In the U.S., pigs during the nursery phase receive vaccinations for circovirus, Mycoplasma hyopneumoniae, erysipelas, salmonellosis and ileitis and these vaccinations are typically administered via intramuscular injection (circovirus, Mhyo +/- erysipelas) or drinking water (ileitis, salmonella +/- erysipelas). It has been noted by swine practitioners (Anon Communication) that approximately 6-h after vaccination via intramuscular injection has been completed, pigs lie down, become more lethargic and reduce their feed consumption. Therefore, the objective of this study was to determine if field observations of markedly reduced pig activity following vaccination with certain Mycoplasma hyopneumoniae vaccines could be confirmed and quantified by observing post-vaccinal pig behavior changes for a 15 sec period over a 28 h period. A total of 1832 weaned crossbred (GPK35 x EB5, Monsanto Choice Genetic, St Louis, MO) pigs 17 to 23 d of age were obtained from a PRRS and SIV-negative, Mycoplasma hyopneumoniae positive production system. Research was conducted over 4 consecutive days in October 2007 at a commercial, mechanically ventilated nursery facility in South Central Missouri. Treatment one; MycoFLEX (n = 36 pens), defined as a single intramuscular dose of 1ml MycoFLEX® (Boehringer Ingelheim, St. Joseph, MO) vaccine injected into the lateral cervical musculature on the right side of the neck at 5 wks of age using a 16 gauge needle. Treatment two: RespiSure-ONE (n = 36 pens), defined as a single intramuscular dose of 2 ml RespiSure®-ONE (Pfizer Animal Health, New York, NY) vaccine injected into the lateral cervical musculature on the right side of the neck at 5 weeks of age using a 16 gauge needle. Willingness to approach observations was performed in the same pen on two occasions 24 h apart. The d -1 (baseline) WTA observation occurred between 3:00 PM and 4:00 PM and was defined as the WTA percentage baseline for each pen (pens were observed in the same order that vaccine was to be administered). On d 0 (post-immunization), vaccination procedures began at 7:00 AM and were completed by 10:00 AM. On d 0, WTA observation occurred between 1:00 PM and 4:00 PM and was defined as the WTA percentage post-immunization for each pen.

The percentage of pigs willing to approach on d -1 and d 0 were analyzed using a Pearson Chi-square test in JMP v.6.0.0 (Cary, NC) software comparing the percentage of pigs approaching on a pen basis. Results were considered significant when P values were ≤ 0.05.

Baseline willingness to approach was not different (P > 0.05) between the two treatment groups. Six h post vaccination both treatment groups had reduced their willingness to approach to the observer, however nursery aged pigs that received the MycoFLEX® vaccination were more willing to approach (P < 0.0001) than their RespiSURE® -one counterparts. In conclusion, vaccines do seem to have some short term behavioral effect on the pig and producers and veterinarians should be mindful of this when strategizing herd health management techniques.