Role Of Dietary Factors On Nutrient Excretion And Manure Characteristics Of Growing Pigs

Abstract

In the U.S. pork industry, feed represents the largest proportion of the total production cost. Therefore, pork producers are continually trying to improve feed efficiency and reduce feed cost. This has become more important because the prices of conventional feed ingredients, including corn and soybean meal, has increased dramatically in recent years. As a result, the addition of increased amount of high fiber ingredients such as corn distillers dried grains with solubles (DDGS) and soybean hulls (SBH) to swine diets, and processing diets to achieve a smaller particle size have become common practices. However, manure foam accumulation on the surface of anaerobic deep pits on commercial swine farms has been a coincidental problem in recent years, and the potential cause has been associated with changes in diet composition. As a result, a better understanding of the connection between swine diet composition and nutrient excretion and manure foaming is critical for developing long-term mitigation strategies. Based on the theory of “froth flotation”, foam formation requires 3 contributing factors, including biogas production, surfactants, and stabilizers, which may come from undigested nutrients in the manure. Results from studies have suggested that specific undigested nutrients in the manure may serve as surfactants (lipids and long-chain fatty acids; LCFAs) and stabilizers (small particles) as well as substrates to produce biogas (fiber and protein) in foam formation. This evidence suggest that adding DDGS and SBH in swine diets may increase overall manure output due to higher levels of indigestible fiber, resulting in more dry matter (DM) and nutrients in manure. In addition, smaller particle size of diets may result in a greater concentration of stabilizers in the manure. As a result, methods to maximize feed digestibility and minimize nutrient excretion appear to be essential for reducing manure pit foaming. The research described in this thesis addressed the effects of feeding alternative feed ingredients (DDGS with variable oil content and SBH) with different particle size on nutrient excretion and manure characteristics of growing pigs. Results in Chapter 2 suggested that manure foaming capability (MFC) was impacted by diet particle size and fiber source. Greater MFC were only observed for pigs fed coarsely ground SBH diet. The relatively high concentration of soluble fiber in the soybean hulls diet compared with DDGS, which contains a high concentration of insoluble fiber, appears to have a greater effect on MFC. In addition, increased DM excretion and changes in manure pH resulting from diet composition were 2 significant factors that contributed to MFC. Results in Chapter 3 suggested that manure foaming does not occur when evaluating fresh manure samples, indicating that microbial fermentation is essential for manure foam formation. Further studies are encouraged to compare the microbial ecology between samples of foaming manure and non-foaming manure. In conclusion, when diets are coarsely ground, manure from pigs fed diets containing significant amounts of soluble fiber source tend to have greater MFC after fermentation. These results suggest that diet formulation strategies to maximize DM digestibility and reduce DM excretion by reducing diet particle size, along with minimizing the amount coarsely ground SBH in diets will decrease manure foaming incidence in anaerobic manure pits.