The FDA-approved label dose for injectable penicillin G procaine is 1 mL per 100 pounds of body weight, given once daily as an intramuscular injection. However, most veterinarians consider this label dose too low to actually clear an infection. In practice, vets commonly prescribe 3 to 5 mL per 100 pounds of body weight, given once or twice daily, to reach effective therapeutic levels in the tissue. Because goats are not specifically listed on the penicillin label, any use in goats is legally considered “extra-label” and requires a veterinarian’s guidance.
Why the Label Dose Isn’t Enough
The 1 mL per 100 pounds printed on the penicillin bottle was established for cattle. Goats metabolize drugs faster than cattle, which means the drug clears their system more quickly and may never reach a concentration high enough to kill bacteria in the udder. This is why veterinarians routinely bump the dose to 3 to 5 mL per 100 pounds. For a 150-pound dairy goat, that works out to roughly 4.5 to 7.5 mL per injection at the higher therapeutic range.
No more than 10 mL should be injected into a single site. If your goat’s dose exceeds that, split it between two locations. Treatment courses for mastitis typically run five to seven days, but your vet may adjust this based on how the udder responds.
How to Give the Injection
Penicillin G procaine is given intramuscularly, meaning into the muscle rather than under the skin. The correct injection site is the triangular area of the neck, in front of the shoulder. Never inject in the hindquarters, loin, or shoulder muscle. These are meat-producing areas, and injections there cause tissue damage that lowers carcass value and can leave drug residues in the meat.
Use an 18-gauge needle, about 2 to 3 cm long, for adult goats. For kids under four months, a 20-gauge needle is gentler. Alternate sides of the neck between injections to avoid soreness in one spot. Keep the injection site clean and use a fresh needle for each dose when possible.
Which Mastitis Bacteria Penicillin Treats
Mastitis in goats is most commonly caused by Staphylococcus aureus, several Streptococcus species, E. coli, and Corynebacterium pyogenes. Penicillin works well against Streptococcus bacteria, which tend to be highly sensitive to it. The picture with Staphylococcus is more complicated. Some staph strains produce an enzyme that breaks down penicillin, making them resistant. Other staph bacteria remain susceptible to penicillin-family antibiotics.
This is one reason a milk culture is valuable before starting treatment. If the infection is caused by a penicillin-resistant staph strain, you could treat for a full week and see little improvement. A culture identifies the specific bacteria and which antibiotics will actually work against it. Your vet can pull a milk sample and send it to a lab, often with results back in a few days.
Extra-Label Use and Milk Withdrawal
Since penicillin is not FDA-approved specifically for goats, using it in your herd falls under extra-label drug use. Federal law (AMDUCA) requires that extra-label use in food-producing animals happen only under a veterinarian’s direct order, within a valid vet-client-patient relationship. This isn’t just a formality. Your vet is legally responsible for setting an appropriate milk withdrawal period so that no drug residues end up in milk or meat.
Withdrawal times for goats receiving penicillin at higher-than-label doses are longer than what’s printed on the bottle for cattle. Your vet will establish a specific discard period based on the dose and duration of treatment. During this time, all milk from the treated goat must be dumped. Do not feed antibiotic-contaminated milk to kids you plan to sell for meat, as the residues transfer.
Supportive Care During Treatment
Antibiotics alone don’t fully address mastitis. Stripping out the infected half of the udder several times a day helps flush bacteria and inflammatory debris from the gland. Research from Ohio State University’s veterinary college suggests that combining antibiotic therapy with frequent stripping is more effective than either approach on its own. Aim to strip the affected side every few hours during the acute phase, wearing clean gloves each time to avoid spreading bacteria between halves or to other goats.
Keep the doe in a clean, dry area with fresh bedding. Wet, dirty conditions allow bacteria to re-enter the teat opening and worsen the infection. Warm compresses applied to a hard, swollen udder can improve blood flow and make stripping easier. Monitor the milk’s appearance at each stripping. You’re looking for a gradual shift from clotted, watery, or discolored milk back toward normal consistency and color. If the udder stays hot and hard after three to four days of treatment, or if the goat develops a fever, stops eating, or seems lethargic, the current antibiotic may not be covering the bacteria involved, and a vet reassessment is warranted.
Dose Quick Reference by Body Weight
These figures use the common veterinary therapeutic range of 3 to 5 mL per 100 pounds, once or twice daily. Your vet should confirm the specific dose and frequency for your goat.
- 75-pound goat: 2.25 to 3.75 mL per injection
- 100-pound goat: 3 to 5 mL per injection
- 125-pound goat: 3.75 to 6.25 mL per injection
- 150-pound goat: 4.5 to 7.5 mL per injection
- 175-pound goat: 5.25 to 8.75 mL per injection
Weigh your goat rather than guessing. Underdosing fails to clear the infection and promotes antibiotic resistance. Overdosing increases the risk of injection site reactions and extends the withdrawal period unnecessarily. A livestock scale or a weight tape designed for goats gives you a reliable number to work from.