January 02, 2019

Interpretive Summary: A model for feed additive evaluation

Interpretive Summary:  The effects of group size and subtherapeutic antibiotic alternatives on growth performance and morbidity of nursery pigs: a model for feed additive evaluation.

By: Dr. Caitlin Vonderohe

Public concern regarding antibiotic resistance, coupled with increases in legislation related to antibiotic use has resulted in the swine industry focus on reducing use of antibiotics, and in some cases, the production of antibiotic-free pork. Producers are turning to antibiotic alternatives instead of antibiotics to protect animals against disease and improve growth performance. However, the efficacy of many antibiotic alternatives has been shown to be inconsistent. This inconsistency in efficacy may be due to differing experimental methods when the antibiotic alternatives are being tested, including differences in diet, health status, environment and genetics. It is necessary to standardize protocols used to evaluate antibiotic alternatives to have more consistent data about the efficacy of antibiotic alternatives that may be applied to production.

Many of the published studies that evaluate antibiotic alternatives were conducted in academic settings which may differ from commercial facilities and therefore limit the applicability of the study to commercial production standards. One of the primary differences between academic research institutions and commercial facilities is the number of pigs housed in each pen. Olsen et al. recently published a study entitled “The effects of group size and subtherapeutic antibiotic alternatives on growth performance and morbidity of nursery pigs: a model for feed additive evaluation” in Translational Animal Science that examines how group size affects the efficacy of antibiotic alternatives on nursery pig performance.

Pigs were selected and statistically blocked based on weaning date, sex and genetics. The pigs were of a similar health status. 1300 barrows and gilts were fed one of four different diets, a negative control with no antibiotics or antibiotic alternatives, a positive control that included subtherapeutic doses of chlortetracycline and tiamulin, a diet that included zinc oxide and a dietary acidifier, and one diet that included a direct fed microbial. Pigs were housed in groups of 31 or 11. Illness, mortality and treatments were recorded, and oral fluid samples were collected to test saliva for Porcine Respiratory and Reproductive Syndrome Virus, Influenza A, Porcine Epidemic Diarrhea Virus, Porcine Delta Corona Virus and Mycoplasma hyopneumoniae. Pigs were weighed at the beginning and end of the experiment, and at the end of each dietary phase.  The amount of feed that was offered was also noted.

There were statistical interactions between diet and group size for average daily gain and average daily feed intake. Pigs fed the diet that contained subtherapeutic doses of antibiotics grew faster and consumed more feed than the pigs fed the diet without antibiotics or antibiotic alternatives. Pigs housed in large groups and were fed the diet that included zinc had greater average daily gain and feed intake than the pigs that received no antibiotics or antibiotic alternatives. Pigs that were housed in small groups grew faster than pigs in large groups fed diets that contained no antibiotics or alternatives and a direct fed microbial. There were no interactions between diet and group size for growth efficiency, disease morbidity or mortality. However, fewer pigs were removed for treatment from small groups than large groups.

Overall, Olsen et al. (2018) demonstrated that group size can affect the efficacy of antibiotic alternatives, relative to each other and negative controls. Here, the growth advantage that was observed when pigs were fed zinc was only found in animals housed in large groups. Because these authors also had greater numbers of removals from large groups, it is possible that housing pigs in larger groups is more stressful.

In the future, it is important to consider multiple factors when studying the efficacy of antibiotic alternatives to improve growth rates, feed conversion, and disease challenges.

To view the full article, visit Translational Animal Science