LA-300 is a long-acting injectable antibiotic used in cattle to treat a wide range of bacterial infections, from respiratory disease and pinkeye to foot rot and scours. The “LA” stands for “long-acting,” and the “300” refers to the concentration: 300 mg of oxytetracycline per milliliter. This high concentration allows for sustained antibiotic levels in the animal’s body, often from a single injection, which makes it especially practical for range cattle that are difficult to handle repeatedly.
Conditions LA-300 Treats
LA-300 is labeled for use in beef cattle, non-lactating dairy cattle, and calves, including pre-ruminating (veal) calves. Its approved uses cover a broad list of bacterial infections:
- Shipping fever and pneumonia caused by Pasteurella and Histophilus bacteria, the primary culprits behind bovine respiratory disease (BRD)
- Pinkeye (infectious bovine keratoconjunctivitis) caused by Moraxella bovis
- Foot rot and diphtheria caused by Fusobacterium necrophorum
- Scours (bacterial enteritis) caused by E. coli
- Wooden tongue caused by Actinobacillus lignieresii
- Leptospirosis caused by Leptospira pomona
- Wound infections and acute metritis caused by staphylococcal and streptococcal organisms
It’s also labeled for prevention: a single dose can control respiratory disease in cattle at high risk of developing BRD, such as newly arrived feedlot calves that have been stressed by transport.
How It Works
Oxytetracycline is a broad-spectrum antibiotic, meaning it works against both gram-positive and gram-negative bacteria, as well as some other organisms like mycoplasmas. It stops bacteria from growing by binding to their ribosomes, the cellular machinery that builds proteins. Without new proteins, bacteria can’t multiply or repair themselves, giving the animal’s immune system time to clear the infection. This makes oxytetracycline bacteriostatic rather than bactericidal: it holds bacteria in check rather than killing them outright. A functional immune system in the animal is essential for the drug to work effectively.
Dosing and Administration
LA-300 can be given intramuscularly (IM), subcutaneously (SQ), or in some cases intravenously (IV), depending on the condition being treated. The dose varies by indication.
For BRD prevention in high-risk cattle, the label calls for a single injection at 13.6 mg per pound of body weight. That same dose range (9 to 13.6 mg per pound) applies to pinkeye and bacterial pneumonia in calves and yearlings, particularly when retreatment isn’t practical because the animals are on range or difficult to restrain again.
For most other conditions, the standard dose is 3 to 5 mg per pound of body weight per day. Foot rot and advanced cases call for the higher end of that range, at 5 mg per pound daily. Regardless of the dose, you should not exceed 10 mL per injection site in adult beef and non-lactating dairy cattle. Injecting too much in one spot increases the risk of tissue damage and can cause antibiotic residues that persist beyond the withdrawal period.
Withdrawal Period
Any animal treated with LA-300 cannot be sent to slaughter for human consumption until the withdrawal period has passed. For oxytetracycline 300 mg/mL products, the slaughter withdrawal is typically 28 days in the United States (check your specific product label, as this can vary by brand and country). In Australia, the withholding period for comparable products like Alamycin LA 300 is 35 days. LA-300 is not approved for use in lactating dairy cattle whose milk is intended for human consumption.
Exceeding the recommended dose, giving more treatments than the label allows, or injecting too much volume per site can all push residues beyond the stated withdrawal period. Following label directions exactly protects both the animal and the food supply.
Side Effects and Precautions
LA-300 is generally well tolerated. The most common reaction is mild swelling or irritation at the injection site, which usually resolves on its own. More serious but uncommon side effects include gastrointestinal upset, allergic reactions, and photosensitivity (increased sensitivity to sunlight). In very rare cases, severe allergic or anaphylactic reactions can occur.
There are a few situations where extra caution is needed. Weak or debilitated animals are at higher risk of collapse after receiving tetracyclines. Excessive doses can damage the kidneys. Using LA-300 during late pregnancy or while calves are developing teeth and bones can cause permanent discoloration of those tissues, so timing matters if you’re treating bred cows close to calving.
Storage and Shelf Life
Store LA-300 at room temperature, between 68°F and 77°F, and never let it freeze. Once you puncture a 100 mL bottle, use it within 60 days and don’t puncture the stopper more than 24 times. Larger bottles (250 mL and 500 mL) allow up to 36 punctures within the same 60-day window. If you use a needle or draw-off spike larger than 16 gauge, discard whatever is left in the bottle immediately, as the larger hole compromises sterility.