Allen D. Leman Swine Conference, September 18-21, 2010, St. Paul, MN
Respiratory diseases continue to have an important welfare and economic impact for the swine industry worldwide. Recent investigations in the area of immune responses and their relationship with the gut microbiota have opened the door to new approaches for disease treatment and control. In this study, we explored the possibility of using a non-pathogenic oral inoculum to decrease the detrimental effect of Mycoplasma hyopneumoniae (M. hyopneumoniae) infection.
Materials and Methods
Twelve, naturally farrowed/artificially raised piglets were housed in controlled research units. Piglets were fed bovine colostrum during the first 2 days of life, and a medicated milk replacer thereafter until week 4. Pigs were gradually introduced to a commercial dry feed formula, which eventually replaced the liquid feeding. Piglets were split into 2 groups at weaning. One group was orally exposed (E) to a non-pathogenic inoculum 1x/day over 1 week. The second group was left un-exposed (UE). The non-pathogenic inoculum consisted of a 1:1 mixture containing a fresh fecal slurry (obtained from a boar in a high health herd) and phosphate buffer saline. Four weeks after the oral exposure was completed, pigs were experimentally infected with 20 ml of 1x105 CCU/ml of M. hyopneumoniae. Experimental groups were evaluated daily for clinical signs. Serum samples were obtained from all pigs during the first weeks after infection. Weights were measured at 0, 15 and 22 dpi. Pigs were humanely euthanized 4 weeks after infection and lung lesions were blindly scored. Lung samples were collected at euthanasia. Data were evaluated using the Students t test and Kruskall-Wallis one way analysis of variance, were appropriate. The proportion of seropositve pigs was compared using a Hypothesis test. The pig was the experimental unit for all comparisons.
Results and Discussion
All pigs were negative to M. hyopneumoniae, porcine respiratory and reproductive virus (PRRSv) and swine influenza virus (SIV) at the beginning of the study, and remained negative to PRRSv and SIV throughout the experiment. No GI tract clinical signs were observed in pigs before or after the oral inoculation. Experimentally infected pigs in group E seroconverted to M. hyopneumoniae as early as 9 dpi, while all pigs in groups E and UE had seroconverted by day 14 after infection. Onset of clinical signs differed between the groups, being earlier for the UE group than for the E group. The number of dry coughs, suggestive of M. hyopneumoniae infection, was greater (p < 0.005) in the UE group than in the E group. Microscopic lung lesions suggestive of M. hyopneumoniae infection were apparent in all research subjects. Pigs in the UE group tended to have greater (p = 0.07) lung lesion scores than pigs in the E group. Under the conditions of this study, pigs in the E group had less respiratory clinical signs and lesions, and seroconverted earlier than pigs in the UE group, suggesting a beneficial effect of the oral non-pathogenic inoculation on the severity of mycoplasmal pneumonia. Physiological aspects for the differential response between the two groups are under study. In this investigation, we have tested the effect of gut microbiota manipulation involving a solely respiratory infection. Therefore, other studies involving multiple infectious agents may be needed before field implementation of this technique. It is also important to note that this model of oral non-pathogenic inoculation does not go against all-in/all-out management practices, neither suggests stopping its application, but implies a feedback from older animals (extremely healthy), during early stages of pig life.