Pennox 50 Label Broadens Oral Oxytetracycline Use Across Livestock and Bees
The updated DailyMed label for Pennox 50 places oxytetracycline in a familiar but still clinically important role: broad-spectrum oral antimicrobial control in food animals and honey bees. This is a Type A medicated article intended for manufacture into medicated feeds, not a product to be fed undiluted. The label also makes the practical limits impossible to miss. It is for dry feeds only, and it is not for liquid feed supplements.
At the center of the product is oxytetracycline, supplied from oxytetracycline dihydrate base and equivalent to 50 grams of oxytetracycline hydrochloride per pound in the labeled concentrate. The inactive ingredients are calcium carbonate, roughage products, and mineral oil. Pharmgate Animal Health markets the product, and the label carries FDA approval under NADA 138-938.
The pharmacology is straightforward, but the management consequences are not. Oxytetracycline remains useful because it reaches a wide range of susceptible bacterial and atypical organisms, making it a practical feed medication in herd, flock, and apiary settings where group treatment is more efficient than individual dosing. Its value depends on correct formulation, correct species use, and strict attention to withdrawal intervals and residue control.
Poultry Claims Center on Respiratory Disease, Synovitis, and Mortality Reduction
In chickens, the label lists control of infectious synovitis caused by Mycoplasma synoviae and control of fowl cholera caused by Pasteurella multocida susceptible to oxytetracycline. The feed is to be given continuously for 7 to 14 days at 100 to 200 g/ton, which corresponds to 2.0 to 4.0 lb per ton of feed. For chronic respiratory disease and air sac infection caused by Mycoplasma gallisepticum and Escherichia coli susceptible to oxytetracycline, the label calls for 400 g/ton, or 8.0 lb per ton, for 7 to 14 days.
Broiler chickens have a separate indication: reduction of mortality due to air sacculitis caused by E. coli susceptible to oxytetracycline. In that setting, the labeled regimen is 500 g/ton, or 10.0 lb per ton, for 5 days. The shorter course fits the urgency of an acute flock event, when rapidly spreading respiratory compromise can translate into culling pressure, poor feed conversion, and downstream carcass losses.
Residue restrictions shape poultry use as much as the antimicrobial claim itself. The label prohibits use in chickens producing eggs for human consumption. It also warns against use in low-calcium feed containing less than 0.55% dietary calcium because violative residues may result. A 24-hour withdrawal period applies at the 500 g/ton use level, while no withdrawal period is required at the 100 to 200 g/ton and 400 g/ton levels when used according to labeling.
A single residue warning can determine whether a flock medication is legal or not.
Swine and Ruminant Sections Emphasize Enteric and Respiratory Disease Control
For swine, the label supports treatment of bacterial enteritis caused by Escherichia coli and Salmonella choleraesuis, as well as bacterial pneumonia caused by Pasteurella multocida susceptible to oxytetracycline. The recommended approach is continuous feeding for 7 to 14 days, with feed adjusted to provide about 10 mg/lb body weight/day at approximately 400 g/ton. Breeding swine have an additional indication for control and treatment of leptospirosis caused by Leptospira pomona, with the stated goal of reducing abortion and shedding of leptospirae. That use also calls for 14 days of continuous feeding at approximately 400 g/ton.
The swine section carries a zero-day withdrawal period. In commercial production, that matters because treatment can be integrated into herd management without creating an added marketing delay, provided the drug is used exactly as labeled.
In calves, beef cattle, and nonlactating dairy cattle, the label addresses several familiar feedlot problems. Growing cattle over 400 lb may receive 75 mg/head/day continuously for reduction of the incidence of liver abscesses. Cattle may also receive 0.5 to 2.0 g/head/day for prevention and treatment of the early stages of the shipping fever complex, beginning 3 to 5 days before arrival in feedlots and continuing afterward. For calves, beef cattle, and nonlactating dairy cattle, the drug may be fed for 7 to 14 days to treat bacterial enteritis caused by E. coli and bacterial pneumonia, including shipping fever complex, caused by Pasteurella multocida susceptible to oxytetracycline.
The most consequential warning in this section is the dairy restriction. The product is not approved for use in female dairy cattle 20 months of age or older, including dry dairy cows. Use in those animals may leave residues in milk or in calves born to those cows. At the 10 mg/lb body weight/day use level, the withdrawal period is 5 days. No withdrawal period is required at the 75 mg/head/day and 0.5 to 2.0 g/head/day use levels when used as directed.
Sheep carry a narrower claim: treatment of bacterial enteritis caused by E. coli and bacterial pneumonia caused by Pasteurella multocida susceptible to oxytetracycline, with 7 to 14 days of continuous feeding at 10 mg/lb body weight/day and a 5-day withdrawal period.
Honey Bee Use Adds Apiary-Specific Mixing and Residue Controls
The honey bee section turns this label into something more than a feedlot document. Oxytetracycline is labeled for control of American foulbrood caused by Paenibacillus larvae and European foulbrood caused by Melissococcus plutonius susceptible to oxytetracycline. The dosing instructions are highly specific: 200 mg/oz for dusting, 200 mg/5 lb for syrup, and 800 mg/patty for extender patties.
The manufacturing directions matter because the product is not used directly in finished honey bee feed without preparation. For a Type B medicated feed containing 20 g/lb oxytetracycline hydrochloride activity, 10 lb of Pennox 50 are mixed with 15 lb of powdered sugar. For a Type C medicated feed delivering 200 mg per ounce for dusting, 14 lb of Pennox 50 are mixed with 204 lb of powdered sugar. Dusting is then applied at 1 oz per colony every 4 to 5 days for a total of 3 applications, with the dust placed on the outer parts or ends of the frames.
The label gives a clear caution: dusting uncapped brood cells has been reported to cause death of larval honey bees. The syrup and extender patty instructions are equally detailed, with fresh syrup prepared for each application and a single extender patty placed on the top bars of the brood nest frames.
Residue control is central in the apiary setting. The label requires removal at least 6 weeks before the main honey flow. Type C medicated feeds should be consumed before honey flow begins to avoid contamination of production honey, and honey stored during medication periods in combs for surplus honey must be removed after the final medication and not used for human food. State apiary laws also remain controlling, and the label instructs users to follow local regulations.
The product’s clinical value rests on execution. Mixing accuracy, species restrictions, withdrawal timing, and residue prevention determine whether oxytetracycline remains a usable veterinary tool or becomes a compliance problem.