Mare Reproductive Loss Sydrome Page 2 - Equine Breeding Centre and Veterinary Services

MARE REPRODUCTIVE LOSS SYDROME (MRLS) Page 2

More on the M.R.L.S-

In June 2006 Robyn and I were fortunate to visit Lexington in Kentucky enroute to the UK for their breeding season.

It is an incredible place-truly the American home of the Thoroughbred! There are over 450 studs within a 40 km radius of Lexington and they breed almost 20,000 mares annually to over 380 stallions (average of 51.5 mares per stallion).

The area is serviced primarily by two huge veterinary practices each employing almost 50 vets & 200 lay staff during the breeding season. In addition they have access to the world renowned Gluck Research Station at the University of Kentucky.

We spoke with the principal stud vets at each practice (Dr Michelle Le Blanc at Rood & Riddle and Dr John Steiner at Hagard, Davis & McGee) and with the main researcher at the Gluck Center (Dr Karen McDowell).

There has been an enormous amount of research done there on the M.R.L.S. & almost without exception all we spoke to are convinced that caterpillars are the culprit. The more we heard of the syndrome, the more convinced we became that we have a similar problem.

Let's look at some of their findings:

  • There are two syndromes-an early abortion (resorption) at 15 to 45 days (EFL) & a late abortion at 9 to 10 months (LFL).
  • Time from access to the caterpillars to abortion is 10 (8 to 13) days for EFL or 3 to 15 days for LFL.
  • Growth rate of the foetus is normal up until the time of abortion. There are no warning signs except on ultrasound examination when the placental fluids will appear discolored.
  • LFL abortions are rapid and explosive.
    • Conception rates are unaffected
  • The abortigenic agent is definitely the cuticle or hairs of the caterpillar.
  • The commonest bacteria isolated are non beta Streptococci and Actinobacillus (80%) with some Serratia and Enterococci.
  • Sulphadimidine antibiotics parentally are the most effective but have to be given frequently because of the brief time between exposure and abortion (i.e. every two weeks).
  • The incidence in maidens can be as high as 50%. It is believed that this may be related to the higher incidence of gastric ulcers in younger mares.
  • A regular and effective worming programme is essential in prevention.
  • Eggs hatch in spring to young caterpillars. This is when they are most susceptible to insecticides. Start control measures as soon as hatching begins.
  • Control can be by:
    1. Insecticide sprays such as malathion. These are ineffective & have no residual activity so need to be used every 2 to 3 days. Similarly treatment of the tree trunks with insecticide will not stop the caterpillars coming down the trees.
    2. Follicular sprays. These are ineffective if sprayed on the caterpillars but rely on the caterpillars eating the treated leaves. Crops sprayed with follicular sprays have been fed to horses and shown to have no ill effect. In Australia the only two products that I know are available are Dipel and Spinosad (Trade name Success) Both are very effective against the early stages only so need to be used every 3 weeks. There are a number of other products including Tebufenozide (Confirm) and Bifenthrin (Talstar) which are very good (Talstar is the best) but I have been unable to get them in Australia as yet.
    3. Systemic Pesticides. These are injected into the tree trunk and work by killing the caterpillars when they eat the leaves of treated trees. They work best when the caterpillars are very young. In America there are two such products Abamectin (Abacide) and dicrotophos (Bidrin) I have not located either in Australia at this stage.