Both internal and external parasites represent health and production risks to the beef herd. Each may impact the operation through decreased performance or productivity as well as increased susceptibility to disease and increased risk of mortality. Many of the performance or productivity losses often go unrecognized. Generally speaking, internal and external parasite control programs should be a component of all beef operation herd health plans.
Internal parasites generally impact cattle health and productivity through chronic blood loss. Depending upon the region and environmental conditions, common internal parasites of cattle include stomach worms such as Ostertagia, Haemonchus, and Trichostrongylus; intestinal worms such as Cooperia spp; and protozoa such as Coccidia, as well as grubs (heel fly larvae), liver flukes, lungworms, and tapeworms.
External parasites negatively impact cattle health not only by robbing cattle of required nutrients, but also by increasing animal stress and because they are vectors for other diseases, such as anaplasmosis, theileriosis, and tickborne fever. Depending upon the region and environmental conditions, common external parasites that may impact cattle health and productivity include horn flies, stable flies, face flies, black flies, deer flies, heel flies, horse flies, midges, gnats, mosquitoes, lice, mites, and ticks.
Internal Parasites in Beef Cattle
Under certain conditions, cattle may become hosts to a number of internal parasites. A comprehensive internal parasite control program includes environmental management strategies that minimize exposure to the parasite, along with strategic administration of anthelmintics when necessary.
Selective grazing management practices, such as rotational grazing, can be effective and important components of internal parasite control programs. In addition, intermittently rotating the species that grazes a pasture, or resting pastures if possible, can help to break the life cycle of many internal parasites through removing the host that is necessary for their propagation.
Anthelmintic administration should be based upon target parasite load, parasite susceptibility to treatment, and potential impact that removing or decreasing the parasite load will have on the animal(s). In addition, the focus should be placed on breaking the parasite's life cycle and avoiding pasture reinfestation. Fecal egg counts along with egg, cyst, and oocyst identification conducted before and after anthelmintic administration can be incredibly valuable to developing a treatment plan with a high likelihood of success.
It is important that anthelmintics be transported, stored, handled, and administered in accordance with their labels. Similar to vaccines and other biological products, anthelmintics may be sensitive to certain environmental conditions. In addition, it is important to avoid under-dosing animals in order to minimize the development of resistance to anthelmintics.
Most labeled anthelmintic dosages are based upon animal weight, and therefore individual animal doses should be determined by weighing individual animals. Estimating animal weight, or administering a common dose to each animal in a group based on the group average will result in underdosing some animals, which may increase the rate of resistance development, and overdosing others, which represents an unnecessary expense.
External Parasites in Beef Cattle
Similar to internal parasite control, components of a comprehensive external parasite control program include physical management strategies that minimize exposure to the parasite, as well as administration of products that deter, kill, or otherwise alter the normal life cycle of the parasite.
Removing unnecessary accumulations of feces, old feed, and water are the major physical means through which the life cycle of many external parasites can be disrupted. Nonetheless, it is practically impossible to remove all of these materials, and therefore additional methods of external parasite control are almost always necessary.
A multidimensional approach to external parasite control increases both the short- and longterm likelihood of success. Examples of complementary external parasite control methods include:
insecticide-impregnated ear tags
pour-on or otherwise topically applied insecticides (such as back rubs, for example)
premise sprays
feed-through insecticides, such as an insect growth regulator (IGR) for horn fly control or a larvacide for control of multiple fly species
parasitic wasps
physical traps
For many of these options, timing and judicious use are of critical importance to maximize efficacy and minimize resistance development.
