Lewis Kahn, Associate Professor Animal Science, University of New England

Many of you will know of, or heard about, the value of grazing management in lowering the number of infective worm larvae on pasture.  This is the stage (called L3) that develops from worm eggs deposited in faeces by infected sheep.  It is also the stage that develops into adult worms, females laying eggs, after being eaten by sheep as they go about grazing of pasture, where the L3 reside.  Managing the exposure of sheep to infection from L3 is at the core of good grazing management for worm control and can be highly effective at ensuring sheep graze pastures with low numbers of L3.  As an example, work conducted some years ago by Dr Justin Bailey as part of his PhD at University of New England  demonstrated the effect of lowering the number of L3 on pasture on the performance of spring lambing Merino ewes and lambs in the Northern tablelands of NSW which gets 40% of its rain during the summer.

Pastures were grazed with wormy sheep during the summer period and then were either:

1. Continuously grazed with wethers
2. Continuously grazed with steers or
3. Grazed for 21 days by drenched wethers on two separate occasions (this is the process of Smart Grazing developed by Dr Paul Niven for winter rainfall regions; http://www.wormboss.com.au/programs/sheep/vic/appendices/smart-grazing-for-weaner-worm-control.php)

All treatments were at the same overall stocking rate and went for about 6 months concluding 2 months before spring-lambing in order to get pastures ready for lambing.  At the start of lambing, an estimate was made of the number of L3 on pasture and this was  compared to the number of L3 on pasture at the start of the work, after grazing by the wormy sheep.  A reduction in L3 occurred for all treatments (see Figure 1) because fewer eggs develop to L3 as the weather cools but the biggest reduction (<1% surviving L3 for Barber’s Pole and <4% for Black Scour worm) occurred for Barber’s Pole worm under Smart Grazing.  Clear evidence that grazing management plays a big role in managing L3 numbers on pasture.

Fig 1: Percentage of Barbers Pole worm and Black Scour worm infective larvae (L3) remaining on pasture after 6 months of being grazed continuously by sheep, steers or smart grazing.

Ewes were drenched into these paddocks for lambing, and over the four months up till weaning, ewes that grazed the paddocks prepared with continuous sheep had to be drenched twice while those that grazed paddocks prepared with steers or Smart Grazing did not require treatment and had a worm egg count of 200-400 epg at weaning.  Despite fewer drenches, ewes from the steer and Smart Grazed paddocks were 2.2 kg heavier at weaning.  The lambs from continuous sheep paddocks were drenched at weaning with a worm egg count of 1,000 epg whereas lambs from the steer and Smart Grazing treatments were not drenched and had worm egg counts of 50-100 epg.  In the same manner as the ewes, lambs from the steer and Smart Grazed paddocks were 2.4 kg heavier at weaning than lambs from the paddocks prepared with continuous sheep.

Grazing management can play a big role in reducing exposure of sheep to infective larvae and help provide good worm control and good production.  In conjunction with selecting worm resistant rams, regular worm testing and knowing the effectiveness of drenches on your farm, grazing management plays a role in regional worm control programs. Visit WormBoss at www.wormboss.com.au to find a worm control program for your region.