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IMPORTANCE AND PREVIOUS WORK

Less than one-third of the phosphorus (P) contained in feed ingredients of plant origin is biologically available to monogastric animals (NRC, 1994). The remainder of the phosphorus is tied up as phytate (phytic acid or myoinositol hexaphosphate) and monogastrics as a general rule lack the enzyme(s) necessary to hydrolyze phytate down to phosphorus and inositol (Peeler, 1972; Lynch, 1996). Therefore, inorganic sources of phosphorus (monocalcium phosphate, dicalcium phosphate, etc.) which have a high biological availability to the animal are supplemented in the feed to provide adequate intake levels necessary for bone and tissue growth and development as well as other metabolic needs (ATP/ADP, enzymes, egg and shell production, etc.). The unavailable plant phosphorus (phytate) is passed undigested from the animal in the manure.

The usual method of manure disposal on most livestock operations is land application. There has been increasing concern in recent years relative to nutrient accumulation in the soils upon which poultry (and other livestock) manure is applied as microorganisms in the soil can break down phytate.

Phosphorus is one of the two nutrients that have received the most attention in this regard (nitrogen is the other). In the soil, phosphorus forms insoluble complexes with elements such as iron (Fe), aluminum (Al) and calcium (Ca) and tends to be immobile in the soil; thus it is not readily leached out of the soil into ground water like nitrogen. Phosphorus levels in the soil tend to build up quite high with continued application of animal waste. Runoff due to improper manure application or weather conditions that cause erosion of soils into lakes or waterways can result in phosphorus pollution and eutrophication of those bodies of water.

The United States has approximately 240 million laying hens, many in large concentrations on individual farms. This results in the generation of very large amounts of manure in numerous very localized areas around the country. Egg shell quality in these birds is highly influenced by the available phosphorus as well as the calcium in the feed. Since land spreading has been the traditional disposal method of animal waste, reducing the amount of phosphorus in the bird manure could have significant implications for being able to continue this method of disposal. In many areas land application of animal waste is strictly limited because of phosphorus disposal legislation (Ferket, 1996). In some areas of Michigan (where this research was done), the soil phosphate levels are above the state Department of Natural Resources acceptable limits and manure spreading on these tracts of land is prohibited.

In the past few years, several enzymes which can be added to the feed have become commercially available from several companies, and these may release some or all of the unavailable phosphorus in the feed grains of poultry diets and make it available. This could decrease the need for inorganic phosphorus supplements in the feed. The use of these enzymes as a feed supplement and the effect on animal health, productivity and manure phosphorus content is currently being investigated by numerous researchers and is the topic of this paper.

Phytate also forms insoluble complexes with numerous ions including copper (Cu), zinc (Zn), Ca, magnesium (Mg), Fe and potassium (K).As the phytase enzymes are used in animal feed and the phytates are broken down in the gastrointestinal tract, these ions are released and the effect on their requirements and the effects on productivity have yet to be understood. Phytate can also complex with proteins in the neutral pH environment of the intestine, essentially rendering the proteins and the phytate indigestible. The addition of proteases and phytase to the feed to increase the breakdown of proteins prior to the intestine is also a topic for further research.


LITERATURE REVIEW

Numerous recent publications document that microbial phytase supplementation in the feed improves the availability of phytate-bound phosphorus in broiler chickens (Simons et al., 1990; Roberson and Edwards, 1994; Sebastian et al., 1996; Qian et al., 1996a; Mitchell and Edwards, 1996a,b; Yi et al., 1996; van der Klis et al., 1994; Scheideler et al., 1992), in swine (Lei et al., 1994; Simons et al., 1990; Ketaren et al., 1993; Young et al., 1993; Yi et al., 1994) in turkeys (Qian et al., 1996b) and in laying hens (Roland and Gordon, 1996; Lynch, 1996; Simons et al., 1992; Simons and Versteegh, 1992, 1993; van der Klis and Versteegh, 1991).
In laying hens, Simons and Versteegh (1992) reported that when phytase (200 to 2,000 phytase units (FTU) per kg of feed) was added to phosphorus deficient diets (only 1.4 g/kg available P), deficiency symptoms of low feed consumption, weight loss and decreased egg production were eliminated and these parameters were not significantly different from birds receiving higher levels of available phosphorus.

