Farm stock have been back on pasture again for some time and the perennial issue of picking a suitable anthelmintic has come sharply back into focus for most herd or flock owners. There are a number of categories of anthelmintic available for use in cattle and sheep. Some of these include the macrocyclic lactones including avermectins and milbemycins. Avermectins include ivermectin, abamectin, doramectin, eprinomectin, and selamectin), The Milbemycins include moxidectin. Other families include the Benzimadazoles (including fenbendazole, albendazole and triclabendazole), the imidathiazoles(levamisole) and the more recently developed amino-acetonitrile derivatives (montepantel), the benzene-sulphonamides (Clorsulon) and the salicylanilides (Closantel). Each of these individual compound classes has a slightly different range of activity and mode of action due to its chemical structure.

As all Irish cattle farmers know, Housing is a key time of year for addressing endo-parasite issues in the herd. UK summers often see a lot of rain; which provides the ideal conditions for the development of a number of parasites including stomach worms (Trichostrongylosis), lungworm or husk and liver fluke (Fascioliasis).

In this article, we will look at the different parasite problems cattle may face at this time of year and how the Bimectin product range can help farmers address this challenge.

Farm stock have been back on pasture again for some time and the perennial issue of picking a suitable anthelmintic has come sharply back into focus for most herd or flock owners. There are a number of categories of anthelmintic available for use in cattle and sheep. Some of these include the macrocyclic lactones including avermectins and milbemycins. Avermectins include ivermectin, abamectin, doramectin, eprinomectin, and selamectin), The Milbemycins include moxidectin. Other families include the Benzimadazoles (including fenbendazole, albendazole and triclabendazole), the imidathiazoles(levamisole) and the more recently developed amino-acetonitrile derivatives (montepantel), the benzene-sulphonamides (Clorsulon) and the salicylanilides (Closantel). Each of these individual compound classes has a slightly different range of activity and mode of action due to its chemical structure.

As all UK cattle farmers know, Housing is a key time of year for addressing endo-parasite issues in the herd. UK summers often see a lot of rain; which provides the ideal conditions for the development of a number of parasites including stomach worms (Trichostrongylosis), lungworm or husk and liver fluke (Fascioliasis).

In this article, we will look at the different parasite problems cattle may face at this time of year and how the Bimectin product range can help farmers address this challenge.

PARASITIC DISEASES OF SHEEP

Internal Parasites In Sheep

There are a number of important internal parasites in sheep. Bimectin Injection is licensed for the treatment and control of many of these.

Teladorsagia (Ostertagia) circumcincta

This small brown stomach worm is one of the most economically important gastro-intestinal (abomasal) nematode parasites of sheep in many regions. Its life-cycle is similar to Ostertagiosis in cattle, as are the symptoms.

Haemonchus contortus

The Haemonchus contortus is also known as the Barber’s Pole worm. This parasite is very obvious to the naked eye. A blood sucking parasite, it can cause severe anaemia and death. In acute cases, death can be sudden.

The symptoms of sub-acute infections are similar to those for liver fluke infection, such as bottle jaw. Symptoms of chronic infections are weight loss, poor condition, bottle jaw and a general failure to perform. In contrast to other endo-parasitic infections, diarrhoea is not a symptom of Haemonchus contortus infection and animals are actually more likely to suffer constipation.

Haemonchosis also unusual in that it can cause disease in adults as well as young sheep as they do not develop immunity after exposure.

Haemonchus eggs and larvae do not survive well on pasture over winter so their main way of survival from year to year is via hypobiosis. Haemonchus prefers warmer conditions so it is most commonly associated with warmer climates. However it is now widespread and often occurs in flocks in cool temperate regions now also.

Parasites of The Small Intestine:

Trichostrongylus spp

This parasite causes the black scour traditionally seen in the autumn in store lambs. Now it is frequently encountered earlier in the summer months, causing losses in younger lambs. Conversely, in mild winters, it has been shown to continue with its lifecycle, causing severe disease during the winter and early spring months.

