Susanne Leth Musse:

Effect of intramuscular Lawsonia intracellularis vaccination on production parameters, antimicrobial consumption and mixed-pathogen intestinal infections in grower pigs

Phd Student: Susanne Leth Musse
Contact: susanne.leth.musse@merck.com

BACKGROUND
Lawsonia intracellularis (LI) causes proliferative enteritis (PE) in pigs. The infection is widespread and 90–100% of pig herds worldwide are considered to be infected with the pathogen, resulting in significant economic losses and reduced animal welfare. LI has a negative impact on Feed Conversion Ratio (FCR) and Average Daily Weight Gain (ADWG) and contributes to increased antimicrobial (AM) consumption. Whether the degree of mortality is affected depends on whether the LI infection manifests as acute proliferative haemorrhagic enteritis (mortality >50% of infected pigs) or chronic PE (mortality 1–5%). Losses resulting from reduced production efficiency and increased mortality depend to a large extent on the level of infection, management strategies and the age group of pigs that are infected. Excretion levels of LI exceeding 4.8 log(10) bacteria/gram faeces have been found to be associated with reduced productivity even in cases of subclinical infection. In Denmark, LI infection most often establishes as a subclinical chronic infection in grower pigs.

PURPOSE
The purpose of the project was to improve productivity and welfare in grower pigs by controlling LI via vaccination using the newly launched Porcilis® Lawsonia Vet. The overall objective was to quantify the effect of vaccination and to increase the knowledge of mixed infections in Danish grower pigs in herds naturally infected with LI by means of four specific objectives: I) To estimate the prevalence and bacterial excretion level of single- and mixed-pathogen intestinal infections with LI, Brachyspira pilosicoli (BP), Escherichia coli fimbria type 4 (F4) and Escherichia coli fimbria type 18 (F18) at herd level in samples collected from commercial pig herds with or without a diarrhoeic outbreak during the late weaner and early finisher periods; II) To evaluate whether the herd-level prevalence and bacterial excretion level of LI, BP, F4 and F18 in weaner and finisher herds change after LI vaccination using Porcilis® Lawsonia Vet.; III) To estimate the change in productivity parameters and AM consumption at herd level in weaner and finisher herds after LI vaccination using Porcilis® Lawsonia Vet., and IV) To estimate the effect of LI vaccination using Porcilis® Lawsonia Vet. on production parameters, the occurrence of diarrhoea, antimicrobial consumption and within-herd infection dynamics at pig and pen level in grower pigs.

RESULTS
In an observational study (Study A1), 41 grower herd complexes had an overall LI, BP, F4 and F18 prevalence of 84.0%, 45.3%. 4.7% and 20.8%, respectively and a positive correlation between the occurrence and excretion levels of LI and BP. When evaluating28 weaner and 41 finisher herds in a before-and-after-study (Study A2), LI vaccination resulted in a significant 15–30% reduction in the prevalence and more than one log unit in excretion level of both LI and BP. Furthermore, FCR decreased by 0.12 FU/kg and 0.08 FU/kg in weaners and finishers, respectively; ADWG increased by 45.6 gr/day in finishers; the risk of mortality was reduced by 8.8% in weaners, and AM consumption decreased by 15.2–21.1% and 33.8–38.3% in weaners and finishers, respectively.

In a field trial (Study B), LI vaccination significantly improved FCR by 0.05 FU/kg and 0.09 FU/kg,  ADWG by 30.7 gr/day and 43.1 gr/day in Herds 1 and 2, respectively, with reduced growth variation and reduced variation in lean meat percentage, reduced the AM treatment by 69.2% in Herd 1 and reduced the occurrence of diarrhoeic blots in pens by more than 56% in both herds. A significant reduction in LI prevalence, excretion level and duration of excretion was identified in both herds. Study B also found a positive correlation between LI and BP.

PERSPECTIVES
Based on the results of the project, vaccination with Porcilis® Lawsonia Vet. in LI-infected herds improves productivity along with a reduction in the prevalence and excretion level of LI, the occurrence of diarrhoea and AM consumption. The concordant results obtained from two different studies, both of which must be considered conservative in their estimations, provide strong evidence for the efficacy of the new LI vaccine when used in commercial herds, and these results are presumably applicable to all LI-infected pig herds with restrictive AM use. The results suggest that LI vaccination should be considered as part of the intervention strategy to control LI infection with the aim of improved productivity, animal welfare,  AM consumption and sustainability of grower pig production.