Effects of a second annual strategic anthelmintic treatment in dairy sheep in Northern Spain

Our goal was to optimise the patterns of strategic anthelmintic treatment in dairy sheep flocks in the Basque Country, Northern Spain. Sixteen Latxa-breed commercial necks were monitored for almost 2 years. All the animals included in the study were treated with netobimin (Schering-Plough) at lambing. Ewes were then allocated into three groups. Animals in group M were also treated before mating, and animals in group A were treated during the autumn (middle to end of the gestation period); owes in group C bad no further treatment. The effects of the three anthelmintic strategies were assessed in parasitological and production terms. All three groups showed similar output dynamics of trichostrongyle and Dicrocelium eggs. Trichostrongyle egg output means were lower in groups M and A compared to group C, though the percentage of reduction (30%) was low. Despite a negative correlation between trichostrongyle egg shedding and body-condition scores, no significant differences were found between the treated groups. The highest fertility was observed in the animals in group M with only 4.9% barren ewes, compared to 7.7% in group A and 9.4% in group C. A higher percentage (82.2%) of ewes in group M were pregnant within the first 30 days following the introduction of rams into the flock, compared to 78.6 and 77.1% in groups A and C, respectively. All three groups were similar on prolificacy and recorded milk production. The results obtained during this study suggest that a strategy where ewes are treated at lambing and pre-mating would be the best alternative since the highest economic benefits are obtained in addition to an efficient reduction in parasite burdens. (C) 2002 Elsevier Science B.V. All rights reserved.