In general, you should search for open access articles on your topic in the same way you search in the rest of the literature.  However, these several OA journals might be useful for browsing.  What is AVMA publishing this month?

These journals, and others, can be accessed individually.  But usually you will search in your favorite search interfaces and link easily to articles from a variety of publishers. Remember that if full text does not appear available, double check with your DOI or PMID at Libkey.io.

Favorite search interfaces: APPsearch, PubMed, Google Scholar, Scopus

University of Toronto Press

Journal of Veterinary Medical Education

Wiley
Veterinary Clinical Pathology
Equine Veterinary Education
Equine Veterinary Journal
In Practice
Journal of Fish Diseases
Journal of Small Animal Practice
Journal of Veterinary Emergency and Critical Care
Journal of Veterinary Internal Medicine
Transboundary and Emerging Diseases
Zoonoses and Public Health
Journal of Veterinary Pharmacology and Therapeutics
Medical and Veterinary Entomology
Reproduction in Domestic Animals
Veterinary and Comparative Oncology
Veterinary Clinical Pathology
Veterinary Dermatology
Veterinary Medicine and Science
Veterinary Nursing Journal
Veterinary Record
Veterinary Record Case Reports
Veterinary Surgery

Sage
Journal of Feline Medicine and Surgery
Journal of Veterinary Dentistry
Journal of Veterinary Diagnostic Investigation
Laboratory Animals
Veterinary Pathology

Springer
Veterinary Research Communications
Animal Diseases
Acta Veterinaria Scandinavica
Veterinary Research
Canine Medicine and Genetics

ScienceDirect (Elsevier)
Advances in Small Animal Care
Advances in Small Animal Medicine and Surgery
Animal Behaviour
Animal Reproduction Science
Applied Animal Science
British Veterinary Journal
Clinical Techniques in Equine Practice
Clinical Techniques in Small Animal Practice
Journal of Dairy Science
Journal of Equine Veterinary Science
Journal of Feline Medicine & Surgery
Journal of Veterinary Anaesthesia
Journal of Veterinary Behavior
Journal of Veterinary Cardiology
Preventive Veterinary Medicine
Proceedings of the Association of Veterinary Anaesthetists
Research in Veterinary Science
Theriogenology
Veterinary Anaesthesia and Analgesia
Veterinary Clinics of North America: Equine Practice
Veterinary Immunology and Immunopathology
The Veterinary Journal
Veterinary Microbiology
Veterinary Parasitology