Phytase applications in commercial broiler diets in Maryland

THE WATER QUALITY IMPROVEMENT ACT OF 1998 IN MARYLAND

During the summer of 1997 the state of Maryland experienced outbreaks of Pfiesteria in several of its rivers and tributaries. These dinoflagellate microorganisms were implicated in several fish kills that closed affected rivers to fishing and tourism. Similar outbreaks were experienced in North Carolina and other east coast areas, and although not proven there was thought to be a link between these outbreaks and nutrient over-enrichment of the soil due to manure application and subsequent runoff, as phosphorus runoff into surface water has been identified as one of the possible causative agents.

In the fall of 1997 the governor of Maryland established a Blue Ribbon Citizens Pfiesteria Action Commission to study the problem and make recommendations to the legislature. In the spring of 1998, the Water Quality Improvement Act of 1998 was passed by the Maryland Senate and the House and signed by the governor. This bill mandates that any farm using sludge or animal manure must have a nitrogen- and phosphorus-based nutrient management plan.

The nitrogen plans must be developed by 2001 and implemented by 2002, while the phosphorus plans must be developed and implemented by 2004 and 2005, respectively. Farms using chemical fertilizers must also have nutrient management plans, but the deadlines are 2001 and 2002, respectively, for nitrogen and phosphorus. One additional regulation included in the Water Quality Improvement Act of 1998 is that all contract feed manufactured for chickens must contain phytase or some other enzyme or additive that reduces phosphorus excretion. This must be implemented by the end of the year 2000.


BARLEY UTILIZATION AND MANURE PHOSPHORUS REDUCTION: RESEARCH AREAS ON THE DELMARVA

INCREASING THE POTENTIAL FOR BARLEY UTILIZATION IN BROILER DIETS

Modern broiler diets are composed in large part of a mixture of corn and soybean meal fortified with vitamins and minerals; however there has been interest in the last few years on the Delmarva peninsula in the use of barley instead of corn. Corn is a high energy ingredient and soybean meal is rich in protein.When these two ingredients are combined the resulting feed provides a relatively good combination of amino acids and a high metabolizable energy (ME) level for maximal growth and feed efficiency.

The use of barley in this region is of interest because farmers are able to harvest barley several weeks before wheat, which enables them to plant soybeans earlier to increase yield. Historically, barley has been considered a less desirable grain for use in broiler diets due to its high fiber content and the presence of ß-glucans, which are poorly digested nonstarch polysaccharides (NSP). ß-glucans increase digesta viscosity resulting in reduced intestinal absorption of nutrients as well as causing wet litter. These factors contribute to the low ME value for broilers and limit the use of barley, particularly for young birds. Adding the enzyme ß-glucanase has been shown to improve the digestibility of NSP in barley (Petterson and Aman, 1990); however, this practice increases the cost of the diet and makes it more expensive than using corn.

Part of our research has focused on inclusion of locally-produced barley varieties in diets fed to growing broilers with and without the use of the supplemental enzyme ß-glucanase. Because preliminary studies have shown that younger birds performpoorly when fed barley in comparison to corn, we have concentrated on finding ways to maximize the inclusion levels of the Callao and Nomini barley varieties in broiler chicken diets from 21-42 days of age.We also compared the 1996 and 1997 harvests of these two varieties grown in the same location in Virginia. Samples were submitted for in vitro metabolizable energy (ME) determinations at the University of Georgia. These ME values were then used in feeding trials to provide comparisons with the ME values reported by the National Research Council. Supplemental ß-glucanase enzyme was also evaluated in growing broilers fed graded levels of barley.


PHOSPHORUS REDUCTION IN DIETS CONTAINING CORN AND BARLEY

The Delmarva is a peninsula on the northeastern US coast that separates Chesapeake Bay from Delaware Bay and the Atlantic Ocean. It includes all of Delaware and parts of eastern Maryland and Virginia (Figure 1). There are approximately 625 million commercial broilers produced annually on the Delmarva peninsula resulting in approximately 53 million pounds of manure nitrogen and 22 million pounds of manure phosphorus. These figures are based on feeding typical corn-soybean meal based diets formulated to National Research Council recommendations.

Simmons et al. (1990) reported that 60-80% of the total phosphorus present in many grains, oilseed meals and plant products is bound in the form of phytic acid (myoinositol hexaphosphate) in the material. Since nonruminants contain relatively little intestinal phytase (Nelson, 1976) the phosphorus content of plant-source ingredients is considered to be only 30-40 % bioavailable.

