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.