Treating lice: when, how and what chemical group

  • Cattle lice rarely need to be treated because they generally cause little economic impact to animals.
  • Only treat when live lice are found and irritation causes cattle to rub on fences, or other structures.
  • Few treatments are registered for lice alone so consider timing for optimal effect against other parasites.

When

There are no set times to treat for lice. Louse numbers peak over cooler winter months so if heavy infestations are seen, the optimal timing of treatment is late autumn.

In Australia, cattle lice generally cause little economic impact except when very heavy infestations develop on susceptible or stressed stock. In addition, most populations of lice naturally fall to low levels in summer when they are exposed to high levels of solar radiation. Nevertheless, lice can cause irritation to affected cattle, can give the cattle a ‘rough’ appearance, which may reduce prices at sale, and cattle rubbing can cause damage to skins, fences and other infrastructure.

Most lice control products are registered for use against more than one parasite and often where treatment of lice is required it is possible to choose a product that will also control the other parasites. Consider timing lice treatments to provide optimal effect against other more important parasites.

How

Lice treatments can be applied as pour-ons, sprays or dips. Some injectable products may have action against sucking lice. A dust formulation of rotenone and sulfur is registered for control of lice in calves.

Some insecticidal ear tags, registered primarily for use against buffalo flies, also have a claim for ‘control’ or ‘aids in the control’ of lice. Where insecticidal tags are used for buffalo fly control they may also provide some control of lice.

What

Chemical actives registered for cattle lice control are in four main groups:

Lice control products

(See also the LiceBoss cattle products search guide in ParaBoss)

Table 1. Lice control chemical groups and actives, application methods and parasites targeted.

Lice control chemical groups

Chemical actives

Application methods

Parasites targeted

Can kill dung beetles?

Synthetic pyrethroids (SP)1

Deltamethrin,

Cypermethrin,

Zeta-cypermethrin,

Permethrin

Backline pour-on, sprays, dips, ear tags

Lice, buffalo flies, ticks

Y2

 

Organophosphates (OP)1

Diazinon

Chlorfenvinphos

Backline pour-on, sprays, dips, ear tags

Lice, buffalo flies, ticks

N

Macrocyclic lactones (ML)

Abamectin,

Ivermectin,

Doramectin,

Eprinomectin,

Moxidectin

Backline pour-on, injection, oral

Lice (injection and oral are effective in the treatment and control of sucking lice only), worms, buffalo flies, ticks

Y2,3

 

Insect growth regulators (IGR)

Diflubenzuron

Backline pour-on

Lice

N

Rotenone and sulfur

Rotenone,

Sulfur

Dust

Lice

N

1 Some spray/dip compounds contain both an SP and OP.

2 If applied as ear tags the actives do not affect dung beetles.

3 MLs vary in their harmful effects on dung beetles with moxidectin less harmful than the other MLs