22 Aug 2016
Louise Silk discusses control strategy options for endoparasites and ectoparasites that affect beef and dairy herds.
Louise Silk
Job Title
The author says vets must consider the whole picture before putting parasite control strategies into place.
Control of parasites in cattle, be they beef or dairy, requires an approach that takes into account the large array of parasites that may be problematic on farm.
It is only when considering the whole picture that the most appropriate control strategies can be put in place.
It is important to consider that, at any time, multiple parasites may be infecting a group of cattle and the ability of an animal to cope with a parasitic infection may vary, depending on its body condition and nutritional status. It is possible the effects of parasitism may be lessened by high protein nutrition or exacerbated by the simultaneous presence of another parasite or concurrent disease.
Despite the fact management practices tend to be relatively constant on many farms, all parasites are affected by environmental conditions, which, inevitably, will vary year on year. For this reason, it is essential parasite control is not fixed in stone, but comes in the form of a more fluid conversation between the farmer and vet or advisor – that way, the control measures can be tailored to the relevant risks on the farm for that particular year or season.
Information from sources such as the National Animal Disease Information Service Parasite Forecast can be used to gain up-to-date information regarding the relevant risks for certain parasites, such as liver fluke and gastrointestinal (GI) nematodes.
At the start of the grazing season, the level of infective larvae on pasture is likely to be low. The number of larvae surviving the winter on the pasture will depend not only on the type of parasite, but also the environmental conditions.
Grazing cattle acquire new infections and multiply the parasite numbers, resulting in increasing worm burdens in the cattle, as well as infective larvae on the pasture. In general, GI nematodes and lungworm burdens increase from July onwards, with liver fluke being significant slightly later in the summer.
When it comes to controlling internal parasites in cattle, these seasonal patterns can be used to plan grazing and treatments in a strategic way. The Control of Worms Sustainably (COWS) technical manual (2014a) discusses a range of options that could be considered for the control of endoparasites (including fluke, GI nematodes and lungworm). These options will now be summarised.
New lays or pastures not grazed by cattle (or sheep, if fluke is a risk on farm) in the previous year will be considerably lower risk for cattle in terms of the acquisition of new infections. Vaccination against the lungworm Dictyocaulus viviparus will not only protect cattle from clinical disease, but also reduce pasture infectivity for subsequent years.
Early season anthelmintic treatment will reduce the multiplication of the gut and lungworms and, therefore, limit reinfection of the pastures until the majority of the overwintered larvae on the pasture have died out. Treatment of cattle that grazed the previous year with an effective flukicide at housing will prevent fluke eggs from being shed and snails acquiring new infections in the spring.
Cattle could be grazed on high-risk pastures (for GI nematodes) until around mid-July with a low risk of developing clinical disease. They can then be moved to lower risk grazing, such as silage aftermath, for the second half of the grazing season.
To prevent immediate contamination of the low-risk pastures, the cattle may need treatment prior to the move. It is recommended the best 10% of the group are left untreated to reduce the risk of anthelmintic resistance developing rapidly on lower risk pastures.
Pastures with a high risk of liver fluke may be avoided in late summer/early autumn to reduce the risk of infection. Other options include fencing off wet areas or early housing.
If young stock (which were not vaccinated or strategically treated with anthelmintics) remain on high-risk pastures in the second half of the grazing season, they will be at considerable risk of parasitic gastroenteritis and husk from around mid-July onwards.
Regular monitoring and appropriate anthelmintic treatment become the only options with the associated inevitable check in performance. Careful monitoring of the nutrition status of susceptible animals at this time is useful to help reduce the impact of worms on growth rates.
It is worth noting, in the UK, the majority of cattle are housed during winter and this provides a good opportunity to remove parasitic infections, not only preventing clinical disease, but also preventing the contamination of pastures on turnout in the following spring.
When treating cattle with any parasite control product, it is important to consider the withdrawal period of the product being used. The range of products available will vary depending on whether the cattle are beef or dairy, as well as factors such as whether they are dry dairy cows or fat stock close to slaughter.
A detailed list of all available options is outside the scope of this article, but the author would refer readers to the COWS Cattle Parasite Control Guide (2014b). The limitations on lactating dairy cows, in terms of available products (particularly flukicides), means good management and planning is essential.
The two major ectoparasites in cattle are mange mites and lice, and both thrive in the warm, high humidity environment created when cattle are housed.
Close contact at housing also facilitates transmission of these parasites between individuals and clinical disease is most commonly seen several months after the start of housing, typically from around January onwards.
Other parasites of note are ticks, which mainly cause problems through the spread of infectious disease, and flies, which spread disease and disrupt normal behaviour, resulting in reduced productivity.
Heavy infestations with ectoparasites are usually associated with old or debilitated animals and with young stock. As is the case with endoparasites, individuals will vary in terms of the parasite burden, as well as their ability to tolerate that burden. Selecting the most appropriate control measures for each ectoparasite will depend on:
In terms of available products for ectoparasite control, topical pyrethroids are licensed for the control of lice, but not mites – except for permethrin, which will kill both. Macrocyclic lactones are licensed for treatment of mites and lice, as well as helminths, but their efficacy for each species varies with the formulation used.
A range of pour-on pyrethroids or macrocyclic lactones may give protection against ticks, but none have a license for this use in cattle in the UK and, therefore, must be used under the cascade. Products will require regular application during high-risk periods to provide protection.
For fly control, a number of options are available in cattle. Impregnated ear tags or tail bands containing pyrethroids or pyrethroids in the form of pour-on, spot-on and spray products are widely used to control flies. Within buildings, environmental control methods may include fly traps, screens, sprays or impregnated strips. Improving on-farm hygiene may also help reduce the fly populations by limiting breeding sites for a number of fly species (Table 1).
Anthelmintic resistance seems, as yet, to be much less of a problem in cattle as it is in sheep. This is, however, all the more reason to act now and tailor the way anthelmintics are used, to reduce the rate of resistance development, therefore, preventing problems in the future.
Anthelmintic resistance is a significant – and, in some areas – production-limiting problem for the UK sheep industry and it is vital we do not allow the same situation to develop for cattle. In the UK, the species in which reduced sensitivity or incomplete efficacy to certain parasiticides have been observed include Cooperia species (one of the main causes of parasitic gastroenteritis in young cattle in their first grazing season; Bartley et al, 2012), Psoroptes ovis to macrocyclic lactones and Fasciola hepatica to triclabendazole.
It is essential that, when planning a parasite control programme for a group of cattle, the COWS guidelines on avoiding resistance are followed. Of particular importance are:
It is important to note, while there may be a seasonality and pattern to parasite control in cattle, all parasite control plans should be tailored to each individual farm and take into account topography, farm type and management practices, as well as environmental conditions.
Regular risk assessment is key to ensuring control plans are appropriate and the ability to remain flexible is also of vital importance. As key players when it comes to ensuring farmers have the most effective control plan in place, it is essential vets and advisors have a full knowledge of the parasite control products available and that farmers are well-versed in correct product administration. This includes dosing to the correct weight, correct product storage and calibration of dosing equipment.
Grazing should be managed to minimise the risk of disease with particular attention paid to the age of the stock and potential pasture larval burdens. Any control plan should be in place early in the season to allow for strategic preventive measures, such as vaccination or bolusing to be carried out prior to the relevant risk period. If regular monitoring through faecal egg counts is to be carried out, a plan should be in place to ensure critical testing windows are not missed.
Finally, it is important to encourage farmers to set growth targets for their young stock and then regularly monitor them throughout the season. This information can be used to monitor the effectiveness not only of the grazing strategy in terms of nutrition, but also their parasite control plan.
