From Crypt Depths to Carbon Dioxide Equivalents: Characterizing the Interactions between Swine Nutrition, Health and the Environment

There are many ways to measure the relative success and sustainability of a swine production system. The most economically relevant measures are growth performance and feed conversion. However, other measures such as greenhouse gas emissions, nutrient excretion, health and degree of intestinal inflammation can also be significant reflections of the interaction between nutrition, genetics and environment. Three experiments were conducted to characterize how swine nutrition and management affect the environmental footprint of swine production. The objective of experiment 1 was to determine the effect of reducing dietary crude protein and supplementing synthetic amino acids on growth performance, greenhouse gas emissions and nutrient excretion in wean to finish pigs. Three diets were fed: 1) control diet, balanced on lysine with no synthetic amino acids, 2) a diet containing a CP concentration intermediate between diets 1 and 3, balanced to meet all amino acid requirements, using synthetic amino acids where needed, and 3) a low CP diet balanced to the 7th limiting amino acid with synthetic amino acids, replacing soy proteins. Pigs fed the lower crude protein diet had reduced N excretion and NH3 emissions, however growth performance in the pigs fed the diet balanced to the 7th limiting amino acid was reduced compared to the control. The objective of experiment 2 was to determine how antibiotic-free management affected growth performance, frequency of clinical signs, and the environmental footprint of swine production. Pigs were either reared with antibiotics or antibiotic alternatives. There were no observed differences in greenhouse gas emissions, nutrient excretion, growth performance or feed conversion, but significantly more animals were removed when reared without antibiotics than reared with antibiotics due to health concerns. The objective of experiment 3 was to evaluate and validate a novel, digital method for measuring intestinal inflammation. Intestinal tissues from pigs selected for high, mild or no allergic response to soy protein were collected, fixed in 10% NBF, embedded and stained with Hematoxylin and Eosin, Alcian blue, and CD3+ IHC. The H and E slides were analyzed for villus height and crypt depth by two technicians in Aperio® Imagescope and Adobe Photoshop software to compare the accuracy and consistency of measures. The measures taken in Aperio® Imagescope more accurately reflected the severity of soy allergy than the measures taken in Photoshop, but Photoshop measures were more consistent between observers. The H and E, Alcian Blue and CD3+ IHC slides were colorimetrically analyzed by Aperio® Imagescope software using algorithms designed to quantify eosinophils, goblet cells and CD3+ T cells. These counts were compared to manual cell counts performed by two blinded observers, and analyzed to determine how accurately the cellular infiltrate reflected the severity of soy allergy and inter-observer variation. There was greater (P\u3c0.05) inter-observer variation in cell count observations collected manually than cell counts calculated by Aperio® Imagescope software and the Aperio® Imagescope measurements did not correlate, in nearly all measures, with the manual counts. In conclusion, the methods used can significantly alter the conclusions reached about holistic animal health and the sustainability of a swine production system, therefore it is important to use a variety of methods, from intestinal histology to production system-level greenhouse gas emissions to support these conclusions