What should your pre-foaling worming plan be?

Mares in foal are more susceptible to parasite infections, as well as bacterial, viral and fungal infections, as their natural immunity is lowered during pregnancy. The reduced ability to fight off even low levels of parasites can affect the function of the digestive system and can even pose more life threatening danger. The unborn foal will take the first cut of the available nutrients; a mare with a defective digestive system will not gain the necessary nutrients she needs to run her own body.

It is tempting to reduce the number of chemicals administered to the mare during this vulnerable time, and with good reason: when women are pregnant many medicines are careful to point out they should not be taken during pregnancy or nursing. This is often due to a lack of data surrounding the safety of the drugs to the unborn foetus.

As with other medicines, wormers must undergo strict and thorough research before a license is granted for its use in animals. In order to get a license for use in pregnant and lactating mares, further specific trial work is required. This can cost many thousands of pounds and can delay the launch of the product onto the market.

However, to fail to treat horses most at risk can do more harm than good. A mare in foal with a good history of worm control, on low risk pasture should still be monitored for parasite infections using regular worm egg counts. These should be conducted on a regular basis in order to identify sudden lapses in immunity.

If the horse has required regular treatment and there is known infection on the pasture, these treatments must not be removed without good reason and the advice of a veterinary surgeon.

Many mares will successfully produce a good foal without their health being compromised. However, close monitoring and careful treatments are recommended to keep the mare and her foal in optimum health. A small or weak foal born to a weakened mare will have a much more difficult time to grow and develop.

Throughout the gestation period, the mare will need an annual treatment for tapeworms, and possibly a second treatment in high risk areas. Roundworms should be treated for according to the risk of the yard – dependent on pasture management and other horses present on the grazing – as well as the known infection level inside the horse. This information can be gained through the use of faecal egg counts where a sample of dung is tested for worm eggs that are passed by the horse. Horses with egg counts over a certain level,  will require treatment.  The advisers at Intelligent Worming can provide guidance on how to interprete faecal egg count results, for mares that are in foal.

The eggs seen by the parasitologist during this test can be identified by species and Intelligent Worming will also be able to prescribe an appropriate treatment.

The treatment prescribed must be licensed for use in pregnant mares. This is to make sure the horse is given a product that has shown sufficient safety levels when used during pregnancy.

All of the active ingredients available in the UK are licensed for use in pregnant mares, but crucially not all brands and preparations have received the necessary license and so care must be taken when selecting the treatment. Some of the brands licensed include Equimax, Equest, Panacur Equine Guard and Strongid-P.

If the mare has been having consistently low or zero egg counts during her early pregnancy it is still advisable to treat for encysted small redworm and bots over the wintertime, as these are not detected in worm egg counts.

Finally, near the end of gestation, the mare may become carriers of the Intestinal Threadworm. This is unlikely to cause her any harm but around five days after foaling, this worm will be in her milk and can be transferred to the foal. The foal can then suffer with heavy infestations in just a few weeks and so it is recommended to treat the mare as close to foaling as possible. This can be with either an ivermectin or moxidectin based wormer.

Worming the foal and the lactating mare will be covered in later issues. Be sure to get your copy!