Post-weaning diarrhea caused by F18+ Escherichia coli (ETEC) is a growing health and economic challenge in swine production. Not only does it lead to significant morbidity, mortality and growth performance losses in nursery pigs, but emerging evidence indicates that some E. coli strains exhibit resistance to commonly used antibiotics, further complicating treatment strategies and underscoring the need for alternative approaches.
“We need to find new ways to disrupt mechanisms by which ETEC is exerting high toxicity and mortality,” said Joel Spencer with United Animal Health during the American Association of Swine Veterinarians (AASV) Annual Meeting. “If we can knock down some of these mechanisms, we have the opportunity to increase the efficacy of technologies that can improve pig survivability.”
A recent United Animal Health study aimed to evaluate the efficacy of one of their products, ProVent ECL, a direct-fed microbial (DFM) positioned for use in sow and nursery diets. This DFM was launched in 2016 to support health and performance through multiple mechanisms of protection against complex pathogen challenges.
Previous ProVent ECL field evaluations and internal research have been presented at AASV annual meetings showing improved health outcomes in commercial environments. The United Animal Health team wanted to further understand how ProVent ECL could influence intestinal health and mortality, so they set up a controlled nursery challenge study.
How Did the Study Work?
A total of 140 barrows were weaned, transported to a BSL-2 research facility, and randomly allotted to one of four dietary treatments by bodyweight in a randomized complete block design:
- F18+ ETEC challenge only
- F18+ ETEC challenge + 0.05% DFM in the nursery diet
- F18+ ETEC challenge + 0.15% DFM in the nursery diet
- F18+ ETEC challenge + 2500 ppm Zn from Zinc Oxide
All pigs were from sows consuming 181 g/ton tilmicosin in lactation, and all pigs were injected with tulathromycin at processing and weaning, respectively. Pigs were placed in elevated solid-sided pens containing five pigs/pen with eight or four replicate pens per treatment.
During the study, the pigs received a two-phase nursery diet and were placed on dietary treatments at weaning, and for the entire 28 day experimental period. On day 14, all pigs received a single oral gavage of F18+ ETEC that was positive for EAST1, LT, and Stx2 toxin genes.
Mortality and health were monitored by a consulting veterinarian, and these metrics were the focus in this controlled challenge study. Serial rectal swabs from one pig per pen were tested via qPCR to quantify inoculum F18 adhesin gene on days 2, 14, 17, 21 and 28. Each pig was euthanized on day 28 and ileum intestinal segments were collected to measure villous height, crypt depth and F18 adhesin gene quantities adhered to the intestinal mucosa. The data was then analyzed with pen or pig as the experimental unit and treatment was used as the fixed effect.
ProVent ECL Reduces Mortality
The model proved highly effective in evaluating the impact of a health-focused direct-fed microbial during a controlled E. coli infection, Spencer says. There were no differences in animal growth among treatments; however, there were significant impacts on infection and mortality.
“This model proved effective to separate out differences among treatments when dietary treatments were fed for 14 days prior to challenge and continued for 14 days post challenge,” he says. “The higher dietary inclusion of direct-fed microbial significantly reduced mortality and frequency of F18 adhesin gene adhered to the ileal mucosa of challenged pigs.”
Spencer says this higher level appeared to reduce infection of pigs and also improve intestinal recovery post challenge due to reduced adhesion and colonization of F18+ ETEC in the intestine.
“While this specific health-focused direct-fed microbial, ProVent ECL, did significantly reduce mortality under controlled conditions, other therapies will likely be required alongside the direct-fed microbial to optimize pig health under commercial conditions where co-infections and additional stressors must be considered,” Spencer says.
