Strongyles (Roundworms/Redworm)
Strongyles are a group of parasitic roundworms that affect a wide range of animals, including horses, donkeys, cattle, sheep, goats, and poultry. They are among the most common internal parasites worldwide and play a major role in poor health, reduced productivity, and disease when not properly managed.
Although the specific species differ between animals, strongyles share similar life cycles, methods of transmission, and overall effects on the body.
Why Strongyles Matter
Strongyles live in the digestive tract, where they either feed on blood or damage the gut lining. Over time, this reduces the animal’s ability to absorb nutrients properly, leading to a slow but often unnoticed decline in health.
A significant burden can result in:
Poor growth or weight loss
Reduced feed efficiency
Anaemia
Diarrhoea or soft manure
Weakness and lethargy
Poor coat or feather quality
Reduced milk, egg, or meat production
Young animals, older animals, and those under stress are particularly vulnerable.
Strongyles in Different Animals
Equines (Horses & Donkeys)
In equines, strongyles are among the most important internal parasites. Some species migrate through blood vessels that supply the intestines, which can lead to inflammation, reduced blood flow, and severe colic. Others encyst (become dormant) in the gut wall and can emerge in large numbers at once, causing sudden diarrhoea, weight loss, and illness.
Livestock (Cattle, Sheep & Goats)
In ruminants, strongyles are often referred to as gastrointestinal nematodes. Heavy burdens can cause chronic ill-thrift, scouring, anaemia, and poor growth. In production animals, this translates directly into financial losses through reduced weight gain, milk yield, and general performance.
Poultry (Chickens and other birds)
In poultry, strongyle-type worms typically infect the intestines or caeca. Birds may appear dull, lose weight, lay fewer eggs, or develop diarrhoea. Young birds are especially at risk, and heavy infestations can be fatal if left untreated.
How Strongyles Spread
Strongyles have a direct life cycle, meaning they do not require an intermediate host.
Eggs are passed in manure or droppings and hatch into larvae in the environment. These larvae are then ingested while animals graze, forage, or feed. Once inside the host, the larvae mature into adults and begin producing eggs, continuing the cycle.
Warm, moist conditions allow larvae to survive longer on pasture and in enclosures, increasing the risk of infection.
Signs of a Strongyle Burden
One of the biggest challenges with strongyles is that animals may carry a significant burden before obvious signs appear. When symptoms do occur, they often include:
Poor body condition
Dull coat or feathers
Reduced appetite
Diarrhoea or soft droppings
Lethargy
Poor growth in young animals
Reduced productivity
Detection
Strongyle infections are most commonly detected using a faecal egg counts (FECs). These tests measure how many parasite eggs are being shed and provide valuable insight into the actual parasite burden.
Testing helps to:
Identify when treatment is truly needed
Monitor parasite levels over time
Assess the effectiveness of deworming
Reduce unnecessary medication
Slow the development of resistance
Treatment & Long-Term Control
Effective control of strongyles is about more than just deworming. Overuse and incorrect use of antiparasitic drugs have led to widespread anthelmintic resistance, making many treatments less effective than they once were.
A responsible parasite control programme includes:
Targeted treatment based on testing
Good hygiene and manure management
Avoiding overcrowding
Pasture or enclosure management
Quarantine and testing of new animals