Smart grazing to control scour worms in weaner sheep

WormBoss worm control program for goats

NSW central, southern and southwest

Smart grazing to control scour worms in weaner sheep

By Norman Anderson & John Larsen, Mackinnon Project, University of Melbourne
Source: Mackinnon Project website (10 December 2011)

Introduction

Smart grazing is an improved, yet simple and reliable strategy for the control of worms in weaner sheep during their first winter. It can counter the negative effects of summer rainfall that reduces the effectiveness of the '2-summer treatment strategy' in the winter rainfall areas of southern Australia.

The why and how of 'Smart grazing'

Merino weaners are very susceptible to worms in their first winter. Consequently, they need to graze pastures that have as few worm larvae as is practicable. 'Smart grazing' combines intensive grazing for 30 days with each of the 2 'summer' drenches to ensure that virtually no worm eggs are deposited on a chosen pasture from the first summer drench (November) until after the autumn break (March–April), when the weaners are put into these pastures.

Intensive grazing means using 2½–3 times the normal stocking rate for no longer than 30 days after each of the summer drenches are given. After the intensive grazing period, the paddocks are de-stocked to allow the pastures to re-grow. This means that the total stocking pressure for the 'Smart grazed' paddock will be the same as that for a paddock continuously stocked at the farms normal stocking rate.

The intensive grazing will reduce pasture residues to around 800–1000 kg DM/ha after the first summer drench, and around 600 kg DM/ha after the second. If there is insufficient feed, the periods of intensive grazing can be reduced. On the other hand, if there is excess feed the summer drenches can be 'staggered' for different mobs so as to provide a longer intensive grazing period or cattle can be used as well.

Finally, the weaners must be drenched with an effective drench before they start grazing the 'Smart grazed' paddock after the autumn break.

Smart grazing on a typical farm

A typical self-replacing flock of 5,000 DSEs in southern Australia is made up of 1,500 ewes, 1,500 wethers and 1,000 weaners, running at a winter stocking rate of 15 DSE/ha.

70 ha of 'Smart grazed' paddocks must therefore be prepared for the weaners. Thus, 2600 DSE (70 x 15 x 2.5) are needed to stock the 70 ha at 2½ times the normal stocking rate for each of the two intensive grazing periods—this uses all of the wethers and 70% of the ewes on the farm.

A timetable for 'Smart grazing'

OCTOBER: Select the 'Smart grazing' paddock—choose one with a history of good winter pasture.
NOVEMBER: Give the first summer drench (this must be an effective product), then intensively graze the paddock at 2½–3 times the normal stocking rate.
DECEMBER: Remove the sheep to another part of the farm after 30 days intensive grazing. Ideally, the pasture residue should be 800–1000 kg DM/ha (2–3 cm in height).
JANUARY: Paddock remains unstocked until the second summer drench.
FEBRUARY: Give the second summer drench, then intensively graze the 'Smart grazing' paddock with the drenched sheep (again, not for greater than 30 days).
MARCH: Paddock remains de-stocked until the autumn break.
AUTUMN BREAK (MARCH–APRIL): Drench weaners and set-stock on the 'Smart grazing' paddock when pasture is greater than 600 kg DM/ha (1.5 cm). Weaners can remain there until spring but monitor their worm egg counts every 4–6 weeks.

Why does smart grazing work?

The intensive grazing periods:

• Reduce the amount of pasture dry matter, making the pasture less suitable for the survival of worm larvae.
• Ensure that there is no deposition of worm eggs on the pasture from the time of the first summer drench until the autumn break.
• Probably allow the drenched sheep to 'vacuum' up infective larvae in much the same way as cattle do when they are used in alternate grazing programs with sheep.
• Have the same cumulative stocking pressure from November to March as set-stocked paddocks grazed continuously by wethers.
• Are quite flexible. What must not be changed is the need (i) not to exceed 30 days grazing after each summer drench, and (ii) for a fully-effective product to be used at the summer drenches.

What are the benefits?

Results from a controlled experiment over 2 years in western Victoria show that, compared to weaners grazing paddocks prepared the usual way (grazed by wethers over the summer/early autumn), weaners grazing 'Smart grazing' plots:

• grew 13% more clean wool (2.29 vs. 2.03 kg) which was 3.5% broader (17.1µ vs. 16.5µ)
• were 3 kg heavier in October (46.5 vs. 43.2 kg).

During winter, the egg counts from the 'Smart grazed' weaners didn't go higher than 250 epg, a trigger for drenching weaners used by many farmers and their advisers. In contrast, the weaners on the paddocks prepared by set-stocked wethers exceeded 400 epg in both years.

The numbers of worm larvae on the 'Smart grazed' pastures in winter were from one-half to a one-third of those on pastures in paddocks prepared by grazing with set-stocked wethers.