New Lice Control Options
Livestock Update, January 1998
W. Dee Whittier, Extension Veterinarian, Cattle
Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech
The avermectin parasite control products may make lice control easier this winter for some beef cattle producers. Three pour-on products are now commercially available in the US. The three are Ivomec Pour On¨, Dectomax PourOn¨ and Ivomec Eprinex¨. All three pour-on products now have a persistent lice control guarantee.
These lice guarantees all have similar components. All cattle must be treated shortly after they enter a cattle herd. The Dectomax¨ guarantee provides that a group of cattle must be put together within a 30 day period of time. Cattle must be treated according to label directions and at appropriate dosage levels. They must also be housed so that they do not become exposed to non-treated cattle.
Cattle that meet these requirements are then guaranteed to stay free of clinical lice infections for an extended period after treatment. The Dectomax¨ claim is for 240 days, the two Ivomec¨ products for 180 days. If cattle do become infected the guarantee provides free product to retreat them and a handling fee for readministering the products. Cattle that are thought to have become reinfected must be so certified by a veterinarian.
Historically, even when cattle were treated for lice as a group in the fall, there has been a concern about reinfection. Producers have either retreated cattle routinely mid-winter or observed them closely for reinfection and treated if signs of infestation occurred. These new products will hopefully allow cattle producers to forego this mid-winter treatment. This is due to the essentially 100% kill rates these products achieve coupled with the persistence of the active ingredients on the hair and skin for some time after their administration.
Lice infestations result in production decreases in cattle. The most common cattle lice are blood suckers that also irritate cattle. Irritated cattle scratch themselves in pens, mangers, etc. causing damage to their skin, unsightly hair loss and damage to facilities. In severe cases young calves may become ill and even die if infestations become severe enough.
There are several approved lice treatment products in the US. Systemic organophosphates are popular because of their pour-on convenience. They are also available in spray, back rubber and dust forms. Pyrethroid products are likewise available in pour-on, spray and dust forms. The newer pour-on avermectins listed above give producers another tool in controlling lice. Because of their high cost, they would typically be used in young cattle where their excellent stomach worm control characteristics along with their ability to control external parasites would make their use economically advantageous.
Regardless of the product or route chosen, lice control should be a priority for all beef cattle producers during late fall and winter when lice populations begin to increase. The most advanced cases of lice are seen in Virginia in February and March but losses probably begin before the worst hair loss and scratching begin.