Setting the record straight on amino acid response to phytase
By Adam Smith, DSM Nutritional Products
Including phytases in diets for pigs and poultry has become standard practice. The matrix values manufacturers recommend and nutritionists use, however, are frequently a subject of debate. This is particularly the case for claimed amino acid release values where there is often huge discrepancy between products on the market. This divergence isn’t necessary logical, particularly when the stated phosphorus release of products is often similar. Part of the issue can be the relatively small amount of data available on amino acid release that phytase manufacturers have available to make decisions. To make a more precise judgement on the effect of phytase on
amino acid release, a meta-analysis of the scientific literature was recently carried for both poultry and pigs. In theory, a direct relationship between phosphorus and amino acid release would be expected, as it is associated with the increasing degradation of phytate. However, whilst this effect was seen at lower phytase doses, as inclusion levels increased there was a clear disconnect between the two. Differences in the magnitude of response from one amino acid to another were also seen, as well as between pigs and poultry. An improved understanding of these trends will help nutritionists better decipher the confusing variety of product recommendations currently on the market. More informed decisions on phytase dosing for optimal animal performance and diet cost will also be possible.
The usefulness of phytase Phytic acid is one of the most important anti-nutrients in monogastric nutrition. It is present in plant seeds where it forms 60-80% of the phosphorus present. Commonly used raw materials contain differing amounts from 7-8g per kg in maize to 50-60g per kg in some cereal by-products and vegetable protein meals. In monogastric diets phytic acid has the effect of reducing the digestibility of several key nutrients. By adding phytase to the ration, phytic acid is degraded and its negative effects reduced. As a result, the digestibility of nutrients including phosphorus (P), calcium, sodium, amino acids, and trace minerals, are increased.
The effect of phytase on amino acid release The ability of phytase to improve phosphorus and calcium digestibility is well proven and there is a wealth of data on the magnitude of the response. However, the effects of phytase on other nutrients, including amino acids, have been less consistently reported. Trials that evaluate ileal amino acid digestibility are expensive to carry out. There is also a high level of variation in the resulting data. This means that manufacturers of phytase must devise amino acid matrix values for
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their products based on relatively small and highly variable data sets. In this situation whether they extrapolate with either a conservative or aggressive philosophy can make a huge difference. It is perhaps therefore not surprising that recommended values for amino acid digestibility improvement, with phytase addition, vary widely between manufacturers, with associated confusion for the end user.
BROILER EVALUATION From a scientific point-of-view decisions should be made based on as wide a body of evidence as possible, to reduce the likelihood of error. The aim of a recently published meta-analysis was to provide clarity on phytase amino acid release values in broilers. A review of all published data, on the effect of phytase on ileal amino acid digestibility, from the last 20 years was carried out. The results of 24 independent peer-reviewed papers were included. The diets fed were based on a variety of different cereals, protein meals and by-products. Trials with all the most commonly used phytase products were included.
Amino acid responses The analysis showed that the mean coefficient of apparent ileal amino acid digestibility in the control diets/ingredients was 0.80 and that this increased by an average of 4.1% to 0.84, when phytase was added. Such improvements were associated with a mean dose of phytase of 880 FYT kg feed and a digestible phosphorus release of ~0.07%. Although the digestibility of all amino acids was increased there were also different patterns of response observed for individual amino acids. The coefficients of apparent lysine, methionine, cysteine and threonine digestibility, were increased by 3.4, 1.3, 7.2 and 6.0% respectively (Figure 1).
Figure 1. Individual mean amino acid responses to phytase addition in broilers
7 6 5 4 3 2 1 0
ala
arg
asp
cys
glu
gly
his
ile
leu
lys Amino Acid
Phytase improved amino acid digestibility, supporting matrix values of 2-6% in broilers.
met
phe
pro
ser
thr
trp
tyr
val
Mean % improvement in digestibility with phytase
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