Heading into a new year is often a time to reflect. I was asked recently for a recommendation on what one should do differently for horses in 2025. With almost 8 decades under my belt & a 50+ year career in equine veterinary practice, two simple thoughts immediately came to mind: ROTATE & RETURN (to feeding oats. But that is another blog topic!).
Currently, the hottest topic in Irish Veterinary medicine is the issue of the EU/Department of Agriculture Statutory Instrument (S.I.) limiting the use of worm medicines. The new mandate dictates the use of prescription only medicine (POM), authorized by a veterinarian familiar with the herd. In December 2024, Veterinary Ireland called an emergency meeting to discuss matters relating to the Veterinary Medicinal Products, Medicated Feed and Fertilisers Regulation Act 2023 which will come into effect the National Veterinary Prescription System (NVPS) from 13th January 2025. Current thinking is to have TARGETED worm treatment based on Fecal Egg Counts( FEC) and Saliva Tests( Immuno-assay). The goal of a focused worm intervention is to reduce costs and in theory prolong the efficacy of the prescription based medicines. But what does this mean for the horse owner?
From the outset, understanding the importance of managing exposure to worm infestation is the key not only to maintaining health but also managing costs for horses under your care.
My own exposure to the battle against parasites began from the start of my veterinary career. I had been armed with the latest scientific research on parasites, their life cycles & effects on nutrient absorption, disease transmission and at worst case, death. But it was time spent with legendary orthopaedic veterinary surgeon Dr.William O Reed at his practice in Belmont Park that impressed upon me the importance or worming. I interned with him for 6 months in 1968 & mastered the art of stomach tubing horses with worming medicine. With iconic horses such as Dr Fager, Damascus, In Reality, Buckpasser and Dark Mirage under his care, I vividly recall him telling me that the most important thing he could do for a horse is worm him. But it wasn’t just a matter of getting an effective medicine. It was imperative to ensure that all the medication was taken by the horse. My second veterinary internship at the famed Tartan Farms in Ocala, Florida confirmed for me the importance of “always have a good man at the head” (an expression used by Professor MeGeady during my Final Year Viva). On arrival, my first job was to administer worm medicine via stomach tube to the 30 barren mares in Barn 1. Supported by the best groom and a twitch, I showed him how to hold the head in the flexed position for ease of passing the stomach tube & we took on the task. It took minutes per horse and all were definitely wormed without distress and with the correct amount of prescription wormer.
Once treated medically, maintaining clean pastures is essential to avoid re-exposure. Back in the 1980’s, a clinical trial was conducted in Newmarket, UK and documented in Robinson’s “Current Therapy in Equine Medicine” of 20 mares, divided into two groups of 10. Fecal egg counts were conducted on all mares and the first group (Group A) of 10 were wormed and left in the same paddock for 5 weeks. The second group (Group B) of 10 mares were NOT wormed but instead enjoyed WEEKLY grazing rotation for 5 weeks. To conclude the trial, both groups had FEC counts done after 5 weeks and Group B (that were NOT wormed, but rotated) had lower Eggs Per Gram ( EPG) than Group A (that were wormed but left in the same paddock). The take away learning here is to maintain a practice of daily manure removal from (dry & grazing) paddocks to limit exposure to larvae & prevent re-infestation.
Continuous grazing with horses leads to severe deterioration in the quality of grassland. Where swards are overgrazed, the ‘lawns’ become depleted in plant nutrients, with the more productive grasses being suppressed and weed grasses, as well as broad-leaved weeds becoming established. Wet winters , a feature of Irish life means that the ground becomes poached and the resulting bare ground then becomes colonised by weeds and undesirable grasses. Land like this is often referred to as ‘horse sick’. Back in 1982, I took over as General Manager of a significant breeding & training thoroughbred farm in Upstate NY and felt the impact of over grazed or ‘horse sick’ pastureland. Despite the ‘state of the art’ facilities, dock leaves were abundant. When I blood tested the resident stock, the eosinophil count was very high in many cases ( indicating migrating parasites with 95% accuracy or 5 % chance of food allergy - Dr Kieran Bredin, personal communication). According to Professor Giorgio of Cornell University at the time, the larvae could “survive New York winters”. Unfortunately, parasite exposure is not beyond stabled horses with no access to turn out either. I have found similar high eosinophil counts at a US Standardbred Training track where the horses were briefly hand grazed in the morning after training (along a grass strip beside the barn) and a second case when I was at an Italian Training centre where the riders all dismounted at the same spot to briefly graze the horses before returning to the stables. Both practices were discontinued and as predicted the blood eosinophils returned to normal parameters highlighting the importance of avoiding re-exposure.
Today, there is plenty of documented research on the benefits of mixed grazing of horses with cattle (in the summer) & sheep. Pastures benefit from the grazing preferences of each species & significant improvements in parasite control as well as grass yield of up to 30% have been noted (The Irish Field 04.2024). This practice has long been recommended, with the most successful thoroughbred breeder of his era, J.J. Maher, of Williamstown House, Clonee, Co. Meath noting how he kept his horses - “they are out with the cattle in the summertime and in the wintertime, I bring them in and feed them oats”.
So, on the eve of heightened regulations & veterinary led worming constraints for equines, there is plenty that can be done to manage costs & ensure compliance. Planned grassland management & in particular timely rotation limits exposure to parasites at the larvae stage & is paramount to keeping your horses healthy. TEAGASC, Grange Agriculture Institute recommends the following steps for optimal management of grass for horses
Step 1: Divide your grazing into 7 paddocks
Step 2: Move stock every 5 days ( thus removing them from the infective larval stage which is 7-10 days after eggs are deposited/manure on the ground)
Step 3: Maintain adequate stock grazing rates (1 horse to 1.5 acres)
Step 4: Monitor grass height (with optimal nutrition being available at 4cms)
Legendary owner & thoroughbred breeder Madam Etti Plesch (3 February 1914 – 29 April 2003) was a committed advocate of rotational grazing . Not only famous for earning her place in The Guinness Book of Records (as the only woman owner to have won the Derby twice, with PSIDIUM in 1961 & with HENBIT in 1980), she accounted for the purchase of an additional 100 acres across the road from her magnificent 400 acre Dollanstown Stud “so my horses do not get worms” (Horses & Husbands, Plesch 2007). Madam Plesch enjoyed incredible successes from her small band of broodmares including a Prix de l’Arc de Triomphe with SASSAFRASS.
No matter the scale of your facilities, there is scope to focus on timely rotation. It may seem daunting but the benefits far outweigh any inconvenience or additional ‘set up’ costs. Lower worm burdens, fewer veterinary visits, better health & less barriers to performance success are key advantages in horse ownership. So if you do one thing different in the New Year ahead, get ahead of worm burdens & review your facilities to allow for rotation. Your horses & your pocket will thank you!
Author : Dr. Richard McCormick, M.V.B., Dip. Eq.Sc., M.R.C.V.S. Licensed Veterinarian (Ireland & UK, Kentucky, USA) Dunboyne, Co. Meath, Ireland
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