Lice Infestation

Lice infestation, medically termed pediculosis, represents one of the most common ectoparasite problems affecting farm animals worldwide, caused by host-specific wingless insects that spend their entire life cycle on the host animal. These obligate parasites cannot survive for extended periods away from their preferred host species, making direct animal-to-animal contact the primary mode of transmission within and between herds and flocks. Lice affecting livestock fall into two functional categories: sucking lice that pierce the skin to feed on blood and tissue fluids, and biting or chewing lice that feed on skin debris, hair, and surface secretions. Both types cause significant irritation leading to scratching, rubbing, and self-trauma that compromises animal welfare and productivity across all major livestock species.

Lice infestations occur in virtually all livestock species maintained in agricultural production systems, with different louse species adapted to each host type. Cattle are affected by multiple species including the short-nosed cattle louse, long-nosed cattle louse, little blue cattle louse, and cattle biting louse. Sheep harbor the sheep body louse and face louse, while goats support goat-specific populations. Pigs are parasitized by the hog louse, one of the largest louse species affecting domestic animals. Poultry experience infestation by numerous species of biting lice adapted to different regions of the bird's body. Prevalence peaks during winter months when animals are housed together and hair coats or fleece provide optimal conditions for louse survival and reproduction.

The economic and welfare impact of lice infestations affects livestock operations through reduced productivity, treatment costs, and compromised animal wellbeing. Heavy infestations cause significant blood loss from sucking lice species, particularly problematic in young or debilitated animals where anemia may develop. Constant irritation from both lice types reduces feeding activity and disrupts rest, leading to decreased weight gains, reduced milk production, and impaired reproductive performance. Hide and fleece damage from scratching and rubbing represents direct economic loss to producers. The animal welfare implications are substantial, with heavily infested animals experiencing chronic discomfort that significantly diminishes quality of life.

Treatability of lice infestations is generally excellent, with numerous effective antiparasitic products available for livestock use that achieve rapid parasite elimination when properly applied. The importance of correct product selection, application technique, and treatment timing cannot be overstated, as inadequate treatment may fail to eliminate infestations or permit rapid reestablishment from surviving parasites or untreated in-contact animals. Strategic treatment programs coordinated with production cycles and seasonal patterns achieve superior long-term control compared to reactive treatment of heavy infestations. Prevention through biosecurity measures and appropriate monitoring reduces both the frequency and severity of lice problems in well-managed livestock operations.

The primary cause of lice infestations in farm animals is colonization by host-specific louse species that complete their entire life cycle on the host animal. Lice are wingless insects with flattened bodies adapted for living among hair, wool, or feathers, possessing specialized legs with claws designed for gripping host integument. Female lice cement their eggs, called nits, to hair shafts or feather bases where they hatch after one to two weeks. Nymphs resemble small adults and pass through several molts over two to three weeks before reaching reproductive maturity. Adult lice survive only days to weeks off the host, making direct animal contact essential for transmission. Different louse species demonstrate specific preferences for body regions based on microclimate conditions including temperature, humidity, and light exposure.

Genetic and breed predisposition to lice infestations relates primarily to hair coat or fleece characteristics and individual immune responsiveness rather than inherent genetic susceptibility to parasitization. Breeds with denser, longer hair coats provide more favorable microhabitats for louse survival and reproduction. Fine-wool sheep breeds may support higher louse populations than coarse-wool or hair sheep varieties. Individual animals within populations vary in their apparent attractiveness to lice and ability to mount effective immune responses limiting parasite numbers. Some evidence suggests familial patterns of susceptibility that might respond to selective breeding, though management factors typically exert stronger influence than genetics on louse population levels.

Environmental and management factors significantly influence lice infestation occurrence and severity through effects on transmission opportunities and animal susceptibility. Winter housing congregates animals in close contact, facilitating louse transmission while dense winter hair coats or fleeces provide optimal conditions for louse survival. Overcrowding increases both direct contact frequency and stress levels that may compromise immune resistance. Poor nutrition weakens host defenses while supporting parasites with readily available nutrients. Concurrent disease or physiological stress from production demands creates conditions favoring louse proliferation. Introduction of infested animals represents the primary route for new species or population establishment in previously clean herds or flocks.

