Bovine External Parasites Study Guide

Overview and Clinical Importance

External parasites (ectoparasites) of cattle represent a significant category of integumentary disease with major economic and welfare implications. These parasites cause direct damage through blood feeding, skin irritation, and hide damage, while also serving as vectors for important pathogens including Anaplasma marginale, Babesia species, and various viral and bacterial agents.

Economic losses from ectoparasites include reduced weight gain (10-20 pounds per grazing season from horn flies alone), decreased milk production (10-20% reduction with heavy infestations), hide damage, treatment costs, and losses from transmitted diseases. The estimated annual economic impact in the United States alone exceeds $2 billion.

Section 1: Bovine Pediculosis (Lice)

Pediculosis is infestation with lice, which are small, wingless, dorsoventrally flattened insects that spend their entire life cycle on the host. Cattle lice are host-specific obligate parasites that cannot survive more than a few days off the host. Infestations are most prevalent during winter months when cattle are housed together, have longer hair coats, and experience reduced sunlight exposure.

Cattle Lice Species Classification

Morphological Differentiation

Bovicola bovis (Chewing louse): 1-2 mm length, reddish-brown head, yellowish-white body with dark transverse bands across abdomen. Feeds on skin debris, hair, and sebaceous secretions. Most common cattle louse species. Reproduces by parthenogenesis (females can produce eggs without mating).

Haematopinus eurysternus (Short-nosed sucking louse): Largest cattle louse at 3-5 mm. Grayish-brown coloration. Most commonly found on older animals. Life cycle approximately 28 days with eggs hatching in 13 days.

Linognathus vituli (Long-nosed sucking louse): Approximately 2.5 mm, bluish coloration, distinguished by long slender head. Serves as mechanical vector for Anaplasma marginale. More common in calves than adults.

Solenopotes capillatus (Little blue cattle louse): Smallest sucking louse at 1-2 mm, bluish coloration. Found primarily on face and muzzle, especially around eyes and nose.

Clinical Signs and Findings

Pruritus and restlessness: Affected animals rub against fences, posts, and other objects, leading to hair loss and skin abrasions

Alopecia: Patchy hair loss, particularly over shoulders, topline, and neck regions

Poor coat condition: Rough, dull hair coat with matting

Anemia: Severe sucking lice infestations can cause significant blood loss, particularly in young calves

Production losses: Decreased weight gain, reduced milk production, decreased feed conversion efficiency

Diagnosis

Visual examination of predilection sites using a bright light and magnifying glass. Part the hair and examine the skin surface for adult lice and nits (eggs attached to hair shafts). Nits appear as small white, yellow, or brown barrel-shaped specks. Microscopic examination confirms species identification based on head shape and mouthpart morphology.

Treatment Options for Bovine Lice

Section 2: Bovine Mange (Mites)

Mange (acariasis) is caused by mite infestation of cattle skin. Mites are arachnids (8 legs in adults) approximately 0.2-0.6 mm in length. Three main genera cause clinical disease in cattle: Chorioptes (most common), Sarcoptes (most severe), and Psoroptes (reportable in some regions). Mites complete their entire life cycle on the host in 2-3 weeks.

Cattle Mange Mite Comparison

Chorioptic Mange (Most Common)

Lesions typically begin at the tail head and spread to legs, udder, and perineum. Clinical signs include dry, scaly skin with localized hair loss and mild crusting. Bulls may develop scrotal lesions causing temporary infertility. Many cattle are subclinically infested. Lesions often spontaneously regress in summer when cattle are on pasture.

Sarcoptic Mange (Most Severe)

Rare but serious. Mites burrow into epidermis creating tunnels. Causes INTENSE pruritus that is largely immune-mediated. Lesions include thickened, wrinkled skin with crusting and serum exudation, primarily on head, neck, and brisket. Can become generalized. ZOONOTIC - causes transient pruritic dermatitis in humans handling affected cattle.

Psoroptic Mange (Reportable)

Surface-feeding mites that puncture epidermis, causing serous exudation. Lesions on withers, back, and shoulders with extensive crusting. Severe cases cause significant hide damage and welfare concerns. Reportable disease in many jurisdictions due to potential for rapid spread and economic impact.

Diagnosis

Skin scraping is the gold standard. Scrape the edge of lesions until capillary bleeding occurs. Place material in mineral oil or 10% KOH on a slide and examine microscopically. Multiple scrapings may be needed as mite numbers can be low. For Sarcoptes, superficial scrapings may miss burrowing mites - use deep scrapings.

Treatment

Macrocyclic lactones: Ivermectin (0.2 mg/kg SC or pour-on), Eprinomectin (pour-on), Doramectin, Moxidectin. ONLY pour-on formulations are effective for Chorioptes as systemic absorption is required for burrowing mites but Chorioptes lives on skin surface.

Lime sulfur dips: Effective for all mite types when applied correctly. Requires thorough wetting.

