What are Pour-ons?

Pour-on treatments are applied epicutaneously to livestock for the control of ectoparasites and tsetse flies and the various diseases that they transmit. The pour-on treatment is one of several live-bait techniques and one that is simply administered, as it is purchased as a ready-to-use formulation and does not require dip tanks, spray races or hand-held, pressurised spray equipment. Instead, oil based formulations are provided is sachets or bottles for pouring over the back of the animal, normally from the base of the neck to the tail. For the control of tsetse flies, suspension concentrates of pyrethroids are the most popular, with coconut oil acting as a ‘spreader’. Other classes of insecticides are employed to control ticks but normally through the use of dip tanks and spray techniques.

To give good control of tsetse by contact action, the concentration of active ingredient in pour-ons is high compared with dip and spray formulations. This is reflected in the cost of pour-ons, but the cost of the ‘spreader’ oils and the real convenience factor contributes significantly to their cost. Examples of pyrethroids used as pour-ons are:
 

Compound	Trade Name *	Formulation*
Deltamethrin	SPOTON	1% S.C.
Alphacypermethrin	Renegade	3% S.C.
Flumethrin	Bayticol & Drastic Deadline	1% S.C.

(* trade names and formulation may vary with country)

Other pyrethroids such as lambda-cyhalothrin and cyfluthrin have undergone trials as has the phenyl pyrazole insecticide, Fipronil.

Fiscal problems, deteriorating infrastructure and the recent trend away from large-scale public tsetse control operations have placed considerable pressures on farmers in some tsetse affected countries to undertake their own disease control measures. Many departments of veterinary services in Africa now actively encourage disease control interventions at farmer and community levels in order to offset the recurrent cost of their disease prevention and treatment programmes. The poorest, tsetse-infested countries are among those planning control operations that rely on the pour-on technique, partly because it places the responsibility and costs on to the user. Donor agencies already support the development of the technique and Zimbabwe, Tanzania, Zambia, Uganda, Ethiopia and Burkina-Faso already have tens of thousands of insecticide treated cattle each. The treatment of cattle with pour-on formulations is an effective technology that is being rapidly adopted by rural farmers, communities and ranchers in tsetse-affected areas. Pour-on products are now available in E,W and southern Africa.

Environmental Impacts

The environmental impacts of pyrethroids used in pour-on and dip formulations have not been a focus of livestock related research. Little is therefore known about their potential effects on user health and the surrounding environment. Inevitably, their misuse, including poor user safety and disposal practices will result in measurable impacts.
 

Reports from farmers, research stations and recent literature suggest a causal connection between the use of insecticide treated cattle (for tick and tsetse control) and the mortality of dung beetles (Scarabaeidae). Research conducted in South Africa associated the effect with the contaminated dung of treated animals.  Recent work in Zimbabwe showed that alphacypermethrin and deltamethrin residues in the dung of treated cattle were high enough to be acutely toxic to dung beetles (Onthophagus, Copris and Onitis spp) and significant residues were found in samples of dead beetles surrounding treated cattle.  Dung beetles are important decomposers of animal dung and benefit plant and soil by recycling nutrients, aerating the soil, improving OM content, water retention and plant root penetration. Most work on dung beetles has focussed on the avermectins (parasiticides), but the broad spectrum pyrethroid insecticides in faecal residues have the potential to disrupt a much wider fauna associated with dung, such as termite spp, that also assist the dispersion and incorporation of dung in soil, particularly in dry season.  Ornithologists have also questioned the potential impacts of treated cattle on oxpecker health.

Use of Pour-ons is linked  to dung-beetle mortality

Insecticides appear to gain entry to the animal via grooming and absorption through the skin. The presence of insecticides in the alimentary canal raises the question of possible residues in livestock products like milk and meat. Residues of crop protection chemicals left on straw and used as feed have reduced the quality of animal products in Asia, and raised questions of consumer safety. An additional public health risk is that caused by dung-breeding nuisance flies, whose numbers rapidly increase when dung burial is delayed (the reason for importing dung beetles as fly biocontrol agents in Australia). Research is required to assess the potential health and ecological implications of insecticide-treated cattle and to put them in perspective with other techniques of vector control, such as target technology, ground and aerial spraying of insecticides. Once this is done, the relative impacts can be used to influence policy decisions.
 

See Also

Animal Health Control

Integrated Control of Ticks and Tick-borne Diseases. The CARICOM/FAO/IICA Caribbean Amblyomma Program. http://www.ruu.nl/tropical.ticks/nwl497e.htm

B. Wahlstr`m. 1997. Alternatives to Persistent Organic Pollutants. Presentation to the UNEP Sub-regional Meeting on Identification and Assessment of Releases of Persistent Organic Pollutants, St Petersburg, Russian Federation, 1-4 July 1997. http://www.chem.unep.ch/pops/stpeter/stpet15b.html

List of Federally Registered Restricted Use Pesticides. http://entweb.clemson.edu/pesticid/Document/fedrup.htm