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This article was published in 1956
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INSTITUTE OF INSPECTORS OF STOCK OF N.S.W. YEAR BOOK.
STOMACH WORM INFESTATION
E. A. FARLEIGH, B.V.Sc., Inspector of Stock, Glen Innes - Inverell.
(Extension work is not by any means the least important phase of the extremely varied duties of an Inspector of Stock. It goes on all the time, of course, and in many shapes and forms; so much so that it was thought very worthwhile to publish this example of one particular form--from an article prepared by one of our number for circulation in his District EDITOR).
It will be some time before landholders forget the recent abnormal rains and this might be more forcibly imprinted on their minds by the acute worm attack which is likely to follow within the next month or so. However, the impending build up in worm numbers can perhaps be more easily controlled if a few facts concerning the life history of worms is more clearly understood.
The Large Stomach Worm or Barber's Pole Worm (Haemonchus) will be the worm which will concern sheep-owners during the warmer weather.
This worm is of great importance in the higher summer rainfall areas of the tablelands and slopes of N.S.W. The worm eggs survive best at a temperature of 75 to 85 degrees F. Eggs hatch on the ground and the larvae go through several stages of development and reach an infective stage in 4 to 5 days. The infective larvae are capable of survival in sunlight for some weeks. The larvae are swallowed by sheep after migrating on to blades of grass; travelling in a film of moisture on the grass. Further changes are undergone in the abomasum, or fourth stomach, of the sheep. Maturity is reached in about 18 days and eggs may be found in the faeces from 21 days onwards.
The stomach worm is a prolific egg layer; up to 10,000 eggs being laid in a day by the female. If a sheep were infested with 50 female worms, in theory that one sheep could pass 34 million eggs on to the pastures in a week. When running 2 or 3 sheep to the acre it can be seen readily how a massive contamination of pastures can be built up in a very short time.
These worms are active blood suckers and the effect of the parasite is attributable principally to the blood loss. Under ideal conditions an infestation of 500 worms might not be very noticeable, but as soon as the nutrition level falls the symptoms of anaemia and weakness soon become manifest.
Most drenches on the market are fairly efficient in killing a large percentage of stomach worms, but it cannot be expected that a single dose of any of the drugs will be sufficient and the drench should be repeated at least once about 2 weeks later, and thereafter from 3-4 weeks until cold weather sets in.
Nor can it be expected that drenching alone will ever eradicate worms, and equally as important as the drench is the efficient management of the flock following the drench.
Firstly the nutritional level of the sheep must be maintained or even improved. This is important; weak sheep will never build up again unless the food intake is of a high enough quality to enable the animal once more to get into strong condition by building up the red blood corpuscles, which are reduced to a very low figure by an Haemonchus infestation.
Provision must be made on all properties for the spelling of paddocks, so that sheep can be rotated. As has been stated before, the larvae of the worms can survive for some weeks in the paddocks, but unless wet weather is continuous most larvae die in about four weeks, so sheep that are drenched and placed into a paddock that has been spelled for that time have much less chance of becoming re-infested. The folly of drenching sheep and placing them back into the old paddock is readily appreciated, as they will pick up fresh infestations as fast as they are drenched. A paddock that has been spelled for a month or more will provide also the improved nutrition that is so essential.
Stomach worm infestation is not usually serious on well-managed properties, for such owners naturally follow wise rotation, but it can be very serious on over-stocked or poorly managed properties, where owners lack a knowledge of the life history of the worm and depend purely on drenches to keep their stock healthy.