slaughter), and on the daily weight gain during the fattening period. The prevalence of Salmonella Typhimurium field strain excretion was low; in total, 4% of the faecal and over- shoe samples collected in the non-vaccinated control group were Salmonella Typhimurium field strain positive. No signifi- cant differences were detected between farms, production
cycles and experimental groups regarding the excretion of Salmonella Typhimurium field strain. In the second production cycle, compared to the non-vacci- nated control group, a protective effect of vaccination on the number of Salmonella Typhimurium field strain positive lymph nodes was detected when applying vaccination either in sows and piglets, sows and fattening pigs or in piglets only. In the first production cycle, this protective effect was absent. Vaccination of sows and piglets resulted in the most consist- ent reduction of Salmonella Typhimurium field strain posi- tive lymph nodes at slaughter. The vaccine strain was detect- ed in samples collected in the sows as well as in the growing and fattening pigs and in the lymph nodes of 13 pigs at slaughter, indicating the possible persistence of the vaccine strain until slaughter.
Vaccination The attenuated histidine-adenine auxotrophic vaccine Sal- moporc (IDT Biologika) is currently the only Salmonella Typhimurium vaccine commercially available for pigs in Europe. Therefore, this was the attenuated vaccine under investigation in this thesis. The research evaluated the application of several different vaccination protocols in one farrowing batch and compared these to a non-vaccinated control group in three subclinically infected pig herds during two consecutive production cycles. The protocols included: 1. Vaccination of sows; 2. Vaccination of sows and piglets; 3. Vaccination of sows and fattening pigs; 4. Vaccination of piglets; and 5. Vaccination of fattening pigs.
Vaccination and bacterial prevalence Attention was paid to the effect of the different vaccination protocols on Salmonella bacteriology (prevalence in faecal and overshoe samples and in ileocecal lymph nodes at
Vaccination and serology The next point of attention was the effect of the different vaccination protocols on Salmonella serology. Vaccination of sows induced a serological response and increased the level of maternally derived antibodies in three-day-old piglets. Also, a significant correlation between the serological results in sows and their offspring was present, indicating the trans- fer of maternal antibodies by the sow colostrum. Slaughter pigs that had been vaccinated either as piglets or as fatten- ing pigs had significantly higher sample/positive (S/P) ratios than non-vaccinated pigs. The S/P ratios in unvaccinated pigs from vaccinated sows (experimental group 1) were not significantly different from S/P ratios in non-vaccinated pigs at slaughter. These results suggested that vaccination of piglets and fattening pigs
Table 1 – Previous and currently applicable serol- ogy-based Salmonella monitoring programmes in fattening pigs in various European countries.
Belgium
Type of programme Possible consequences Currently: not compulsory
the Netherlands Compulsory Germany
Compulsory Denmark Compulsory
Implementation of herd-specific action plan; no financial consequences. None.
Obliged on-farm intervention; separated slaughter; financial consequences.
Penalties and rewards; slaughter under hygienic precautions.
Source: Adapted from L. Peeters, On-farm control measures against Salmonella Typhimurium infections in pigs (PhD-thesis, 2019).
▶PIG PROGRESS | Volume 36, No. 2, 2020 7
PHOTO: ROYAL GD
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