Heartwater infectious disease

General info with focus on South Africa. 

Heartwater is an acute infectious disease responsible for severe losses among susceptible cattle, sheep and goats. Its causal organism, Cowdria ruminantium, is transmitted by the bont tick, Amblyomma hebraeum. In nature the disease can be transmitted only by this tick in its nymphal and adult stages and occurs only where this tick is present.

The bont tick prefers warm and moist lowveld and bushveld areas and is found in Mpumalanga, Kwa-Zulu-Natal, the Northern and Northwest Provinces, Eastern and Western Cape Provinces, as far south as Mossel Bay. It also occurs in parts of Swaziland and Botswana.

Bont tick distribution in South Africa.

Affected animals have a fever of between 40 and 42 °C, are listless, loose their appetite and lag behind the rest of the herd. As the disease progresses, movement becomes more impeded. Animals often develop a high-stepping gait. Breathing becomes more labored and animals may push their heads up against firm objects. The affected animals eventually lie on their side with the head pulled backwards and the legs extended. They are sensitive to intensive light and twitch their eyelids rapidly when exposed to it. The eyes roll from side to side in the orbita. The body temperature rapidly drops to below normal prior to death.

A postmortem examination reveals varying quantities of straw-colored fluid, which may sometimes be blood-tinged, in the chest cavity and the heart sac (hence the name of the disease). The lungs are heavy and have a soaked appearance. White foam is often abundant in the air passages. Some or all of these changes may, however, also be observed in animals dying from other causes and only a veterinarian can make a final diagnosis by microscopical examination of a smear prepared from brain tissue.

Heartwater occurs throughout the year. The incidence varies according to the tick population and its activity and the disease is therefore less frequently encountered during winter. The disease occurs when an infected tick feeds on a susceptible animal. Bont ticks become infected with the heartwater organism when they feed on an infected animal in which the organism is circulating in the blood at that particular time. Engorged larval and nymphal ticks drop from the host, moult within 4 to 6 weeks and are ready to seek new hosts on which they can feed as nymphae and adults, respectively. If such a host is susceptible to heartwater they will transmit the infection to it. Infected adult female ticks play no further role after having engorged, dropped and laid their eggs, because they then die and the heartwater organisms are not transmitted through the eggs to the next generation of ticks. Only 2 to 5 % of bont ticks found in heartwater areas are infected.

The movement of animals carrying infected ticks into or through an area free from the disease, can result in losses among susceptible stock if they are infected by ticks which drop from the infested animals. The ticks, however, seldom survive longer than one season in an area which is climatically unsuitable for them.

Apart from cattle and small stock, large and small game animals, hares and some ground dwelling birds (eg guineafowl) can also become subclinically infected with heartwater, and although they may show no clinical signs of the disease, they may have the organism circulating in their blood and therefore be able to infect ticks that feed on them. As healthy carriers of the infection, these animals and birds play an important role in the maintenance of the infection in ticks and consequently also in the occurrence of the disease. Because they cannot be dipped like cattle, these animals and birds also regularly serve as hosts on which the ticks can feed. It is clear that the bont tick, and therefore heartwater, cannot readily be exterminated on a farm where large and small game are present.

Cattle, particularly indigenous breeds, older than 1 year and newborn calves up to an age of 4 to 6 weeks, have nonspecific resistance to the disease and when infected many of them show no clinical signs, or at most develop a mild fever reaction.

Heartwater organisms seen in a brain smear (arrow).

They are magnified approx. 1000 times!

Cattle and small stock may be resistant to infection by infected ticks for two reasons: animals may be immune (either as a result of an earlier infection or through vaccination) or they may have a varying degree of natural resistance against the disease. Animals born in a heartwater area are usually, but not necessarily always, exposed to infected ticks (and become infected) when they are still young and have an inborn natural resistance. In this way they acquire an early immunity, which is thereafter boosted by regular reinfection by ticks. 

Losses as a result of heartwater most often occur when animals born and reared in areas free from the tick and the disease are moved into areas where the disease occurs (endemic areas) or when animals in endemic areas loose their immunity, because they are not exposed to reinfection by ticks (eg as a result of a too intensive dipping program).