Due to this poor bioavailability of plant source phosphorus, nutritionists are forced to supplement practical feeds with inorganic phosphorus to ensure proper growth and bone development. It has been demonstrated, however, that phosphorus in the phytate ring can be released through the action of phytase enzyme. Typically, phytase has been reported to increase phosphorus bioavailability by 25-50% and reduce phosphorus excretion by 15-40% in grain based diets for swine and poultry.




Factors that also affect the efficacy of the phytase enzyme include dietary calcium and phosphorus levels (Wise, 1983), the age of the birds (Edwards, et al.1989) and dietary vitamin D3 (Edwards, 1991; 1993; Mohammed et al., 1991). An additional factor influencing bioavalability of phosphorus in chickens is the types of ingredients in the diet.

Several ingredients have been reported to contain endogenous phytase activity (Bartnik and Szafranska, 1987) but the levels vary widely in different cereal grains. Eeckhout and De Paepe (1994) reported that out of 50 feedstuffs analyzed only rye, triticale, wheat and barley contained appreciable amounts of phytase activity (5130, 1688, 1193 and 582 units/kg, respectively). Corn, oats, sorghum and oilseeds were reported to contain little endogenous phytase activity. Templeton et al. (1965a,b) demonstrated that diets containing 32-36% wheat and 10% barley without supplemental inorganic phosphorus provided chicks with usable phytate phosphorus due to endogenous phytase in the grains.

With interest in nutrient management becoming more and more important we have also begun to evaluate the availability of phosphorus in broiler diets containing 30% barley. Barley contains endogenous phytase that may result in an increase in phosphorus digestibility and reduce the need for supplemental phosphorus. Ultimately, this would reduce the amount of phosphorus excreted in the manure, resulting in a more favorable nitrogen:phosphorus ratio for soil application if used as a fertilizer.


EFFECTS OF PHYTASE IN DIETS CONTAINING EITHER CORN OR 30% BARLEY AND SUPPLEMENTAL ß-GLUCANASE

While it is likely that the inclusion of phytase will be commonplace in broiler feeds on Delmarva owing to the provisions of the Water Quality Act, there are no data currently available on its effects in diets containing the types of barley grown in this region. The objective of the following trial is a comparison of barley with corn in the grow/finish diet while using ß-glucanase to reduce gut viscosity and phytase to increase phosphorus bioavailability. Using the two enzyme products in the same diet allowed the opportunity to observe both enzyme response and any interactions that might exist between the two enzymes.


EXPERIMENTAL PROCEDURES

Four hundred male broiler chicks were fed a commercial starter diet from 0-21 days of age. Following an overnight fast at 21 days of age birds were individually weighed, wingbanded and a homogenous group of 180 birds were selected for the experiment. Birds were allotted to treatments in a manner that ensured similar average weights and weight ranges for all pens.

The grow/finish test diets were formulated to contain 0.90% calcium and 0.35 or 0.25% available phosphorus (Table 1). The experimental design was a randomized complete block with eight treatments (Table 2) with four replicate groups per treatment and five male broilers per replicate. All diets contained the NRC-recommended ME:crude protein ratios of 160; and minimum crude protein:lysine and crude protein:total sulfur amino acid ratios were 20.0 and 27.78, respectively. Feed and water were offered ad libitum. Birds were housed in floor pens with wood shaving/sawdust litter.

Growth performance and efficiency during the 21-42 days period were evaluated. At 42 days of age birds were weighed, slaughtered and gut contents were collected (post-duodenum to Merckel’s diverticulum), pooled within pen, centrifuged and viscosity of the supernatant determined using a Brookfield Digital Viscometer (Brookfield Engineering Laboratories, Inc., Stoughton, MA). Bone breaking strength and ash content were determined on the right tibias from two birds/pen. Data were analyzed using the General Linear Model with treatment and replicate as sources of variation. Duncan’s Multiple Range Test was used to separate treatment means where appropriate.





RESULTS

Reducing available phosphorus (AP) content from 0.35% to 0.25% in the corn/soy diets did not statistically decrease weight gain, however the group given 0.25% without enzyme had the lowest weight gain (Table 3, Figure 2). Bone breaking strength was reduced by lowering available phosphorus (20.63 kg vs 18.40 kg) (Table 4). The addition of Allzyme Phytase improved bone breaking strength in both the adequate phosphorus (22.83 kg vs 20.63 kg, respectively) and the phosphorus deficient diets (25.57 kg vs 18.40 kg, respectively). Bone ash content followed a similar trend.




