While the northern, summer-rainfall producers are well used to barber’s pole worm (Haemonchus contortus), their southern*, winter-rainfall brethren have less experience with this blood-sucking worm. But 2021 will likely be the “Year of southern barber’s pole worms” with clinical disease shaping up to be more widespread than has been seen for many a year.
If you are in a more typical southern Australian scour worm region and your property has had a little to a lot more summer rainfall than usual, barber’s pole worms may have flourished, and the more significant rainfall events that have occurred over summer (greater than 10 mm within a period of a week), the worse the problem will be. The worm larvae that hatched during these warmer, rainy periods survive on the pasture for many months—even through frosts—and sheep will progressively ingest more worms, building an ever-increasing burden for some time. Review of past monthly reports indicates a problem could appear well into autumn and early winter.
1. WormTest every month; add a LARVAL DIFFERENTIATION in occasionally (only experienced labs can do this). What burden of Haemonchus do they have right now? 600 epg of barber’s pole worm is the lower threshold for drenching when sheep are in poor condition on poor pastures, but if you have fat sheep on good pastures you don’t need to drench until 1200 epg. But signs typically don’t show until the mob average is about 3,000 to 5,000 epg—if you wait until you see some sheep showing signs there’s a good chance you’ve already missed one or more dead sheep in the paddock. The drenching threshold range is the most economic time to drench (balancing drenching and mustering costs against production loss) and you can only pick it with a worm egg count because the sheep can look remarkably good till quite close to when they drop dead (remember, there is no scouring and weight loss is right in the last stages when they stop eating).
2. If you are already drenching for scour worms during autumn and/or early winter, or doing a strategic drench, include levamisole, closantel, monepantel or derquantel in your drench choice (ideally in a combination product, or use concurrent drenching, i.e., two drenches given at the same time, but not mixed together). Even one such drench has a good chance of preventing a developing infection from becoming clinical under southern Australian conditions (but continue WECs as there will likely still be larvae on the pasture). While levamisole and closantel are not good choices for scour worms, and Haemonchus resistance to them is reasonably common in summer-rainfall areas, they are often completely effective choices in the south against barber’s pole worm. Monaro Farming Systems group conducted DrenchTests on about 20 farms a few years ago and both of these older drenches were still highly effective against barber ‘s pole worm in that region.
3. Finally, if it beats you and stock collapse during muster, LEAVE THEM WHERE THEY FALL, then come back and drench them in the paddock (better still, carry some drench with you and do them on the spot so they don’t have to be found and caught if they are able to wander off). An inspection of the inside of their lower eyelids (not the third eyelid that extends across from the inside corner of the eye when the eye is squeezed, as it is always paler anyway) will confirm the extent of anaemia (lack of blood)—this should be quite a dark pink even with burdens producing about 1000 eggs per gram. Any sign of paleness inside the eyelid, or swelling under the jaw (“bottlejaw”) is serious, especially when it’s almost white. Trying to keep walking them to the yards or carting them there can often be enough to kill them. That added handling stress causes a high oxygen demand, but with few red blood cells left, they can’t transport oxygen around the body—a collapsed sheep from barber’s pole worm is already dicing with death.
*Areas referred to as “southern” are typically at a latitude further south than Sydney in the eastern states, and anywhere in the farming areas of South Australia and Western Australia.