Lice and Angora GoatsMonday, 2nd March 2020
By Dr Mackie Hobson
Lice can have a big impact on both the quantity and quality of mohair with a study by Grootfontein (Brown et al 2005) showed that treated Angora goats produced 271g (2.12kg Vs 1.85kg) more hair than untreated goats. Surprising however the fact that the same study showed that there was no significant impact on the weights of the goats.
It is thought that the lice irritation causes the skin to thicken and effect the skin structure so reduce hair produced as well as the physical loss of hair through damage by scratching. The fibers are weakened, lack luster, and become matted, tangled, and discolored.
There are two species of lice commonly found on Angora goats are red lice (chewing lice) which feed on the dead flakes of skin and secretions and blue lice (sucking lice) which feed on blood. Blue lice tend to be larger than red lice with a narrow head and wider dark brown to bluish in colour due to the blood ingested when feeding.
Red lice visible on Angora goats
How can lice be transmitted?
Lice are generally transmitted from one goat to another by contact and are most often introduced to herds by bringing infested animals into the flock.
It is a mechanical transmission so shears and clothing can potentially also transfer lice.
Most farmers complain about how quickly the flock is re-infested. This may be due to the fact that most re-infestation occurs because the pesticides does not kill the eggs and these eggs hatch and the lice are seen to be back on the goat when checked again with 9-18 days!
This is the reason that many treatments advise repeating the treatment within 14 days.
How long can lice survive away from the Angora goat?
Lice cannot survive more than a week away from their host however under favourable conditions, eggs clinging to shed hairs may however still continue to hatch for 2 to 3 weeks later. A trial at Grootfontein showed that adult red lice can survive away from the Angora goat for only 36 hours under optimum environmental conditions.
What about sheep, goat contact?
Although lice tend to be host specific Ligognathus africanus (blue lice) infests sheep and Angora goats.
The red lice Damalinia caprae/limbata differ from the red lice of sheep Damalinia ovis and have a preference for Angora goats.
A study where an adult Angora goat ewe was kept with an adult Boer goat ewe in the same pen for seven months demonstrated that red lice from the Angora goat ewe never parasitised the Boer goat ewe. (J Joubert)
- The importance of knowing the Life Cycle of the lice.
One of the main reasons that Angora goats getting re-infested is that fact that treatments are not ovicidal (don’t kill the eggs) so the eggs hatch after treatment and the cycle continues. This is why many products advice repeating the treatment again after within 14 days.
Lice spend their entire life cycle on the goat with female lice gluing eggs on the hair close to the skin. These eggs hatch in 1 to 2 weeks (9 to 18 days).
The entire life cycle of goat from the time the eggs laid until maturity is 14 to 75 days. The adult lice usually live for about a month.
- Using pour on products on different sites of the body.
Using pour on products along the back of Angora goats can potentially effect the fleece, especially in long hair. Greasy appearance of fleece after pour on treatment in photo below.
For this reason M.A.Snyman, J.N. Snyman and M. van Heerded conducted a study to demonstrate that applying pour on pesticides to different part of the body was effective. For more info see their study.https://www.angoras.co.za/article/pour-on-products-application-to-alternative-sites-on-angora-goats-and-the-effect-of-hair-length#289
This was also demonstrated in a field study by the SAMGA vet using fipronil/abamectin applied to the axilla skin rather than along the back. https://www.angoras.co.za/article/fipronil-abamectin-atilla#258
- The effect of long and long hair on the effectivity of pesticides
The trial by M.A.Snyman et al also demonstrated that the pour on pesticide was equally effective in long and short hair animals. For more info follow the link above.
However it seems that the insect growth regulator was more effective when applied to short hair goats, although lice counts in the long hair animals were also reduced.
Dips are more effective in shorter than longer hair and treating after shearing (2-6 weeks) is often a good time after any shearing wounds have healed.
Because blue lice don’t move around in the fleece as much as red lice do, it is thought pour-on remedies don’t work as well for blue lice as the do for red lice.
- Treatment Options
Whatever treatment is used in order for it to be effective, the whole herd must be treated simultaneously.
The export of Mohair to Europe is regulated by strict residue criteria regulated by OEKO-TEX which has resulted in guidelines being set for the use dips and pour-on products for Mohair producers in South Africa. These guidelines may change in future as determined by the OEKO-TEX® standards and as further information obtained from residue trials and testing becomes available.
Current SAMGA Guidelines are on the website and get regularly updated.
Some of the current treatments (Dips, Pour on and injectable) available to treat lice can be seen by following the link https://www.angoras.co.za/article/ectoparasite-treatment-guidelines#357
How can farmers reduce resistance to pesticides by lice?
- The product label instructions must be followed closely. If the label states two treatments, then two treatments must be administered. The first treatment will only kill active stages of parasites present at the time of treatment. The second treatment will kill any eggs that have hatched since the first treatment.
- All oncoming stock should be quarantined for at least three weeks (21 days), and observed for signs of infestation. Do not mix with the main flock until treatment is complete and the parasite eradicated.
- ‘Good Dipping Practice’ should be followed. Saturation dipping must be carried out. Heads must be submerged at least twice. Goat rams with long horns that do not have their heads submerged may carry lice populations causing re-infestation. Just one incorrectly dipped goat can be a source of infection.
- Farmers often do not correctly determine the concentration of the dip. Too weak a dip mixture will lead to more rapid resistance development. Calibrated dip tanks with known volumes and dip made up accordingly. Note that initial filling of dip tank and replenishment concentrations may be different. Length of hair may also determine the manufacturers dipping concentration.
- Farmers often make the mistake of only re-filling the dip tank when the levels get a bit low rather than constant rate replenishment. (The active ingredient gets ‘stripped’ by the hair from the dip concentration while dipping)
Dr Mackie Hobson