Risk factors for lice infestation development encompass animal-level, environmental, and management variables determining infestation probability and severity. Young animals, particularly during their first winter, often experience heavier infestations due to immunological naivety. Older or debilitated animals with reduced grooming activity and compromised immunity may harbor higher parasite loads than healthy adults. Winter months consistently show highest infestation rates due to combined effects of housing, coat condition, and environmental factors limiting natural louse mortality. Animals in poor body condition face increased susceptibility compared to those in good nutritional status. Previous treatment history affects likelihood of infestation, with regularly treated populations maintaining lower parasite pressure.

The pathophysiology of lice infestation involves direct tissue damage from parasite feeding combined with host immune and inflammatory responses to parasite presence and antigens. Sucking lice insert piercing mouthparts through the skin to access blood and lymph from dermal vessels, causing localized tissue damage and blood loss that may become significant with heavy infestations. Biting lice create superficial abrasions as they feed on epidermal cells, skin debris, and surface secretions. Host immune responses to louse saliva, feces, and body antigens produce hypersensitivity reactions increasing pruritus beyond the direct effects of feeding damage. Scratching and rubbing in response to irritation causes secondary skin trauma including hair loss, skin thickening, and wounds potentially susceptible to secondary infection.

Early warning signs of lice infestations often appear as behavioral changes before parasites or their damage become readily visible during routine observation. Increased rubbing against fences, posts, trees, or structures represents one of the earliest observable indicators as animals attempt to relieve itching. Scratching with hind feet at accessible body regions, particularly behind ears and on neck, suggests developing infestation. Subtle changes in coat appearance including roughened areas or small patches of hair loss may precede more obvious damage. Restlessness and frequent position changes indicate discomfort. Reduced feeding activity during periods of active scratching affects intake even before weight loss becomes apparent. Close examination during handling may reveal lice or nits before behavioral signs become obvious to routine observation.

Common symptoms of lice infestations share fundamental characteristics across livestock species while varying in specific presentation based on louse type and host animal characteristics. In cattle, infestations typically produce patches of roughened, thinning hair coat with characteristic distribution patterns reflecting preferred locations of different louse species. Sheep exhibit fleece derangement with broken wool fibers and tags from rubbing, potentially severely impacting fleece value and yield. Goats show similar patterns to sheep but with more visible skin changes due to shorter coats. Pigs develop skin irritation with thickening and wrinkling, often concentrated behind ears and in protected body regions where the large hog lice congregate. Poultry demonstrate feather damage, skin irritation, and decreased egg production with heavy infestations.

Behavioral changes associated with lice infestations reflect the chronic irritation these parasites cause and the ongoing efforts of affected animals to obtain relief. Constant rubbing against available objects becomes increasingly frenetic as infestations intensify. Animals may be observed biting or licking accessible body regions attempting to address unreachable irritation. Reduced grazing or feeding time as animals prioritize scratching activities affects intake and subsequent performance. Restlessness interferes with normal rest patterns, with affected animals frequently rising, repositioning, and resuming lying as discomfort prevents sustained rest. Irritability may manifest as altered responses to handling or interactions with herdmates.

Physical signs of lice infestation become progressively more apparent as parasite populations increase and accumulated damage from scratching intensifies. Hair loss occurs in characteristic patterns corresponding to areas animals can reach for scratching and rubbing, often producing a distinctive moth-eaten appearance. Skin thickening, scaling, and hyperpigmentation develop in chronically affected areas. In light-colored animals, the parasites themselves may be visible as small moving specks on the skin surface or attached to hair shafts. Nits attached to hairs appear as small white to yellowish specks that do not easily dislodge. Excoriation and scabbing result from intense scratching in heavily infested animals. Secondary bacterial infection may develop in traumatized skin.

Symptom progression in untreated lice infestations follows seasonal patterns superimposed on gradual intensification as parasite populations grow. Initial light infestations may produce minimal obvious signs while populations establish and expand. Increasing parasite numbers during fall and early winter produce progressive intensification of clinical signs. Peak severity typically occurs during late winter when parasite populations reach maximum levels and animals exhibit most severe rubbing damage and hair loss. Some natural decline occurs during spring as hair coat changes and increased sunlight exposure create less favorable conditions for lice survival. However, residual populations persist to reestablish infestations the following season without intervention.

