There has been a gradual increase in the incidence of external parasites, namely sheep scab and lice, in recent years. Both of these parasites are the most common causes of sheep scratching at this time of year. Sheep scab and lice are highly contagious and, once they gain entry into a flock, can establish and spread very quickly.
There has been a gradual increase in the incidence of external parasites, namely sheep scab and lice, in recent years. Both of these parasites are the most common causes of sheep scratching at this time of year.
Sheep scab and lice are highly contagious and, once they gain entry into a flock, can establish and spread very quickly.
Many farmers and vets point in particular to a higher incidence of lice in recent years, which is also the case in housed cattle.
However, many producers are not aware of an increased incidence of lice and where not carrying out plunge dipping are incorrectly treating sheep for sheep scab.
No match for plunge
It is important to note at the outset that there is no other treatment route that will match plunge dipping in terms of providing control for all external parasites including sheep scab, lice, ticks, keds, etc.
Plunge dipping lessens the importance of identifying the external parasite present. It is also important to note there are no veterinary products licensed for use in sheep showers or other spray units in Ireland.
Identifying scab and lice
Identifying the parasite causing the problem can be difficult to carry out and may require veterinary assistance.
Sheep scab mites are brown in colour, round and are tiny – barely visible to the naked eye. They feed on flesh and are generally found on the skin where scabby lesions and wool loss are characteristic of scab.
In contrast, lice are easier seen by the naked eye and move through the wool. Lice are long, shaped similar to a wasp with a yellow or pale brown colour.
Your vet will be able to diagnose by examining using magnification or taking a sample for examination under a microscope.
Treatment options
Options for farmers who do not have access to a dip are generally more complicated and require a combination of injectable and pour-on products.
Discussing dipping, Morgan Lane of Bimeda says that dipping requires investment in time and purchasing products and, as such, it is important to follow best practice guidelines to ensure optimum control and a good return for this investment.
“There is no doubt that dipping works excellently and also gives sheep an overall boost. However, we regularly see farmers not getting the most out of dipping by flawed practices," he said.
Morgan says the following guidelines are all critical in ensuring effective control.
Do not add colours: adding colouring agents to prepare sheep for shows or sales may seem worthwhile by completing two tasks at once, but it can be detrimental. It can cause chemicals to separate, making dipping useless in combating external parasites or, worse still, it can lead to a risk of poisoning sheep. Reduce the pressure on sheep: sheep should be dipped early in the morning or on a cool dry day. Allow sheep to rest pre-dipping if they have been active for a period while flocking. Ideally, dip sheep when empty; it puts less stress on the animal and also the operator in handling the sheep. Post-dipping lameness: post-dipping lameness occurs when sheep are dipped in solution from the previous day or in heavily contaminated mixture. Where it hits, it can be a big problem, with sheep going lame two to four days after dipping. Problems can last for a few weeks and, in worst cases, require continuous and costly veterinary intervention. Sheep should only be dipped in solution prepared before dipping takes place and sheep should never be dipped in solution prepared the previous day. Follow manufacturers' guidelines: this is self-explanatory – different products vary in their control, usage guidelines and also chemical composition (organophosphate (OP) and non-organophosphate dips). For example, Cyperguard and Ectoflits are very similar, but Cyperguard probably shades it in terms of giving better control of ticks and, as such, this is the dip we recommend most for hill areas. Some farmers also have preferences on using OP or non-OP dips. Correct concentration: I have left this until last as, for me, it is one of the most important that I want to spend a bit of time on. Every time a sheep passes through a dipping tub, she removes solution and generally walks away with two litres of solution, part of which is returned through flow back from the draining pen. However, it is important to note that the active ingredient strips to wool (holds to wool) and, therefore, while there is solution returning to the dip tub, it is mostly water.
If the active ingredient concentration drops below a certain level sheep won’t receive adequate treatment. It is for this reason that it is critical to monitor the number of sheep passing through and top up the tub with the recommended volume when required.
Over time, the solution will become weaker, even if topping up is taking place, and, at a certain stage, it is highly recommended to mix a fresh batch of dip.
This will also depend on contamination brought by sheep into the tub, but a general rule of thumb is that one sheep can be dipped for every two litres that the dipping tub holds before replacing.
For example, if the dipping tub holds 1,000 litres, it is recommended to replace and mix a fresh solution after 500 sheep have passed through. Alternative non-dipping treatment
Outside of dipping, there is no product available that covers both sheep scab and lice. As such, it is hugely important to identify parasites correctly.
For sheep scab, there are numerous products on the market with active ingredients, such as ivermectin, moxidectin or doramectin.
Take note that most products require retreatment seven to 14 days later to address eggs that were unhatched at time of treatment.
The exception to this is products such as Dectomax or Cydectin 2% LA, which has been recently relaunched on the market and is marketed as a single-treatment product.
Options for treating lice include injectable and pour-on products. It is advisable to study product characteristics closely to assess if biting and suckling lice is targeted.
Irrespective of the type of treatment selected, it is important to treat all sheep in the batch at the same time and prevent mixing of sheep post-treatment.
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