Veterinary education, training, and employment shifted to support military needs in wartime. Conflicts around the world, including World War I, relied on millions of horses, dogs, and food-producing animals to supply armies. Wartime disruptions, and the movement of so many animals, sparked outbreaks of diseases that challenged animal owners, healers, and veterinarians. The use of horsepower declined in industrialized areas, depriving veterinarians of their most important patients. Many turned instead to livestock and food production. National campaigns against bovine tuberculosis, brucellosis, and other zoonoses employed many veterinarians. Others worked on vaccines and therapeutics in biomedical research. With the outbreak of World War II, ethical questions troubled veterinarians who contributed to the development of biological weapons. Rebuilding the world’s food production systems after the war stimulated international veterinary cooperation and incorporated new tools, such as antibiotics. Veterinarians also helped make intensive animal production ("factory farming") possible by controlling diseases, while more and more vets in wealthier areas treated companion animals (pets).

In the late twentieth century, the global human population grew dramatically. Global meat production more than doubled as industrial animal production rapidly accelerated. Mechanization, artificial insemination, growth promoters in feed, and disease control contributed to successful "factory farms," while smaller farmers adopted vaccines and antimicrobials. By 2000, 90 percent of the mammals living on earth were humans and their domesticated animals. Veterinarians became "herd health" managers and worked for governments around the world to carry out vaccination programs, provide medications and anthelminthics, and complete inspections and certifications. The OIE and WHO coordinated international campaigns against rinderpest, foot and mouth disease (FMD), and swine fever; but outbreaks of FMD resulted from disagreement over the value of vaccination versus testing. Prion diseases (scrapie and BSE) became major sociopolitical problems after people acquired a form of BSE from infected meat in Britain. Public concerns about food safety, antibiotic resistance, and animal welfare began to challenge intensive livestock production and veterinarians’ role, but most veterinarians in wealthy areas focused on companion animals. By 2000, racial and ethnic diversity in the veterinary workforce was slowly increasing, while the profession rapidly feminized after 1980 in most parts of the world. Responding to client demand, veterinary schools began offering courses in complementary and alternative veterinary medicine (CAVM).