Nematodirus battus

Also known as the thin-necked intestinal worm, Nematodirus battus is a particularly nasty disease in lambs. It will stunt growth and, in a very high number of cases, result in death.

The difficulty with this worm is that it has a different life-cycle to other sheep worms and under certain climatic conditions can strike very quickly, with no warning signs in the lambs this means that sheep farmers have to be on their guard.

The main advantage that Nematodirus has compared with other parasitic worms, is that development to an infective larvae takes place within the egg, meaning that once they hatch in warmer weather they are immediately infective to grazing lambs. In this way, infection passes from one lamb crop to the next year's crop.

Before they can hatch, the eggs have to undergo a period of cold weather followed by warmer temperatures of 10oC or more. If these conditions occur over a short period of time, triggering a mass hatch, the result can be devastating if it coincides with the time when lambs are starting to take in significant amounts of grass.

High risk factors for Nematodirus Battus:

• Lambs grazing pasture that carried lambs the previous spring
• A sudden, late cold snap which is followed by a period of warm weather
• Lambs that are old enough to be eating significant amounts of (6–12 weeks old)
• Groups where there is also likely to be a challenge from Coccidiosis
• Lambs that are under other stresses e.g. triplets, fostered, on young or older ewes

The damage to lambs is done by massive numbers of immature larvae and can be astonishingly rapid. This means that farmers cannot afford to wait for symptoms to appear in their lambs. Unfortunately we cannot rely on faecal egg-count monitoring to time Nematodirus treatments, as the disease is mainly caused by worm larvae, and significant damage can occur before eggs appear in the faeces. Historically seen as a spring problem, Nematodirus Battus is now seen at varying times of the year.

PARASITIC DISEASES OF PIGS

Bimectin Injection is licensed for the treatment and control of a number of important internal and external parasites in pigs.

Internal Parasites in Pigs

How common are internal parasites in pigs?

Internal parasites are an uncommon problem in the weaned, growing and finisher pig unless they are housed in continuously occupied straw based or bare concrete pens in which case ascarids may become a problem.

In the sow the important internal parasites are:

• Ascaris suum (the large white worm or Ascarids)
• Hyostrongylus rubidus (red stomach worms)
• Trichuris suis (whipworms)

In piglets, an important internal parasite is:

• Threadworm (Strongyloides ransomi)

Bimectin Injection is also licensed for a range of external parasites in pigs.

Ascaris suum (the large white worm or Ascarids)

The pig ingests the egg with an L2 larva inside. The L2 migrates to the liver, moults to the L3 form, and then migrates to the lungs. L3 Larvae enter the alveoli, are coughed up and then swallowed. They then moult two further times and become adults.

What are the symptoms and impacts of the large white worm?

L2 an L3 cause small pulmonary haemorrhages and oedema, congestion of the air pathways and pneumonia when large infestations. Secondary bacterial infections can exacerbate the problem and lead to death.

Clinical signs include coughing, rapid shallow breathing, un-thriftiness, colic, weight loss and poor FCE.

Hyostrongylus rubidus (red stomach worms)

The red stomach worm is found world-wide in the stomach and is a common parasite of outdoor pigs, but is rare in growing pigs. The adult worms burrow into the mucous lining of the stomach where they suck blood and cause an inflammation (gastritis).

What are the symptoms and impacts of red stomach worms?

The worms cause inflammation (gastritis) through burrowing into the mucous lining of the stomach and sucking blood. Heavy infections cause anaemia, poor growth rates, loss of condition, thin sows and occasional episodes of diarrhoea.

Trichuris suis (whipworms)

Whipworms are a common world-wide parasite. After ingestion the larvae hatch out and penetrate the intestinal wall before moving to the large intestine and caecum where they mature into adults.

What are the symptoms and impacts of whipworms?

