENK RISWICK
NUTRITION ▶▶▶
Dietary phosphorus: how low can we go?
Feed additives Precision feeding improves the economics of production and reduces potential negative environmental impacts. Canadian researchers looked at how precise we can be when adding dietary phosphorus to poultry diets.
BY EMMY KOELEMAN P
hosphorus (P) − one of the most expensive nutrients in poultry feed − is an essential element for bodily functions, bone and egg shell formation. However, excessive faecal excretion of phosphorus has in-
creasingly become an environmental issue due to the over- supply of P in layer rations. Supplementing with microbial phytase helps to minimise excessive excretion by unlocking the plant-bound phosphorus in the feed ingredients. When poultry can use more P from the feed itself, less P needs to be supplemented in the diet (in theory). This will decrease the risk of oversupply and associated feed costs, and will put less pressure on the environment.
Reducing dietary non-phytate P A group of researchers affiliated with the University of Manito- ba in Canada hypothesised that phytase supplementation, along with properly reducing dietary inorganic P levels, would reduce P excretion and achieve comparable performance compared to birds fed high-P diets devoid of phytase. So a study was conducted to determine the effects of microbial
phytase supplementation to diets containing levels of dietary non-phytate P (NPP) lower than the NRC requirement (2.5 g/ kg) on production performance, plasma biochemistry, egg and bone quality and P excretion in laying hens. A 12-week feeding trial (22-34 weeks of age) was set up with 48 Lohmann white laying hens. The birds were randomly allocated to one of six maize-soybean meal-oat-based diets: containing 2.0, 2.5 or 3.0 g/kg NPP without phytase, or containing 1.0, 1.5 or 2.0 g/kg NPP with phytase (1,000 U/kg diet) where phytase in- clusion was expected to provide 1.0 g/kg NPP to laying hens, thus making the phytase-unsupplemented treatment serve as a control for the phytase-supplemented treatment.
Results with and without phytase Egg weight and egg production, feed consumption, body- weight and the feed conversion ratio of laying hens fed lower NPP diets supplemented with phytase were comparable to those of hens fed high NPP phytase-unsupplemented con- trols. Eggshell thickness, specific gravity, Haugh units, tibia bone mineral density, tibia ash percent, plasma P and other biochemical parameters were not significantly different be- tween the dietary treatments. Total P intake, excretion and re- tention were affected by diet (P<0.001) but its deposition in eggs was not significantly different. Contrast analysis further showed that total P excretion of phytase present vs. phytase absent was on average reduced by 40.4 mg/hen per day (P<0.01). Moreover, total P excretion was linearly (P<0.01) re- duced by reducing dietary NPP and this relationship was sim- ilar regardless of whether phytase was supplemented or not.
Conclusion The results from this study indicated that NPP levels in laying hen diets could be reduced to 1.0 g/kg (excluding the portion of NPP released by phytase) with the inclusion of phytase with- out negative effects on the production performance and health of the hens, thus reducing P excretion into environment.
Phosphorus is vital for egg shell formation.
34 ▶ POULTRY WORLD | No. 5, 2022
This article is a summary of an original paper: Effects of phytase supplementation on production performance, egg and bone quality, plasma biochemistry and mineral excretion of layers fed varying levels of phosphorus, by M. Jing and others, University of Manitoba, Canada, published in Animal, Volume 15, Issue 1, January 2021.
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