2011 Annual Report
1a.Objectives (from AD-416)
The goal of the project is to develop a comprehensive understanding of the interrelationships between nutrient inputs in livestock production systems, as derived from agricultural and industrial byproducts, and the impact on nutrient utilization, animal health, gastrointestinal ecology, and pathogen shedding in an effort to minimize environmental impact, accomplished through the four interlinked objectives as outlined and depicted below:
1. Manipulate swine dietary ingredients to improve nutrient utilization and reduce nutrient excretion and the emission of gasses into the environment.
2. Quantify and modify swine gastrointestinal microflora to improve nutrient utilization and reduce the emission of gasses into the environment.
3. Quantify the impact of swine dietary regimens on nutrient metabolism and immune function of the gastrointestinal tract and the whole animal in order to assess the potential tradeoffs between environmental concerns and production.
4. Exploit genetically-mediated mechanisms involved in Salmonella colonization of the swine gastrointestinal tract to reduce subsequent shedding into manure.
1b.Approach (from AD-416)
The impact of dietary ingredients on nutrient utilization in the pig and subsequent nutrient excretion and emission of gasses into the environment will be assessed through altering the source and level of dietary protein and carbohydrate. The protein level will be adjusted relative to the level of soybean meal and amino acid supplementation utilized in diet formulation, while the protein source factor will be accomplished by replacing soybean meal with either canola meal, corn gluten meal, or poultry meal. The source and level of complex carbohydrate will be accomplished by utilizing barley, beet pulp, distillers dried grains with solubles, soybean hulls, and wheat bran as a partial replacement of soybean meal. Nutrient retention, excretion, and gas emissions will be accomplished using animal metabolism trials and the employment of a manure storage system currently in place at the lab. Microbial ecology of the large intestine (via fresh feces) and manure, as affected by the source and level of protein and carbohydrate, will be assessed by classical and molecular methods currently employed at the Unit, using the same pigs and diets as described above. The impact of dietary regimens on nutrient metabolism and immune function will be accomplished by utilizing similarly formulated diets as above, but on a separate group of pigs, with assessment of systemic and intestinal immune system function using techniques currently being utilized within the Unit. Lastly, reduction of Salmonella colonization of the swine gastrointestinal tract for subsequent reduction of shedding into the environment will be accomplished by administration of a chemical compound to disrupt pathogen sensing, vaccination using an attenuated S. Typhimurium strain, and manipulation of crude protein levels in the diet (as described above).
Scheduling of pigs at the Iowa State University Swine Nutrition Farm has become more difficult with the addition of four new faculty members at Iowa State University. Because the Unit does not have its own animal facility or control the Iowa State University swine research facilities, we must fit into the animal flow at this farm. Also, because of additional research being conducted at this farm, we were not able to obtain pigs from which to conduct the project relative to Objectives 1, 2, and 3. We are currently scheduling pigs for 2012 and should be able to conduct the research as planned.
Swine can carry the foodborne pathogen Salmonella in their gastrointestinal tract without becoming sick. Stress, including pig mixing and transport, can increase the amount of Salmonella in the feces of pigs that carry Salmonella. The increased shedding of Salmonella in swine feces is a health risk for other pigs and a food safety risk for consumers following consumption of Salmonella-tainted pork. During stress, the concentration of the hormone norepinephrine is increased in swine. We have previously shown that Salmonella enterica serovar Typhimurium can respond to the host stress hormone norepinephrine by increasing bacterial motility. This norepinephrine-enhanced motility by Salmonella can be prevented by using the alpha-adrenergic antagonist phentolamine. We are currently evaluating whether administration of phentolamine can reduce or prevent Salmonella colonization in the swine gastrointestinal tract by feeding pigs phentolamine before, during and after exposure to Salmonella Typhimurium. If phentolamine has a significant effect on clinical parameters or Salmonella colonization of the swine gastrointestinal tract, we will have identified a potential strategy for Salmonella intervention. That is, if norepinephrine produced by the pig during stress is a signal for Salmonella to emerge from its carrier status, the use of hormone antagonists by swine producers prior to transport may reduce Salmonella shedding incidence. This research is not currently being utilized by the livestock industry, but is being used by research scientists to refine intervention strategies.
Pigs selected for increased feed efficiency have improved indicators of immune function. Improving feed efficiency decreases the cost of livestock production and frees up the use of commodities for other uses, thereby improving global food security. It has long been known that decreasing the microbial burden in swine improves animal growth performance, but little information regarding biological mechanisms and genetic factors regulating host-microbial interactions in swine is available. Agricultural Research Service researchers, in Ames, Iowa, in collaboration with faculty at Iowa State University, where one of only two genetic populations of swine selected for feed efficiency in the world are located, discovered that pigs selected for improved feed efficiency have reduced serum bacterial cell wall components, decreased indicators of intestinal inflammation, and improved gastrointestinal defense function. Also, these pigs demonstrated increased activity of antimicrobial defense systems. This will serve as a valuable model from which to characterize how host-microbial interactions regulate the efficiency of growth and nutrient utilization in swine.
Identification of bacterial enzymes that breakdown plant cell wall carbohydrates. Two Bacteroides isolates were investigated for their ability to breakdown plant cell wall carbohydrates. Agricultural Research Service researchers in Ames, Iowa, in partnership with other investigators, identified proteins that were increased or decreased when each bacterium was grown on either cellulose or xylan compared to growth on glucose. Changes in the physical structure of the carbohydrates as well as production of fermentation products (glucose and other sugars and short chain fatty acids) were determined. Over 1,200 additional bacteria have been isolated from plant cell wall carbohydrate enrichments of cow and goat fecal bacteria. Initial results indicate that the bacteria isolated from the cows and goats are closely related to those previously isolated from pigs and humans. These results will impact animal production by elucidating how bacteria in the large intestine supply energy to the animal through breakdown of plant cell wall carbohydrates, thereby increasing the efficiency of the animal fed dietary ingredients with high fiber concentrations.
Design and use of a Salmonella vaccine strain to reduce Salmonella presence and disease in swine. The foodborne pathogen Salmonella is a leading cause of food-related disease and death in the U.S. Salmonella are often present in the gastrointestinal tracts of both wild and domesticated animals. For example, Salmonella can be isolated from over 50% of swine production facilities. However, pigs that have Salmonella usually do not show clinical disease, but because they carry the bacteria in their gastrointestinal tracts, they are a potential food safety risk for pork consumers. Agricultural Research Service researchers in Ames, Iowa, designed and evaluated a Salmonella vaccine strain in swine to determine if vaccinated pigs would have reduced disease severity and gastrointestinal colonization upon exposure to a pathogenic Salmonella strain. Disease severity, Salmonella shedding in the swine feces, and Salmonella gastrointestinal colonization were significantly reduced in the vaccinated pigs compared to the non-vaccinated pigs. This Salmonella vaccine is a promising intervention for the reduction of Salmonella in swine, resulting in enhanced pork safety and decrease potential risks for the consumer.
Schieck, S.J., Johnston, L.J., Kerr, B.J., Baidoo, S.K., Shurson, G.C. 2010. Use of Crude Glycerol, a Biodiesel Co-product, in Diets for Lactating Sows. Journal of Animal Science. 88:2648-2656.
Gaines, A.M., Kendall, D.C., Allee, G.L., Usry, J.L., Kerr, B.J. 2011. Estimation of the standardized ileal digestible valine to lysine ratio in 13- to 32-kilogram pigs. Journal of Animal Science. 89:736-742.