Any bought-in cattle have to be drenched with a flukicide before entering the flock in order to avoid increasing fluke burden. The reduced stocking rates in organic farming also reduce the fluke burden.
Other management methods of reducing the fluke burden include fencing off snail habitats or excluding stock from fluke areas from the end of August until February. Another possibility is drainage of snail habitats, but the cost is high and, in most cases, not a suitable solution on an organic farm. Furthermore, many snail habitats exist in undrainable high rainfall areas and, again, draining these areas is not in the interest of organic farming.
There has been increasing interest in plants with molluscicidal (snail-killing) activity, such as some Eucalyptus spp. (Hammond et al., 1994) and the latex of Euphorbiales spp. (Singh and Agarwal, 1988). However, this research is in its early stages and there is no work quantifying the effect of these plants in the field. More research is required.
Certain sciomyzid fly larvae have been shown to eat lymnaeid snails, and this has been put forward as a possible method for the control of snails. Work has been conducted in Ireland on Ilione albiseta to see if this insect could be exploited in the control of fasciolosis (Gormally, 1987; Gormally, 1988; Gormally, 1989).
Research is being undertaken to develop a vaccine against secretary proteins, which would prevent fluke survival. There are still significant problems to overcome, but there do appear to be some realistic prospects of producing a vaccine against F. hepatica (Mulcahy et al., 1999). This may be useful to some organic farmers who do have a continuous problem with bovine fasciolosis.
The level of control measures needed is based on the fasciolosis forecast for a particular year. Until recently, fasciolosis forecasts were based on the system of Ollerenshaw in England and Wales and on that of Ross in Northern Ireland and Scotland. Both these systems relate meteorological data to the probable incidence of fasciolosis in particular years. However, computerised systems have now been developed (Goodall et al., 1991; McIlroy et al., 1990), based on the time series analysis of a multivariate model that includes both climatic data and the prevalence of liver condemnations in cattle and sheep from previous years.
Conventional farming in endemic fluke areas routinely uses flukicidal drugs. The continuous prophylactic use of flukicides is not acceptable under organic standards (UKROFS, 2000). However, dosing may be useful during the conversion period on farms with a high incidence of fasciolosis, where treatments may be reduced or dispensed with once organic. A product that kills both immature fluke and adults is advisable.
In beef cattle, the first treatment is given at housing or, if the cattle are not housed, during late autumn and early winter. A second treatment in the spring will kill any fluke that have survived the housing treatment or, in the case of outwintered cattle, are the result of reinfection. These cattle will not be able to infect the pasture. In some areas, a third treatment in the summer may be necessary to kill any fluke which result from the winter infection of snails. Over time, the number of treatments may be reduced to a single treatment at housing, and eventually treatment may be dispensed with.
In dairy cattle which calf in the spring and are in conversion, treatment at drying off in the winter can be recommended. Young stock can be treated at the same time. Triclabendazole will remove all the flukes and would be the treatment of choice (see table for withdrawal times). Cows calving at other times of the year are more difficult to treat, as they may be lactating during the winter housing period. It may be possible to treat selectively cows with the heaviest burden of parasites (judged by faecal egg count) rather than blanket treating the whole herd. This will require close observation and regular faecal egg counts during the risk period. Only oxyclozanide, albendazole and netobium can be used during lactation, and these are only effective against adult fluke. In certain areas with high infestations, consideration should be given to synchronising the calving pattern during the conversion period, so that the animals are not lactating during the period of maximum transmission in the autumn when treatment can be given. Together with other management changes, this may be enough to keep liver fluke under control. It would also be advisable to keep lactating dairy cattle on drier, less fluke-infested pasture (Torgerson, 1999).
When fully organic, regular parasitological examinations and abattoir checks are necessary to keep an eye on the disease.