Nutrition can help reduce the impact of pork production on the environment and improve pig gut health. The formulation of diets based on highly-digestible feedstuffs and which meet the exact requirements of the pigs, markedly reduces the excretion of minerals such as nitrogen and phosphorus into the environment. The presence of fermentable dietary fiber in the diet can also decrease the emission of gaseous nitrogenous compounds by shifting nitrogen excretion from urine to feces. It is also hypothesized that fermentable dietary fiber can improve gut health by favoring the development of health-promoting bacteria such as Lactobacilli, at the expense of pathogenic ones.
The overall objective of the project was to evaluate alternative feedstuffs for their potential impact on the character of the manure excreted, on the formation of odor-causing compounds and on the gut health of the pig. More specifically, it aimed at screening a series of feedstuffs for their ability to enhance colonic fermentation and thus reduce the emission of ammonia and other odor-causing compounds and improve the gut health of the pig by favoring the development of a beneficial microflora at the expense of a pathogenic one. The evaluation was performed in the lab (in vitro) and directly on pigs (in vivo).
The first experiment focused on gut health. In particular, we wanted to see if it was possible to take advantage of the variation in carbohydrate composition of a specific ingredient in order to improve the pig gut health. Barley was used as a model for two reasons. First, it is widely used in swine nutrition. Second, its carbohydrate composition is extremely variable. It has, for example, hulled and hulless varieties. The latter have very variable contents in soluble dietary fiber (called β-glucans) and starch composition. Oats were used as a reference. The rate of fiber fermentation in the intestines was first studied by means of a lab technique. The results demonstrated that hulless barleys provided the highest rates of fiber fermentation, especially in the colon. An experiment carried out on pigs confirmed that the fermentation of the soluble fiber in the gut led to an increased production of lactic acid, to a lower pH value in the colon (which means a more acidic content) and to a modification of the microbial diversity and of composition of the intestinal bacteria. As a consequence, noxious bacteria such as Enterobacteria and Streptococci were not detected, by molecular techniques, in the small intestine of pigs fed with the hulless barleys having the highest β-glucan contents. This important finding shows that prebiotic effects (i.e. development of health-promoting bacteria in the gut by adding favorable substrates in the diet) can be obtained by a judicious selection of feed ingredients rather than by the addition of antibiotics, of probiotics (living bacteria) or of prebiotics (purified carbohydrates used by bacteria as a substrate). In other terms, it is possible to improve the pig gut health through feed formulation and not only with additives.
The second experiment was designed to compare the effect of non-conventional feed ingredients differing in their dietary fiber and protein content on nitrogen excretion in pigs. The feedstuffs included wheat bran, cellulose, peas, pea inner fiber, pea hull fiber, sugarbeet pulp, flaxseed meal and corn Distiller’s Dried Grains with Solubles (DDGS). Pigs were fed with diets based on these ingredients and the content of their small and large intestines was analyzed for fiber fermentation and the metabolites produced, namely odorous compounds such as ammonia and butyric acid. The results show that diets equally balanced in digestible energy and N content produce very different levels of N excretion, fermentation metabolites, depending on the dietary fiber nature. The sources of dietary fiber thus have a major incidence on nitrogen excretion and the emission of malodorous compounds.
Finally, the economic impact of the incorporation of sources of fermentable dietary fibers for the reduction of ammonia emission in the environment was evaluated. Based on the current feed costs and the properties of some dietary fiber sources, it can be concluded that a reduction in the level of crude protein in the diet is more efficient than the use of fiber sources, with the possible exception of citrus pulp, which has a good nutritional value, is cheap and has demonstrated interesting properties for the reduction in ammonia emission.
