Animal health following drought

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Users of agricultural (or veterinary) chemical products must always read the label and any Permit before using the product, and strictly comply with the directions on the label and the conditions of any Permit. Users are not absolved from compliance with the directions on the label or the conditions of the Permit by reason of any statement made or not made in this publication.

Introduction

The transition from drought is an important time to be concerned about livestock health. Even though the drought appears to have broken, there is no time to relax on matters that concern livestock health. More care and attention needs to be given both to your current stock and to any newly purchased stock.

With the advent of drought-breaking rains, the feed and water supply situation may dramatically change. A comment often made by graziers is that they managed to keep their stock alive through the drought only to suffer losses when the drought broke. Bloat, pulpy kidney, plant poisonings and hypothermia would be among the most common problems causing deaths at the end of a drought because, at such times:

• stock may be in poor condition;
• stock may have become accustomed to eating restricted quantities of unusual types of feed;
• water supplies may be restrictive in terms of quantity and quality;
• stock are not accustomed to eating green forage, especially lush grasses and clovers;
• stock may be suffering from long-term vitamin and/or mineral deficiencies;
• the usual disease prevention measures, such as vaccination or worming, may not have been given.

Potential problems following drought

Cold, wet and windy weather

Adverse weather conditions are frequently associated with drought-breaking rains. Even in the middle of summer, extreme cold weather conditions can be experienced, and stock in poor condition can be highly susceptible. Poor body condition, poor or inadequate feed, lack of shelter, an interruption to provision of supplementary feed, and recent shearing are just some of the factors that can contribute to a disaster.

Be alert to weather changes and ensure that susceptible stock have access to shelter. Bring forward supplementary feeding if there is any chance that feeding may be interrupted as a result of rain. Sheep that have been recently shorn are the most susceptible, especially if they are in poor condition. You may need to keep them in sheds, or confine them to small paddocks with feed and shelter.

Water

If sufficient rain falls to replenish surface water supplies, the surface run-off may carry excessive amounts of livestock manure into the water storage, making it unacceptable or even dangerous to stock. This can be avoided by restricting stock access to these water supplies. You may need to pump water to troughs or tanks from an area of the storage that is relatively free of the contamination (the contamination tends to accumulate around the edge of the water).

See Primefact 394 Reassessing water requirements after a drought and Primefact 326 Water requirements for sheep and cattle.

Feed

Initially, the ‘brown’ drought becomes a ‘green’ drought—the newly germinating plants do not contribute significantly to the nutritional needs of stock (see Primefact 364 Grazing management following drought). Stock, especially sheep, can waste precious energy ‘chasing the green pick’ if drought feeding is stopped too soon.

Following the rain, continue with the usual drought feeding regime until the feed really comes away. Then progressively reduce the supplementary feed over about 2 weeks. In this way the major nutritional upsets associated with a sudden change in feed (such as enterotoxaemia or pulpy kidney) can largely be avoided.

Feed changes

As mentioned above, sudden changes in the amount or type of feed can have disastrous consequences. Major problems relate to digestive upsets and plant poisonings. Avoid these problems by allowing stock a gradual transition between feed types, such as limiting access to the pasture to an hour or two each day, then gradually increasing the amount of time each day until they can be left on the pasture permanently.

Never, ever, put hungry stock in a fresh paddock. They will indiscriminately gorge themselves on the first available feed, often leading to poisonings or digestive upsets. Pre-feed with hay, restrict daily access or provide access to a safe, preferably mature grass paddock to overcome the hunger before allowing access to rapidly growing, lush ‘different’ feed.

Bloat

Rapidly growing legumes, such as lucerne, clovers and medics, frequently cause bloat, especially in young cattle.

If pastures contain a significant amount of legume, bloat protection is an absolute must. A variety of techniques exist, including the use of:

• bloat capsules;
• pasture sprays with anti-bloat preparations;
• bloat blocks;
• bloat oils mixed with supplementary feed.

Grass tetany

Grass tetany can be regarded as a deficiency of magnesium, and most frequently affects breeding cows grazing grass-dominant pastures in winter. It is usually associated with cold, wet weather and mainly affects cows in late pregnancy and early lactation. Unfortunately the first sign is often sudden death, sometimes affecting significant numbers of cattle.

