DIETARY PHYTATE IN BROILER NUTRITION AND GROWTH

– Joaquin Percebal-Morlanes, DVM, MSc, MRCVS

 

Plants naturally store phosphorus in the seeds in form of phytate. This molecule (Fig 1) can be found in cereal grains, legumes and oilseeds (Ravindran et al., 1995) and form complexes in the seed with proteins; later on, the action of phytase enzymes breaks the molecule down making the phosphorus available for the development of the plant during germination (Carla E. Hegeman et al., 2001).

Feeds for animals based on cereals and legumes contain phytate of which approximately 28.2% is phosphorus (Ravindran V, 2010)

Phytate in feeds not only interferes with the absorption of phosphorus but this molecule can bind proteins (Selle et al., 2000), cations (Morris 1986) and form complexes with starch (Thompson and Yoon, 1984), lowering the availability of nutrients present in the diet for the chickens.

Plant-based feedstuffs must be formulated with more phosphorus available to the animal from inorganic sources such as mono- or dicalcium phosphate that is 95- 98% available to the broiler, adding cost to the production (Leeson S & Summers J, 2001). In addition to this problem, the undigested phosphorus in the phytic acid is excreted and when the manure is spread to agricultural land, it may lead to contamination of the land if the amount applied exceeds the amount of phosphorus taken by the crops and contamination of water due to high concentration of phosphorus being lixiviated (Pote et al., 1996).

Phosphorus is an important mineral for the nutrition of broilers as it is necessary for the formation and maintenance of bones, metabolism and fertility (in the case of broiler parent stock) and is a expensive feed component in the broiler diet.

There are different strategies in order to minimize the problems associated with the phytic acid present in the plant seeds and improve the utilisation of dietary protein, energy, phosphorus and other minerals by the broilers and reduce the excretion of phosphorus:

• Low phytate crops
• Addition of microbial phytase enzyme
• Control of Ca/tP ratio in the feed
• Addition of additives (vitamin D, citric acid)

Low Phytate Crops

There are mutations identified in some cultivars (maize, barley, rice) that have been selected for their low content of phytate in the seeds. Two low-phytate alleles have been identified (lpa1-1, lpa2-1); the content of phosphorus in these lines with the allele of low phytate content (lpa) is the same as the non-mutants lines but the amount of phytate-P is 50 – 95% lower, with more inorganic Phosphorous (Raboy V, et al., 2001).

Likewise, there are soybeans low-phytate variants that contain approximately 45-65% inorganic phosphorus whereas the non-mutants variants contain 10-15% inorganic phosphorus (Wilcox RJ et al., 2000).

Addition of Microbial Phytase Enzymes

Chickens have some specific and unspecific phytase activity mediated by enteric phytase and phosphatase enzymes respectively in the small intestine but this enteric phytase activity is insufficient to break down all the phytate ingested in a typical diet based on soya and corn. The addition of exogenous phytase enzyme helps to make more phytate-P available for the chickens and reduce the negative effects that phytate has on the utilization of minerals, proteins and energy (Cowieson AJ, et al., 2006).

Effect of exogenous phytase on protein and energy utilization

Phytate not only binds to dietary protein (Selle et al., 2000) and starch (Thompson and Yoon, 1984), making them less available for chickens but also interacts with enteric enzymes such as amylase (Knuckles BE & Betschart AA 1987) and proteases (Caldwell, 1992), provoking more secretion of enzymes, mucins and increasing losses of endogenous protein (Pirgozliev V et al., 2005).

In addition to that, phytate makes Na⁺ less available for the chicken in the lumen of the intestine, interfering with systems of transport of amino acids and glucose, Na⁺-dependant in the intestinal wall (Ravindran V, 2010). All these actions lead to a decrease in the digestibility of the dietary protein in the order of 9 – 14% (Knuckles et al., 1989).

Depending on the amount of phytate in the diet and phytase added, we may expect different digestibility and retention of amino acids (see table 1 & Fig 2), minerals and energy.

	Diets containing 5 g of casein and different amounts of phytate (IP6) and phytase
	0.5 g IP6/0 FTU	0.5 g IP6/1000 FTU	1 g IP6/0 FTU	1 g IP6/1000 FTU
DM digestivility	0.5	0.73	0.37	0.74
TAA digestivility	0.92	0.96	0.89	0.93
TMN	0.21	0.7	0.02	0.54

Table 1 (Cowieson AJ, et al., 2006) DM: dry matter; TAA: total amino acid; TMN: true metabolizability of nitrogen

Digestibility of dry matter and utilization of the energy, amino acids, phytate-P and minerals increase when phytase is added to the diet (Fig 3)

There are different types of exogenous phytases commercially available from fungal (i.e..: Aspergillus niger, Aspergillus ficuum) to bacterial (i.e.: Escherichia coli) origin, being the phytases of bacterial origin more efficient releasing phosphorus form phytate (Augspurger RN , et al.2010).

The products commercially available, express the activity of the enzyme by phytase units (FTU)[1]. However, different phytases have different activities depending on pH (see Fig 4),

and the activity of the enzymes standardised at pH 5.5 may not be the best predictor of the biological activity (see Fig 5).

