Streptococcal meningitis in pigs: field trial to study the prophylactic effect of trimethoprim/sulphadiazine medication in feed.

Half the progeny in a 200-sow herd (2045 pigs) was given feed medicated with 500 g/tonne of a 1:5 trimethoprim/sulphadiazine mixture from three to nine weeks of age. The other half (1989) acted as controls. The trial lasted 12 months. No difference was observed between the two groups in the incidence of streptococcal meningitis and the morbidity and mortality from all disease causes during the growing/fattening periods did not differ significantly. The main diseases encountered were pneumonia (7.24 per cent), streptococcal meningitis (5.12 per cent), leg and foot disorders (3.34 per cent) and the after-effects of vices (1.86 per cent). The resistance of faecal coliforms to trimethoprim was studied during the six-week period of trimethoprim/sulphadiazine feeding. Faecal coliforms in both medicated and non-medicated groups developed almost 100 per cent resistance. However, resistance developed more slowly in the untreated pigs. The medicated pigs showed a small overall improvement in feed conversion rate up to 18 weeks of age mainly because of a marked improvement between three and six weeks.