Emergency symptoms requiring immediate veterinary intervention are uncommon with lice infestations alone but may develop when heavy sucking lice populations cause significant anemia, particularly in young, debilitated, or heavily pregnant animals. Signs of anemia including pale mucous membranes, weakness, and exercise intolerance in young cattle with heavy infestations warrant urgent evaluation. Secondary skin infections progressing to systemic illness require intervention. Severe self-trauma creating open wounds at risk for fly strike during warm months demands attention. Concurrent disease potentially masked by attribution of weight loss to lice infestation may require diagnostic evaluation to identify additional problems.

Clinical examination for lice infestations combines recognition of characteristic clinical signs with direct visualization of parasites or their eggs on affected animals. Visual examination of the hair coat or fleece identifies areas of damage, roughening, or thinning suggesting louse activity. Parting the hair coat or fleece in suspected areas exposes the skin surface where lice may be directly observed, appearing as small moving insects ranging from one to several millimeters in length depending on species. Use of a magnifying glass or hand lens facilitates observation of smaller species and identification of nits cemented to hair shafts. Examination should include characteristic predilection sites for different louse species, as distribution varies by parasite type. Comparison of suspected animals with apparently unaffected herdmates helps assess infestation extent.

Diagnostic tests for lice infestation primarily involve direct examination techniques to confirm and quantify parasite presence. Systematic examination at multiple body sites provides assessment of infestation intensity and distribution. Collection of suspected parasites by combing, tape impressions, or direct removal enables laboratory identification confirming louse species and distinguishing from other ectoparasites. Microscopic examination of collected specimens identifies morphological features distinguishing sucking from biting lice species, with species identification guiding treatment product selection in some cases. Examination of hair samples for nits provides evidence of active reproduction and helps estimate infestation duration. Quantitative assessments including louse counts per unit area enable monitoring of treatment response and comparison between animals or over time.

Differential diagnosis for lice infestations includes other causes of pruritus, hair loss, and skin lesions potentially confused with pediculosis. Mange caused by various mite species produces similar clinical signs but typically with more severe skin changes and different parasite morphology upon examination. Ringworm creates circular lesions with characteristic appearance distinct from lice damage patterns. Photosensitization affects non-pigmented skin in predictable distributions. Zinc or other nutritional deficiencies produce skin and coat changes without pruritic behavior. Allergic conditions including insect hypersensitivity cause seasonal pruritus and skin damage requiring historical and distributional differentiation. Behavioral issues including stereotypic rubbing without underlying cause occasionally occur. Combined infestations with multiple ectoparasite species require identification of all parasites present.

Herd-level diagnostics become important when lice infestations affect multiple animals or when monitoring treatment program effectiveness across populations. Systematic sampling examining representative animals from different groups, ages, and management situations assesses overall herd infestation status. Mapping of affected individuals within facilities may identify environmental or management factors concentrating infestation risk. Comparison of infestation levels between treated and untreated groups evaluates product efficacy. Seasonal monitoring tracks population dynamics guiding optimal treatment timing. Post-treatment evaluation confirms elimination of parasites and identifies potential treatment failures requiring alternative approaches. Documentation of species present and their distribution informs targeted prevention strategies.

Emergency treatment for lice infestation is rarely required since the condition develops gradually and seldom produces acute life-threatening effects. However, young calves with heavy sucking lice infestations developing significant anemia may require supportive care including nutrition support and housing modifications reducing stress while antiparasitic treatment eliminates parasites. Animals with severe secondary skin infections may need antimicrobial therapy. Treatment should be initiated promptly upon diagnosis to prevent further production losses and welfare compromise, but truly emergency intervention remains unusual for this condition.

Medical management of lice infestations utilizes various antiparasitic products available in formulations appropriate for different livestock species and production circumstances. Pour-on and spot-on formulations containing macrocyclic lactones, synthetic pyrethroids, or organophosphates provide convenient application with systemic or contact activity against lice. Injectable macrocyclic lactones including ivermectin, doramectin, and moxidectin provide systemic activity against sucking lice, though biting lice with their surface-feeding habits may be less effectively controlled. Sprays and dips provide thorough coverage for contact-active products. Dusting powders offer options for some species, particularly poultry. Product selection considers louse species present, host animal species and production status, withdrawal time requirements, and practical application considerations. Treatment of all in-contact animals simultaneously prevents reinfestation from untreated individuals.

Surgical options for lice infestation do not exist as the condition responds to medical antiparasitic treatment without surgical intervention. Management of secondary complications such as abscess drainage from infected skin wounds might rarely be required but represents unusual scenarios unrelated to primary lice treatment.

