However, a variety of external and internal parasites may compromise your cattle’s current performance and pose a long-term threat for future generations. A few simple steps can ensure that you don’t jeopardize the health and productivity of your operation.
First, the skin and behavior of incoming animals should be assessed for external parasites, including ticks and lice, and the animals should be promptly treated if necessary. Winter lice infestations are irritating and can lead to property damage from itching; severe infestations of either lice or ticks can be debilitating.
While producers in the southern Texas border counties must be especially vigilant for any signs of the cattle fever tick, domestic ticks are also an important vector for several diseases. Anaplasmosis is the most notable concern in the U.S. beef herd; this red blood cell parasite causes anemia, production losses and death, especially in mature cattle. Biting insects, such as horse flies, stable flies and mosquitos, can also transmit anaplasmosis, as well as the bovine leucosis virus. Topical permethrin products can help control lice and aid in control of horse flies, stable flies, mosquitos and ticks; two applications two to three weeks apart may be needed for lice control.
Secondly, the cattle should be assessed to determine if they need to be treated for gastrointestinal roundworms. This category of gastrointestinal parasites includes cooperia, the brown stomach worm (Ostertagia ostertagi), the barber pole worm (Haemonchus placei) and the nodular worm (Oesophagostomum radiatum). In addition to the direct effects of parasitemia, uncontrolled roundworm infestation is associated with negative indirect effects on the cattle’s immune status, demonstrated by decreased response to vaccination and increased susceptibility to other diseases.
These nematode roundworms can be found in all classes of cattle operations, from the cow-calf herd to the feedlot, and almost all cattle are infested to some degree – the key is to balance managing the parasite against preserving the efficacy of deworming medications.
Herd additions may act as a Trojan horse, introducing both parasites and anthelmintic resistance into your operation. While modern macrocytic lactone dewormers (e.g., moxidectin) are a mainstay in most herd programs, a significant amount of drug resistance has been documented, especially with cooperia species, and in some cases, the older white benzimidazole dewormers may be more effective.
For this reason, it is recommended to work with your veterinarian to tailor your deworming program to the class of cattle, season and known parasite burden. A fecal egg count can identify if the cattle have a significant roundworm burden, while a fecal egg count reduction test can be performed to identify parasite resistance to common dewormers.
As a general rule, the cleanest pastures should be reserved for youngstock; stocker cattle should not utilize permanent pastures; and replacement heifers should be managed separately from the high-risk stocker groups. New herd additions should be evaluated for parasite load, treated if necessary and co-grazed with mature cattle before accessing clean pastures.
Finally, it is not recommended to add youngstock such as nurse calves to a herd with other calves, especially those under a month of age. These calves may introduce parasitic scour pathogens such as cryptosporosis and coccidia. Cryptosporosis is most common in younger calves, approximately 1 to 2 weeks old, while coccidia generally affects older calves 1 to 6 months old. These scouring calves contaminate the environment with high numbers of parasites, posing an especially high risk to any younger or new calves in the group. Some calving management programs, such as the Sandhills Calving System, are specifically designed to minimize neonatal diarrhea from parasitic as well as viral and bacterial causes.
In conclusion, incorporating parasite assessment and control into your biosecurity plan can both reduce your exposure to costly diseases and synergize with other efforts to improve your herd’s health and productivity. Your herd veterinarian and local extension office can provide advice on the threats to your operation and help you tailor your herd health program. 
Kelly Still-Brooks, DVM, MPH, DACVPM, is a food animal clinician at the Iowa State University College of Veterinary Medicine. Email Kelly Still-Brooks.
PHOTO: Herd additions may act as a Trojan horse, introducing both parasites and anthelmintic resistance into your operation. Staff photo.