Magnesium supplements, in the form of blocks or as treated oats or hay, are recommended for prevention.

Coming out of a drought, it is likely that both breeding cows and ewes will be more prone to magnesium deficiencies.

For further information, see Primefact 420 Grass tetany in cattle and Primefact 421 Grass tetany in cattle — treatment and prevention.

Vaccination

Stock should be brought up to date with their vaccinations if any have been missed during the drought.

In particular, a booster dose of pulpy kidney vaccine is recommended for both sheep and cattle. This is because the protection afforded by vaccination may only last for 3 months after a booster dose of vaccine. Sudden changes in the amount and type of feed available exposes both sheep and cattle to a very high risk of developing pulpy kidney.

See also the sections on Leptospirosis and Brucellosis in rams and vibriosis in cattle.

Blowflies

Because of the prolonged dry weather, most sheep will not have been given a preventive fly treatment. In addition, in order to minimise stress on stock during drought, many lambs may not have been mulesed. If the weather stays warm following the rains, all the factors are present for a fly problem to develop.

Susceptible sheep should be protected by jetting using Cyromazine (e.g. Vetrazin®, Jetcon®), giving up to 14 weeks’ protection. Adding an organophosphate (OP) insecticide is not recommended, because an OP insecticide increases the risk of residues in wool and does not provide any extra protection. Where possible, fly-struck sheep should be separated, the strike treated, and a preventive jetting applied (see Agnote DAI-72 Hand jetting sheep).

For further information on blowflies and flystrike, see External parasites.

Sheep worms

Through a drought, sheep worm eggs tend to accumulate because there is insufficient moisture to permit them to hatch normally. This, coupled with relatively higher stocking densities where sheep have been hand fed, can lead to the build-up of a large reservoir of worm eggs. After rain there can be a mass hatching of eggs, and stock can be exposed to a severe worm challenge. At the end of a drought there is often very little choice of paddocks, and stock may need prolonged protection.

In the warmer months, barber’s pole worm can cause problems (anaemia, ill-thrift and death) in as little as 3–4 weeks.  Most barber’s pole worm drenches are short-acting, but one, Closantel, keeps killing barber’s pole worms for up to 6 weeks. This is very useful if you can’t turn sheep onto a fresh paddock after drenching. Closantel is marketed as Seponver® and Razar®.

If the normal drenching program has not been carried out during the drought, it is wise to catch up as soon as possible. Seek advice from your local veterinary adviser on the best worm control programs to suit your area.

For further information on sheep worms, see Internal parasites.

Purchasing stock

There is always a risk of introducing diseases with any purchased stock. If possible, be selective in the stock you buy and make sure they appear to be in a satisfactory state of health. Obtain as much information as possible about the health, vaccination and recent treatment (for lice, worms etc.) of the stock. The vendor should be prepared to provide this information — a reluctance to do this may suggest a potential problem with the stock.

When restocking, it is wise to contact your Rural Lands Protection Board veterinarian in order to check on the disease status of the areas of origin of your new stock.

On arrival, the stock should be isolated from existing stock for at least 2–3 weeks and inspected daily. During this time any necessary treatments or vaccinations can be applied to bring the new stock up to the same standard as your current stock.

Health concerns with purchased stock

Worms in introduced stock

It is recommended that you drench new stock with an effective worm drench and, if necessary, a fluke drench, both for the well-being of the introduced stock and in order to limit the introduction of resistant species of worms onto the farm. There is no way to easily determine the drench resistance status of worms in purchased stock, so use the drenches that are most likely to be effective (e.g. Avomec®, Ivomec®, Oramec®, Cydectin®).

Footrot

Footrot is the last disease you want to introduce onto your property. If you are purchasing sheep, make sure they are inspected and are free of any lameness. You should ask the vendor for a footrot vendor declaration—it is a safeguard against the introduction of the disease. Where possible, buy sheep from properties in the Footrot Control Areas and Protected Areas of NSW. It is a legal requirement to obtain a footrot vendor declaration and supply it to the local Rural Lands Protection Board if you are introducing sheep into a Footrot Control Area or Protected Area from a Residual Area.

