Be warned, worms could kill your sheep and goats besides low yields

Worms reduce weight gain, predispose shoats to other opportunistic diseases, reduce feed intake and lower skin and wool quality.

Small ruminants refer to goats and sheep also collectively called shoats. These form an important segment of livestock production system in Africa. Most small scale farmers in Kenya keep sheep and goats alongside cows but on a large scale they are kept in ranches or under nomadic pastoralism in large herds.

Internal parasites or worms as they are commonly called are a major cause of death and poor productivity in sheep and goats. Worms reduce weight gain, predispose shoats to other opportunistic diseases, reduce feed intake and lower skin and wool quality.

Affected organs and tissues or the whole carcass can be condemnation at slaughter not to mention the cost of treatment and withdrawal periods during which milk from these animals cannot be consumed by human beings. Some of these worms are zoonotic and can be spread to human beings for example the hydatid cyst disease whose effective treatment is surgery.

There are many internal parasites which are classified based on the type of the organ they infest; they include lung worms, stomach worms, intestinal worms and liver flukes. Worms normally become a health problem when they occur in large numbers by causing irritation, mechanical obstruction and loss of function in the organ affected. But there are a few exceptions to this rule; one leech is enough to cause a lot of trouble to sheep; its irritation as it sucks blood in the mouth or throat can make the sheep to stop eating completely.

In most cases there will be multiple infestations occurring in the same animal. How these worms spread and what determines their severity? Most worms go through a life cycle where the adult lay eggs that are shed through feaces, that hatch into larval stages that are normally picked by the animal as they feed or drink water.

Some larval stages can scroll for a few centimeters from the dung onto grass blades to increase their chances of being picked up by their hosts. Others will penetrate through skin and travel through circulatory into their target organs where they mature and cause the specific clinical signs.

The spread of these worms is determined by a number of factors as described below: Animal husbandry practices: farm practices like over stocking and poor hygiene greatly increase chances of contamination of pasture and risk of your goats and sheep picking worms.

In ranches, minimal rotational grazing will increase contamination and contact with worm eggs. Some studies have shown that tethering (a grazing practice where an animal is restrained by a rope and allowed to graze within a given circumference) and over stocking will force the animal to graze very close feacal material or ground therefore easily picking infective stages of worms.

Crowding of animals at communal watering points will increase the egg count and number of larval stages and thus increase chances of infestation. Feeding hay and grains on the ground instead of using feeding troughs will predispose shoats to worm infestation.

Environmental factors

Environmental factors: Distribution of worms is determined by the climatic conditions and as such there are specific worm infestations in various geographical locations. For example, the liver fluke is common in Kenyan highlands and rice fields where their intermediate hosts the snails are abundant.

Gastro-intestinal (stomach and intestinal) worm infestation follows a pattern as most have a life cycle that depend on environmental factors during their free living stage.  Moisture and temperature affect larval stages of worm development and spread to hosts.

However, some developmental stages of worms can adapt to harsh conditions through arrested growth awaiting suitable conditions. Hot and humid conditions are the best for the development and spread worms.

Host factors: The breed of the host, its health status, age and physiological status affect the severity of the infestation.

Malnutrition and pregnancy increases the susceptibility to worms. The young ones are more susceptible to worm infestation compared to mature animals.

There is also breed differences for example the red Maasai sheep is relatively resistant to certain worm infestation.

What are the clinical signs of worm infestation?

The transit and ultimate location of worms in various organs will result in specific clinical signs that a veterinarian will use to do the diagnosis and subsequent treatment regime to be adopted. Lung worm infestation will interfere with breathing and you will observe excess mucus production, coughing, sneezing and laboured breathing.

Liver flukes will destroy the liver as they migrate leading to scar tissue formation and greatly lowering the functionality of the liver. Stomach and intestinal worms will result in diarrhoea that may be bloody as they interfere with the digestion process when they attach themselves on the gut lumen.

The feaces will also contain worm segments. Bottle jaw which describes the swelling of the upper part of the neck is a characteristic sign for heavy worm infestation. Other signs are dehydration, fever and cold extremities. In prolonged cases as a result of continual loss of body nutrients the animal will growth thin, have a rough hair coat, anemia and death.

How can they be controlled?

There are several chemical compounds commonly called anthelmintics (dewormers) targeting various worms with very good efficacy. They are available in liquid solutions, pastes or tablets and can be administered orally, through injection or externally.  It is always advisable to use broad-spectrum anthelmintics since mixed infestations are a common feature.

Choose a dewormer with a rapid metabolism to minimise the withdrawal period although sometimes it is inevitable to use a dewormer with a prolonged activity to target all the stages of a worm. These dewormers should be used strategically and under close supervision by a veterinary doctor.

This may involve a preventive approach where they given a prophylactic dose or curative when there is infestation already. Misuse of dewormer is gradually becoming a major problem in the pharmaceutical world as resistance is quickly developing.

The writer is a veterinary surgeon at the Kenya Tsetse and Tryaonsomiasis Eradication Council (KENTTEC)