| | Take home message | Introduction | Biology | Diagnosis and symptoms | Louse management | Louse control products | Reference
This is a fact sheet from the Health Management section of the Alberta Feedlot Management Guide, Second Edition published September 2000. The 1200 page guide is available for purchase on CD-ROM.
Take Home Message
- Lice can have a substantial impact on feedlot cattle, affecting their gain, efficiency and appearance.
- Keeping cattle well fed, in clean, dry, and sheltered will aid the management of lice.
- Strategic, appropriately timed, treatment programs will aid the management of lice.
- The benefits of effective louse management will be evident in increased efficiency, improved appearance and in reduction of damage to facilities.
Introduction
Lice result in production losses, in both beef and dairy sectors, that exceed $30 M annually. Producers spend an additional $8-10 M for treatments. Losses associated with lice result from blood loss, irritation and from changes in behaviour, which reduce efficiency. Losses are also seen as reductions in hide value that results from the response to sucking louse activity. Damage to facilities and equipment, resulting from scratching to relieve the skin irritation, is an additional cost associated with louse infestations.
Lice are a winter season problem. The interaction between louse biology and the Canadian climate make it important to consider several factors in developing a management scheme aimed at reducing louse populations. Effective antiparasitic products that provide long lasting protection are a critical element in the management of louse populations on cattle.
Biology
Lice are wingless insects that spend their entire life cycle on the host animal. There are no stages that are free-living. Two types of lice are found on feedlot cattle. They are distinguished by their shape and feeding habits.
Sucking lice
Sucking lice have narrow, pointed heads with antennae that point forward. The head is narrower than the rest of the body. The legs are stout and have strong claws used for holding on to hair shafts. A firm grip is needed to keep the louse near the skin surface and to keep the mouthparts firmly anchored in the host. When observed on the host sucking lice are relatively immobile. The abdomens are broad and usually pointed at the end. Females are larger than the males and they are usually more abundant.
Chewing lice
Chewing lice are distinguished by having a rounded head with antennae pointing toward the rear. The head is as wide as the rest of the body. The legs are slim with poorly developed claws. These lice are highly mobile and are often observed moving over the skin surface when hair is parted.
There are three species of sucking lice and one species of chewing louse that are found on cattle in Canada.
The chewing louse and one species of sucking louse, known as the long-nosed sucking louse, are currently the species most frequently found on feedlot cattle. Examination of randomly selected cattle entering feedlots in southern Alberta showed that 70% were positive for one or both of these species. Similar observations have been made on 6-8 month old calves at fall weaning. The two other species of sucking lice, known as the little blue louse and the short-nosed louse, are found much less frequently and when found they are usually on mature cattle.
Sucking lice have fine needle-like mouth parts that are carried hidden within the head. During feeding the mouthparts are inserted into small blood vessels in the upper layers of the skin. Saliva injected by the lice helps to increase the blood flow and prevent clotting. Cattle develop immune responses to these salivary secretions and circulating antibodies can be detected in the blood. Immune responses may affect blood flow in localized areas of the skin and influence distribution of the lice on individual hosts. Changes in blood flow and other responses to louse feeding may result in hair loss. However, a wide variety of other factors can result in hair loss and the correlation between louse presence and hair loss is very low.
Lice have three larval, or nymph stages followed by the adult stage (Figure 1). Each life stage looks very similar to the adult, but is smaller and not capable of reproducing. All life cycle stages of the sucking lice require a host. Nymphs and adults take numerous blood meals each day and as a result survival off the host is very short, usually less than 48 hrs.
Figure 1. Stages in the Life Cycles of Lice.
Eggs are attached to the hair shafts and have species specific characteristics. Recent research shows that female lice can lay up to six eggs per day, although more typically they will lay 2-3 eggs per day. The rate of egg production does not appear to be influenced by temperature variation on the skin.
Development rates for eggs and nymphs are affected by temperature. Generally, developmental rates increase as the temperature rises. However, there is a lower threshold temperature, below which no development takes place and there is an upper threshold temperature, above which the insects will die. Eggs of the long-nosed sucking louse have a lower developmental threshold near 25°C and an upper threshold near 40°C. The range for other species is probably similar.
The upper threshold temperature for eggs is important in understanding the decline of louse populations in the early spring and summer. Temperature of skin exposed to sunlight can quickly surpass the upper threshold and thus as the photoperiod lengthens in spring there will be increasing mortality of eggs. The absence of development at temperatures below 25°C suggests that eggs not on the host will not develop. Thus, eggs left on fences and equipment are unlikely sources of re-infestation by sucking lice.
