An experimental field study on the build up of lungworm infections in cattle

Targeted selective treatment of lungworm infection in an organic dairy herd in Sweden

The effect of targeted selective anthelmintic treatment on the seroprevalence of the lungworm Dictyocaulus viviparus in cattle was investigated. The study was commenced on an organic dairy enterprise in Sweden in November 1998 after the observation of an outbreak dictyocaulosis in the herd, and then continued for almost 3 years. The first year sampling was conducted on a monthly basis and then biannually with the exception of between August and November 2000 when sampling was performed monthly following a second outbreak of dictyocaulosis. Throughout the study, blood samples were examined for specific IgG(1) levels from all animals in the herd that had been grazing for more than 3 months. At the first sampling occasion, 13% out of the 90 blood samples were seropositive. One month later, after targeted selective treatment with eprinomectin (Eprinex), Merial), the whole herd was seronegative. Seroprevalence then gradually increased and 1 year later it returned to levels similar to those observed at the start of the study. At turnout in April 2000, seroprevalence was 1.3% but it then rapidly increased to 28% and 30% in August and September, respectively. This increase was mainly due to an increase in FSG animals of which many were coughing. Consequently, all seropositive animals were injected with ivermectin (Ivomec), Merial) at 0.05 mg/kg body weight in late August 2000. Although all animals recovered, seroprevalence was only reduced to 12% 1 month later. The differences in seroprevalence after both of these anthelmintic treatments were probably attributed to the timing. The first deworming with eprinomectin was conducted in November when the infection already was transient, whereas ivermectin in connection with the second outbreak was injected in a more acute phase of the infection cycle. Infection levels in 2001 were low with seroprevalences of 2.3% and 5.6% in May and September, respectively. These results show that dictyocaulosis in Sweden can be effectively controlled by the use of macrocyclic lactones. However, the infection was not eradicated from the herd despite close monitoring of the seroprevalence and targeted selective treatment of every seropositive animal on two occasions.

Treatment vs non-treatment of helminth infections in cattle: defining the threshold

Helminth infections are an important cause of lost productivity in livestock world-wide, often necessitating anthelmintic treatment. However, a large part of the anthelmintics are used indiscriminately because the parasite levels are too low to justify treatment or because the treatments are not correctly programmed, resulting in undertreatment or overtreatment. The objective of this paper is to discuss possible thresholds for anthelmintic treatment of some of the more important helminth infections in livestock, i.e. gastrointestinal nematodes, lungworms and liver fluke, to promote a more appropriate use of anthelmintics. When possible, a distinction is made between therapeutic thresholds, production-based thresholds and preventive thresholds. A "therapeutic threshold" is intended to identify (an) animal(s) with parasite levels that necessitate immediate treatment. The therapeutic threshold is basically the diagnosis of clinical disease, and can be determined relatively easily for the parasites discussed in this paper. A "production-based threshold" is intended to measure the effects of sub-clinical parasitism on productivity parameters, such as weight gain and milk yield, before clinical disease occurs. Finally, a "preventive threshold" is meant to predict future infection levels, to enable the application of appropriate control measures.

The sensitivity of the Baermann method for the diagnosis of primary Dictyocaulus viviparus infections in calves

Data from calves infected experimentally with 20 larvae of Dictyocaulus viviparus demonstrate that the Baermann method, using 30 g of faeces per calf is extremely sensitive for diagnosis of patent infections in young cattle. Between 5 and 7 weeks after primary infection it is sensitive enough to diagnose the presence of one patent female worm.

The combined effect of fenbendazole treatment and a move to aftermath 7 or 9 weeks after turnout on Dictyocaulus viviparus infections in calves

A grazing study was performed with the main objective of examining the effect of fenbendazole (FBZ) in a 'dose and move' system on nematode infections in calves with special emphasis on Dictyocaulus viviparus. Three groups of six calves were grazed from May to October 1993. One group (DM7) was treated with FBZ and moved to aftermath (pasture which had only been mown) 7 weeks after turnout. The second group (DM9) was similarly treated and moved 9 weeks after turnout and the third group served as untreated pasture control group (PC) and was moved to aftermath 9 weeks after turnout. FBZ treatment removed adult lungworms from DM7 and DM9. Tracer calves grazed during the first 7 or the first 9 weeks after turnout acquired mean burdens of 18 and 125 lungworms, respectively. In PC faecal larval counts increased until the end of August. Most of the animals in this group were then suffering from lungworm disease and emergency treatment with ivermectin was given. In both FBZ-treated groups, larvae reappeared in the faeces of some of the calves 4-5 weeks after treatment. Subsequent reinfection resulted in higher mean faecal larval counts in both groups 2 months after treatment, although variation in faecal larval counts was high. In DM7 values tended to be higher than in DM9. These higher larval counts were associated with mild signs of parasitic bronchitis in some calves of DM7, whereas no signs were seen in DM9. At the end of the experiment, all calves, and also a group of six permanently housed non-infected control calves (HC), were infected experimentally with 5000 D. viviparus larvae to evaluate development of immunity. The worm counts at necropsy showed that all calves on pasture had developed immunity.