SIGNS OF WORMS
Almost all sheep have internal parasites. They often don’t cause any disease and sheep can look normal or even in good condition. However if worms get out of control, sheep can suffer from both subclinical disease (signs that can be measured but not seen visually) or clinical disease (signs range from very subtle to obvious, including death).
Table 1: Effects of worms on production of sheep
A sheep with a zero worm burden has no compromise to its production, wool, lamb or meat as a result. There is an impact on production from the lowest worm burden through reduced appetite, refocus of immune system to the parasite, damage to the gastrointestinal system and potential protein and blood loss.
The visual effects (clinical signs) are apparent when the worm burden becomes high and there is substantial reduction in production and a negative impact on the health of the animal. It is the non-visual (sub-clinical) effects which accounts for the majority of production loss in a sheep enterprise as it can go un-noticed over a long period of time.
COMMON WORMS AND LIFECYCLES
ROUNDWORMS
Step 1
All roundworms begin as eggs. These eggs are produced by female adult roundworms living in the gut of the animal.
Step 2
These eggs are passed out in the animal’s dung onto the ground.
Step 3
The eggs hatch into larvae, given the right environmental conditions (sufficient moisture levels and temperature).
Step 4
The larvae develop and become infective. They move up blades of grass in water droplets, where they can be eaten by grazing sheep.
Step 5
Once ingested, the larvae enter the gut of the animal and either develop into adults quickly, or they may stay in an “inhibited” stage until a later time (for example, during a summer drought or winter cold). When the external conditions are favourable for worm survival, the inhibited larvae develop into adults.
The table below offers a summary of the most important roundworms of sheep in NZ
BARBERS POLE WORM
Haemonchus contortus
What is it?
- Barbers Pole is a round worm nematode that resides in the abomasum (4th stomach).
- The females have a banded (barber pole) colouration and can be 20mm to 30mm in length (males are pale pink and 15mm in length)
- Each female can lay 10,000 eggs per day and an animal can have thousands of females feeding off it
- These eggs are laid and passed with the faeces to hatch and develop to L3 larvae in 7 days, under ideal conditions.
- The ideal environmental conditions are warm moist spring, summer, and autumn seasons
- The L4 larval stage can become inhibited from transitioning to adult stage and migrate into the abomasal wall until seasonal conditions become more viable for egg laying
- Widespread resistance to anthelmintic groups and even multi-combinational drenches
What are the Symptoms?
- These parasites are blood feeders and can consume 0.05ml / day each. This can lead to anaemia, lethargy, weakness and death
- Animals will show pale gums and pale eyelids
- Sheep with good nutrition and with high condition scores can be affected, collapse and die but are more resilient than poorer condition score sheep
What does it mean for you?
- Affects all sheep irrespective of condition score, age or breed
- Clinical and sub-clinical production losses
- Loss of condition and depressed growth rates, or death by anaemia
- Reduction in meat and wool production
BLACK SCOUR WORM
Trichostrongylus spp
What is it?
- Black scour worm is a round worm nematode
- There are several species T. colubriformis, T.vitrinus, T. rugatus (arid regions) & T. axei (found in abomasum)
- 6-8mm in length and the L4 larvae burrow into the GI mucosa of the abomasum or small intestine to mature
- Females produce 200 eggs per day
- Causes diarrhoea, especially in young sheep
- The ideal environmental conditions are in late summer and autumn
- T. colubriformis occurs in the warmer summer rainfall areas while T. vitrinus occurs more frequently in winter rainfall areas
- Widespread resistance to anthelmintic groups and even multi-combinational drenches
What are the Symptoms?
- Black scour worm causes damage to villi of the small intestine
- Symptoms include:
- Appetite loss
- Lethargy
- Malabsorption
- Scours (generally black in colour)
What does it mean for you?
- Affects all sheep irrespective of condition score, age or breed
- Clinical and sub-clinical production losses
- Loss of condition and depressed growth rates, or death through scouring
- Reduction in meat and wool production
SMALL BROWN STOMACH WORM
Teladorsagia circumcincta
What is it?
- Small Brown stomach worm is a round worm nematode
- Small in size (8-12mm)
- Resides in the abomasum (4th stomach) - causes lesions on the mucosal wall
- Females can lay 100 eggs per day
- Small brown stomach worm has a winter dominant lifecycle
- Widespread resistance to anthelmintic groups and even multi-combinational drenches
What are the Symptoms?
- Small brown stomach worm causes inflammation to the mucosal wall
- Interferes with digestion resulting in less metabolisable energy and protein available
- Symptoms include:
- Scours
- Rapid weight loss
What does it mean for you?
- Affects all sheep irrespective of condition score, age or breed
- Clinical and sub-clinical production losses
- Death through scouring and malnutrition
- Rapid loss of condition and depressed growth rates
- Reduction in meat and wool production
SMALL INTESTINAL WORM
Cooperia spp
What is it?
- 6-9mm in size, often seen coiled up
- Live in small intestine
- Lay 1-400 eggs per day
What are the Symptoms?
- Increases the symptoms of mixed infections
What does it mean for you?
- Affects all sheep irrespective of condition score, age or breed
- Clinical and Sub-clinical production losses
- Death through scouring
- Rapid loss of condition and depressed growth rates
- Reduction in meat and wool production
THIN-NECKED INTESTINAL WORM (PRIMARILY LAMBS)
Nematodirus spp
What is it?
- Live in small intestine
- Require frosts to trigger hatching
- Large, hardy eggs (reside in the environment for months)
- Larva develops within egg (50-100 eggs/day)
What are the Symptoms?
- Ill thrift, scours, dehydration
- Death within 2-3 days with large infestations
What does it mean for you?
- Affects all sheep irrespective of condition score, age or breed
- Clinical and Sub-clinical production losses
- Death through scouring
- Rapid loss of condition and depressed growth rates, particularly in pre-weaned lambs.
- Reduction in meat and wool production
DRENCH RESISTANCE
WHAT IS DRENCH RESISTANCE?
Drench resistance is caused by internal parasites developing inherited tolerance to commonly used drenches. It results in animals with worms that don’t respond to drenching.
Theoretically, drench resistance occurs once a population of a species of worm can survive a dose of a drench that would have previously killed it. Initially resistant worms are rare in a population of worms. When a sheep is treated the resistant worms survive and, if they find a mate, can reproduce. The resultant offspring are resistant and if they survive as larvae on the pasture and infect another sheep. Over time, and with continued treatment, the overall resistance level to the treatment within the worm population increases.
Drench resistance is a major concern for NZ sheep farmers, resulting in production losses and increasing costs to control parasites.
THE CURRENT DRENCH RESISTANCE STATUS IN NZ SHEEP
2016-2017 national FECRT data from Gribbles Veterinary Laboratories
HOW DO I AVOID DRENCH RESISTANCE?
