The use of enzymes in poultry rations has increased significantly in the last 20 years.
For example, virtually no enzymes were used in broiler diets in the U.K. in 1988, while current usage exceeds 90%, according to Dr. Mark E. Jackson of Continental Grain Co. Jackson, in a paper published in the proceedings from the 1999 Midwest Poultry Federation Convention, said a similar trend exists in the rest of Europe, Asia and Canada.
However, with the exception of phytase, enzymes are rarely used in U.S. poultry diets, he said, with the main reason being that diets in the U.S. are typically corn-soybean meal-based, which is relatively well utilized by poultry. However, Jackson said, several commercial products have been introduced to the marketplace for layer diets.
The nutritional value of corn may sometimes be lower than estimated, he said, which may also be shown in the variance of bird performance for unexplainable reasons. He said starch digestibility, lysine digestibility and metabolizable energy (ME) can all vary in corn and influence bird performance.
Soybean meal can also vary in quality, he said, despite processing, which is intended to minimize antinutritional factors such as trypsin inhibitors, [TABULAR DATA FOR TABLE 1 OMITTED] [TABULAR DATA FOR TABLE 2 OMITTED] [TABULAR DATA FOR TABLE 3 OMITTED] [TABULAR DATA FOR TABLE 4 OMITTED] [TABULAR DATA FOR TABLE 5 OMITTED] lectins and pectins. Processing does not affect B-mannan levels, he said, which are known to be antinutritive at high concentrations.
Enzymes are designed to overcome antinutritional factors, said Jackson, and have the potential to improve animal performance. However, their efficacy is dependent on the concentration of antinutritional factors, the bird's sensitivity to the factors and the animal's health status.
Despite such problems with corn and soybean meal, digestibility and utilization of key nutrients in the ingredients is greater than wheat and barley, he said, which translates to a 'less dramatic' improvement in performance for enzyme supplementation in corn/soybean meal diets.
Many enzyme studies focus on broilers, although there are advantages of using enzymes in laying hens, such as layer diets not being pelleted, so post-pelleted application systems are not necessary and heat destruction of enzymes is not a concern, said Jackson. Nitrogen and phosphorus pollution resulting from manure produced by laying hens is usually of greater concern due to its greater concentration and volume produced on one site, he said.
To examine the effects of enzymes on layers, Continental Grain performed several studies, with products that demonstrated a response in broiler chicks being used for laying hen research. For the broiler chick studies, two identical trials were conducted to 21 days of age by adding enzyme products to a corn-soybean meal diet that contained 2,890 kcal/kg ME and 95% of National Research Council (NRC) recommended levels of amino acids.
In the first experiment, all enzyme treatments exceeded controls in terms of growth, three of which were statistically significant (Table 1), said Jackson. Feed intake was unaffected and feed conversion improved 2-6 points. In the second experiment, growth was not affected by enzymes, but feed consumption was lower with all products and significantly lower with two.
Jackson said these experiments demonstrate that enzyme products improve performance of broiler chicks, either by stimulating growth or reducing appetite. 'It is interesting that the enzymes behaved differently in the two experiments,' he said.
A second chick trial was conducted to determine if two enzyme products behaved in an additive manner and if they were more effective under marginal circumstances with respect to energy and amino acids.
When added to a 'marginal' basal diet, the enzyme mixture yielded a nonsignificant 8 g increase in growth, but the B-mannanase enzyme resulted in a 22 g increase in growth, although it also was not significant (Table 2). With both enzyme products, growth increased 46 g with the marginal diet, which suggests the products may be functioning synergistically, said Jackson.
When added to the control diet, however, the enzyme products increased gain and decreased intake slightly and non-significantly.
A third trial was conducted with approximately 6,144 laying hens from 18 to 66 weeks of age in order to examine the effects of B-mannanase supplementation. Two energy levels were used in the diets, with other nutrients being maintained at commercial levels but changed as birds changed stages of production. Jackson said the energy levels were intended to represent high and low averages by industry standards with a difference of about 95 kcal/kg.
According to Jackson, and shown in Table 3, B-mannanase significantly increased egg weight in the peak period with the high energy regime and increased egg production during the three subsequent periods with both energy regimes. He said this is 'very meaningful' to egg producers with young flocks where egg size is an important factor in affecting egg revenue.
Another study was performed to judge the effect of three corn-soybean meal enzyme products on post-molted laying hen production. Birds used in the laying hen trial were molted and used in this experiment. Two basal diets were then made with commercial levels of all essential nutrients except energy. The control diets contained ME levels close to what industry uses, while marginal levels were about 100 kcal/kg lower.
Jackson said all three enzymes in this test increased egg production, although the difference was significant only with product C (Table 4). Product B increased egg weight, with the greatest effect occurring with the marginal diets. He said this product, B-mannanase, increased egg weight in the previous trial as well.
There was also an energy x enzyme interaction for feed consumption, he said, and the enzyme products seemed to stimulate feed consumption only with the marginal energy diets. Product C resulted in the greatest feed consumption and egg production, he said.
These experiments examined enzymes at various energy densities. Jackson said a major function of corn-soybean meal enzymes is assumed to be that of increasing the energy available to the bird.
Results from the molted layer trial tend to support this, he said, since the response was much greater with marginal diets. When considering data from the first cycle layer trial, it seems there may be more involved in enzyme function than energy since production was increased with the enzyme both in the high and low energy diets. To examine this further, another thai was conducted to see if amino acid availability and/or utilization may be influenced by enzymes.
This final trial was conducted with two commercial strains of layers and four amino acid densities, Jackson said. Amino acid levels were designed to be at 80, 90, 100 and 110% of commercial levels.
He said this translates to 0.70, 0.78, 0.87 and 0.96% for lysine. The levels of other nutrients were held constant across diets and were intended to represent commercial levels, but on the high side to minimize the likelihood of deficiencies that the enzyme may overcome, Jackson said. ME was maintained at 2,910 kcal/kg for the trial.
An egg production response was observed at the lower amino acid densities, but only with the Hyline W36 strain (Table 5), said Jackson. In addition, he said, egg weight was negatively impacted by the enzyme at the lower amino acid levels but only with the B300 strain. These results are in contrast to the earlier experiments, where egg weight was increased, he said.
Overall, Jackson said the three laying studies yielded differing, but 'generally positive' results with respect to bird performance.
In one study, he said, production increased regardless of the energy content of the diet, while in another study, production increased only with low-energy diets. He said this variability suggests that the mechanism is more complex than simply an increase in energy available to the bird.
Trials that utilized diets marginal in amino acids had the largest response to enzyme addition, he said, which suggests there may have been an increased amino acid utilization. The ability to increase egg size may also be of interest, he said.
Jackson said responses in terms of egg production, egg size and feed consumption need to be integrated with the strains used, stage of production, ingredient costs and the value of eggs in different size categories to determine the economic potential of using enzyme products in a layer operation.