In a similar experiment, Vahl et al. (1993) fed layers with diets ranging from 1.8 g/kg to 3.6 g/kg available phosphorus. Birds fed the 1.8 g/kg available phosphorus diet had significantly lower egg production, lower body weights and increased mortality; but when this level of available phosphorus was supplemented with 300 FTU/kg feed, egg production, body weights and mortality were not significantly different from the birds eating the diets with higher levels of available phosphorus.

van der Klis and Versteegh (1991) and van der Klis et al. (1997), reported that breakdown of phytate by phytase is significantly decreased in diets with higher calcium levels. They compared diets containing 3 or 4% calcium and reported that phytate breakdown by phytase decreased from 34 to 10%, respectively. They also reported that there was a significantly lower intestinal absorption of phosphorus in birds consuming the 4% calcium diet.

To date, no reports in the literature have been found comparing different sources of calcium in combination with phytase enzymes. This paper reports on the use of limestone (LS) versus LS plus oyster shell (OS) in combination with phytase and reduced inorganic phosphorus.


MATERIALS AND METHODS

Fourteen hundred and forty Dekalb Delta laying hens were divided into six experimental groups of 240 hens. The birds were housed in Choretime stair step cages with five birds per cage, 12 cages per tier on four tiers. Each tier was considered a replication. They were housed at 18 weeks of age and given stimulatory lighting at that time. All birds were fed a commercial layer diet until peak production at 32 weeks of age at which time the experimental diets were introduced. The six diets were as follows:

1. Control diet 1 – NRC requirements with all Ca from LS.
2. Control diet 2 – NRC requirements with half of Ca from LS and half of Ca from OS.
3. 80% of available phosphorus of control diet with 1 kg Allzyme Phytase per ton of feed, Ca source = all LS.
4. 80% of available phosphorus of control diet with 1 kg Allzyme Phytase per ton of feed, Ca source = half LS + half OS.
5. 60% of available phosphorus of control diet with 1 kg Allzyme Phytase per ton of feed, Ca source = all LS.
6. 60% of available phosphorus of control diet with 1 kg Allzyme Phytase per ton of feed, Ca source = half LS + half OS.

Egg production was recorded daily. One day each week, one flat of 30 eggs was collected from each replicate tier (720 eggs total each week) and tested for specific gravity. Seven specific gravity solutions from 1.060 to 1.090 (increasing in 0.005 increments) were used. Eggs which did not float in 1.090 were assigned a value of 1.095 for statistical analysis. The trial lasted 48 weeks. Manure samples were collected from each of the six treatment groups during the experiment and analyzed for phosphorus content. At the end of the experimental trial, 10 birds from each treatment were killed and a tibia from each bird was harvested. Each tibia was gently scraped clean, weighed, extracted to remove the lipids and ashed to determine mineral content.


RESULTS AND DISCUSSION

EGG PRODUCTION

Neither total eggs nor average weekly egg production was affected by treatment (Table 1). This is in agreement with Simons and Versteegh (1992, 1993) andVahl et al. (1993) who reported that egg production in phosphorus deficient diets supplemented with phytase was not significantly different from phosphorus deficient diets supplemented with monocalcium phosphate. This also agrees with Lynch (1996) who reduced available phosphorus approximately 25% with 300 FTU added to the feed and reported no difference in performance or egg shell quality.

At week 34 of the trial, there was a noticeable drop in production in the Treatment 1 group after a new delivery of feed was received. The old feed was replaced as soon as it was noticed and a sample sent to the state lab for analysis. The analysis indicated that nothing was different from calculated nutrient values of the diet. The feed was not tested for mycotoxins. The decreased egg production lasted about 6 weeks and then returned to a level comparable to the other diets. If these 6 weeks are removed from the statistical analysis for all treatments, there are still no differences in production.


