Helminthiasis in small ruminants
- control strategies

Helminthiasis is one of the most important causes of mortality and morbidity in goats and sheep. It is caused by nematodes, cestodes and trematodes, the most important being Haemonchus contortus, Trichostrongylus, Oesophagostostomum, Cooperia and other strongyles. Helminthes cause anemia, diarrhoea, oedema and consequently severe debility and finally death if not treated. Diagnosis of helminthes infection is by regular faecal examination for worm eggs in grazing animals using the McMaster technique. Animals with faecal egg counts of 500 - 1,000 epg (egg per grams) should be treated with the appropriate anthelmintic. Do regular packed cell value (PCV)determinations as this is a good indicator of anemia or use the KARI card to estimate the necessity to treat. There are several strategies to control helminthiasis and it is advisable to incorporate an integrated approach towards worm control depending on the farm management and animals.

ANTHELMINTIC THERAPY
Mixed use of broad and narrow spectrum drugs at regular intervals should control heavy worm burdens. The same drug should NOT be used more than 6 times a year as the worms will develop resistance to it. It would be ideal to use e.g. Closantel and Benzimidazole alternately to increase the lifespan of each drug. Some common drug groups :

• Closantel ( narrow spectrum )

• Benzimidazoles e.g. Oxfendazole, Fenbendazole ( broad spectrum )

• Avermectins e.g. Lvermectin, Cydectin, Doramectin ( broad spectrum )

• Levamisole ( broad spectrum )

Precautions for drenching :

• All new animals entering farm should be drenched before mixing with existing stock.

• Drenching dose rate based on heaviest animal (highest weight) in group.

• Starve animals before and after drenching (keep in shed and give water only)

• Do regular faecal egg counts.

• Check for drug resistance in farm.

• Reduce larval contamination especially around shed.

RAPID ROTATIONAL GRAZING
Rotational grazing can reduce pasture contamination and control helminthiasis. Animals should not graze the same paddock for more than 4 days and should not return to original paddock for at least 30 days. Animals should be treated before commencing rotational grazing.

Safe Grazing

• Safe paddocks (these have the last worm larvae )

• New patterns

• Paddocks not grazed at all (paddocks grazed only by cattle)
  (paddocks grazed only by dry sheep over 2 years old)

• Paddocks spelled for at least 1 month

• Use safe paddocks for weaners and lambing ewes   

MEDICATED UREA MOLASSES BLOCKS
These blocks contain 0.05% Fenbendazole and can be given to animals in the shed on a daily basis. Any incoming larvae from the day's grazing will be killed by the small regular doses of anthelmintic that the animals consume. The blocks also provide added nutrition and the animals can withstand helminthes infections better on a higher plane of nutrition.

REAR WORM RESISTANT SHEEP

Some breeds of sheep and goats (especially tropical breeds) are more resistant to worm infections. This is because they have the ability to initiate and maintain responses to suppress the establishment of parasites and / or eliminate the parasite load. Some of these breeds are the Malin goat, Kajang, Barbados Black Belly, Florida native and their crosses. Farmers are advises to breed the animals that are consistently showing low egg counts as this has proven to be an effective selection criterion for improving resistance.

Test For Drench Resistance
     o Is your drench effective
     o Test drench groups for efficiency (FECR)
     o The best test is on lambs at weaning
     o Result at least every 2 years
     o Plan your drenching (unnecessary drenching selects for drench resistance)
     o Test sheep (FEC) to check that drenching it needed
     o Drench strategically (Lambs at weaning) (Ewe pre + post parturition)
     o Dose for goats
     o Don't under dose under dosing selects for drench resistance
     o Check accuracy of drench gun - use a measuring cylinder
     o Weigh the heaviest sheep in group
     o Dose all sheep in group to this weight