Benefit of Phytate Breakdown Through Superdosing in Broiler Breeders

By Rob ten Doeschate, Technical Director EMEA and Gustavo Cordero, Global Technical Manager AB Vista

Chickens  have  a  limited  ability  to break  down  dietary  phytate (IP6) but  a  substantial part  of dietary phosphorus is bound  in this form. Thus, exogenous phytase has been added to poultry diets to increase phosphorus release for decades now. Traditionally, phytase was used to release phosphorus; at that  point, the  phytase levels added to the diet were between 250 and 500 FTU/kg of diet. Higher doses of phytase (superdosing) are  nowadays commonly  used to move  closer  to full destruction of phytate (IP6) and  its lower esters (IP5-IP1) and  thus achieve “extra-phosphoric effects”. The  use of superdosing in poultry diets started with broiler diets, where the concept is now well accepted by integrators and feed producers. When looking at more mature animals, like laying hens or breeders, the question is whether phytase superdosing would give similar benefits as older animals may  suffer less from the antinutritional effects of phytate.

But there are several ways near complete destruction of phytate can benefit the animal: either through  reduction of the direct antinutritional effect of phytate; or through improved protein and amino acid digestibility; or through  improved availability of minerals other  than  phosphorus (Calcium, Iron, Zinc, Manganese etc); as well as through the production of inositol in situ in the animal after full dephosphorylation of phytate. Inositol, which has a wide range of functions in metabolism, is the backbone of the phytate molecule. One  of the roles  of inositol is to improve energy metabolism, helping animals utilise dietary energy more efficiently.

To achieve fast and near  complete destruction of phytate a highly efficient phytase can be added at several times the normal dose. If the phytase can  take  IP6 down to IP1, this can  then  be hydrolysed by the animal’s own  enzyme, alkaline phosphatase, releasing inositol. The release of inositol may have  a critical role in the benefits observed from adding  the higher phytase levels; inositol has  been linked to enhancing mood,  cell growth and  survival, and  development of peripheral nerves as well as roles in osteogenesis and reproduction. Past studies  in  commercial  laying  hens have  shown benefits  of superdosing in terms of improved productivity as well as improved yolk mineral  levels.  In broiler  breeders an  improvement  in  nutrient  levels in the egg  could translate to better  hatch  outcomes and  chick quality. One  challenge with broiler breeders is that nutrient  and  feed  intake  is normally restricted to avoid birds getting  too fat so an improvement in nutrient availability from enzymes may need to be balanced by either adjusting diet composition or feed  allowance. Where  this is not done  it should  be noted  that, whilst any response indicates that the concept of superdosing is working, sometimes an increased nutrient supply may mean a deterioration in production responses.

In a trial reported in two posters at ESPN  2019 it was investigated whether increasing phytase dose in broiler breeders had effects on hen performance, egg  quality, hatchability and  progeny performance. The phytase doses used were 500, 1500 and 4500 FTU/kg (Quantum Blue, AB Vista).  The  nutrient  release  accounted for in  the  diet  formulation was 0.15%  available phosphorus and  0.16%  calcium, so any  further improvement in nutrient availability such as amino acids, energy or trace minerals would have  a direct effect on the nutrient supply of the birds. The trial lasted from 27 until 50 weeks of age, with 18 pens of four hens per experimental treatment. Levels of nutrients in eggs were determined at 35 and 40 weeks of age whilst hatchability and performance of chicks was based on eggs produced when hens were 38 weeks of age.

Whilst egg production was within expected levels for all groups, the 1500  FTU/kg group  performed best with an overall production of 5.35 eggs/week which was significantly (P<0.05) higher than the 4500 FTU/ kg group  at 5.21  eggs/week with the  500  FTU/kg group  intermediate at 5.29  eggs/week. External egg  quality was equal across all dietary groups but there  were  effects of diet as well as age  on yolk nutrient levels.  With regards to minerals, there  were  significant  differences as a result of both  dietary treatments as well age  of the  hens and  some interaction between age  and  diet which confused the picture. Calcium and Copper were highest at 1500 FTU/kg whilst Phosphorus was lowest.

Zinc  increased  with  increasing  phytase dose. Inositol  and  glycerol  in the egg  yolk responded clearly to the increasing dietary  phytase level, with glycerol increasing but inositol decreasing (Figure 1). This may be the result of conversion of inositol to triglycerides, which could then be utilised by the chick at hatch.  When  incubating the eggs it was found that  increasing phytase levels resulted in lower % late dead and  a lower % dead in shell after pipping, which supports the hypothesis that energy supply  for hatching may  have  been improved.  Early  dead % was increased though,  resulting in equal overall hatchability. Inositol in the yolk sac at day of hatch  showed an increase with the highest dose of phytase, which may  have  been used by the  embryo  as an  energy source during hatching.

Figure  1: Yolk Inositol and Glycerol concentration, μmol/g

When  the  chicks that  hatched were  grown  on it was found that chicks  from  hens fed  higher  phytase levels  were  heavier  at  7 days post hatch,  indicating that the hen’s diet supported better  growth of the progeny (FIgure 2).

Figure  2: Yolk Influence  of  breeder  hen  diet  on  progeny  body
weight (g) at 0 and 7 days of age

This work allows us to conclude that  the  principle of using high doses of phytase to achieve near  complete breakdown of phytate also works in adult breeder hens and that this can achieve nutritional benefits. It is highly likely that, when applying this in practice in broiler breeders, this is best  combined with some further  nutrient  reduction in the  diet, especially with regards to essential amino  acids  so as not to not allow egg size increases.

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