Enzymes and amino acid analogs in swine nutrition

The objectives of the first 3 studies in this dissertation were to determine the efficacy of Met hydroxy analog (MHA) relative to DL-Met (DLM), and to determine the primary site of their absorption in swine. Percent N retention (NR) and biological value (BV) increased linearly (P \u3c 0.01) in response to supplemental DLM and the free acid form of MHA (MHA-FA). Grams of N retained per day, NR, and BV increased linearly (P \u3c 0.01) in response to supplemental DLM and the Ca-salt of MHA (MHA-Ca). The relative efficacy of MHA-FA and MHA-Ca and were not different from that of DLM on an as-fed basis using N-balance criteria in young pigs. Absorption of MHA-FA begins in the foregut and is complete by the end of the duodenum, whereas absorption of free Met occurs primarily in the proximal small intestine. Wheat middlings inclusion had no effect on absorption of MHA-FA, but it did decrease free Met absorption at the duodenum (P \u3c 0.01) and the terminal ileum (P \u3c 0.05). The objectives of the final 2 studies were to determine the effect of exogenous enzymes on the apparent ileal digestibility (AID) of DM, energy, CP, and AA, and the apparent total tract digestibility (ATTD) of DM, energy and P in pigs. The first xylanase (XylA) improved the AID of energy, Ile, Leu, Thr, Val, Ala, and Ser ( P \u3c 0.05; linear), as well as Ile, Trp, Cys, and Ser ( P \u3c 0.05; quadratic). The second xylanase (XylB) improved the AID of DM, energy, CP and all AA (P \u3c 0.05; quadratic). Addition of the final xylanase (XylC) improved the AID of DM, energy, CP, and all AA (P \u3c 0.01; quadratic), and maximized nutrient and energy digestibility compared with the other 20% DDG-based diets. The combination of a protease (PRO), xylanase (XYL), and phytase (PHY) improved the AID of energy, Ile, Leu, Phe, Thr, Trp, Val, and all nonessential AA except Cys (P \u3c 0.05) and maximized the AID of DM, energy, CP and AA. Supplementation with PRO + XYL + PHY also improved the ATTD of energy and P, and maximized the ATTD of DM, energy, and P. Addition of XYL improved the AID of Ile and Val (P \u3c 0.05), and resulted in AID of DM, energy, CP and most AA that were not different from the diet supplemented with PRO + XYL + PHY. Addition of PRO had no effect on AID or ATTD. Addition of PHY reduced (P \u3c 0.05) the AID of Met and Cys, and had no effect on ATTD. The data from these studies indicate that the efficacies of MHA-FA and MHA-Ca are not different from that of DLM in swine, despite differences in their site and degree of absorption along the gastro-intestinal tract. The data also indicate that supplemental enzymes can be used to improve nutrient digestibility in swine diets