With poor husbandry it can become a major pathogen, resulting in depressed growth rate and impaired feed conversion efficiency. The larvae burrow into the intestinal wall forming nodules, causing irritation, inflammation, haemorrhage and anaemia. Diarrhoea with blood and mucous occur in heavy infections.

Worms of Piglets

The threadworm (Strongyloides ransomi)

The threadworm is a parasite common to neonatal piglets. In severe infections, the piglet will suffer from anaemia, diarrhoea, dehydration, emaciation. In extreme cases, death can result. Most mortality occurs in piglets less than two weeks old. Diarrhoea, dehydration and un-thriftiness can occur in pigs up to three months old.

External Parasites

Lice including Haematopinus suis and Mange Mites including Sarcoptes scabiei var.suis also affect pigs. Bimectin Injection is licensed for the treatment and control of these external parasites in pigs.

Large Strongyles

(Red worms)

Large Strongyles

There are three major species of Large Strongyles, which are Strongylus vulgaris, S edentates, and S equinus. Of these, the most common is Strongylus vulgaris.

Horses become infected through the ingestion of infective larvae, which ex-sheath in the intestine and migrate, before developing to maturity in the large intestine.

Large Strongyles are blood feeders and they ingest mucosal plugs as they move through the intestine. Anaemia can result from this blood loss. Large Strongyles also cause weakness, loss of weight and diarrhoea. As a result of damage to mesenteric artery, Large Strongyles can also cause colic.

Life Cycle of Large Strongyles

Large Strongyles can be extremely dangerous to the horse. However, low resistance levels mean that control is relatively straightforward.

Lungworm

(Dictyocaulus arnfieldi)

Lungworm can cause coughing and respiratory difficulty in horses, although they are relatively uncommon. These worms are common in donkeys and easily transfer to horses grazing the same pasture.

Horses become infected by eating the worm larvae from the pasture. The larvae will then move to the lungs, where they become adult. These adults, living in the airways, can cause obstruction leading to coughing and breathlessness. The adults lay eggs which are coughed up and swallowed to then be passed out in the droppings; thus continuing the cycle.

Diagnosis usually takes place on the basis of clinical symptoms and the presences of eggs in faeces.

Small Strongyles

(Cyathostomes)

Small Strongyles are the most common equine worm, and the adult worms alone cause little ill effect.

Cyathostomes Infestation
in Small Intestine

It is the hypobiotic larvae emerging from gut wall which cause disease. Once ingested, the small larvae have the ability to burrow into the lining of the intestine. When they emerge, they can do so in very large numbers, causing severe intestinal damage and diarrhoea.

Treatment using ivermectins can control the adult and immature stages of this parasite and will minimise the numbers eggs being shed onto the pasture. The larvae are difficult to treat and resistance to wormers is a major issue. Pasture sweeping, wormer rotation, FECRTs and paddock rotation are all good ways to minimise risk.

The Typical Life Cycle of Small Strongyles

The Typical Life Cycle
of Small Strongyles

Pinworms

(Oxyuris equi)

The pinworm is a grey/white worm with a long tail, which tapers to a point. While the male is significantly smaller, the female pinworm can reach up to 20cm in length.

Adult pinworm emerging to lay eggs

Although pinworms live in the large intestine and colon, the adult worm emerges at night to lay eggs on the skin around the rump. After laying her eggs, the female pinworm will then return inside the rectum. A female pinworm can lay up to 60,000 eggs per day.

Pinworm infestations commonly occur in horses older than 18 months, but rarely cause the animal major problems. Unlike many other worms, the pinworm will cause damage to the horse's digestive system, nor will it cause other internal damage. However, they will cause significant irritation.

Pinworms cause irritation to the horse. Look out for rubbing of the rear end against fences, which can result in damage around the anus

When the adult worm lays her eggs it can cause intense irritation leading to rubbing and self-harm around the anus. Biting and licking of hindquarters may also be observed. There are no eggs on faecal examination. However, eggs may be seen in a gelatinous mass around the anus.