A cattle producer phoned recently, exasperated that the older cattle lice control options, such as the organo-phosphate pour-ons (Tiguvon and Warbex) are no longer available. He asked about his options. The first question though is does he need to treat cattle for lice?
From the livestock performance perspective, treating cattle for lice usually doesn't pay. Experiments such as those conducted by Leo Cummins and Neil Tweedle in western Victoria illustrate this.
They divided a mob of 48 Hereford weaners into eight groups. Half the groups were treated twice with famphur (Warbex), while the others were left untreated and half of each group (equal numbers of treated and untreated) were fed either a low growth ration or a high growth ration.
While the cattle on the low ration only gained 3kg over the three months of the trial and had higher lice levels than the calves on the high growth ration (that gained 44kg), lice treatment did not improve body weight in either group. Most (but not all) other researchers made similar findings.
However, there is more to livestock management than just economics. Lice affected cattle rub and scratch from the irritation, can damage hides, fences and gates and look scruffy. While most cattle are only mildly affected by lice, some, either because of immune problems or because they are down in condition, can suffer heavy, even life threatening lice burdens.
While we have a range of options, the most popular now are the mectin drenches or pour-on and the synthetic pyrethroid pour-on. The mectin pour-ons are effective against both biting and sucking lice, while the injectable mectins are only fully effective for sucking lice.
Synthetic pyrethroid pour-ons are effective against both types of lice. However, none of the lice control options used as a single treatment eradicate lice, because while lice are killed, the eggs are not. Some eggs will hatch up to three weeks later, by which time the treatment is no longer effective. Lice then recur a few months later. So cattle early in the autumn may suffer a recurrence in the spring. For late winter/spring calvers, anytime now is a good time to treat cows for lice, combined with other pre-calving treatments such as vaccinations (and perhaps drenches but that is another story).
It is possible to eradicate lice from cattle herds, just as most people eradicate lice from sheep flocks. To do this, all cattle need to be treated twice about three weeks apart with an effective chemical such as a synthetic pyrethroid.