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Nutritional and ecological importance of phytate
SOURCE :
TIME : 2014-06-12

Nutritional and ecological importance of phytate

 
For global feed production, phytate and phytic-P have significant nutritional and ecological importance:
To meet the essential P requirements of the animal, diets are supplemented with P sources such as dicalcium phosphate or meat and bone meal. Inorganic P sources are non-renewable and can be costly for producers.
 
Excess and undigested P excreted by pigs and poultry can enter watercourses, contributing to the cause of algal blooms and the death of fish (eutrophication)
 
In animal nutrition, phytate is important as a possible source of P for poultry and swine. Ruminants have a fermentation process where phytate can be broken down by rumen bacteria, releasing P to be absorbed by the animal. However, phytate has long been recognised as a non available P “source” for poultry and swine, as monogastrics are less efficient at hydrolysing phytate.
 
Why is P in phytate not available to monogastrics?
This is primarily due to interactions with other minerals and proteins present in the intestinal tract, making phytic P less available (or digestible) for poultry and swine.
 
When reacting with other nutrients present in the intestinal tract of poultry and swine, phytate reduces the digestibility, and also causes an increase in endogenous secretions of these nutrients. Both of these effects highlight the anti-nutritional effects of this molecule.
 
A better understanding of the anti-nutritive effect of phytate on nutrient digestibility creates an opportunity to improve animal performance beyond viewing phytate as a possible P source for the animal
 
Impact on mineral digestibility
As phytate passes through the monogastric digestive tract, it goes from an acidic pH (in the stomach/gizzard) to a nearly neutral pH in the distal intestine. As pH increases, phytate becomes more negatively charged and as a consequence becomes more strongly attracted to cations such as calcium (Ca), zinc (Zn) and copper (Cu). As a result, stable salts are formed which precipitate out of solution at higher pH values
 
Phytate binds to Ca
The binding of phytate to Ca is of importance in animal nutrition due to the higher concentration of this mineral in animal feeds. In vivo trials have shown that high Ca diets reduce phytic P absorption, and an increase in phytate concentration in the diet increases the animals’ requirement for Ca.
 
Phytate binds to Cu and Zn
In some feeds, primarily piglet pre-starter and starter diets, Cu and Zn may also be important cations where high inclusion rates of these minerals are used to promote growth. Blood concentrations can be an indication of animal mineral status and a recent study showed that serum Zn concentrations were reduced in the presence of high concentrations of phytate, suggesting that high dietary phytate may reduce the availability of Zn and potentially Cu
 
Impact on protein digestibility and endogenous loss
Protein digestion starts in the stomach, where secreted pepsinogen is activated to pepsin, the enzyme that initiates the breakdown of feed protein. Research has shown that the presence of phytate reduces pepsin activation between pH 0.8 and 2.8. This may result in less protein being initially digested in the acid phase of the digestive tract in poultry and swine, and as a consequence, reduce overall protein digestibility.
 
Digestive secretions are regulated by intrinsic and extrinsic stimuli. Gastric secretions of hydrochloric acid (HCl) and pepsinogen, for example, will be regulated by factors such as visual and odour stimulus, stomach distension (more important in swine than poultry) and the presence of specific components in the gut.
 
Presence of undigested protein in the lower part of the intestinal tract will stimulate hormone secretions that in turn can increase HCl and pepsinogen secretion in the stomach while reducing gastric empting. An increased concentration of peptides and amino acids in the lower part of the gut will have the opposite effect.
 
Another consequence of this increase in HCl and pepsinogen production is an increase in endogenous losses by the animal. This is because higher HCl and pepsinogen production has an irritant effect on the gut mucosa, which is then compensated by an increased production of mucus as a protective layer.
 
Also, once the digesta gets to the duodenum, a greater amount of sodium bicarbonate will need to be secreted by the pancreas to increase pH and compensate for the lower stomach pH.
This excess sodium usage can compromise the absorption of amino acids. Figure 3 demonstrates the increase in sodium (Na) and sialic acid (mucus marker) due to the
Superdosing is the addition of sufficient phytase to quickly destroy all phytate present in the diet. As phytate is an anti-nutrient, this will lead to performance improvements in the target animal greater than those expected from the simple release of nutrients due to added phytase.
 
This method of phytase use moves away from the application of a dose dependent matrix and focuses more on optimising performance.
 
Improving post-weaning pig performance is always a key focus of the swine production system as it is important that the pig gets off to an optimal start. 21 days post-weaning performance is known to be strongly linked to lifetime pig performance and consequently producer profitability. This often leads to the use of specialist starter feeds which are typically more complex (higher use of animal proteins and whey products) than later nursery feeds, and have traditionally used lower levels of vegetable-protein sources in the early phases. This is due to the lower nutrient digestibility associated with plant protein when compared to the animal/whey proteins, as well as the presence of anti-nutrient factors

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