Course: Livestock pests | Last Updates: 7th October 2015
Whether they cause you a problem this winter will largely be down to how you manage your herd, rather than circumstance.
A small number of lice on cattle may be common and cause no problem. But a severe infestation can be more serious. It is the irritation that has the most impact, causing skin lesions and damage to buildings as animals rub themselves.
The preoccupation with an irritation may also bring about a loss of productivity through reduced food intakes, although it’s hard to put this in financial terms. They can cause anaemia, a potentially serious concern, particularly in calves. There is also the welfare issue to consider where infestations are not properly managed, while other health issues can exacerbate a lice problem.
What types of lice affect cattle?
There are two main types – sucking and biting lice. It’s important to know which you have to control them effectively.
Sucking lice (have smaller heads than biting lice and penetrate the skin.
Biting lice, Bovicola bovis, lay an egg every two days. These hatch seven to 10 days later, and pass through three nymph stages before they become adults at about two to three weeks. They survive for about 10 weeks, which is how populations can build.
There are three main species of sucking lice – Linognathus vituli, Haematopinus eurysternus and Solenopotes capillatus. They have a life cycle of a month, with eggs hatching after 10-15 days. These pass through three nymph stages and reach adulthood at two to three weeks.
How do you spot them?
Both adults and eggs are visible to the naked eye and, if present in large numbers, can be seen by parting the hair, particularly along the back. While eggs are whitish in colour and glued to hair shafts, adult biting lice are reddish brown, about 2mm long with a brown head. Sucking lice have smaller, narrow heads, designed for piercing the skin. Microscopic examinations of hair samples are required to identify species, although symptoms will usually point to which type of lice are present.
Both biting and sucking lice can cause skin irritation. The signs are baldness and skin damage, particularly across the head and back, and frequent scratching. Sucking lice can cause anaemia, particularly in young calves, and are more common around the head and neck area. Infected cattle will tend to be more listless and withdrawn as a result.
What effects do lice have on cattle?
This will depend on the burden in cattle as many light infestations cause no ill effects at all.
Biting adult lice feed on outer layers of skin and the hair shaft, causing hair loss and skin reactions. These are exacerbated as the animals rub themselves, leading to self-trauma. If there is a heavy burden and a skin irritation is driving your cattle mad, milk yield or liveweight gain is likely to be affected. Rubbing themselves on gates and other building structures can cause costly damage, while irritated animals are more likely to cause stress within the herd.
Sucking lice can cause irritation, but also penetrate the skin and feed on blood. In severe cases the anaemia can cause weakness and even death.
Lice are probably the primary cause of light spot and fleck. This is a blemish visible on the hide of cattle which downgrades the value of leather, costing the leather industry about £20m a year.
Both sucking and biting lice can exist within a herd at sub-clinical levels, and you may never even know your herd is infected. But put them under stress, particularly if there are other chronic health issues, such as pneumonia, and symptoms will start to show and animals will lose condition.
How do lice become a problem?
Lice may be present in most herds at low levels, but cannot survive for long away from the host animal. They spread via animal-to-animal contact, and populations will slowly build up over time. This tends to happen fastest in winter when cattle are housed. Conditions here are ideal: Coats are thickening up, providing the perfect environment for the light-shy lice. Cattle are also closer together, helping spreading, and shelter from the weather also favours louse development. Lice also prefer cooler skin temperatures.
The standard of your cattle building has little direct bearing on whether you will have a problem, although dirty housing cannot be completely ignored. Tighter stocking will favour spread, however, and again the standard of housing will affect an animal’s well-being, which in turn affects whether lice become a problem.
What treatment is necessary?
If properly applied and managed, treatment can control lice on-farm. Specific treatment choices where necessary should be discussed with your vet and recorded in the farm’s health plan.
Housed cattle can easily spread lice between themselves, so pre-housing treatment can be beneficial.
There are two main classes of product – synthetic pyrethroids and macrocyclic lactones (MLs). ML treatments are available as pour-on or injectable formulations. Injectables can only aid in the control of biting lice, while pour-ons will be effective against both types.
Care is needed to get the best out of a pour-on. Common mistakes are to underdose or not apply properly. You’re most likely to get it wrong if you try to corner animals in a field. The only way to apply the correct dose is to pass the herd through a race and crush.
When cattle are still outside, bear in mind that heavy rain may reduce the efficacy of a pour-on treatment.
It is important to ensure you treat every animal in a group, however, or the entire treatment will be wasted. Any cattle bought in may also need to be treated. MLs are broad-spectrum and will treat for worms and other skin parasites, too. But if applied to a dairy herd, make sure you adhere to withdrawal guidelines.
Pyrethroid-class pour-ons are effective against lice and other external parasites of cattle. One treatment is usually effective, successfully treating a louse burden. But in rare circumstances with heavy burdens a follow-up treatment is required.
How do you prevent lice becoming a problem?
Consider the risks based on previous experience with the herd and discuss any routine treatments with your vet.
An important factor is the general well-being of the herd or animal. Provided you take steps to keep your animals stress-free and free of other diseases, lice are less likely to pose a problem.
Healthy calves will self-groom, reducing the burden of louse eggs. Animals that are ill for some other reason will neglect their own self-care and louse numbers will build.
The thicker the winter coat, the more lice will thrive. This means the practice of clipping coats, often done in a strip down the back to reduce overheating, also has benefits for reducing lice.
But generally speaking a good herd health plan and daily checks to identify any problems will help reduce reliance on chemical treatments and lice will bother neither you nor your cattle.
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