| Feed additives are often included in swine diets to increase digestibility of certain nutrients, improve intestinal function, and prevent or mitigate illness, ultimately with a goal of improved productivity. Whenever additives are introduced into diets, it is imperative that their efficacy be demonstrated with thorough research, and the elucidation of information such as proper inclusion rate and effects on the pig is necessary for their inclusion to be practical and economically favorable. Thus, proper evaluation of feed additives is critical. The objective of this thesis was to investigate the methods with which phytase and alternatives to antibiotic growth promoters (AGP's) are evaluated. Phytase is commonly added to swine diets to improve availability of dietary phosphorus (P), and its P releasing efficacy is usually determined using pigs fed diets deficient in P. Chapter 2 used 72 growing barrows (BW = 22.95 +/- 1.87 kg) and 8 dietary treatments to test the effects of adding phytase to a P adequate diet compared to a P-deficient diet on P and Ca digestibility and balance, and to generate a P release curve for phytase. Phytase improved ATTD and STTD of P (quadratic P) and absorbed P (linear, quad). Urinary P excretion increased linearly with phytase inclusion; retention of P also increased (P). Phytase was predicted to release 0.049% STTD P for 200 FTU/kg added to P-adequate diets, and this number may be lower than release values observed in P-deficient diets (STTD P release was estimated to be 0.059% for 200 FTU/kg; P < 0.05); this corresponded to a 28% increase in P digestibility in the P-deficient diet whereas there was only a 12% improvement in the P-adequate diet. The results demonstrated that urine P excretion could not be used as a predictor of phytase P release, and evaluation of phytase in P-adequate diets, rather than P-deficient diets, may be advantageous to making precise estimates of P release values. Results of AGP alternative studies have thus far been inconsistent, and part of this may be due to inconsistencies in experimental methodology and lack of helpful information being reported in individual studies. In Chapter 3, the objective was to model a framework for studies evaluating AGP alternatives and investigate the impact of AGP alternatives, pig group size, and their interaction on nursery pigs. A total of 1,300 weaned pigs (6.14 +/- 0.18 kg) were assigned to 8 different treatments: 4 diets evaluated across 2 group sizes. The 4 dietary treatments were: negative control (NC), positive control (PC; NC + in-feed antibiotics), pharmacological levels of zinc oxide plus a dietary acidifier (blend of fumaric, citric, lactic and phosphoric acid, ZA; NC + ZnO + acid), and a bacillus-based direct-fed-microbial plus resistant potato starch (DR; NC+DFM+RS). The 2 group sizes were 31 or 11 pigs/pen. Collection and testing of oral fluid and serum samples, and necropsy of deceased pigs allowed for characterization of pig health status and identified specific pathogens as potential influential factors in the study, including a natural porcine reproductive and respiratory syndrome virus challenge in wk 4-6. The PC diet improved ADG, ADFI, and G:F (P < 0.05) regardless of group size. The ZA diet improved ADG and ADFI when pigs were housed in large groups, but not in small groups (P < 0.05). This indicates that group size may be a contributing factor to outcomes of AGP alternative experiments. Careful study design, protocol implementation, sample collection, and recording of important information allowed for characterization of the health status of this group of pigs and determination of treatment effects on growth performance and morbidity. Similar methods of collecting and reporting crucial information in future studies evaluating AGP alternatives may lead the industry toward quicker progress in identifying and implementing effective alternatives to AGPs. |