Supportive care complements antiparasitic treatment by addressing secondary effects of infestation and supporting recovery of damaged skin and hair coat. Environmental management including clean, dry housing reduces stress during recovery. Nutritional support helps restore body condition lost during active infestation. Treatment of secondary skin infections with appropriate antimicrobials promotes healing of damaged areas. Fly control measures protect healing skin wounds during warmer months. Monitoring during the post-treatment period confirms parasite elimination and identifies any need for retreatment.

Herd treatment protocols address population-level lice control through coordinated treatment of all animals and implementation of measures preventing reinfestation. Whole-herd treatment eliminates reservoir populations that might otherwise reinfest treated individuals. Treatment timing coordinates with production cycles to optimize effectiveness while minimizing withdrawal time impacts. Strategic treatment before winter housing or during late autumn targets populations before peak proliferation occurs. Repeat treatments may be required to address newly hatching nits not killed by initial treatment, with timing based on parasite life cycle duration. Environmental treatments of housing and equipment reduce survival of off-host stages though lice survival away from hosts is limited. Integration of treatment with biosecurity measures prevents reintroduction from external sources.

Treatment decision factors for lice infestations include infestation severity, number and type of animals affected, production status affecting product selection and withdrawal times, and cost-effectiveness of different treatment approaches. Light infestations may warrant monitoring with strategic treatment timing rather than immediate intervention. Heavy infestations causing obvious welfare compromise or production impacts justify prompt treatment. Product selection considers efficacy against identified louse species, particularly distinguishing between sucking and biting lice when systemic versus contact products offer different effectiveness. Withdrawal times for meat and milk affect product choice for food animals approaching marketing or in lactation. Economic analysis compares treatment costs against productivity losses from continued infestation.

Recovery timeline following successful lice treatment involves both parasite elimination and healing of secondary damage to skin and hair coat. Antiparasitic treatment typically eliminates live lice within days of application, with most products providing rapid knockdown of susceptible parasites. However, eggs present at treatment may continue hatching for up to two weeks, potentially requiring repeat treatment depending on product residual activity. Pruritus and rubbing behavior generally decrease within days of parasite elimination as irritation subsides. Skin healing from secondary trauma including excoriations, thickening, and infections requires several weeks. Hair regrowth in damaged areas may take weeks to months depending on severity and the animal's coat growth cycle.

Post-treatment care and monitoring ensure complete infestation elimination while supporting recovery of damaged integument. Examination at two to three weeks post-treatment confirms parasite elimination, with absence of live lice and minimal new egg deposition indicating successful treatment. Observation of behavioral changes documents cessation of excessive rubbing and scratching. Skin condition monitoring tracks healing of damaged areas. Hair or fleece regrowth assessment estimates timeline for complete coat restoration. Monitoring of body condition and productivity measures indicates recovery from infestation impacts. Documentation of treatment response informs future prevention and treatment planning.

Prognosis factors influencing recovery from lice infestation include infestation severity and duration, treatment product effectiveness against the species present, completeness of treatment coverage, and prevention of reinfestation from untreated sources. Light infestations of short duration carry excellent prognosis with rapid recovery following treatment. Heavy, long-standing infestations with significant secondary damage require extended recovery periods. Treatment product selection appropriate for the specific louse species present optimizes elimination success. Treatment of all in-contact animals prevents rapid reinfestation. Biosecurity measures preventing introduction from external sources support sustained control.

Return to production considerations following lice infestation treatment include confirmation of parasite elimination, withdrawal time compliance for any medications used, and assessment of residual effects potentially affecting animal value or performance. Meat animals may proceed to marketing once treatment withdrawal times have elapsed and any secondary skin damage affecting hide quality has healed. Dairy animals in lactation require attention to milk withdrawal periods for products with dairy animal clearances. Wool sheep face particular considerations regarding timing of treatment relative to shearing and fleece quality impacts of infestation damage. Breeding animals may proceed with reproduction once general condition supports successful breeding. Animals with persistent poor condition despite successful parasite elimination warrant evaluation for concurrent problems.

Vaccination protocols for lice prevention do not exist as these are ectoparasites not amenable to immunization approaches developed for infectious diseases. Research on potential vaccines targeting louse antigens continues but has not yet produced practical prevention options. Current prevention relies on management practices, strategic antiparasitic treatment, and biosecurity measures rather than vaccination. General herd health programs maintaining strong immune function may provide some indirect benefit in limiting louse population growth.

