Hello, this is Charmaine Espinosa, and I will be discussing recent results that we have generated from an experiment to determine effects of a novel phytase variant on nutrient digestibility in diets fed to young pigs. 

A traditional US swine diet mainly consists of corn and soybean meal, and these feed ingredients contain phytate, which consists of 6 phosphate molecules bound to a myo-inositol ring. Pig diets may also include feed ingredients such as canola meal and rice bran due to availability of these feed ingredients to some areas. And if we take a look at the phytic acid profile of these ingredients, corn and soybean meal contain 0.5-1.7% phytate and these concentrations are less compared with canola meal and rice bran. Therefore, if we include a significant portion of these feed ingredients in the diet, it is expected that the concentration of phytate will increase in the diets. With that in mind, we wanted to determine if supplementation of high doses of phytase is needed to reduce the negative impact of high concentration of phytate in the diets.

Therefore, the use of microbial phytase in diets for pigs is a common standard practice to increase digestibility and availability of minerals from plant feed ingredients. Microbial phytase is pretty successful and well-established in hydrolyzing those ester bonds between Phosphorus and the inositol ring in phytate. But in terms of amino acid digestibility, this has not been the case. Unlike in broiler experiments where it was demonstrated that phytase increased amino acid digestibility, the effect of phytase on amino acid digestibility in pig diets is not consistent- and this may attributed to differences in phytase source and inclusion rate of phytase in diets.

With that in mind, a next generation bacterial 6-phytase has been developed and it is believed to increase Phosphorus availability in diets for pigs. Indeed, in an experiment we conducted last year, we demonstrated that this novel phytase increased mineral digestibility and bone ash of pigs. We also compared this novel phytase with a different phytase source, and results from this study indicated that the novel phytase increased Phosphorus digestibility more than the Buttiauxella phytase. However, there are still limited data to demonstrate the efficacy of this phytase on nutrient digestibility.

Therefore, an experiment was conducted to test the hypothesis that inclusion of increasing levels of the novel phytase in diets for growing pigs increases the apparent ileal digestibility (AID) of minerals, crude protein, and Amino acids. We also wanted to test the hypothesis that the apparent total tract digestibility (ATTD) of Gross Energy and minerals is increased upon inclusion of increasing levels of the novel phytase.

In this experiment, we prepared 6 diets. First a negative control diet was formulated based on corn, soybean meal, and canola meal to contain 0.28% phytate-bound Phosphorus in the diet. This negative control diet was also formulated to be deficient in total Calcium by 0.15%, standardized total tract digestible Phosphorus by 0.16%, and in standardized ileal digestible amino acids by approximately 0.02%. Five additional diets were then formulated by adding 250, 500, 1,000, 2,000, or 4,000 FTU/kg of the novel consensus bacterial 6-phytase, and therefore, we have 6 levels of phytase in this experiment.

Eighteen pigs (initial body weight: 17 kg) were equipped with a T-cannula in the distal ileum. Pigs were allotted to a 6 × 3 incomplete Latin square design with six diets and three 11-day periods. There were three pigs per diet in each period; therefore, there were nine replicate pigs per diet.

The initial 5 d of each period were considered an adaptation period to the diet. For each period, fecal samples were collected on day 6, 7, 8, and 9, whereas ileal digesta were collected on days 10 and 11. These samples were then processed for nutrient analysis for us to be able to determine apparent ileal digestibility of Crude protein, Amino acids, and minerals and also apparent total tract digestibility of Gross energy and minerals. 

Moving on with the results of this experiment, this slide shows the apparent ileal digestibility of Calcium and Phosphorus in experimental diets. Just to briefly set up the slide- here in the y-axis we have our response paramenter and in the x-axis we have our 6 dietary treatments representing the increasing levels of phytase. Blue bars are for Calcium whereas orange is for Phosphorus. And we can observe that inclusion of increasing levels of microbial phytase quadratically increased the Apparent ileal digestibility of Calcium and Phosphorus in diets. Formation of phytate complexes reduces the solubility and digestibility of these minerals, and therefore, the observed increase in mineral digestibility indicates that the novel bacterial phytase was able to hydrolyze the Calcium-phytate complexes, as well as some of the ester bonds between Phosphorus and the inositol ring of phytate.

We can also observe here a quadratic increase in the digestibility of crude protein with increasing levels of the novel phytase in experimental diets. Protein-phytate complexes may occur due to electrostatic interactions between the negatively charged inositol phosphate isomers and positively charged groups of protein, therefore, the increased concentration of phytate in diets due to inclusion of canola meal, which consequently increased phytate:protein ratio, likely increased the positive influence of phytase on protein digestibility. 

And if we dive deeper and take a closer look on amino acid digestibility, where lighter to darker bars represent the increasing levels of phytase, we demonstrated that there is a quadratic increase in amino acid digestibility, for Lys, Met, Thr, and Trp- as inclusion rate of phytase increase in the diets. This is something we do not usually observe with all our phytase experiments but with the current study we used relatively younger pigs and therefore it’s possible that the impact of phytase on amino acid digestibility is greater in younger pigs than in older pigs, but further experiments are still needed to investigate if body weight of pigs influences how phytase affects digestibility of Amino Acids.

This graph shows the apparent total tract digestibility of calcium and Phosphorus in experimental diets and here we can also observe a quadratic increase in the digestibility of these minerals which also validates the results that we have generated for the apparent ileal digestibility of calcium and Phosphorus. 

We have also determined the effect of the novel phytase on energy digestibility, and here, we can observe that increasing levels of phytase linearly increased the apparent total tract digestibility of gross energy. Phytate may negatively influence starch digestibility by inhibiting activity of digestive enzymes and by chelating Calcium that is required for amylase activity. Therefore, we hypothesized that the observed increase in digestibility of Gross energy upon phytase supplementation is likely due to increased degradation of phytate, which consequently increased starch and energy digestibility.

In summary, we have demonstrated that the novel phytase increased apparent ileal digestibility of amino acids and minerals. We have also demonstrated in this experiment that the novel phytase increased apparent total tract digestibility of gross energy and minerals. And these results are likely due to the ability of phytase to hydrolyze phosphate groups from phytate, reduce the anti-nutritional effect of phytate, and consequently increase energy and nutrient digestibility.

Based on the results we generated from this experiment in comparison with the inconsistent effect of phytase on amino acid digestibility, we likely need to revisit and take a closer look on some factors that may influence the effect of phytase on nutrient digestibility. It is possible that the impact of phytase on amino acid digestibility is dependent on composition and nutrient levels in our diets. Concentration of phytate and phytase may also play a huge role, and it’s also possible that pig maturity can influence the effect of phytase on digestibility and therefore further research is needed to investigate if and how these factors influence phytase efficiency on amino acid digestibility.

With that, we would like to acknowledge IFF for their valuable inputs and financial support.
Thank you for your interest in this presentation, and if you would like to know more topics about pig nutrition, you can always visit our website at nutrition.ansci.illinois.edu.