Birds given the diets with 30% barley performed as well or better than those given corn-based diets, particularly when ß-glucanase was added. When available phosphorus was decreased from 0.35% to 0.25% in the diets containing 30% barley there was no significant decrease in either bone breaking strength or bone ash (Figure 3). Birds consuming the 30% barley diet formulated to contain 0.25% AP had bone ash values of 51.73% compared to 47.62% when fed the low available phosphorus corn diet. Bone breaking strength followed a similar trend (20.12 kg vs 18.40 kg, respectively). Supplemental phytase in the barley diets did not significantly improve either bone breaking strength or bone ash content. These results suggest that phosphorus in barleymay be more digestible than phosphorus
in corn.




These results suggest that there is no adverse reaction when combining supplemental ß-glucanase and phytase enzymes in the same diet for broiler chickens. Although there were no statistical differences detected, supplemental ß-glucanase tended to reduce gut content viscosity when added to the barley diet.


CONCLUSIONS

The inclusion of barley into broiler grower diets represents a market opportunity for grain producers.With over 2 billion tons of feed fed annually to Delmarva broilers, the industry could absorb all the local barley produced if it were an acceptable ingredient source for broilers. In this trial barley replaced 30% of the corn in a commercial broiler grower diet with no detriment to performance when supplemental ß-glucanase enzyme was added. This work also determined that the ß-glucanase and phytase enzymes can be mixed without any interference in the mode of action of either product. The benefit of endogenous phytase in barley is not clear and additional work may be needed in this area.







REFERENCES

Bartnik, M. and I. Szafranska. 1987. Changes in phytate content and phytase activity during germination of some cereals. J. of Cereal Sci. 5:23-28.

Edwards, H. M. Jr., Palo, P., Soonchaerenying, S. and M.A. Elliott. 1989. Factors influencing the bioavailability of phytate phosphorus to chickens. In: Nutrient Availability: Chemical and Biological Aspects (southgate, D. Johnson, I. andG.R. Fenwick, Eds). The Royal Society of Chemistry, Cambridge, pp. 271-276.

Edwards, H. M. Jr. 1991. Effects of phytase utilization on monogastric animals. Proc. of the Georgia Nutr. Conf. For Feed Manufacturers, Atlanta, pp.1-6.

Edwards, H. M. Jr. 1993. Dietary 1,25-dihydroxycholecalciferol supplementation increases natural phytate phosphorus in chickens. Jour. of Nutr. 123:567-577.

Eeckhout, W. and M. De Paepe. 1994. Total phosphorus, phytatephosphorus and phytase activity in plant feedstuffs. Anim. and Feed Sci. Tech. 47:19-29.

Mohammed, A.,M.J. Gibney and T.G. Taylor. 1991. The effect of dietary levels of inorganic phosphorus, calcium and cholecalciferol on the digestibility of phytate-P by the chick. Br. Jour. of Nutr. 66:251-259.

Nelson, T.S., 1976. The hydrolysis of phytate phosphorus by poultry: a review. Poultry Sci. 46:862-871.

Petterson, D. and P. Aman. 1990. Enzyme supplementation of broiler chicken diets based on cereals with endosperm cell walls rich in arabinoxylans or mixed-link (-glucans. Anim. Prod. 51:201-207.

Simons, P.C., H.A.J. Versteegh, A.W Jongbloed, P.A. Kemme, P. Stump, K.D Bos, M.G.E. Wolters, R. F. Beudeker and G.J. Verschoor. 1990. Improvement of phosphorus availability by microbial phytase in broilers and pigs. Br. Jour.of Nutr. 64:525-540.

Templeton, H., J. Dudley and G. J. Pickering. 1965a. Phosphorus requirements of poultry. IV. The effects on growing pullets of feeding diets containing no animal protein or supplementary phosphorus. Br. Poultry Sci. 6:125-133.

Templeton, H., J. Dudley and G. J. Pickering. 1965b. Phosphorus requirements of poultry. IV. The effects during the subsequent laying year of feeding growing diets containing no animal protein or supplementary phosphorus. Br. Poultry Sci. 6:135-141.

Wise, A. 1983. Dietary factors determining the biological activities of phytate. Nutr. Abs. And Rev. 53:791-806.


Author: JEANNINE HARTER-DENNIS
University of Maryland-Eastern Shore, Princess Anne, Maryland, USA