| Porcine reproductive and respiratory syndrome virus (PRRSV) and Brachyspira hyodysenteriae (Bhyo) are two economically significant pathogenic agents in which their diseases impact pig production worldwide. Although different nutritional strategies have been utilized to ameliorate the negative impacts of disease in pigs, the mechanisms remain undefined. Interestingly, little is known about how these diseases, or several others, impact pig apparent total tract digestibility (ATTD) and apparent ileal digestibility (AID) or basal endogenous losses (BEL) of amino acids (AA), and therefore, standardized ileal digestibility (SID) values for AA have not been determined. Thus, the overall objective of this dissertation was to determine how PRRSV or Bhyo impact AID and BEL values. From these, more accurate SID values can be calculated. Hindgut nutrient disappearance in the face of these two pathogens was also determined from AID and ATTD values. Further, we evaluated the optimal lysine-to-metabolizable energy ratio (g SID Lys to metabolizable energy; Lys:ME) in PRRSV challenged pigs. To accomplish these objectives, a series of experiments were conducted and are outlined in three research chapters (Chapter 2, 3 and 4).;In Chapter 2, an experiment was conducted to assess the impact of soybean meal (SBM) and PRRSV on AID, BEL, and calculated SID values of N and AA near peak viremia (5-8 days post inoculation; dpi) and seroconversion (16-19 dpi). Similarly, in Chapter 3 an experiment was conducted to determine the impact of Bhyo on AID and BEL of N and AA, and from these SID of N and AA were calculated. The final research chapter (Chapter 4) aimed to determine the ideal dietary Lys:ME for 25 and 50 kg BW pigs challenged with PRRSV.;The results from this research indicate that the mechanism by which high SBM improves the outcome of PRRSV challenged pigs does not appear to be related to increased digestibility of N or AA as there were no interactions of SBM and PRRSV (Chapter 2). There were no reductions in ATTD of nutrients or energy from PRRSV infection; however, AID of DM and GE were reduced at 7-8 dpi only. Similarly, AID of AA were not changed due to PRRSV challenge at either collection. In contrast to PRRSV challenge, Bhyo reduced ATTD of nutrients and energy but did not change AID values outside of increasing AID of Gly (Chapter 3). Interestingly, BEL of Arg, Ala, and Pro were reduced at 7-8 dpi due to PRRSV while no BEL differences were detected at 18-19 dpi. This lead to reductions in SID of Arg, Gly, and Pro at 7-8 dpi and SID of Pro at 18-19 dpi. Only BEL of Pro was reduced due to Bhyo challenge, and when SID values were calculated, SID of N, Arg, Lys, Ala, Gly, Pro, and Ser were reduced.;When hindgut disappearance of nutrients and energy were calculated, PRRSV and Bhyo acted in an opposite manner (Chapter 2 and 3, respectively). Compared to control pigs, PRRSV increased hindgut disappearance of DM and GE at peak viremia only. In contrast, Bhyo challenge resulted in a general appearance of N and GE as opposed to control pigs that had a general disappearance. These data suggest that overall energy balance may be improved by increased energy disappearance in PRRSV challenged pigs while N and energy needs may be increased in Bhyo challenged pigs to accommodate increased losses in the hindgut.;In the final research chapter (Chapter 4), commercial pigs were utilized in an industry style production setting in which we reported that increasing the SID Lys:ME improved growth and feed efficiency in 25 kg BW and 50 kg BW PRRSV challenged pigs. Further, growth and feed efficiency were optimized at 110% to 120% Lys:ME compared to control pigs. In pigs experimentally or naturally infected with PRRSV, the Lys:ME requirement for growth and feed efficiency was similar.;In summary of this dissertation, both systemic/respiratory (PRRSV) and colitis (Bhyo) challenges did not greatly impact ileal digestibility of nutrients, energy, and AA. Further, we did not report major changes in ileal endogenous AA losses, but hindgut disappearance of nutrients was increased and decreased in PRRSV and Bhyo challenged pigs, respectively. The AA SID values were minimally impacted by PRRSV while Bhyo reduced the SID of Arg, Lys, and some nonessential AA; however, SID values of pigs challenged with Bhyo were all above 90%. This body of work also showed that increasing dietary Lys:ME to 110% or 120% of control pig requirement was ideal for growth and feed efficiency in PRRSV challenged pigs. These results will allow pork producers and nutritionists to better formulate diets to improve performance and feed efficiency in health challenged pigs. |
