Date Full Report Received


Date Abstract Report Received


Heightened interest in reducing antibiotic usage in pork production leaves producers looking for effective alternatives to antibiotic growth promoters (AGPs) in swine diets. While there are a substantial number of alternative products available, inconsistencies in existing literature make drawing conclusions about products and making comparisons across studies difficult. Therefore, the objectives of this study were: 1) to develop a protocol defining essential study components that can be used in studies evaluating antibiotic alternatives; 2) to evaluate the effects of specific AGP alternatives on nursery pig growth performance 3) to evaluate the effect of two different group sizes on growth performance and efficacy of AGP alternatives. To achieve these objectives, an experiment was conducted in a commercial research facility using 1,300 pigs weaned at 21 d of age in a 6-week nursery study. The four dietary treatments were: a negative control diet (NC), a positive control diet (PC; NC + antibiotics), a combination of zinc oxide and a dietary acidifier (ZA; NC + ZnO + acid), and a combination of a bacillus-based direct-fed-microbial and resistant potato starch (DR; NC+DFM+RS). Pigs were housed in groups of 31 (large pens) or 11 (small pens). Pens were modified so that floor space per pig was 0.41 m2 (4.4 ft2) and 0.42 m2 (4.5 ft2) per pig in large pens and small pens, respectively. Data were analyzed using a 4×2 factorial design with four levels of diet and two levels of group size. Pen was considered the experimental unit; with 60 pens total: 15 pens per dietary treatment, 32 replicates of large pens and 28 replicates of small pens. Pigs were weighed by pen and feed disappearance recorded to calculate ADG, ADFI, and G:F using pig days. Over the course of the project the pigs experienced two naturally occurring health challenges (acute diarrhea and septicemia in week 1 and PRRSV in week 4), which impacted performance and health during the study.

Summary of results:
• There was a significant interaction between diet and group size for ADG; the PC diet improved ADG by 27% in large pens and by 14% in small pens, the zinc/acid diet improved ADG by 8% only in large pens and had no effect in small pens. Small pens had higher ADG than large pens when fed the NC or DFM/RS diet.
• There was a significant interaction between diet and group size for ADFI; the PC diet improved ADFI by 18% in large pens and by 9% in small pens, the zinc/acid diet improved ADFI by 8% in large pens but had no effect in small pens.
• Small pens had greater G:F than large pens, and pens fed the PC diet had greater G:F than pens fed the NC, zinc/acid, or DFM/RS diets.
• Pigs fed the PC diet required 40% less individual medical treatments than pigs on the NC diet, and the zinc/acid diet was intermediate of the NC and PC.
• Depending on the performance variable, the interaction between diet and group size suggests group size should be an important consideration in design of future studies.

In order to make progress towards identifying effective AGP alternatives as rapidly as possible, it will be important for studies evaluating alternative products to include as much information as possible on a consistent basis. Recommended study components and information to report should include:
• Genetic background of pigs used in the study
• Vaccination and medication program
• Characterization of health status
• Report of mortality and morbidity
• Report number of pigs treated, according to treatment, and details on the treatment regime and type
• Diet formulation must include a negative control
• Diet analysis to verify inclusion of test ingredients
• Clear description of experimental design (pigs per pen, replications per treatment, blocking, etc.)
• Description of study environment (time of year, temperature, pen specifications, barn design, etc.)