Biosecurity measures form the cornerstone of lice prevention by preventing introduction of parasites from external sources and limiting spread within operations. Quarantine of new animal introductions with examination and treatment before mixing with resident populations prevents establishment of new infestations. Isolation of returning animals from shows, fairs, or breeding facilities allows observation and treatment before potential transmission to home herds. Visitor restrictions and sanitation protocols reduce potential for mechanical transmission on clothing or equipment. Boundary fencing preventing contact with neighboring animals of uncertain infestation status limits transmission opportunities. Equipment sanitation between different animal groups, though lice survive poorly off-host, addresses potential mechanical transmission.

Nutritional prevention strategies support animal health and immune function that may limit louse population growth and improve tolerance of light infestations. Balanced nutrition meeting all macro and micronutrient requirements maintains optimal health status. Adequate protein nutrition supports hair coat and skin integrity. Vitamin and mineral supplementation addresses any deficiencies potentially compromising resistance. Body condition maintenance through appropriate feeding programs reduces susceptibility to heavy infestations. Stress reduction through adequate nutrition supports immune competence. Well-nourished animals may better tolerate light parasitism without significant production impacts.

Management practices preventing lice infestations address transmission reduction, early detection, and strategic treatment implementation. Stocking density management reduces direct animal contact and associated transmission opportunities. Grooming and handling equipment hygiene minimizes potential mechanical transmission between animals. Regular monitoring through periodic examination enables early detection before heavy infestations develop. Strategic treatment programs timed to target populations before winter buildup reduce peak infestation severity. Integration of treatment with routine management activities such as fall processing in cattle operations improves compliance and coverage. Record keeping tracks infestation patterns guiding prevention program refinements.

Quarantine and testing protocols support lice prevention through identification and treatment of potential introduction sources. Examination of all incoming animals for evidence of current infestation or recent infestation damage enables treatment before introduction. Quarantine periods allowing observation identify developing infestations that might not be apparent at arrival. Treatment of all incoming animals as a standard protocol eliminates parasites regardless of apparent infestation status. Source qualification considering supplier lice management practices reduces introduction risk. Documentation of incoming animal origin and health status supports traceback if problems develop.

Daily management and monitoring for lice prevention integrates observation for early signs into routine farm operations enabling prompt detection and response. Visual observation during feeding, handling, and general husbandry notes excessive rubbing, scratching, or coat condition changes suggesting possible infestation. Periodic close examination of animals during routine handling opportunities allows direct assessment of skin and coat condition. Staff training ensures all personnel recognize behavioral and physical indicators of louse infestation. Recording of observations enables pattern identification across animal groups, seasons, or following management changes. Integration of lice monitoring into existing animal health surveillance programs optimizes detection without adding substantial labor requirements.

Housing and environmental management influences lice infestation risk through effects on transmission opportunities and parasite survival conditions. Facility design providing adequate space reduces forced close contact between animals. Ventilation and humidity management affect microclimate conditions influencing lice survival and reproduction. Separation capabilities enable isolation of affected individuals for treatment and monitoring. Equipment and housing cleaning between animal groups removes debris potentially harboring any off-host parasites though survival away from hosts is limited. Appropriate stocking density balances production efficiency against disease transmission risks including lice spread.

Herd health programs incorporating lice monitoring and control provide systematic frameworks for prevention and early intervention. Routine surveillance schedules define timing and methods for population monitoring. Threshold criteria specify infestation levels triggering treatment intervention. Treatment protocols define products, dosages, application methods, and timing for different animal groups and circumstances. Record systems document surveillance results, treatments, and outcomes. Program review identifies successes and improvement opportunities. Veterinary involvement ensures protocols reflect current best practices and product availability. Integration with other parasite control programs optimizes overall herd health while avoiding unnecessary treatments.

Record keeping and monitoring systems support evidence-based lice management through documentation of occurrence patterns, treatment responses, and control program outcomes. Surveillance records capture examination results by date, animal group, and body location enabling trend identification. Treatment records document products used, animals treated, and subsequent monitoring results. Infestation severity assessments provide quantitative data for comparison across time and between management approaches. Economic tracking estimates costs of infestations and control programs informing investment decisions. Benchmarking against industry standards or neighboring operations identifies improvement opportunities.