The enzyme activity measured at low pH (2.5 – 3.5) has better correlation with the biological performance in broilers than the phytase activity at 5.5 and in this case, increasing the particle size of the feedstuff of low-phosphorus diets with added phytase would keep the feed in the proventriculus and gizzard longer and release more phosphorus (Bedford M & Greiner R, 2010).

Despite the importance of the addition of microbial phytase for the improvement on the utilization of phosphorus in the diet, exogenous phytase hydrolyses less than 35% of dietary phytate in broiler feeds (Selle PH & Ravindran V, 2007). The use of low-phytate cultivars (high available phosphorus) along with exogenous phytase improves the performance of the flock, allowing a reduction of total phosphorus in the feed in the order of 23 – 28% and reduction of phosphorus excreted (Huff WE, et al.1998).

The future on phytase research is focused on including it at higher concentration in the feed, discovery of new phytase enzymes, combination of phytase with other enzymes (amylase, xylanase, …) and optimisation of Ca/P ratios (Ravindran V, 2010)

Ratio Ca/P in the Diet

High Ca/P ratios in the feed have a negative effect in the utilisation of phytate-P by the broilers (Ballam et al., 1984). It is thought that Ca binds with phytate, making the complex Ca-phytate less soluble and more resistant to the action of phytase enzymes. The deposition of minerals in the bone decreases with high Ca/P ration; the influence of Ca/P is greater when no exogenous phytase is added into the ration (see Fig 6).

Addition of Vitamin D₃

Vitamin D₃ improves the absorption of P in the intestine (Table 2) by activation of a transport system different to the transport of Ca in the intestine (Edwards, 1993) and it is been proposed that vitamin D₃ also activates phytases and phosphatases to hydrolyse phytate (Biehl RR et al., 1995) with an additive effect when both vitamin D₃ and exogenous phytase enzymes are incorporated in the feed (table 2 & Fig 7).

	Weight gain (g)	Tibia ash (g/100g)
Control	195	29.1
Control + 20 mg vit D/kg	235	40.9
Control + 1200 FTU/kg	245	38.5
Control + 20 mg/kg + 1200 FTU/kg	253	42.7

Table 2.(Biehl RR et al.,1995) Weight gain and tibia ash in chicks fed during 12 days with vit D or phytase or vit D+phytase added to the control diet

And as we saw with the addition of phytase, the addition of vitamin D₃ also improves the metabolic energy of the diet (Table 3).

	Control diet	Control diet + 75 FTU	Control diet + 5mg vit D
Kcal ME	2883	2983	2993

Table 3 (Edwards HM Jr, 1993)

 

Addition of Citric Acid in the Feed

It has been observed that supplementation of organic acids, especially citric acid has a positive effect in the utilization of phytate-P by the chickens (Boling SD, et al., 1998). Citric acid is also a potent chelator, so it would compete for Ca in the lumen of the intestine and that would reduce the number of phytate-Ca complexes, making phytate more vulnerable to hydrolysis (Boling SD, et al., 2000).

The effect of the addition of different amounts of citric acid to the diet can improve the weight gain (Fig 8) and the minerals deposited in the bones using diets deficient in phosphorus.

As mentioned before, citric acid binds Ca but does not interfere with the availability of Ca for the chickens in the intestine (Boling-Frankenbach et al., 2001).

Despite these positive effects on the utilization of phytate-P by the chickens with the addition of citric acid, the use of this organic acid in the diet at 4 – 6% is not economically viable, (Boling SD, et al., 2000), so it should be used in combination with the other measures already discussed. See Fig 9.

 

Conclusions

The addition of phytase in animal feeds may release phosphorus for the absorption in the intestine, increasing the energetic value of the feed and the availability of other nutrients such as amino acids and minerals. The cleavage of phytate makes more phosphorus available, improving the deposition of minerals in the bone and the growth of the flock, reducing the total amount of phosphorus needed in the feed and likewise reducing the excretion of phosphorus to the environment.

The action of this enzyme can be potentiated by the addition of vitamin D₃ and organic acids.

 

 

REFERENCES

(1) Augspurger RN, Sheridan IN and Baker DH.2010. The high cost of phosphorus for pigs and poultry: what are the options.<http:// www.enzyvia.com/research.html>

(2) Ballam GC, Nelson TS and Kirby LK, 1984. Effect of fiber and phytase source and of calcium and phosphorus level on phytate hydrolysis in the chick. Poultry Science 63: 333-338.

(3) Bedford M and Greiner R. (2010) International Phytase Summit 2010. Effect of pH on enzyme activity. 28-30/09/10, Washington D.C.

