When talking about livestock grazing, we regularly highlight the positive environmental benefits but there can be a negative impact. RBST Trustee Cate Le Grice-Mack, an early pioneer of organic farming, considers the question of parasite control and how to avoid consequences for soil and biodiversity.

Breeders of sheep and goats will be only too aware of the need to control intestinal worms. These parasites can cause debility and disease, and prevention of their development is essential to the creation of a healthy flock.

As animals graze they are of course also defecating on the pasture. The parasite reproduction cycle shown in the diagram requires the animals to take in the larvae of the next generation as they graze. Once ingested the parasite matures and egg laying resumes, and this entire cycle can be completed within three weeks. Most damage to the host animal is caused by either large numbers of maturing larvae, or by the adult parasites.

Sheep and goats carry parasites that can be transmitted to each other, and there is some evidence that the same parasites may also contaminate cattle where there is major infestation.

The effects of wormers

The standard modern treatment of stomach worms was to dose the animals with anthelmintics every six weeks throughout the warmer months of the year. Such treatment is effective in reducing the parasite problem, but it is becoming increasingly evident that regular use of these wormers has major consequences for both soil and biodiversity, with the chemical residues remaining in the droppings, and continuing to act against other creatures and soil organisms (microorganisms such as bacteria and fungi up to larger creatures such as earthworms and nematodes).

These all have an important part to play in the incorporation of plant residues and animal excreta into the soil, and the synthesis of valuable organic compounds and mineral nutrients. If you walk across a field that is full of old hard cow-pats or sheep droppings it is likely that regular use of anthelmintics is the cause, rather than drought or overgrazing.

Keep them moving

So is there an alternative? The old mantra was that the stock shouldn’t hear the (Sunday) church bells ringing three times over the same pasture. In other words move them every two weeks, and for the best results don’t return them to the same pasture for four weeks more.

This process has the effect of disrupting the life cycle of the parasite, and is reinforced if the field is left for the pasture to grow for a few weeks and then either grazed by cattle, or cut for silage/hay. Basically by dividing the holding into a minimum of three fields/paddocks, with gates to allow easy livestock movement between them, it will become straightforward to move the stock every other week. You will be surprised how quickly the livestock get the hang of the joys of moving to a clean paddock, and how beneficial the system is for the pasture as well as the stock.

Getting the grass right

For grass to continue to provide quality grazing, meeting the full needs of the animals, it should be the right length for them to graze easily (under 10cm for sheep, twice as long for cattle). Grass needs to rest and re-grow, and the regular movement of the stock also allows time to ‘top’ the empty paddocks to remove the seed heads of any invading weeds and create the ideal sward. It may seem like a bit of a chore at first, but if successful it will of course reduce the cost and time.

We used this system on my organic farm for many years. We had the opportunity to graze cattle and sheep together in some of the fields, which has the advantage of reducing the stocking density of the host species as cattle and sheep worms are different. Just occasionally we had an animal or two (out of a total flock of 300) that looked as if they were suffering from an early worm burden. In that case we used the option of a drench of garlic in cider vinegar. This is not quite as cranky as it may sound, as the combination reduces the number of parasites in the sheep’s stomach: the only disadvantage is the lingering odour of raw garlic on the handler.

There is still much to learn about these parasites, and good pasture and flock management remains at the basis of a healthy flock. It is well documented that sheep under nutritional stress are less able to withstand the parasite challenge. Condition scoring of ewes, and creep feeding of lambs are all a part of avoiding the problem. 


There have been a number of articles circulated warning livestock keepers about the current parasite situation, in particular with cattle and sheep. It is reported the worm burdens are still at a high level due to the mild weather at the start of the autumn that led to a prolonged breeding season for parasites.

Due to the current situation then undertaking Faecal Egg Counts is an accurate way of understanding the worm levels in your herd/flock.

What is a Faecal Egg Count?

This is a method of determining the levels of internal parasite eggs that are present in the dung sample taken. This can be used to monitor the worm burden and then be used to determine:

  1. If treatment is needed
  2. What treatment is needed
  3. The contamination that is occurring to the pasture
  4. Understand the effectiveness of treatment and resistance levels

A fresh sample is need, where testing a group of animals it is important to make sure a sufficient number of animals are tested. FEC can usually be undertaken by a vet or sent to a specialist company who can provide you with the results.