Grazing and farm management of broodmares as an exposure to leptospirosis on commercial equine properties in New Zealand

Abstract: Leptospirosis is a worldwide zoonosis endemic in many countries throughout the world. The seroprevalence in Thoroughbred broodmares in New Zealand has recently been studied and the horses were positive to all five serovars tested (Ballum, Pomona, Hardjobovis, Copenhageni and Tarassovi). Little is known about how the broodmares in New Zealand get exposed to Leptospira spp. and the aim of this study was to collect horse- and farm management information and evaluate potential risks in the horse management for exposure to Leptospira spp. Four stud farms in the Manawatu region on the North Island were visited during five weeks during breeding season and observations about farm-, pasture-, horse- and pest management were recorded. Observations and answers from a farm questionnaire were recorded in Microsoft Excel and compared in between the farms. On each farm three different categories of mares were followed (empty mares, pregnant mares and mares with foals). The management on the farms were similar with co- and cross-grazing with livestock, flooded pastures and pests present. The stud farm with stallions had a high density of mares in the paddocks with low pasture herbage mass while the boutique farms had a lower density and higher pasture herbage mass. Thoroughbred broodmares that were empty were grazing with a low pasture herbage mass at high densities, constantly moving in between paddocks, sorted according to breeding status and mixing with mares from other stud farms with different serostatus to leptospirosis – all factors associated with risks for leptospirosis. Pregnant mares close to foaling were sorted and put together with other mares before and after foaling due to expected foaling date and breeding status post partum, also this management is associated with risk factors to leptospirosis. The foaling paddocks were small with decreasing pasture herbage mass and a stressful environment where mares shed urine, blood and placentas containing leptospirosis. The risk factors associated with the management of the Thoroughbred broodmares in New Zealand are areas for future studies to examine where mares get exposed to Leptospira spp., how it spreads in between the horses and what impact the disease has on the horses clinically and economically.