At least 2.25kg of hay per day should be given to racehorses in work, a study has found.
The results of the study are published in the New Zealand Veterinary Journal.
The authors surveyed the feeding, management and faecal pH of thoroughbred racehorses in the North Island.
The authors, A. Williamson, C.W. Rogers and E.C Firth, aimed to identify feeding and management variables associated with variation in faecal pH within a population of intensively managed thoroughbreds.
The researchers conducted a cross-sectional survey of 16 racehorse trainers. Interviews were conducted at the trainers' stables to get information on feeding and management of the horses. Horse faecal samples were collected and the pH measured.
The researchers found that 97% of horses surveyed were confined in an area no bigger than 5m by 5m for 12 hours or more a day.
They found that faecal pH was unaffected by the trainer's age, the number of years they had trained horses, the age and gender of the horses, the number of weeks in race training, racing class, the frequency of feeding, bedding type, or exercise workload.
Acidic faecal pH (less than or equal to 6.32) was associated with stables with 12 or fewer horses, and trainers at these stables offered more concentrated feed than those at stables with more than 12 horses.
Acidic faecal pH was associated with trainers who offered 4kg of grain as the only form of concentrate fed, or offered 2.25 kg of hay a day, or less.
Horses that displayed stable vices had less acidic faecal pH than horses that did not display stable vices.
The researchers concluded that racehorse management in New Zealand is similar to that observed in other major racing countries.
Trainers with 12 or fewer horses fed more concentrates and their horses' faeces were more acidic than those of trainers with more than 12 horses.
Irrespective of management system, it appears important to provide at least 2.25 kg of hay a day ad libitum, to buffer hindgut acidosis associated with diets high in soluble carbohydrate, the researchers said.