The practice of cross or mixed grazing is often suggested as a useful strategy to manage intestinal parasite infestation, but until recently, evidence of its efficacy was limited. A French team has provided the first evidence of the benefits of mixed grazing with cattle as an alternative to control strongyle infection in horses.
Cross or ‘mixed’ grazing means having different types of animals, as opposed to just horses, graze an area of land. Proponents of the practice explain that, in a natural setting, many different species of animals occupy the same areas of land and, therefore, by using cross grazing, you can get closer to replicating a more natural management system, benefiting your animals and the wider environment in a number of ways.
For example, cross grazing results in more ‘even grazing’ of a pasture – that is, it reduces the establishment of ‘roughs’ and ‘lawns’. Different animal species tend to complement each other in their grazing behaviours by eating different plants and eating parts of the pasture the horses tend to ignore.
But importantly it has always been assumed that cross grazing reduces parasitic worms on the area grazed because different animal species will eat around the dung of other species, but not that of their own.
This is thought to be a parasitic prevention strategy because most parasitic worms are ‘host-specific’ – they can only complete their life cycle in one species of animal. If a parasite is picked up by a different species of animal, it dies in their digestive system without reproducing.
The study by Forteau and colleagues compared the management and worm control of 44 horse breeding farms in two different regions – the more productive grasslands of Normandy, that generally specialise in sport horse breeding, and the less productive northern Massif Central, where leisure horses are bred. Of the 44 farms, 21 specialised in breeding horses and 23 bred cattle as well as horses.
Using field surveys and face-to-face interviews they aimed to quantify breeders’ awareness of the benefits of cross grazing horses and cattle, to establish whether farms that used cross grazing used different strongyle worm control management strategies and to test whether strongyle egg excretion was lower in horses grazed with cattle.
The results show that all breeders were relying on systematic calendar treatments and only 8 out of the 23 farms that breeds both, horses and cattle were aware that cross grazing both species could be used as part of their strongyle control strategy. There was also a high reliance on macrocyclic lactones (ivermecting and moxidectin) despite the well-recognised problem of resistance to these drugs.
Faecal egg counts measured in horses from Massif Central were significantly reduced when horses were grazed with cattle. The researchers also report that out of all the horses that were treated only with macrocyclic lactones, the young horses grazed with cattle had 50% fewer strongyle eggs excreted in their faeces than horses grazed in equine-only pastures.
This study provides the first evidence of the benefits of mixed grazing with cattle as an alternative to control strongyle infection in horses, but shows that the benefits of cross grazing are not widely known amongst French horse breeders.
The study is published by Cambridge University Press: Horses grazing with cattle have reduced strongyle egg count due to the dilution effect and increased reliance on macrocyclic lactones in mixed farms by L. Forteau, B. Dumont, G. Salle and G. Bigot. The abstract can be found here.