Over the past decade, the inclusion of microbial phytase in poultry diets has increased dramatically, largely in response to increasing concerns about environmental pollution by phosphorus (P). The capacity of this feed enzyme to release P-bound phytate and reduce P excretion is now well established. Effectively, phytase is an alternative and economical source of P, and since global phosphate reserves are not renewable, this would be beneficial for their conservation. On the other hand, dietary phytate concentrations may be reduced by considering low-phytate feeds. There is a distinct possibility that phytate negatively affects protein and energy efficiency in poultry, whereas these effects are improved by phytase. The response in amino acid digestion after phytase supplementation is variable and the underlying mechanisms are not fully understood. The effect of phytase on protein and energy utilization may be more positive than is generally understood, but this should become increasingly evident if higher phytate degradation rates can be achieved. The practical use of microbial phytase in poultry diets will redefine nutritional requirements, particularly with regard to phosphorus and calcium, and will increasingly contribute to the sustainable farming of poultry in the future. This will be facilitated by a focus on fundamental research, which was undoubtedly lacking in the past.
What is phytase?
Phytate can be hydrolyzed by phytases. There are three sources of phytase, namely plant phytase, intestinal phytase and microbial phytase.
(I) Plant phytase
The activity of endogenous phytases in foods varies. The highest activities have been reported in rye, wheat and wheat bran. In contrast, maize, eared maize and oilseeds have very low endogenous activity. Published data on the effects of plant phytase activity on animal performance are limited.
(II) Intestinal phytase activity
The existence of intestinal phytase activity in poultry is controversial. Liebert et al. (1993) reported that phytase activity is negligible in the contents of the abomasum, stomach and small intestine of chickens. Kornegay (1999) stated that the importance of phytase produced by microorganisms in the intestine is negligible. However, Maenz and Classen (1998) reported that alkaline phosphatase of the intestinal villi can contribute to the degradation of phytate P. The highest level of alkaline phosphatase activity is in the intestinal wall region in the duodenum and decreases in the jejunum and ileum.
(III) Microbial phytase:
Microbial phytase can be found in a large number of bacteria, yeasts and fungi. Aspergillus is the most widely used fungus in the commercial production of microbial phytase.
Effects on growth performance and feed efficiency
Since the report by Simmons et al. (1990), several hundred studies have been conducted on the various effects of microbial phytases on poultry growth performance, which prevents them from being considered in isolation. Predictably, the addition of phytase to low-P diets has been shown to increase growth performance. In the study by Simmons et al. (1990), the addition of phytase (1500 FTU kg-1) to diets containing 4.5 g/kg total phosphorus increased the weight gain (733 g vs. 338 g) and feed efficiency (1.50 vs. 1.85) of broilers from 0 to 24 days of age. (1999) reported that for broilers from 7 to 25 days of age, phytase supplementation (400 and 800 FTU kg-1) at 2.3 g/kg in phytate-free diets increased weight gain (18.8%), feed intake (0.9%) and feed efficiency (7.9%). However, the response to phytase provided at 4.5 g/kg of phytate-free diet in broilers was relatively lower (increases of 0.5, 0.5 and 0%, respectively), with a significant interaction between phytate-free P level and phytase supplementation for weight gain. Overall, results from phytase supplementation in the diet indicate higher feed intake and weight gain relative to feed efficiency (Onyango et al., 2005) and Bahaduran et al. (2011). Rosen (2003), using multivariate analysis of phytase feeding trials, argues that feed efficiency has declined with phytase supplementation over time, which he attributes to the simultaneous advancement of nutritional and management techniques in poultry farming.
Effect on amino acid digestibility
The extent of amino acid response to phytase supplementation appears to be dependent on the material used. This may be related to the concentration, structure, and storage location of phytate in a particular material. Ravindran et al. (1999) examined samples of soybean meal, canola meal, cottonseed meal, sunflower meal, corn ear, wheat, corn, rice bran, and wheat blends. A significant increase in essential and non-essential amino acids (%) was observed in the treatment group compared to the control group, with the highest response observed in soybean meal, wheat, and rice, and other ingredients. In the study by Dilger et al. (2004), in the treatment group with two levels of phytase (500 and 1000 FTU/kg) both essential and non-essential amino acids were significantly increased compared to the negative control group.
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