Development rate of nymphs is also affected by temperature. The number of days required to reach maturity (i.e. from hatch to first egg deposition) decreases as temperature increases. An upper threshold has not been determined although it is likely to be between 42-46°C. Thus, survival of nymphal stages will also be reduced as photoperiod increases in spring and summer. However, nymphs and adults are mobile and can move to body regions where temperatures are more favourable. These regions act as refugia from which lice can then re-infest other regions and other animals when temperatures become more favourable.
Chewing lice feed on dead skin, hair and other debris on the skin surface. The chewing activity and the deposition of saliva on the skin surface may result in the host developing a limited immune response, which will include the development of circulating antibodies.
All life cycle stages occur on the host. Development rates for eggs and nymphs are influenced by temperature with upper and lower thresholds that are similar to those for sucking lice. Thus, conditions affecting sucking lice will have similar impact on the chewing lice. Chewing lice are capable of living off of the host for several days. Temperature and other environmental conditions will affect survival of chewing lice when off the host.
Females of the chewing louse, Bovicola bovis, produce eggs at a much lower rate than the sucking lice. Each female will produce only one egg every 2-3 days. However, these lice are parthenogenic and produce viable eggs in the absence of males. The vast majority of the eggs will produce female offspring. Population growth can thus be rapid.
Diagnosis and Symptoms
Symptoms of louse infestation are rather vague but may range from excessive licking and scratching to hair loss and in extreme cases anemia. Cattle that are heavily infested with sucking lice will have discolouration around the face and brisket that is the result of excretion of digested blood by the lice.
Hair loss is a poor indicator of louse infestation. A wide variety of other organisms and conditions may lead to hair loss; these include ringworm (a fungal infection), mineral imbalances, and allergic reactions.
Definitive diagnosis of louse infestation requires close examination of the skin surface. The examination should be conducted on restrained animals held in a well-illuminated area. Several 10-15 cm long partings of the hair should be conducted at each of the sites indicated in Figure 2 on the left.
Figure 2. Areas to inspect for louse infestation.
Louse Management
An effective louse management program has four critical elements:
- Adequate nutrition;
- Good husbandry, including provision of shelter and clean bedding;
- Genetics;
- Strategic treatment.
Application of strategic treatments and provision of adequate shelter and bedding are the two elements that are most applicable to feedlot cattle.
Provision of adequate bedding and shelter to keep animals clean and dry are part of husbandry procedures that reduce the stress on animals. The additional drain on energy associated with keeping warm and the impact of stress on immunity can combine to make animals more susceptible to louse infestation. Clean, stress-free animals will actively groom themselves, frequently licking most parts of their bodies. This behaviour is an effective way in which animals reduce louse populations.
Application of an effective treatment is crucial to reduction and management of louse populations. However, it is unlikely that louse management is the only objective of most treatment programs. It is important to approach the management of lice as part of a complete parasite management program and to make treatment decisions accordingly. Thus, timing of treatment should coincide with management of cattle grubs and nematode as much as possible.
Application of treatments should be timed to fit the biology of lice and be timed to prevent population buildup. Thus, treatments should be applied in fall or early winter prior to the population peaks, which occur in January. Delaying treatment as long as is consistent with other management practices reduces the risk of louse populations rebuilding should new, infested animals enter the herd.
Duration of activity of a product is crucial to the assessing the need for retreatment. Hatch of eggs after adults have been killed means that the product must be effective long enough to kill nymphs hatching from the last eggs laid. Since egg development slows at lower temperatures the persistent activity must extend beyond the longest possible development time. Extremely cold winter temperatures, which will slow egg development, will have an impact on the effectiveness of various products.
Choice of product will vary according to treatment objectives. In most situations long term reduction of louse populations is the objective and this fits well with control programs for other parasites. For these circumstances the broad spectrum, macrocyclic lactone based endectocides make the best choice. For spot treatments of infested animals and for treatments that must be done later in the winter it may be more cost effective to select one of the insecticides with a narrow spectrum of activity.
Louse Control Products
Louse control products can be grouped into two major classes (a) the macrocyclic lactone based broad spectrum parasiticides or endectocides and; (b) classical insecticides from several chemical families. The endectocides are active against a wide spectrum of insect/mite and roundworm parasites. Insecticides have a narrow spectrum of activity and are effective against limited groups of insects/mites/ticks. The insecticides can be grouped according to whether they have systemic activity (i.e. are absorbed into the animals blood through which they are spread throughout the body) or whether their effects are topical.
Reference
- Lysyk, T.J., Philip, H.G. and Colwell, D.D. 1999. Recommendations for the control of arthropod pests of livestock and poultry in western Canada. LRC Mimeo Report 11, Agriculture and Agri-Food Canada, Lethbridge Research Centre. 115 pp.
Douglas Colwell, Ph.D., Agriculture & Agri-Food Canada, 2000. Alberta Feedlot Management Guide. |
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