Helminth surveillance as a prerequisite for anthelmintic treatment in intensive sow herds.

Helminth prevalences in pigs in intensive production systems are often very low due to housing and management factors, and the present study was carried out to examine whether routine anthelmintic treatment in such herds can be replaced by coprological surveillance of the helminth status combined with anthelmintic treatment when necessary. After an initial examination, 25 out of 28 large herds of Danish sows (> or = 50 sows, production of fatteners) were found to have such light helminth infections that routine deworming could be replaced experimentally by coprological examination every 6 months of 10 weaners (10-12 weeks old), 10 fatteners (5-6 months old), 10 dry sows and 10 lactating sows. This coprological surveillance continued in 21 herds of the selected 25 herds for a 3-year period, while it was stopped immediately in one herd due to increasing Ascaris suum prevalences, and ceased after one year in three herds due to other reasons. A. suum was found in all but one of the 25 herds. The most heavily infected age group was the sows, in which the A. suum prevalence was consistently low in approximately half of the herds, while it increased slowly or rapidly in the other half. When this happened, treatment of the breeding stock was recommended which resulted in low prevalences for varying periods of time. Few farmers neglected the recommendations for some time or for all 3 years, which resulted in consistently high prevalences in the sows (e.g. 40-60%). The fatteners were in general more lightly infected with A. suum than the sows, and in approximately 3/4 of the herds the prevalence remained at a low level, while it fluctuated in the remaining herds. No weaners were ever found to excrete eggs, most likely due to unfavourable conditions for egg development in the farrowing pens. Throughout the study Oesophagostomum sp. eggs were found sporadically in the sows of two herds, and in a third herd, Oesophagostomum sp. was introduced after 2 years, probably due to close contact with a neighbour herd. Oesophagostomum sp. was not found in the remaining herds. Eggs of Trichuris sp. were found sporadically. In conclusion, it is recommended that veterinarian advisers evaluate the production systems before suggesting an anthelmintic routine. If helminth infections may be controlled by intensive management and housing alone, coprological surveillance combined with anthelmintic treatment when necessary may replace routine use of anthelmintics. If the surveillance reveals that the infection levels continue to be low unnecessary medication is avoided, and if the infection levels increase, the coprological data obtained can be used to optimize the anthelmintic strategy.