In veterinary medicine, ampicillin is used in cats, dogs, and farm animals to treat:
* Anal gland infections
* Cutaneous infections, such as abscesses, cellulitis, and pustular dermatitis
* E. coli and Salmonella infections in cattle, sheep, and goats (oral form). Ampicillin use for this purpose had declined as bacterial resistance has increased. 
* Mastitis in sows
* Mixed aerobic–anaerobic infections, such as from cat bites
* Multidrug-resistant Enterococcus faecalis and E. faecium
* Prophylactic use in poultry against Salmonella and sepsis from E. coli or Staphylococcus aureus
* Respiratory tract infections, including tonsilitis, bovine respiratory disease, shipping fever, bronchopneumonia, and calf and bovine pneumonia
* Urinary tract infections in dogs
Horses are generally not treated with oral ampicillin, as they have low bioavailability of beta-lactams.
The half-life in animals is around that same of that in humans (just over an hour). Oral absorption is less than 50% in cats and dogs, and less than 4% in horses.