Economic considerations in lice management encompass prevention investments, treatment costs, and productivity impacts requiring ongoing cost-benefit analysis. Prevention measures including biosecurity protocols, quarantine facilities, and monitoring programs require investment justified by reduced infestation severity and treatment needs. Treatment costs include product expenses, application labor, and handling facilities. Productivity impacts of infestation include reduced weight gains, decreased milk production, diminished fleece yield and quality, and hide damage affecting value. Withdrawal time considerations affect marketing timing for treated animals. Economic modeling comparing prevention-focused versus treatment-focused approaches informs optimal resource allocation.

High-risk breeds for lice infestation demonstrate susceptibility patterns related primarily to hair coat or fleece characteristics creating favorable microhabitats for louse survival and reproduction. Among cattle, breeds with longer, denser winter coats often support higher louse populations than those with shorter, sleeker coats. Beef breeds adapted to cold climates with heavy winter coats may experience greater infestation challenges than lighter-coated dairy breeds, though all cattle types are susceptible. Sheep breeds with dense, fine wool may harbor more lice than coarse-wool or hair sheep varieties. Angora and Cashmere goats with their dense fiber production may experience different infestation dynamics than dairy or meat goat breeds with shorter coats.

Production type considerations influence lice infestation risk through management intensity, housing practices, and animal grouping patterns characteristic of different operations. Extensively managed beef cattle spending winter outdoors in cold climates develop dense coats highly suitable for lice proliferation. Confined dairy cattle with year-round housing may maintain more consistent louse populations without strong seasonal fluctuation. Feedlot cattle with high stocking densities face increased transmission opportunities. Sheep production systems vary in shearing timing affecting fleece-mediated louse habitat availability. Intensive poultry operations with high bird densities create conditions favoring rapid louse transmission through close contact.

Genetic selection and testing for lice resistance remain limited compared to selection for production traits, though potential exists for improvement through breeding programs. Animals demonstrating consistently lower louse burdens under equivalent exposure might be selected as breeding stock, though distinguishing genetic resistance from management or environmental effects proves challenging. Coat characteristics affecting louse habitat suitability have some heritability and could respond to selection if prioritized. Grooming behavior effectiveness varies among individuals and may have genetic components. Immune responses to louse antigens potentially limiting population growth might respond to selection. Current practical lice management relies primarily on chemical control and management practices rather than genetic approaches.

Commonly co-occurring conditions with lice infestations include other ectoparasite infestations, secondary complications from self-trauma, and conditions predisposing to or resulting from lice presence. Concurrent mange mite infestations may occur, with both parasites causing pruritus and skin damage requiring identification and treatment of all species present. Fly populations may be attracted to skin lesions created by scratching and rubbing. Secondary bacterial skin infections develop in traumatized areas, particularly when scratching creates open wounds. Poor body condition resulting from chronic infestation may increase susceptibility to other diseases. Conditions causing debilitation predispose to heavier louse burdens through reduced grooming and immune function.

Conditions with similar symptoms requiring differentiation from lice infestation include other causes of pruritus, hair loss, and skin abnormalities in livestock. Mange caused by various mite species produces intense itching with characteristic skin changes including crusting and thickening potentially more severe than typical lice damage. Ringworm creates circular lesions with different appearance and distribution. Allergic conditions including insect hypersensitivity, atopy, or food allergy cause pruritus with seasonal or dietary associations. Zinc deficiency produces parakeratosis with skin changes lacking the pruritic component typical of lice. Photosensitization damages non-pigmented skin in characteristic patterns. Contact dermatitis causes localized skin reactions corresponding to irritant exposure.

Complications and sequelae of lice infestations include consequences of chronic parasitism and secondary effects of scratching behavior and skin damage. Anemia from heavy sucking lice infestations particularly affects young or debilitated animals, potentially causing weakness and reduced performance. Secondary bacterial skin infections may progress from localized lesions to more extensive involvement. Hair or fleece damage from scratching and rubbing reduces coat quality and value, with wool break affecting fleece soundness in sheep. Hide damage affects leather quality in animals processed for this purpose. Chronic poor body condition from persistent untreated infestation affects reproductive performance and disease susceptibility. Self-trauma creating wounds during warm months creates risk for fly strike. Behavioral effects of chronic irritation may persist temporarily after successful treatment.