Field evaluation of a ready-to-use combined type 2 and vaccine in Denmark - a historical comparison of productivity parameters in 20 nursery and 23 finishing herds.

Background: In practice, field evaluation of vaccine efficacy in individual herds is often based on a historical comparison of productivity data following initiation of vaccination. Being biased by time, this study design highly contrasts the more controlled, parallel-group design used for most initial vaccine efficacy studies but offers the possibility of including a larger number of animals and herds. As an important add-on to previous findings in controlled studies, the objective of this study was to evaluate the field efficacy of the ready-to-use combination vaccine Porcilis® PCV M Hyo (MSD Animal Health) by an observational historical study design using routinely generated herd productivity data.

Results: Data on mortality, average daily weight gain and feed conversion rate were collected as yearly averages for one year prior to and one year after implementation of Porcilis® PCV M Hyo vaccination from 20 nursery and 23 finishing herds. When comparing pre- and post-vaccination periods, the average improvements in productivity data amounted to - 0.4 percentage points for mortality ( = 0.014), + 5 g for average daily weight gain ( = 0.555) and - 0.06 feeding units(FU)/kg for feed conversion rate ( = 0.074) in nursery herds and - 0.5 percentage points for mortality ( = 0.012), + 34 g for average daily weight gain ( < 0.001) and - 0.04 FU/kg for feed conversion rate ( = 0.133) in finishing herds. Even though some nursery and finishing herds also previously vaccinated against PCV2 and/or , this did not significantly affect the results. For finishers, these results were obtained when difference in arrival weights between the periods and shared ownership of the herds were additionally taken into account.

Conclusion: In these 20 nursery and 23 finishing herds, previous findings from parallel-group vaccination studies concerning average daily weight gain for finishers were confirmed. Additionally, a significant effect on mortality for both nursery and finishing herds was demonstrated in this evaluation based on routinely generated herd productivity data.