Harris, Erin Kay2015-04-092015-04-092014-12https://hdl.handle.net/11299/171125University of Minnesota Ph.D. dissertation. December 2014. Major: Animal Sciences. Advisor: Gerald C. Shurson. 1 computer file (PDF); xvii, 371 pages, appendices p. 317-371.At times the price relationship between corn, soybean meal, and dried distillers grains with solubles (DDGS) warrants the inclusion of more than 30% DDGS in swine growing-finishing diets. However, adding more than 20% DDGS to these diets can cause soft pork fat. Pigs with less backfat, such as immunologically castrated pigs, are more sensitive to dietary fatty acid composition than physical castrates with greater backfat thickness. To overcome soft pork fat resulting from feeding DDGS diets, DDGS can either be removed before pigs are harvested or the dietary inclusion rate can be gradually decreased during the growing-finishing period. However, it is unknown if using these feeding strategies are effective for immunologically castrated pigs that can be harvested 3 to 10 weeks after the second Improvest® (gonadotropin releasing factor analog - diphtheria toxoid conjugate; Zoetis, Inc, Florham Park, NJ) dose. Gradually decreasing the DDGS inclusion from 40 to 10% was more advantageous than withdrawing DDGS from the diet 5 wk before harvest because lean gain/d and lean gain caloric efficiency were greater than feeding 40% DDGS diets throughout the growing-finishing period, and similar to pigs fed corn-soybean meal diets with no DDGS. Feeding diets containing 40% DDGS throughout the growing-finishing period resulted in reduced loin and fat quality. Gradually reducing the DDGS inclusion or withdrawing DDGS 5 wk before harvest were not effective in improving loin quality, but both reduced belly fat iodine value. Delaying the second Improvest® dose to 5 weeks before harvest resulted in the greatest benefit for improving lean gain caloric efficiency. Harvesting pigs at 5, 7, or 9 weeks after the second Improvest® dose did not alter pork loin quality and delaying the second Improvest® dose slightly improved pork fat firmness. However, all immunologically castrated pigs had acceptable fat firmness based on current industry standards. In conclusion, gradually reducing the DDGS dietary inclusion was more beneficial than withdrawing DDGS 5 weeks before harvest, and delaying the second Improvest® dose to 5 weeks before harvest captured the greatest benefit of improved lean gain caloric efficiency and did not result in adverse loin or fat quality characteristics.enDried distillers grains with solubles (DDGS)Feeding strategiesImprovestLean gainLoin qualityPork fat qualityAnimal sciencesThesis or Dissertation