Entering spring there are many changes to consider for our horses' health, fly season is from June to August but flies will begin to be apparent from even earlier. Flies are a huge irritant for horses and can impact their welfare. Biting flies are particular nuisances, horse flies are particularly vicious and one paper found them to be 2.5x more likely to be found on horses than caught on fly traps. Biting flies in particular can impact horses' behaviour, and make them engage in foraging behaviour less and the presence of flies leads to an increase in irritation behaviours like tail flicking, stamping and belly kicking which can be energy intensive. The management of flies varies depending on owner preference and access. Fly sprays and fly creams are go to’s but can it be difficult to determine their effectiveness?
Traditional fly sprays can be very different in their quality and effectiveness, one study looked at a mixture of commercial fly sprays available and found that Ecovet in particular was very effective, it reduced the amount of flies on the horses for over 24 hours at both 100% and 50% concentrations. This makes it a potential money saver as you can double the life-span of one bottle. Citronella sprays are also effective in reducing fly numbers, they are often considered more natural and can be cheaper than other more traditional sprays.
If sprays are aversive, wearable items are also effective methods of fly control and management. Leggings can be used to reduce flies landing on horses legs, and leg bands act in a similar manner to flea collars on dogs. Both of these have been shown to reduce the number of flies landing on horses and the irritation from them, they can be used during turnout, when stabled and when ridden. Research has been done of summer fly sheets and light cotton rugs and the effect they can have. They can help with thermoregulation in very hot environments (especially for dark horses) and specific patterns (stripes, checkers) can specifically reduce flies landing. It is important to only use rugs on fit and healthy horses, overweight horses can suffer from heat exhaustion if wearing a rug. Fly masks can also be used to reduce the irritation of flies around the eyes and some types of masks can aid with photic headshaking.
For the stabled horse, sodium bisulfate can be an effective chemical to use to reduce the number of flies in the stable. The paper found that using 0.5-1.1 kg of sodium bisulfate per stable is the most effective concentration, and the chemical is food safe and had no impact on the horses. Recent preliminary research has also investigated nutriceuticals like Equi-Shield, this product was shown to reduce the number of flies landing on them after 7 days of consumption.
Wild horses do not have any of these to reduce the number of flies, so they instead use movement. One study looked at the movement of Shackleford horses during Summer where fly presence was very high. They started the morning in salt marshes where fly populations are low, and then when wind picked up they went to swales (shallow and wide ditch with lots of vegitation including long grass) which prevent flies from landing and resting. Lastly they would move to sand dunes during the heat of the day, this is an area with very low fly populations but also has limited grazing. If you have the facilities, then allowing horses a variety of environments to choose from can allow them to avoid flies throughout the day, and artificial areas for grazing (hay nets) can maintain forage intake while avoiding flies.
Every horse is an individual, some will find the smell of most fly sprays offensive and never be used to it, others might not cope with leggings on them. We are a few months before fly season really starts so now is time to double check our horses are okay with: fly sprays, fly creams, summer rugs, and any other wearables. Even if your horse has previously had no problems with any of the above, it is always best to assess your horse every year as one bad experience or unexpected stressor can set horses back years of work. As always remember that difficult or dangerous behaviour does not need to be dealt with alone, and assistance from a positive reinforcement trainer can benefit your training and support you in resolving those more difficult behaviours.
References:
Krcmar, S., 2005. Seasonal abundance of horse flies (Diptera: Tabanidae) from two locations in eastern Croatia. J Vector Ecol, 30(30), pp.316-321.
Mottet, R.S., Moon, R.D., Hathaway, M.R. and Martinson, K.L., 2018. Effectiveness of stable fly protectants on adult horses. Journal of Equine Veterinary Science, 69, pp.11-15.
Sweeney, C.R., Scanlon, T., Russell, G.E., Smith, G. and Boston, R.C., 2000. Effect of daily floor treatment with sodium bisulfate on the fly population of horse stalls. American Journal of Veterinary Research, 61(8), pp.910-913.
Tuorinsky, E.V. and Machtinger, E.T., 2020. Behavioral inhibition of the house fly (Diptera: Muscidae) when exposed to commercial equine fly repellents. Journal of economic entomology, 113(1), pp.518-526.
Wagner, A.L., Rowland, R.E. and Girard, I.D., 2021. 101 Impact of Equi-Shield as a nutraceutical fly protectant in adult horses. Journal of Equine Veterinary Science, 100, p.103564.
Rubenstein, D.I. and Feinstein, L.H., 2021. Bothersome flies: How free-ranging horses reduce harm while maintaining nutrition. Frontiers in Ecology and Evolution, 9, p.659570.
Caro, T., Argueta, Y., Briolat, E.S., Bruggink, J., Kasprowsky, M., Lake, J., Mitchell, M.J., Richardson, S. and How, M., 2019. Benefits of zebra stripes: Behaviour of tabanid flies around zebras and horses. PLoS One, 14(2), p.e0210831.
How, M.J., Gonzales, D., Irwin, A. and Caro, T., 2020. Zebra stripes, tabanid biting flies and the aperture effect. Proceedings of the Royal Society B, 287(1933), p.20201521.
Coates, H., 2017. Dealing with sweet itch and other summer allergies in horses. Vet. Times, 3, pp.18-20.
Padalino, B., Loy, J., Hawson, L. and Randle, H., 2019. Effects of a light-colored cotton rug use on horse thermoregulation and behavior indicators of stress. Journal of veterinary behavior, 29, pp.134-139.
Eleanor, M., and Duncan, P., 1986 Temporal Patterns of Feeding Behaviour in Free-Ranging Horses. Behaviour, 96(1/2), pp.105–129
McElligott, P.E., and Galloway, T.D., 1991. Seasonal distribution and parity of host-seeking horse flies (Diptera: Tabanidae) from a pasture near Seven Sisters, Manitoba. The Canadian Entomologist, 123, pp.361-370.
King, S.R.B, and John Gurnell, J., 2010. Effects of fly disturbance on the behaviour of a population of reintroduced Przewalski horses (Equus ferus przewalskii) in Mongolia. Applied Animal Behaviour Science. 125(1/2). pp.22-29
Rubenstein, D.I. and Hohmann, M.E., 1989. Parasites and social behavior of island feral horses. Oikos, 55(3), pp.312-320.
Comments