Small strongyles like it hot, French research shows

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The minimum time for eggs to develop into the third larval stage was between 4 and 22 days. Development of the eggs was slowest at 10°C and fastest at 30°C.
The commonest types of worms that infect equids are the small strongyles (also known as cyathostomins).

The findings of a study on the effect of temperature on the time taken by cyathostomin eggs to develop into larvae in horse manure could help improve mathematical modelling of parasitic risks in grazing horses.

Cyathostomins (small strongyles) are the most important group of intestinal parasites of the horse – both numerically, and through their ability to cause disease. They are becoming increasingly difficult to control as they develop resistance to the drugs used against them.

Infected horses pass eggs in the manure, contaminating the pasture. These eggs are not infective straight away but need time to develop into the infective third-stage larvae (L3).

In a laboratory study, French researchers investigated the effect of different temperatures on the minimum time taken by cyathostomin eggs to develop into first/second stage larvae (L1/L2), and into infective third stage larvae (L3) in horse faeces.

Dr Aurélie Merlin and colleagues assessed the effect of three constant temperatures (10°C, 23°C, 30°C) under laboratory conditions and one fluctuating temperature (mean: 17 ± 4 °C) under outdoor conditions.

Their results, published in Veterinary Parasitology: Regional Studies and Reports, show that, depending on temperature, the minimum time taken by eggs to develop into L1/L2 was between 1 and 3 days. The minimum time to develop into L3 was between 4 and 22 days. Development of the eggs to infective L3 larvae was slowest at 10°C and fastest at 30°C.

The results support the practice of removing droppings at least twice a week, which should prevent significant contamination of the pasture.

Merlin is from the ANSES Laboratory for Animal Health, Physiopathology and Epidemiology of Equine Diseases Unit, in Goustranville. She was joined in the study by researchers from ANSES, the French horse and riding institute (IFCE) in Gouffern-en-Auge, and BioEpAR (Biology, epidemiology, and risk analysis in animal health), a partnership between INRAE (National Research Institute for Agriculture, Food and Environment) and Oniris (Ecole Nationale Vétérinaire, Agroalimentaire et de l’Alimentation), in Nantes.

Effect of temperature on the development of the free-living stages of horse cyathostomins. A Merlin, N Ravinet, C Sévin , M Bernez-Romand, S Petry, M Delerue, L Briot, A Chauvin, J Tapprest, L Hébert. Vet Parasitol Reg Stud Reports (2022) 28:100687. doi.org/10.1016/j.vprsr.2022.100687

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