Section 3: Ticks

Ticks are obligate blood-feeding arachnids that are significant ectoparasites and disease vectors. They belong to two families: Ixodidae (hard ticks) and Argasidae (soft ticks). Ticks have complex life cycles requiring blood meals at each stage and can survive extended periods off the host.

Important Cattle Tick Species

Major Tick-Borne Diseases of Cattle

Bovine Babesiosis (Texas Cattle Fever, Redwater): Caused by Babesia bovis and B. bigemina. Transmitted by Rhipicephalus (Boophilus) species. Clinical signs include fever, hemoglobinuria (red urine), anemia, jaundice, and death. B. bovis also causes cerebral babesiosis with neurological signs.

Bovine Anaplasmosis: Caused by rickettsial organism Anaplasma marginale. Transmitted by ticks (Dermacentor in USA, Rhipicephalus in tropics) and mechanically by biting flies. Clinical signs: fever, anemia, jaundice, NO hemoglobinuria (differentiates from babesiosis). Age-related severity - calves are resistant to disease but not infection.

Tick-Borne Fever/Louping Ill: Transmitted by Ixodes ricinus in UK and Europe. Tick-borne fever (Anaplasma phagocytophilum) causes fever, leukopenia, immunosuppression. Louping ill is a viral encephalomyelitis primarily of sheep but can affect cattle.

Tick Control and Prevention

Acaricides: Pour-on (ivermectin, moxidectin), dips, sprays. Regular application at intervals shorter than tick life cycle interrupts reproduction.

Pasture management: Rotational grazing to break tick life cycles. Pasture spelling for at least 6 months can reduce tick populations.

Cattle Fever Tick Eradication Program (CFTEP): US federal program maintains tick-free status through permanent quarantine zone along Texas-Mexico border. Systematic dipping and inspection of cattle.

Section 4: Flies

Flies cause significant economic losses through direct effects (blood feeding, worry, pain) and as vectors of disease. Major fly pests of cattle include horn flies, stable flies, face flies, horse flies, deer flies, and cattle grubs (warble flies).

Major Fly Pests of Cattle

Horn Fly (Haematobia irritans)

Most economically important fly pest of cattle. Adults remain on cattle continuously, leaving only to oviposit in FRESH cow dung (within 15 minutes of deposition). Feed 24-38 times daily. Economic threshold is 200 flies per animal. Heavy infestations (greater than 4,000 flies) cause significant blood loss and stress. Associated with Stephanofilaria stilesi (dermatitis) and Staphylococcus mastitis transmission.

Fly Control Methods

Insecticide ear tags: Impregnated with pyrethroids or organophosphates. Effective for horn flies and face flies. Apply at start of fly season. Rotate drug classes annually to prevent resistance.

Pour-on products: Eprinomectin and moxidectin pour-ons provide horn fly control with no milk withdrawal (dairy cattle).

Dust bags and oilers: Self-application devices placed at water or mineral sites. Require forced use for effectiveness.

Feed-through insect growth regulators (IGRs): Methoprene passes through cattle into manure, preventing horn fly larval development. Does not affect adult flies.

Biological control: Parasitoid wasps (Muscidifurax, Spalangia) attack fly pupae. Dung beetles compete with horn fly larvae for breeding substrate.

Section 5: Cattle Grubs (Hypoderma Species)

Cattle grubs (warble flies) cause myiasis in cattle. Adults are large, hairy, bee-like flies (11-18 mm) with no functional mouthparts. Two species affect cattle: Hypoderma bovis (Northern cattle grub) and Hypoderma lineatum (Common cattle grub). The use of macrocyclic lactones has dramatically reduced prevalence in North America and Europe.

Hypoderma Species Comparison

Life Cycle (Approximately 1 Year)

Adult flies lay eggs on hair of lower legs during summer (causing 'gadding' behavior - panicked running). First-instar larvae hatch in 4-6 days, penetrate skin, and migrate through tissues for 8-9 months. They overwinter in their preferred location (epidural fat for H. bovis, esophageal submucosa for H. lineatum). In spring, larvae migrate to subcutaneous tissue of the back, create a breathing hole (warble pore), and develop through second and third instars. Mature larvae (grubs) drop to ground to pupate for 1-3 months.

Clinical Signs

Warbles: Subcutaneous nodules (1-3 cm) on the back with a central breathing hole. Each warble contains a developing grub. Cattle may have 1 to over 300 warbles; young animals most heavily infested.

Economic impact: Hide damage from breathing holes and inflammatory changes, carcass trimming, reduced weight gain, decreased milk production.

Treatment and Timing

Macrocyclic lactones (ivermectin, eprinomectin, doramectin, moxidectin) are highly effective against all larval stages. CRITICAL TIMING: Treat in late fall/early winter BEFORE larvae reach critical migration sites (by November 30 in Northern Hemisphere). Treatment after this time risks adverse reactions from dying larvae.