Photo: FW Archive
Internal parasites are a significant problem for farmers the world over, as they can lead to a loss of production or even death in animal production. Parasites are also difficult to control and manage.
In this article, we look at three common internal parasites that affect cattle production in South Africa, and offer some tips on how to manage parasitic infections.
Wireworm (barber’s pole worm)
Wireworm (Haemonchus placei or H. contortus), also known as barber’s pole worm, is a roundworm that is particularly problematic in summer rainfall and tropical regions, says Worm Boss, an online platform that specifically focuses on internal parasites in cattle.
H. contortus infects sheep and goats, and Worm Boss explains that small-stock are more susceptible to the cattle species H. placei than cattle are to H. contortus.
“[Wireworms] are blood-sucking parasites. They can be fatal for young cattle and cows in their first lactation, especially if other blood-sucking parasites such as hookworm (Bunostomum phlebotomum) or liver fluke are also present. Even moderate infections of barber’s pole worm can have a marked effect on the milk production of cows.”
According to Worm Boss, adult female wireworms are clearly visible at 20mm to 30mm long. “They have the characteristic ‘barber’s pole’ appearance due to the pink (blood-filled) intestinal tract of the worm twisted around the paler reproductive tract.”
Adult males, however, are smaller at around 15mm and pale pink, says Worm Boss. Female wireworms lay up to 10 000 eggs per day, which means that egg counts are usually higher with this worm infestation than others.
“Adults can become arrested or inhibited inside cattle for varying periods and resume development when there is a return to favourable external environmental conditions.”
Signs and symptoms
Worm Boss says that cattle with wireworm infestations are likely to suffer anaemia as these worms are blood-sucking parasites. Anaemia can lead to lethargy and collapse. Cattle may also struggle to gain weight, present with bottle jaw (fluid in the lower jaw) and constipation. Those with a serious enough infestation may die.
“In acute outbreaks, stock become critically anaemic, whereas in chronic disease there is time for animals to adapt to anaemia so that decreased food intake and failure to gain weight are more commonly observed.”
Diagnosis
Worm Boss explains that up to the age of 12 months in cattle, and before productivity loss, the only accurate way to confirm wireworm infestation is to conduct an egg count.
“As small intestinal worm eggs are typically ‘strongyle type’, also request a larval culture or DNA test. The results allow you to determine the need for a drench or management action.”
However, Worm Boss adds, “worm egg counting does not always correlate well with the number of adult worms present for cattle over nine months of age”. For this reason, farmers are urged to look for physical signs of infestation, and to use body condition scoring or the monitoring of target growth weights to diagnose worm infestations.
Treatment
There are various drenches and treatments available in South Africa for wireworm (see Table 1).
However, Worm Boss suggests that farmers consider the following before choosing a treatment plan:
- The current size of the burden of this worm;
- What other worms are present and in what proportion;
- Which drenches are effective on your property and the length of protection you are seeking;
- The likely worm risk over the next few months;
- The likely level of worm contamination on your pastures;
- The class of stock affected and their susceptibility to worms;
- The last drench group/s you used on this (and other) groups of cattle;
- The time until these cattle are sold/slaughtered and the withholding period and export slaughter interval of drenches you might use;
- If these cattle are producing milk for human consumption.
Brown stomach worm
The brown stomach worm (Ostertagia ostertagi) is more common in winter rainfall regions.
It is small at around 10mm in length and has a red-brown colour. Unlike the wireworm, the adult female brown stomach worms only lay 50 to 100 eggs per day, says Worm Boss. But, like the wireworm, the brown stomach worm may become arrested inside the ruminant if conditions are not favourable and become active again as conditions improve.
Signs and symptoms
The brown stomach worm may appear less dangerous than the wireworm, as they are not blood-sucking parasites. However, they do cause damage to the lining of the stomach as they mature from larvae to adult worms, and this can cause severe inflammation.
Worm Boss explains that there are three disease types of this particular worm infestation.
- Type 1, it says, affects calves during their first infection.
- “Most of the infection is due to development directly into the adult worm stage without inhibition, producing loss of appetite, anorexia, a profuse watery diarrhoea and rapid loss in live weight. Type 1 disease is the major worm problem of cattle in winter rainfall and other temperate climatic regions.”
- Pre-Type 2 affects yearling and adult cattle, particularly beef cattle, says Worm Boss. This type consists of massive accumulations of fourth pre-adult stage larvae in the wall of the abomasum, the ruminant’s fourth stomach.
“Infection is usually picked up in spring and early summer. Inhibited larvae tunnel into the abomasal wall for up to six months. Clinical symptoms of affected cattle are absent although live weight gains may be sub-optimal.” - According to Worm Boss, Type 2 occurs when the inhibited larvae leave the stomach wall and continue maturing into adult worms.
“Just a few larvae emerging from the abomasal wall may not cause many problems, but when large numbers leave the wall at the same time, severe symptoms can develop.”
