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October 9, 2023
By Tom Molitor, College of Veterinary Medicine, University of Minnesota
At the most recent 2023 Leman Conference Sept. 18-19, there was a breakout session entitled: Endemic commensal bacteria: Elevating respiratory health. The session should’ve instead been entitled –Sage advice from 40-plus-year-old veterans of the swine industry. All three of the speakers, Drs. Joe Connor, Camille Moore and Perry Harms, mentioned early weaning approaches as options to eliminate diseases in swine herds.
Moore, consultant and self-described actor and witness of the North American swine industry, presented a paper on reasons for conventional approach for bugs elimination. The entire session and certainly the discussion of MEW brought me back to the 1980s and 1990, when early weaning approaches were the “rage.”
In 1980 Tom Alexander, a swine consultant from England and a personal friend of Al Leman, published an innovative paper in Veterinary Record on Medicated Early Weaning (Alexander, TJL et al., 1980) to obtain pigs free from pathogens endemic in the herd of origin. The goal of Alexander’s study was to eliminate selected bacterial infections from swine herds. The medicated early weaning as described by Alexander involved isolating sows prior to farrowing, medicating sows and litters, and weaning piglets at five days of age.
Alexander was successful using medicated weaning in eliminating Mycoplasma hyopneumoniae and Bordetella sp from the herds, but not Treponema hyodysenteriae (now named Brachyspira). It was a remarkable initial description by Alexander and others on eliminating endemic diseases with this approach using the diagnostics that were available at the time.
Since the landmark study of Alexander, many variations of MEW have been applied including ISOWEANTM, and modified MEW (MMEW). MEW and MMEW have been proven effective in the elimination of a host of infectious agents including Actinobacillus pleuropneumoniae, Mycoplasma hyopneumoniae, Pasteurella multocida, Brachyspira hyodysenteriae, Streptococcus suis, Glaeserella parasuis, and viral agents pseudorabies, and transmissible gastroenteritis, and presumably others.
In modified early weaning schemes, medication was not always necessary to eliminate selected agents from herds, the act of early weaning alone was sufficient. There were costs and consequences of weaning pigs as early as five days and follow up papers used modified early weaning at anywhere from 10-21 days of age with success, depending on the agent of question to be eliminated. One unexpected observation was that MEW pigs possessed larger thymuses and smaller lymph nodes compared to littermates, maintained on the sow and weaned at 28 days; an Intriguing immunological consequence made by Dr. Barry Wiseman.
With excitement from the Leman Conference and an eye towards a history lesson I embarked on presenting the Alexander et al., 1980 paper to graduate students as part of a University of Minnesota swine journal club in the week following the Leman Conference. I was interested in finding a more recent article as a bookend to Alexander’s paper.
After performing a literature search to examine recent article(s) in using early weaning approaches to eliminate disease in swine herds, to my amazement I discovered the article: Early Weaning completely eliminates porcine cytomegalovirus from a newly established pig donor facility for Xenotransplantation. Egerer et al 2018. Xenotransplantation. Here was a more recent article that used early weaning to eliminate a major problem to xenotransplantation, the use of pig tissues or organs for transplantation into humans.
The challenges for xenotransplantation are first to overcome the major immunological barrier of compatibility and secondarily is that of microbiological safety of potential donor tissues and organs. Porcine cytomegalovirusis o f questionable concern to the swine industry, yet it is of utmost importance in using pig tissues or organs for xenotransplant. In this study, Egerer et al 2018 demonstrated the elimination of PCMV from a positive herd by weaning pigs at one day of age, after receiving colostrum. The PCMV negative status remained in the herd after follow-up testing with two generations of pigs.
Important keys in eliminating diseases from swine herds are weaning to a clean and free facility and strict biosecurity. Joe Connor illustrated in his presentation at Leman 2023 that even with hog cholera elimination in the 1950s and 1960s, before the acceptance of the term, biosecurity played a critical role in the success of elimination.
Alexander’s major goal in his landmark paper was to eliminate selective bacterial infection in swine herds, yet subsequently viral infections have also been successfully eliminated with early weaning strategies, including pseudorabies and TGE and more recently PCMV. Disease elimination from the A in Alexander to the X in Xenotransplantation.
Yet there are consequences to early weaning. The development of the immune system in the pig is affected by the early weaning process and influenced by the environment into which the pig is weaned.
Carlos Pijoan, a legend in swine infectious diseases, raised the concern that through MEW we may be creating a more susceptible pig at a later stage of development. Is this a corollary of the hygiene hypothesis? The hygiene hypothesis, a term used in medicine, is that in early childhood exposure to microorganisms protects against allergies by strengthening the immune system. Looking at from the other angle—a lack of such exposure is thought to lead to poor immune tolerance.
We have learned a great deal on the immunology of the pig from dealing with the challenges of infectious diseases such as PRRSV. We still have much to learn about the immunology, infectious disease processes and disease elimination. And back to the sage Joe Connor from Leman 2023, “we have many successes in disease elimination that will drive the future”.
“Yesterday says, “Forget me, but learn from me.” Today says, “Embrace me, yet utilize me.” Tomorrow says, “Anticipate me, then prepare for me.” ― Matshona Dhliwayo
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