Prevention

Ruminants younger than three weeks of age have a natural resistance to heartwater infection. This resistance does not depend on colostrum intake. When a young animal is bitten by an infected tick, it will build up an immunity, but not become ill. If. however, it is bitten for the first time when it is older than three weeks, it will fall ill and may die if not treated appropriately. Animals that are immune have to be bitten at regular intervals since they may lose their immunity if not bitten within six to nine months. It is thus of the utmost importance that animals in heartwater endemic areas (areas where it occurs naturally) should not be kept free from ticks for extended periods.

Treatment

There are numerous drugs on the market containing Oxytetracycline as the active substance. All of these drugs will be effective against the heartwater organism provided it is used timeously and a high enough dose is given. The earlier treatment is begun the higher the chances of success.

In severe cases, cortisone may be given with the Oxytetracycline. These drugs, however, have serious possible side-effects and are only available on prescription from a vet. If given to pregnant animals, abortion may ensue. Cortisone helps to stabilize the damaged blood vessels to prevent further leakage of fluid and also aids in relieving excess pressure on the brain.

Keep your clip clean

Wool can and should be marketed as a natural, environmentally-friendly quality fiber. Anything that undermines this image can lead to consumer resistance and have a negative effect on the marketability and price of wool.

Contamination of wool by foreign objects – like black hair, bale twine, wire, bolts, cigarette butts, matches, dog hair, pieces of cloth – pose a serious threat to the long-term sustainability and profitability of wooled sheep farming.

Contamination of wool can result in big claims against buyers or processors, and damages the reputation of the clip.

Hard objects in a bale can damage core sampling and wool processing machines, while deviating fibers (black hair, Kemp) can spoil meters of fabric as these only show up at the final stage of processing.

In addition, increasing worldwide antipathy towards any form of pollution, and stricter regulations, particularly by the European Union, about environmental pollution, are putting pressure on the wool industry to eliminate chemical contaminants and ensure that pesticide-free wool products reach the market.

The main sources of contamination are:

·           Foreign objects originating in the shearing shed, e.g. fertilizer bags, baling twine, pieces of metal, clothing, cigarette butts, etc.

·                     Wool packs containing loose material, usually fibers.

·                     Sheep branding inks and certain wound dressing containing discoloring compounds.

·                     Colored fiber resulting from crossbreeding or non-woolled sheep breeds running with Merino sheep.

·                     Residues from pesticides used for the treatment of external parasites on sheep

What producers should do to prevent contamination

 

In the shearing shed:

It is vitally important for all producers to maintain good management principles in the shearing shed to avoid contamination prior to classing and packing. No matter how well-classed the clip, if it is contaminated with baling twine or other foreign objects, the buyer will penalize it.

·                     Clean the shed thoroughly before shearing commences and store away any tools, bolts and other metal objects.

·                     In order to minimize possible contamination with animal hair, feathers, baling twine, etc., ensure that the holding pens are clean.

·                     Educate shearing team and workers about the dangers of contamination.

·                     Provide a rubbish bin with a lid for cigarette buts and other rubbish.

·                     Ensure that proper supervision is exercised during shearing.

·                     No dogs or other animals should be allowed in the shed.

·                     Use a rubber rake rather than an ordinary broom with hair in the shearing shed.

·                     Never use jute bags in the shearing shed, be it for wiping feet or sharpening the shears on.  Rather use carton, paper or a piece of sheepskin.

·                     Never use baling twine in the shearing shed, even for hanging tools or other gadgets against the wall.

·                     Make sure that shearers don’t use twine for their shears.

·                     Shearers should preferably not be allowed to sleep in the shearing shed.

·                     Always shear purebred woolled sheep first.

During shearing and classing: 

·                     Wool stained with branding ink, tar, urine, dung, blood, paints or discolored by fungi or chemicals must be removed before shearing, packed separately and marked as “Brands”

·                     Remove all bloodstained wool during the shearing process.

·                     Request the shearers to remove pieces of skin cut off during shearing. Skin pieces quickly become dry and hard and can damage carding machines.

·                     Topknots and cheek wool can contain hairy fibers and must, therefore, be packed with the lox, irrespective of how long and attractive they look.

·                     Colored fibers are often found around the horns and should not be packed with bellies or pieces to prevent contamination. 

Groenvoer vestiging

Groenvoer maak die beste ekonomiese sin waar dit aangewend word vir die afronding van lammers of ander vee vir bemarking. 

