WORMING HORSES IN SUMMER
Why do we worm our horses? If your answer is to make them healthier, than that suggests your horses have clinical cases, i.e., they are actually sick. Worms rarely cause clinical disease in adult grazing livestock, unless there are underlying conditions (poor nutrition, compromised immune systems etc etc).
The modern method of worming focusses on decreasing the spread of worms, rather than removing worms from the horse. Basically, modern worming is IDing and treating the ‘super-spreaders’; limiting how much they spread worms to other horses. Worming horses with high egg counts will limit the number of infective larvae on the pasture.
In summer, we don’t have to use chemical wormers to limit infective larvae on the pasture. Instead we can just use what comes for free each summer in Australia: the sun. Hot dry weather (emphasis on the dry) will desiccate the eggs and larvae, if manure pats are broken apart. Intact pats can maintain enough moisture to keep eggs and larvae alive. Over summer, you can move from collecting manure to harrowing to break apart the pats, or if you are lucky enough to have dung beetles, they will do it for you.
In addition to summer worming being pointless in the strategic worming regime, here are some other points why worming is not a good idea over summer.
1. Wormers, especially the mectins, have detrimental effects on the insect life that break down manure, such as dung beetles
2. Worming horses will remove the adult worm burden that is living in balance with the horse. If the horse also has encysted larvae, these may suddenly emerge from their over-summer hibernation to fill the void left after worming and you get a colic type disease known as larval cyathostominosis.
3. Ideal time to worm is mid-autumn – if you worm late summer, you will need to worm again in autumn, so to the summer treatment is a wasted treatment
Down here in Southern Victoria we still have a few weeks until the hot, dry weather properly sets in, and so some horses may still require a last spring-time worming, especially if they are young. FECs are still the best method to ID if your horse needs a treatment.
Summer is the easiest time for parasite management, as all you need to do is make sure you harrow/break up the pats, and keep on top of removing bot fly eggs. If you do get a FEC performed, it may be worth considering if the worming cut-off EPG value should be increased to 500 EPG, rather than the normal 200EPG.