Hello, everyone. Today, I will talk about the digestibility of energy and dietary fiber by growing pigs in corn- or sorghum-based diets without or with microbial enzymes.

First of all, I would like to start with some background to remind you that pigs do not secrete enzymes that can digest dietary fiber. And because of that, diets composed with high fiber reduce the total tract digestibility of nutrients and energy. And to increase the digestibility of nutrients, enzyme is needed to ferment fiber. So the enzymes work hydrolyzing fiber and, as a result, increase the utilization of carbohydrate and may also increase the digestibility of fat.

However, to maximize the utilization of enzymes, the enzymes need to match with the substrate. It's already known that the three non-starch polysaccharides present in the cereal grains are cellulose, arabinoxylans, and mixed-linked beta glucans. But if we take a look in this graph, we observe that cellulose and arabinoxylans are the most common fiber content in corn, sorghum, and wheat. And so, to increase the fermentation of those fibers, cellulase and xylanase have to be included to the diets.

Studies have shown that xylanase supplementation increased the digestibility of dietary fiber in wheat-based diets but not in corn-based diets. And this improvement on the digestibility increased the concentration of digestible energy in wheat diets. This indicates that there are differences in the digestibility of dietary fiber fractions among ingredients. And therefore, the results indicate that degradation of dietary fiber varies with structure among ingredients.

However, there had been no study conducted determining the effects of xylanase and cellulase on the digestibility of fiber and energy in corn versus fiber in sorghum. And therefore, the objective of this experiment was to test the hypothesis that the xylanase and cellulase increase the apparent total tract digestibility of gross energy and total dietary fiber and also increase the metabolizable energy in corn-based diets or sorghum-based diets with high fiber included in those diets.

Moving on to the material and methods, a corn-based diet was formulated composed of 63.8% corn and 33% of soybean meal. In order to increase the fiber concentration in the diet, a second diet was formulated included 40% of DDGS, and third diet included 40% of wheat middlings. The fourth diet was a sorghum-based diet composed of 63.7% of sorghum and 33% of soybean meal. And again, to increase the fiber concentration to the diet, the fifth diet included 40 percent of DDGS in sorghum diets, and a sixth diet was formulated included 40 percent of wheat middlings to the sorghum diets. Six more diets were formulated as the same as the previous with the exception that the enzyme premix was included to those diets. And therefore, we had 12 diets in this experiment.

A total of 144 barrows with an initial body weight of 61.7 kg were allotted to a randomized completed block design with 12 diets and 12 pigs per diet. Diets were fed to pigs for 24 days. The first 12 days was considered adaptation period to the diets, and day 13 to 16 was considered adaptation to the metabolism crates. And on day 17 to 22 was a fecal and urine collection.

The statistical model included grain source, byproduct, and enzymes and also interactions between two sources of grain and three levels of byproduct and two levels of enzymes.

Moving on to the results...

To set up the slides, the vertical axis represents the percentage digestibility and the horizontal axis represents the digestibility of each diet. Blue bars represent diets containing no enzymes and orange bar represents diet containing enzyme. So here we have the results for apparent total tract digestibility of total dietary fiber in the diets. And as we expected, the digestibility of fiber decreased as we included byproduct to the diets, regardless of the grain source. However, there was an interaction between grain source and byproduct, meaning that the reduction was greater if the byproduct was included to the sorghum than if the byproduct was included through the corn-based diet. But in terms of enzymes, the ATTD of fiber did not change if enzymes were included to the diets.

So, in the other hand, the supplementation of enzyme improved the apparent total tract digestibility of gross energy in all diets regardless of the source of grain. And there was also an interaction between grain source and byproduct, meaning that the apparent total tract digestibility of gross energy reduced if byproduct was added to the diets; however, the reduction was greater if byproduct was added to the corn-based diets than if added to the sorghum-based diets.

Now in terms of metabolizable energy, diets formulated with sorghum had a greater concentration of metabolizable energy on a dry matter basis than diets formulated with corn. And these results may be explained that sorghum has a greater concentration of crude protein, gross energy, and fat. And also, the total dietary fiber in sorghum may be more fermentable than in total dietary fiber in corn. The concentration of metabolizable energy decreased in all diets as the byproduct was included. There was also an improvement in metabolizable energy in all diets if enzymes were added to the diets, indicating that the enzymes were efficient to ferment fiber and the energy in the diets becomes more digestible. But also, the enzymes can work increasing the release of low molecular weight oligosaccharides and improve the gut health, and as a benefit increase the nutrient utilization.

Based on these results, we can conclude that the enzymes xylanase and cellulase increase the apparent total tract digestibility of gross energy and metabolizable energy in all diets regardless of grain source and fiber concentration. However, we did not observe an improvement on apparent total tract digestibility of dietary fiber.

The implication of that is addition of xylanase and cellulase may improve the nutrient utilization. Also, the concentration of metabolizable energy may be maximized if enzymes are added to the diets.

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