Any sheep that develop lameness should be investigated immediately. Both footrot and foot abscess can develop under similar lush pasture conditions, and it is often difficult to determine which disease is present. If you are unsure of the cause of any lameness in sheep, get advice from your local District Veterinarian or private veterinary practitioner. Act quickly to prevent spread of the disease.

For more information, see Footrot.

Sheep lice

Lice are always a risk when buying sheep. With around 30% of flocks infested at some time of the year, inspect sheep well before introducing them onto your property.

It is difficult to detect lice on sheep that have less than 3 months’ wool, even if they have not been treated after shearing. Remember, even if you can’t find lice in short wool, the sheep could still be infested. Keep them isolated from other sheep for as long as possible, and reinspect them for lice frequently. If lice are detected, consider your options:

• Keep the sheep isolated until the normal flock shearing, and treat after shearing.
  OR
• Treat the sheep immediately, using a product suitable for application to long-wool sheep. Maintain them separately until shearing, and treat again after shearing. Long-wool lice treatment is unlikely to eradicate lice—it will just control them until shearing.
  OR
• Keep sheep isolated, shear as soon as possible, and treat after shearing.

For more information on lice and treatments, see External parasites.

Johne’s disease

Johne’s disease causes wasting, diarrhoea and death. It can affect both cattle and sheep. The strains of the bacteria causing Johne’s disease in cattle rarely affect sheep, and vice versa. But there is a risk, and because it is very difficult to eradicate the disease, it is best to keep Johne’s disease at bay.

When buying cattle, especially from the wetter southern areas, ensure you obtain a vendor declaration in respect of Johne’s disease. See Agnote DAI-77 Bovine Johne’s disease Zoning for information on cattle movements between zones of different status.

See also Primefact 352 OJD and sheep movement.

Comprehensive information on Johne’s disease is available.

Leptospirosis

Leptospirosis is another bacterial disease that is often associated with wet conditions. It is important because of its ill effects on both cattle and people. Protecting cattle by vaccination also reduces the risk of infection in people working with the cattle.

Leptospirosis vaccines for cattle are now available either combined with clostridial disease vaccines (e.g. Cattlevax®, Vaxall Clepto-7®, Vaxicare Cattlemaster 7®, 7-in-1 for Cattle®), or as straight dual leptospirosis vaccines (e.g. Lepto for Cattle®, Vaxicare Lepto HP®, Leptovax®).

Brucellosis in rams and vibriosis in bulls

Both these sexually transmitted diseases can have a major impact on the reproductive performance of the flock or herd.

Buy only those rams that are from flocks accredited free of brucellosis, even if rams are hard to source. Accredited-free flocks will have a certificate which will show an accreditation expiry date. Introducing infected rams will result in a poor lambing performance and will spread the infection to other rams.

Bulls can be carriers of vibriosis, which can reduce calving rates by as much as 20%, sometimes more. It is a wise precaution to determine the disease status of the herd of origin before purchase and to vaccinate all bulls on arrival before they are used; many producers are unaware their herds are infected.

HGPs and residues

When purchasing stock, especially those that you will sell at a later time, it is important to obtain information about their HGP status and residue status, as this will influence your subsequent marketing decisions.

See Agnote DAI-278 HGP-free cattle and correct documentation for comprehensive information on the supply of HGP-free beef for export to the European Union and to other countries that have similar certification requirements.

Residues are usually not a problem, although the feeding of cotton trash and stubble to cattle in the 1994 drought did result in chlorfluazuron (CFZ, Helix®) residues in some situations. Once again, the only protection is to obtain a vendor declaration of freedom from CFZ residues when purchasing cattle. For further information see Quality assurance and residue control.

Further information

• Drought recovery
• Animal health
• Cattle health
• Flock health
• Animal health in drought

Further assistance

For further assistance, contact your local NSW DPI Livestock Officer, Rural Lands Protection Board staff, or your veterinarian.

Acknowledgment

This Agnote is based on information contained in an earlier NSW Agriculture publication, the Drought Recovery Guide.