Ivermectin is a broad-spectrum antiparasitic medication used to treat and control a wide range of internal and external parasites in cattle. As a common practice in the cattle industry, it helps maintain herd health and productivity by preventing production losses associated with parasitic infestations.
Parasites Controlled in Cattle
The medication targets internal parasites, including gastrointestinal roundworms like Ostertagia ostertagi, which causes severe stomach inflammation, leading to poor appetite and weight loss. Ivermectin is also effective against other roundworms like Cooperia species and Haemonchus placei, which can cause diarrhea and anemia. It also controls lungworms, such as Dictyocaulus viviparus, which lead to respiratory issues and coughing.
Ivermectin is also used to manage several external parasites. It is effective against cattle grubs (Hypoderma species) in their larval stage, which migrate through the body and can damage meat and hide. The medication also controls sucking and biting lice, which cause hair loss and reduced weight gain. Mange mites are another external parasite managed by ivermectin, preventing the skin lesions and itching associated with infestations.
Administration Methods and Formulations
Ivermectin is available in several formulations, allowing producers to choose a suitable administration method. The three primary methods are injectable solutions, pour-on applications, and oral drenches, each with distinct procedures.
Injectable ivermectin is administered subcutaneously (under the skin), typically in the area in front of or behind the shoulder. This method ensures a precise dose is delivered into the animal’s system. It requires proper animal restraint to minimize the risk of injury or infection at the injection site. While accurate, this method involves more handling and can be more stressful for the animals.
Pour-on formulations are applied topically along the animal’s backline. This method is less invasive and quicker to apply, reducing animal stress as the solution is absorbed through the skin. The effectiveness of pour-on treatments can be reduced by rain shortly after application. It is also important to apply the product to the skin, not just the hair coat.
Some products combine ivermectin with other drugs to broaden parasite control. A common example is a combination with clorsulon, which specifically targets adult liver flukes, an internal parasite ivermectin alone does not control. This combination allows producers to treat a wider range of parasites with a single application.
Safe Use and Withdrawal Periods
Proper use of ivermectin is necessary for animal safety and food supply integrity. Accurate dosing is fundamental, and cattle should be weighed to determine the correct amount. Underdosing can be ineffective and contribute to parasite resistance, while overdosing increases the risk of adverse reactions.
A withdrawal period is the mandatory time from when a medication is administered until an animal can be legally slaughtered for meat or its milk sold for human consumption. These periods are established by regulatory agencies to ensure no harmful drug residues are in food products. Withdrawal times vary by product formulation and use. For example, one injectable ivermectin product has a 35-day withdrawal period for meat, while a pour-on product has a 48-day period.
Veterinary formulations of ivermectin are developed and dosed specifically for large animals like cattle and should not be used in humans. These products contain concentrations of the active ingredient that are unsafe for people and include inactive ingredients not evaluated for human safety. Using animal health products on humans can lead to dangerous health outcomes.
Managing Ivermectin Resistance
Anthelmintic resistance, the ability of parasites to survive treatments that were previously effective, is a growing concern. Resistance to ivermectin has been reported in several roundworm species. It arises from the repeated use of the same dewormer class, which allows resistant parasites to survive and pass on their genes.
To slow resistance, producers can rotate between different classes of dewormers. This means not using macrocyclic lactones (the class ivermectin belongs to) exclusively. Instead, using a dewormer from another class, like a benzimidazole, reduces the selection pressure for resistance to any single drug.
Using diagnostic tools like fecal egg counts (FECs) helps determine if and when treatment is necessary. An FEC test analyzes a manure sample to count parasite eggs, identifying the infection level in an animal or herd. This allows for targeted treatments instead of treating all animals on a fixed schedule, reducing drug use and slowing resistance.
The concept of “refugia” is a modern parasite management practice that involves leaving a portion of the herd untreated. By not exposing the entire parasite population to the dewormer, a population of susceptible parasites is maintained on the pasture. These susceptible parasites can interbreed with any resistant parasites that survive treatment. This dilutes the resistant genes in the overall population, helping preserve the dewormer’s effectiveness.