Smart Grazing

'Smart Grazing' For Weaner Worm Control

Norman Anderson & John Larsen

 

Introduction
The Why and How of Smart Grazing?
Why does Smart Grazing work?
What are the Benefits?

 

Introduction

Smart grazing is an improved, yet simple & 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 southern Australia.

The strategy hasn't been evaluated in the summer rainfall areas.

The why & 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 is given. Not exceeding 30 days is critical because it takes 3 weeks for a worm larvae (eaten off pasture) to develop into an egg-laying adult in the sheep. 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 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 is 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 (MUST be with 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 (2.2-3 cm).

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 > 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 > 600 kg DM/ha (1.5 cm). Weaners can remain there until spring but monitor their worm egg counts every 4-6 weeks.

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Why does smart grazing work?

The intensive grazing periods:

  • Reduce the amount of pasture dry mater, 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 compound 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.

 

 

 

 

 
Footrot - the disease

Footrot is a highly contagious disease caused by bacteria that infect the feet of sheep, causing severe pain and lameness. It can have an enormous impact on flock productivity and profitability by reducing wool production, causing poor growth rates, lowering ewe fertility and restricting sale options for infected sheep.

What is Footrot?

Footrot is an infectious disease of sheep, cattle and goats. It occurs thoughout Australia but is most prevalent in the medium to high rainfall areas.

Footrot is caused by a bacteria called Dichelobacter nodosus (previously called Bacteroides notodus) which thrives in moist, warm conditions. The footrot bacteria can live indefinitely in pockets of infection inside the feet of affected animals, even under dry conditions. However, the bacteria cannot survive outside the foot (say in soil or sheepyards) for more than 7 days.

There are many strains of the footrot bacteria which vary in their ability to cause disease. Some strains never cause serious footrot in sheep, regardless of the environmental conditions - these cause 'BENIGN FOOTROT'.

Other strains cause severe footrot lesions and spread rapidly in warm, moist environmental conditions. These cause 'VIRULENT FOOTROT'.

In between these two extremes, there is a range of strains that produce from mild to severe footrot. All of these bacteria look identical under a microsope.

Diagnosis of footrot

Before undertaking a footrot eradication program, it's essential to get the correct diagnosis of what strain of footrot is present.

This requires a thorough inspection of 50-100 sheep to determine the number affected and assess the severity or progression of any lesions present.

Treatment of footrot

BENIGN FOOTROT is easy to control, but difficult to eradicate - in fact it's rarely economically worthwhile to attempt eradication of BENIGN FOOTROT. There will be little evidence of lameness, especially when it's dry. However, during spring it may be nessary to control the spread of infection by footbathing.

VIRULENT FOOTROT is quite different - CONTROL and then ERADICATION is the only course of action. This disease not only causes significant production loss, but compromises animal welfare and causes a lot of worry for owners of affected flocks.

Eradication can take up to 2 seasons and requires commitment, good facilities and adequate labour - a specialist footrot contractor is often the best option.

Poor planning is ususally the reason why eradication attempts fail. In particular, pay attention to reinspection of clean sheep, and don't muck about with sheep with severe lesions - "IF IN DOUBT, CHUCK IT OUT". Ideally, 2 clean inspections are required for each mob, then don't mix mobs until after the next spread period (usually spring).

CONTROL - Before attempting eradication, Footrot needs to be controlled during the spring and autumn spread periods. This usually means regular footbathing and sometimes vaccination. Good control reduces the number of affected sheep that have to be treated or culled during the eradication phase. Eradication is undertaken during the non-spread period (summer) and requires inspection of ALL feet of ALL sheep at least twice during the dry period.

Contact the Mackinnon Project

Footrot eradication programs are expensive and must be tailored to each flock. If you think your sheep have footrot, contact us and we will develop a control and eradication strategy for your individual situation.
 
Blowfly Strike
Article Index
Blowfly Strike
Parasite Management
Page 1 of 2

The Australian sheep blowfly (Lucilia cuprina) breeds preferentially on sheep and initiates the majority of flystrike of sheep in Australia. It is thought to have arrived in Australia from South Africa in the mid- to late-1800's, causing major outbreaks of flystrike in many areas of south-eastern Australia in 1897.

An integrated parasite management (IPM) approach to controlling blowfly strike combines the use of insecticide with methods of making sheep less susceptible to both breech and body strike, such as:

  • effective worm control programs to reduce scouring
  • mulesing & tail docking
  • genetic selection against fleece rot, skin wrinkle and breech soiling ('dag').

The proposed phase out of mulesing in 2010 is a major challenge to the industry and a number of alternatives are being explored through research sponsored by Australian Wool Innovation (AWI).

In contrast to control programs for internal parasites ('worms'), the application of insecticides to control blowflies is based more around farm management practices, such as shearing, lambing and cropping.

The use of insecticides has been associated with the development of serious insecticide resistance in L.cuprina - this is summarised in Table 1. Fortunately resistance to the IGR (insect growth regulator) compound cyromazine (Vetrazin® and other brands) has not yet been detected in field strains of Lucilia cuprina. However, field strains resistant to another member of the IGR class of insecticides (Diflubenzuron) have occurred.


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Vaccination against Clostridial diseases

Clostridial diseases are a significant cause of deaths and economic loss in unvaccinated flocks, so clostridial vaccintation is simple and cheap form of stock insurance.

Control by vaccination

Initially two doses of 5-in-1 vaccine, given at marking then weaning, followed by a booster 12 months later, will give a solid life-long immunity against most clostridial diseases. These include Black Disease, Blackleg, Malignant oedema, Pulpy Kidney ('PK' or enterotoxaemia) and Tetanus.

Additional vaccinations are only required in special circumstances, such as when sheep are run on irrigated pastures. In this case Black Disease, associated with immature liver fluke infection, can be a problem.

In addition, immunity to Pulpy Kidney is not as long-lived and may wane in older ewes and wethers (although there are very few of these around at the moment!).

This may be a problem for older ewes and their lambs, particularly with high levels of grain feeding or when sheep are moved onto lush pasture, such as lucerne.

Consequently, if you have had Pulpy Kidney deaths in lambs born from older ewes in the past, it is advisable to give a booster vaccination to older ewes. In addition, if older sheep are being fed grain rations for an extended period (such as during drought), a 5-in-1 booster is worthwhile insurance.
 
Lice

To prevent the introduction of Footrot, lice and OJD, purchased and stray sheep should be carefully inspected and kept isolated from other mobs on the farm.

If lice are detected and significant fleece derangement is occurring it may be necessary to use a long-wooled treatment to control lice until the next shearing. All sheep should then be treated after the next shearing to eradicate lice.

A decision support tool developed by AWI (LiceBoss®) is available to help with these decisions - contact your Mackinnon Project consultant for advice .

The broad Integrated Parasite Management ('IPM') strategies for lice are:

  • Monitor for lice before shearing, crutching, and at other times when sheep are yarded
  • Institute a lice biosecurity plan, which includes:
  • Checking the lice history and quarantining purchased or agisted sheep.
  • Preventing strays with stockproof fences.
  • Guarding against the introduction of lice by contractors or shearers who have recently been on a lice-infested property.
  • If lice are detected, treat with an effective chemical at next shearing, regardless of whether or not a long wool treatment has been used. ALL sheep must be mustered and treated.