This type is usually seen in rising two- to three-year-old cows, says Worm Boss, and may be particularly associated with calving and nutritional stress. “A consequence of infection is that the pH of the stomach rises to between 5 and 7, making protein digestion difficult and allowing overgrowth of bacteria, leading to diarrhoea. Animals do not lose their appetite, but ironically, they often die from starvation because the food ingested is not digested due to the malfunctioning abomasum. Fortunately, Type 2 disease is now rare, possibly as a result of the introduction of effective anthelmintics some decades ago.”
Diagnosis and treatment
As with wireworm, the best way to diagnose brown stomach worm infestation before productivity loss is through an egg count. Even if visual signs are obvious, farmers need to remember that symptoms can be similar across parasitic infestations and diseases.
There are various medications and drenches available for the treatment of brown stomach worm in South Africa (see Table 2).
Liver fluke
Liver fluke (Fasciola hepatica) often shows no symptoms, although a drop in production will eventually become evident, according to Worm Boss.
A range of animals may be infected by liver fluke, ranging from small-stock, such as sheep, to cattle and horses, as well as pigs and alpacas. A fluke is a leaf-shaped parasite with a flattened body that can reach 20mm to 30mm long and 7mm to 14mm broad.
“The economic importance of this parasite is partly due to the downgrading of livers affected by flukes during meat inspection procedures. Failure of young stock to thrive, and significantly decreased milk production in dairy cattle, are unrealised costs in endemic areas where infestations may be heavy,” says Worm Boss.
Liver fluke mostly occurs in watery environments, such as farms with streams, irrigation channels and fountains. The US Department of Agriculture explains that the liver fluke’s life cycle begins as eggs deposited in wet places, such as slow-moving streams.
“Hatching embryos must immediately find and invade the bodies of certain species of freshwater snails. The snails, as intermediate hosts, are essential for the developing of fluke larvae. When they are ready to leave the snails, the fluke larvae form into cysts that attach to plants or float in water until consumed by a grazing animal.
“Immature flukes emerge from the cysts inside the animal host, and then migrate to the liver where they destroy organ tissue on their way to the bile ducts. Mature flukes living in the bile ducts lay eggs. The eggs are passed out of the animal in its faeces, and the flukes’ life cycle begins again.”
In cattle, says Worm Boss, adult liver flukes are mostly found in the bile ducts of the liver and sometimes in the gall bladder, while immature flukes can be found “tunnelling through the liver”.
The adult female fluke can live for several years and produce around 20 000 eggs per day.
Signs and symptoms
Cattle with chronic liver fluke disease, which is the most common type of disease found in cattle, may present with weakness, anaemia and lethargy, as well as a loss of appetite and bottle jaw.
“Cattle develop distended and thickened bile ducts that later calcify to produce what looks like a branching system of clay pipes and referred to as ‘pipe stem livers’, which are thought to indicate protection against reinfection. Some flukes can become encapsulated in the liver tissues and develop cysts, 2cm to 3cm in diameter.
Small adult flukes are not infrequently found in the lungs in semi-caseous nodular lesions,” says Worm Boss.
Treatment
In South Africa, there are various treatments available for liver fluke (see Table 3). An egg count remains the most effective way to determine if an animal is infected.
Control and management of parasites
There are several strategies that farmers can employ, besides the use of parasiticides, to manage and control worm loads on their farms. Used in conjunction with various medications, these strategies can be very successful.
However, it should be kept in mind that no single strategy, or even a combination of all strategies, is foolproof, and that these strategies may merely help lower the worm load burden on a farm or in animals without eliminating the problem altogether.
As roundworms usually enter a cow via grazing, the first strategy that should be employed involves pasture management. By implementing rotational grazing and pasture rest periods, farmers can help break the parasite life cycle by preventing cattle from grazing on contaminated pastures for extended periods.
Resting pastures allows parasite larvae to die off before cattle are reintroduced.
Deworming is, of course, essential in the control of parasites. We have already mentioned numerous medications, oral drenches and pour-ons that work across worm species, but farmers would be well advised to work with a veterinarian or animal health technician when developing a deworming programme for the farm.
This programme needs to bear in mind what the most common parasites are that may be present in a particular area, the farmer’s breeding season, and other environmental factors. It is also essential that the overuse of dewormers is avoided to minimise the risk of parasites becoming resistant.
Farmers are advised to regularly monitor egg counts on their farms. This indicates what parasites may be present, and may help farmers take a more proactive approach to control and prevention. Egg counts help determine the efficacy of deworming treatments and identify high-risk animals that may require targeted treatment.
When breeding, farmers should also consider incorporating parasite resistance traits into their breeding programmes by selecting bulls and replacement heifers from parasite-resistant lines. Breeding for resistance can help reduce reliance on chemical dewormers and minimise parasite pressure in the herd over time.
As an animal’s immune system is also crucial when it comes to fending off infestation, farmers need to make sure that their animals are given adequate nutrition to support their immune function. Farmers should also take care in terms of carrying capacity and avoid overcrowding, as this can increase parasite transmission rates among cattle.
Quarantine new animals before introducing them to the herd, and regularly monitor and treat incoming animals for parasites to prevent introducing them into your herd. Parasites can spread quickly, so this is an important prevention strategy.
In terms of liver fluke, minimise areas of standing water and muddy conditions. Try and keep grazing animals away from watery environments where liver fluke may proliferate.
