Quantification and alleviation of the antinutritional effects of phytate on poultry

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Morgan, NK, 2014. Quantification and alleviation of the antinutritional effects of phytate on poultry. PhD, Nottingham Trent University.

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Abstract

The phosphorus (P) requirements of meat-type poultry cannot be met by plant-based diets because approximately two thirds of total phosphorus in cereals and leguminous feed materials is in the unavailable form of phytate (inositol hexaphosphate or phytic acid). Phosphorus supplements are expensive and over supplementation can increase excretion of P, with negative implications on the environment. For some time, research has focussed on the development of exogenous phytase enzymes capable of releasing phytate phosphorus for absorption, thus reducing the environmental impact of poultry production and requirements for costly dietary inorganic P supplementation. The absolute adoption of this strategy has, however, been stalled by apparent variability in rate of release of phytate by phytase enzyme. The aim of this project was to examine the availability and reactivity of phytate in diets and raw materials fed to broilers in a range of physiological environments, and to develop strategies for combating their effects. A series of in vitro studies and bird trials were conducted to investigate phytate reactivity by observing the relationship between pH, protein phytate interactions and phytate susceptibility to the effects of phytase. A bird trial was undertaken comparing the current commercial level of 500 FTU/kg phytase and a superdose of 5000 FTU/kg phytase in soyabean meal and rapeseed meal based broiler diets. Feeding phytase doses above the commercial recommendation resulted in increased bird performance through phytate destruction, leading to heightened alleviation of the anti-nutritional effects of phytate. This suggests that superdosing broiler diets can improve profitability by both increasing availability of phosphorus and removing restrictions of using cheaper feed ingredients which are viewed as undesirable due to their high phytate content. There is a common misconception that poultry lack any endogenous phytase, but a study sequentially sampling broilers from age d4 to d14 illustrated that phytase activity from intestinal mucosa and bacteria and diet is quantifiable in regulating phytate-P digestion. Endogenous phytase contributes significantly towards degradation of phytate at bird age d4. By d14, ileal phytase activity levels were approximately 45 U/kg and the amount of total dietary phytate hydrolysed ranged from 21% to 36%.
Measurements of total phytate-P content of diets may be deceptive as they do not indicate substrate availability for phytase; measurements of phytate susceptible to the effects of phytase may be a more accurate measure of phosphorus availability to the bird. To verify this hypothesis in practice, a bird study was designed to compare diets formulated to contain high or low susceptible phytate. This study showed that at age d28, birds fed diets with high susceptible phytate content had significantly better cumulative BWG (p=0.015) and FCR (p=0.003) than birds fed diets with low susceptible phytate content. Furthermore, in vitro screening of raw materials revealed that phytate susceptibility varies considerably between ingredients and batches of ingredients, and total phytate content bears no relation to susceptible phytate content of an ingredient. Therefore, for optimum phytase efficacy, it may be advantageous to formulate diets and develop phytase matrix values based on the susceptible phytate content of the individual batch of ingredients being fed. Both total and susceptible phytate content can be measured using simple colorimetric assays. Examination of in vitro digestion models and subsequent correlation to in vivo studies indicate that exposing samples to conditions that mimic the gastrointestinal environment is the most accurate way to predict phytate degradation and mineral availability in diets prior to feeding. The relationship between phytate reactivity and pH was investigated throughout this project. It was found that gastric pH is closer to the optimum for pepsin activity and phytate-complex degradation when in the presence of phytase. This is because phytate reduces protein digestibility, resulting in heightened presence of intact proteins in the tract, which instigates an increase in secretion of HCl and pepsin. More bicarbonate ions are released in response to this increased acidity, causing an increase in intestinal pH and resulting reduction in solubility of phytate-protein complexes. To conclude, dietary phytate that is susceptible to phytase effects as opposed to total phytate content should potentially be considered when determining phytase matrix values. For optimum response to phytase, it may be beneficial to formulate diets based on the susceptible phytate content of the individual batch of ingredients being fed. Some raw materials have high total phytate content but also high susceptible phytate content, meaning they have the potential to be used as replacements for more expensive feed ingredients if in the presence of phytase. This is particularly the case in diets supplemented with high doses of phytase (>500 FTU/kg), because high phytase doses alleviate the extra-phosphoric anti-nutritional effects of phytate as well as increase mineral availability.

Item Type:	Thesis
Creators:	Morgan, N.K.
Date:	September 2014
Rights:	This work is the intellectual property of the author, Natalie Morgan, and the industrial sponsor ABVista. You may copy up to 5% of this work for private study, or personal, non-commercial research. Any re-use of the information contained within this document should be fully referenced, quoting the author, title, university, degree level and pagination. Queries or requests for any other use, or if a more substantial copy is required, should be directed in the owner(s) of the Intellectual Property Rights.
Divisions:	Schools > School of Animal, Rural and Environmental Sciences
Record created by:	Linda Sullivan
Date Added:	25 May 2016 14:44
Last Modified:	25 May 2016 14:44
URI:	https://irep.ntu.ac.uk/id/eprint/27881