(4) Biehl RR, Baker DH and F.De Luca H. 1995. 1a-hydroxylated cholecalciferol compounds act additively with microbial phytase to improve phosphorus, zinc and manganese utilization in chicks fed soy-based diets. American Institute of nutrition 2407-2415

(5) Boling, SD, DM Webel I. Mavromichalis, CM Parsons and DH Baker. 1998. Citric acid enhances phytate phosphorus utilization in young chickens and pigs. Journal of Animal Science 76(Supplement 2):58

(6) Boling, SD, DM Webel I. Mavromichalis, CM Parsons and DH Baker. 2000. The effects of citric acid on phytate-phosphorus utilization in young chicks and pigs. Journal of Animal Science. 78:682-689

(7) Boling-Frankenbach SD, Snow JL, Parsons CM and Baker DH. 2001. The effect of citric acid on the calcium and phosphorus requirements of chicks fed corn-soybean meal diets. Poultry Science 80:783-788

(8) Caldwell R. A., 1992. Effect of calcium and phytic acid on the activation of trypsinogen and the stability of trypsin. J. Agric. Food Chem. 40:43–48.

(9) Carla E. Hegeman, Laura L. Good, and Elizabeth A. Grabau (2001) Plant Physiology, Vol. 125, pp. 1941–1948

(10) Cowieson AJ, Acamovic T, and Bedford MR. 2006. Phytic acid and phytase: Implications for protein utilization by Poultry. Poultry Science 85:878-885

(11) Edwards HM Jr. 1993. Dietary 1,25-dihydroxycholecalciferol supplementation increases natural phytate phosphorus utilization in chickens. Journal of nutrition 123:567-577

(12) Huff WE, Moore PA Jr, Waldroup PW, Waldroup AL, Balog JM, Huff GR, Rath NC, Daniel TC and Raboy V. 1998. Effect of dietary phytase and high available phosphorus corn on broiler chicken performance. Poultry Sciece 77:1899 – 1904.

(13) Knuckles, B. E., and A. A. Betschart, 1987. Effect of phytate and other myo-inositol phosphate esters on α-amylase digestion of starch. J. Food Sci. 52:719–721.

(14) Knuckles, B. E., D. D. Kuzmicky, M. R. Gumbmann, and A. A. Betschart. 1989. Effect of myo-inositol phosphate esters on in vitro and in vivo digestion of protein. J. Food Sci. 54:1348–1350.

(15) Leeson S. & Summers J. 2001. Scott’s nutrition of the chicken. 4^th edition. University books, pp: 358 – 363

(16) Morris, E. R., 1986. Phytate and mineral bioavailability. Pages 57–76 in: Phytate Chemistry and Application. E. Graf, ed. Pilatus Press, Minneapolis, MN

(17) Pirgozliev V, Oduguwa O, Acamovic T and. Bedford M.R. 2005. Effect of dietary phytase on performance, metabolisable energy and endogenous losses of broiler chickens. WPSA. Proceedings of the 15^th European symposium on poultry nutrition, pp 333 – 335

(18) Pote DH, Sharpley AN, Daniel TC, Reddy KR, Moore Jr PA, Edwards DR, Nichols DJ, (1996)Relating extractable soil phosphorus to phosphorus losses in runoff. Soil Science Society. Am J. 60: 855-859

(19) Raboy, V., Young, K. A., Dorsch, J. A. & Cook, A. (2001) Genetics and breeding of seed phosphorus and phytic acid. J. Plant Physiol. 158: 489–497.

(20) Ravindran V. Association de Nutrition Animale du Canada (2010). Eastern Nutrition Conference. Phytate: anti-nutritive effects on energy and amino acid utilization. 11-12 May 2010. Montreal.

(21) Ravindran, V., W. L. Bryden, and E. T. Kornegay 1995. Phytates: occurrence, bioavailability and implications in poultry nutrition. Poult. Avian Biol. Rev. 6:125–143

(22) Ravindran V, Selle PH, Rabindran G, Morel PCH, Kies AK and Bryden WL. 2001. Microbial phytase improves performance, apparent metabolizable energy and ileal amino acid digestibility of broilers fed a lysine-deficient diet. Poultry Science 80:338-344

(23) Selle, P. H., Ravindran, V. 2007. Microbial phytase in poultry nutrition. Animal Feed Science and Technology; 135: 1 – 41.

(24) Selle, P. H., V. Ravindran, R. A. Caldwell, and W. L. Bryden. 2000. Phytate and phytase: Consequences for protein utilisation. Nutr. Res. Rev. 13:255–278

(25) Snow JL, Baker DH and Parsons CM. 2004. Phytase, citric acid and 1 a-Hydroxycholecalciferol improve phytate phosphorus utilization in chicks fed a corn-soybean meal diet. Poultry Science 83:1187-1192

(26) Thompson, L. U., and J. H. Yoon, 1984. Starch digestibility as affected by polyphenols and phytic acid. J. Food Sci. 49:1228–1229.

(27) Wikipedia. 2010. Available from http://en.wikipedia.org/wiki/File:Phytate.png.

(28) Wilcox JR, Premachandra GS, Young KA and Raboy V. 2000. Isolation of high seed inorganic P, low-phytate soybean mutants. Crop Sci. 40:1601-1605.

(29) Mr D.G.Parsons B.Vet.Med., MSc, CertPMP, NSch, MRCVS

 

[1] One FTU is the amount of enzyme necessary to liberate 1mmol of iP/min from 0.00015 mol/L sodium phytate at ph 5.5 at 37^oC (Ravindran V., et al, 2001)