By Roelof Bezuidenhout
Fifteen years ago, a countrywide tick resistance survey indicated that, if left unmanaged, cattle tick resistance to chemical substances used for external parasite control would no longer be effective. That threat has not diminished significantly, but laboratories can now accurately identify blue tick strains that have developed resistance to multiple chemical formulations. This makes it possible to design a strategic tick control strategy for individual farms.
New active ingredients remain a long way off, although a novel product has recently been registered in parts of South America. The development of new chemical treatments takes years, and animal health companies have been criticised for prioritising research into the more lucrative pet market over livestock needs.
The intensive use of insecticides has already led to the development of some tick resistance to three of the five groups of acaricides (the active ingredients) currently available in South Africa. The three main groups affected are amidines, synthetic pyrethroids and organophosphates. Resistance refers to the ability of a particular tick strain to survive exposure to a chemical control substance at concentrations that would normally be lethal to the broader population.
At last count, there were more than 80 compounds or trade names on the market for tick control, many of which contain the same active ingredients. Fortunately, specialists believe it is unlikely that ticks have developed resistance to all active ingredients or their various combinations.
Too many remedies, too little strategy
Experts agree that randomly switching from one plunge-dip chemical to another is risky. When a product appears to lose effectiveness and farmers switch to a different brand – often one that contains the same active ingredient – it only increases the risk of resistance. Using too little of the dip compound also allows resistant ticks to survive and reproduce, further strengthening resistance in the next generation. The use of unregistered or home-made remedies exacerbates the problem.
In essence, resistance develops from repeated exposure – especially at lower-than-recommended dosages – without targeting specific tick species in a controlled, strategic way. Pour-on treatments often fail to reach extremities such as ears and hooves, making them less effective than full-body dipping.
Alternative tick-control methods – such as using tick-resistant cattle breeds, anti-tick vaccines and targeted grazing strategies – can be helpful, but each has its limitations. For now, the most effective approach remains a combination of these strategies with the careful use of acaricides.
Blue ticks and their life cycle
Resistance develops more readily in one-host ticks, such as the blue tick, because their entire life cycle takes place on a single host, allowing for a high turnover of up to four generations per year. Blue ticks are responsible for transmitting diseases such as anaplasmosis, (also called gallsickness) and redwater (bovine babesiosis), and they can cause septic wounds and skin damage.
From the moment a larva attaches to a host, it remains there for about three weeks, progressing through the nymphal and adult stages, and feeding on blood at each stage before moulting. Because it stays on the host for an extended period, a one-host tick is likely to be exposed to acaricides multiple times during its life cycle – unlike two-host ticks (such as the red-legged tick) or three-host ticks (like the brown-ear tick), which spend only a few days to a week on the host once or twice a year.
This higher exposure frequency of one-host ticks – up to four treatments per year – greatly increases the chance of resistance developing, especially when ticks repeatedly encounter the same active ingredient.
Australian researchers have shown that the blue tick’s saliva contains a growth suppressant. A single blue tick completing its life cycle can consume nearly 3 mg blood. Considering that blood makes up about 7% of an animal’s body weight, this loss, combined with the physiological effects of infestation, significantly weakens the animal. Ticks also inhibit grazing and growth. Heavily infested animals only begin to recover after treatment, once their blood volume has been restored and parasite pressure has been reduced.
Note that the blue tick is found not just on cattle but also on sheep and goats, so much of the advice in this article applies to small stock too.
Risks and constraints
Moving stock between areas carries significant risk. Immature ticks are often invisible during inspection, and if animals are not dipped or quarantined before joining the new herd, resistant ticks can be introduced and spread throughout the herd. Some regions are relatively tick-free, but parasites such as the paralysis tick can be introduced by wildlife.
A study found that scrotal damage caused by the long-mouthed heartwater tick can negatively affect the fertility of communal bulls, reducing annual calving rates. In these systems, farmers often rely on spot treatment to kill only the visible ticks, leaving many others untouched. A major constraint is the lack of proper handling infrastructure such as crush pens and dip tanks.
Strategic control
Farmers can take several steps to help manage tick infestations:
• Combine control methods: Use both plunge-dipping and injectable treatments, and consider keeping a cattle breed that is more resistant to ticks. Alternatively, breed selectively with animals in the herd that show higher natural resistance to ticks.
• Dip with care: The most common mistake is dipping too frequently – essentially dipping your herd into resistance. It is possible to maintain effective tick control by avoiding indiscriminate dipping and steering clear of blindly buying products. Dipping less often is also far more environmentally friendly.
Tactical parasite control involves limited and carefully timed use of parasiticides. Strategic treatment early in the season – aimed at breaking the parasite’s life cycle at its first generation – can help prevent a late-season build-up. By integrating various management methods, farmers can keep animals productive while relying less on chemical remedies.
• Maintain herd health: Keep cattle in good condition, as they tend to carry fewer ticks than animals under stress.
• Encourage natural predators: Reintroduce tick-eating birds to the environment. A red-billed oxpecker can consume up to 400 adult ticks per day, and a yellow-billed oxpecker can eat up to 13 000 larvae, or 100 fully engorged adult ticks per day.
• Adapt grazing strategies: Keep a mix of grazers and browsers. Goats, for example, browse the branches of bushes and trees, which helps to open up dense undergrowth. This exposes the soil to sunlight, disrupting the humid, sheltered conditions ticks need for egg and larval survival.
• Get expert advice: For farmers who can afford it, a scientifically based tick management strategy can ultimately save time and money. This approach involves collecting ticks, sending them for analysis to identify resistance patterns, and working with an independent specialist to design and adjust a control plan. Animal health companies also offer assistance in developing and implementing these strategies.
For more information, contact:
Pesticide Resistance Testing Facility
Biology Building Room 105,
PO Box 339, Bloemfontein, 9300
Tel: 051 401 2371
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 | Roelof Bezuidenhout is a fourth-generation wool, mohair, mutton and game farmer and freelance journalist. Attended Free State University, majoring in animal husbandry and pasture science. Other interests include agricultural extension and rural development. |