EGG SPECIFIC GRAVITY

Egg specific gravity means on Diets 2, 4 and 6, all of which contained OS, were not significantly different from each other, but were significantly higher than values for diets containing only LS as a calcium source (Figure 1). It is tempting to speculate about synergism between phytase inclusion and OS, but further work needs to be done.

Comparison of egg specific gravity in groups given Diets 4 and 6 with that in Diet 2 would indicate that egg shell quality is not affected when inorganic phosphorus is removed from the diet and Allzyme Phytase is added. Among diets containing only LS, Treatment 1 (control) and Treatment 5 (40% reduction of available phosphorus with phytase added) were not significantly different. Again, this indicates that egg shell quality is not affected when inorganic phosphorus is removed from the diet and Allzyme Phytase is added. Both of these Treatments (1 and 5) were significantly better than Treatment 3 (no phytase). I have no explanation for why this may have occurred. The observations that diets containing calcium from OS were better than diets containing only LS as a calcium source is in general agreement with much of the past OS research (Scott et al., 1971; Kuhl et al., 1977; Roland 1986a,b).


FECAL PHOSPHORUS CONTENT

Diets 3 and 4 which contained 20% less available phosphorus than control feed produced a 16% reduction in fecal phosphorus when fecal phosphorus content was averaged and compared to the average of the controls (Table 2).

Table 1. Effect of dietary available phosphorus, calcium source and Allzyme Phytase on total weekly egg production.




* Relative to NRC.





Figure 1. Effect of dietary available phosphorus, calcium source and Allzyme Phytase on mean egg specific gravity for 48 weeks of production (AP, available phosphorus relative to NRC (1994); LS, limestone; OS, oyster shell; Standard errors Diets 1 and 2, 0.000067; Diets 3-6, 0.000066).


Birds consuming Diets 5 and 6 (40% less available phosphorus than the control) produced a 25% reduction in fecal phosphorus compared to controls. Again, these results are similar to those reported by Simons and Versteegh (1992) in layers, Simons et al. (1990) and Yi et al. (1996) in broilers, Balander and Flegal (1996) in turkeys and Simons et al. (1990) in pigs. All of these studies indicated that phytase added to diets with lower phosphorus can increase phosphorus retention thus lessening excretion and the environmental burden of the manure.

Table 2. Effect of dietary available phosphorus, calcium source and Allzyme Phytase on phosphorus concentration in dry chicken manure.


* Relative to NRC.
† Relative to controls.




Figure 2. Effect of dietary available phosphorus, calcium source and Allzyme Phytase on average fat free tibial ash content (AP, available phosphorus relative to NRC (1994); LS, limestone; OS, oyster shell).



TIBIAL BONE ASH

There were no significant differences among any of the treatments in average percentage of tibial fat free bone ash (Figure 2). Similar results were reported in layers by Simons andVersteegh (1992, 1993) when tibial ash values from phytase-supplemented or monocalcium phosphate-supplemented diets were compared. van der Klis et al. (1997) also reported that tibial ash content of phytase-supplemented diets was not different than when monocalcium phosphate-supplemented diets were fed; but both groups had significantly higher tibial ash content than the birds on a basal diet containing only 0.13% available phosphorus.


CONCLUSIONS

1. Egg production was not significantly different between any of the six dietary treatments.

2. Egg specific gravity was significantly better when birds were fed diets containing OS as either all or part of the calcium source compared to those receiving only calcium from LS.

3. Fecal phosphorus can be significantly reduced without affecting production or egg shell quality by the use of Allzyme Phytase and lowered phosphorus diets.

4. Allzyme Phytase can be substituted for phosphorus in laying diets without affecting production or shell quality.


REFERENCES

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Ferket, P.R. 1996. Enzymes offer way to reduce waste, improve performance. Feedstuffs, Jan 22 issue, pp. 30–34.

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11/22/2007

Amatzia Eyal Livestock Nutritionist Israel - Israel

Hello. It is a half work you have to give the control diet. The row material and the analysis. To say that the diet according to the NRC do not mean anything. Please send me the control diet and I wiil see if it is like to the Israeli poultry feed, especially to calcium and phosphorus sources. Thank you in advance. Amatzia Eyal Livestock nutritionist Answer Checked by Engormix.com