Produksie van droëland groenvoer is wisselvallig.  Die belangrikste groenvoer-soorte is hawer, korog en rog.

Water is die dryfkrag

‘n Duimreël is dat 100mm plantbeskikbare water, 2,3 ton droëmateriaal / ha kan lewer; 150mm omtrent 3,9 ton droëmateriaal / ha en 200mm omtrent 5,5 ton droëmateriaal / ha.  In die somerreënvalgebied is reënval gedurende die groenvoer groeifase beperk en is dit belangrik om water reeds voor vestiging in die grond op te berg.  Tewens sukses met droëland groenvoer word gewoonlik bepaal deur die boer se vermoë om water beskikbaarheid te bestuur.  Hier is gronddiepte, onkruidbeheer en waterindringing belangrik.  ‘n Grond van 1m diep se waterlewerings vermoë wissel van 120 mm vir kleigrond tot 110 mm vir meer sanderige grond.  Indien daar nie met plant minstens 100 mm water in die grondprofiel is nie, raak droëland groenvoer vestiging in die somerreënvalgebied ‘n groot risiko. 

Kultivar-keuse

rie patrone, naamlik; kort seisoen; medium seisoen en lang seisoen.

• Kort seisoen kultivars het geen koue-behoefte vir blom nie; blom daarom vroeg met ‘n vroeë produksie-piek tot einde Julie.
• Medium seisoen kultivars het ‘n kort koue-behoefte vir blom; blom later met ‘n vroeë produksie-piek tot middel Augustus.
• Lang seisoen kultivars het ‘n lang koue-behoefte; blom laaste met ‘n later produksiepiek en produseer tot einde September. 

Dit geld vir herfs-vestigings. Kultivar-produksie proewe het verder bewys dat lang seisoen kultivars se produksie gemiddeld 50% hoër is as dié van kort seisoen kultivars.  Dit geld vir die onderskeie kultivar-tipes binne al die groenvoergroepe, naamlik rog, hawer en korog kultivars.

Kies die regte tipe volgens jou spesifieke voervloei-behoefte.  As dit laat raak (einde Maart) en voer is teen middel Mei nodig, plant dan kort seisoen kultivars.  ‘n Lang-seisoen kultivar kan so vroeg as moontlik (Februarie) geplant word.  Dit sal ‘n sekerder, langer en hoër produksie verseker.  Met so ‘n praktyk sal moontlike laat-somer en herfsreëns ook beter benut word en groenvoer sal vanaf middel April tot einde September beskikbaar wees.

Bemesting van droëland groenvoer

Hawer

Die volgende algemene aanbevelings geld:

Stikstof (N)

Effek op produksie hang saam met beskikbaarheid van water (reënval).  Met genoeg reën kan stikstofbemesting beide voerproduksie en diereprestasie verhoog.  Neig egter na die konserwatiewe met ‘n maksimum van 30kg N / ha per toediening.

Fosfor (P)

Indien breedwerpig gevestig, word geen P-bemesting aanbeveel nie.  Indien in rye gevestig, mag ‘n P-toediening van maksimum 10kg P / ha voordelig wees.

Kalium (K)

Onnodig onder beweiding.

Plant die raaigras en assegaaiklawer breedwerpig met die rog in ongeveer 40cm rye daarna (verhoed oorskadu effek).  Die rog is relatief vinnig en sorg vir goeie herfs en winter produksie.  Die klawer is stadig en sal vanaf Augustus tot Desember produseer.  Dit bind stikstof en gee baie goeie diereprestasie.  

Enhancer raaigras

Enhancer is ‘n raaigras kultivar met uitstekende diereprestasie potensiaal wat tot Desember sal produseer.

Notas:

1)   Besin oor die rede(s) vir groenvoer in u produksiestelsel.  Afronding van bemarkbare vee is die mees ekonomiese aanwending.

2)     Bestuur en benutting van grondwater is uiters belangrik.  Kies en bewerk lande vir maksimum wateropberging.

3)     Wees bewus van dramatiese verskille tussen:

·         Groenvoer groepe

·         Kultivars binne groepe

Plant met die oog op jou spesifieke behoefte!

4)     Besproeide weidings

·         Let op besproeiings- en bemestings-riglyne

5)     Bemesting

·         Wees konserwatief

·         Onthou die water/stikstofinteraksie vir goeie diereprestasie