A yearling goes under the hammer at the national yearling sales in Karaka.
The research, the findings of which were published in the Equine Veterinary Journal, was prompted by a growing body of research suggesting that early exercise in thoroughbred racehorses may be beneficial to the development of the musculoskeletal system.
Given that evidence, the researchers felt it was important to identify if early conditioning programmes could be developed or modified in order to minimise the risk of musculoskeletal injuries during training and racing.
Researcher Charlotte Bolwell and her fellow researchers - Chris Rogers, Nigel French and Elwyn Firth - collected exercise and health information from 18 farms across New Zealand, covering the preparation of 319 yearlings.
Roughly a quarter of New Zealand's annual thoroughbred foal crop is sold through the national yearling sales series, which consists of Premier, Select and Festival categories.
Most yearlings in the study were catalogued for the Premier sale (139 of 307, or 45.2 per cent), followed by the Select sale (127 of 307, or 39.8 per cent) and Festival sales (41 of 307, or 13.3 per cent).
Of those that went to the sales, 245, or 76.8 per cent, of yearlings were sold and 62 yearlings were passed in, having not met reserve price.
For the study, daily exercise records for individual horses were recorded during the stud farms' preparation for the 2009 sales series.
The researchers found that, of the 319 yearlings, 283, or 88.7 per cent, were exercised (hand walking, mechanical walker and/or lunged) during their preparations.
The median length of their sales preparation was 69 days, with most of the horses falling in the range of 61 to 78 days.
The researchers found that yearling exercise programmes varied between and within farms, and were tailored for each individual horse.
The median number of days spent exercising was 34.
Most of the yearlings undertook hand-walking, with some both hand-walked and exercised in a mechanical walker.
Three stud farms did not exercise all of their enrolled yearlings, they noted.
In total, 150 of the 319 yearlings - 47 per cent - across five farms, experienced changes to their exercise programme as a result of voluntary decisions by the yearling manager.
Horse factors such as ill discipline (18 out of 150), boredom (6/150) and parade practice (10/150) resulted in increased exercise for colts, whilst fillies received more exercise due to being overweight (11/150) and in order to "refresh yearlings on how to walk" (10/150).
Exercising in a mechanical walker.
A total of 31 health events were reported, with lameness being the most common condition recorded (21 cases, one of which was found before preparation of the yearling began), followed by accidental injuries (eight cases) and one case each of laminitis and muscle spasms.
The most common causes of lameness were recorded as "swollen joints" or "swollen tendons" (7/20) or were unspecified (7/20), followed by "splints" (3/20) and foot lameness (3/20).
"Lameness was found to be the most common cause of health problems occurring during a sales preparation, resulting in adjustments to exercise programmes or complete withdrawal from the sales," the authors wrote.
The incidence rates of lameness varied significantly between farms, but not by age, the particular sale the horse was aimed for, or the month of the preparation. The incidence of lameness was lower than that found in studies of young racehorses (0.08 per 100 horse days), but the authors noted that the yearlings had not yet been exposed to the higher intensity exercise of race training.
"Despite this, the study highlighted the potential importance of lameness even during the early stages of a racehorse's career."
Total exercise varied by gender, with colts having more exercise, on average, than fillies.
"Possible reasons for these differences include a number of farms increasing exercise for yearlings perceived as being bored or ill-disciplined; these groups of yearlings were all colts," the authors noted.
"Additionally, previous studies have shown gender to be associated with sales price, with colts achieving higher prices than fillies.
"Therefore, farms may focus more on colts during a preparation, due to the high demand for colts and the potential for a greater financial return.
"Exercise varied not only between farms, but also between individual horses within farms.
"Horse factors such as sire, pedigree, dam, age and parity are part of determining the sales category of the yearling and there is a strong association between the type of sale and price.
"Therefore, the sale category for which a yearling is destined will influence the exercise and management of the horse."
They continued: "The exercise programmes during yearling preparation appeared to be focused on the short-term goal of the sales rather than preparing the horse for its future athletic career as a racehorse."
The authors noted a recent study that indicated a 30 per cent increase in exercise for foals aged from three weeks up to 19-21 months generally had no negative effects on clinical musculoskeletal health or on the horses' racing careers as two and three-year-olds.
"The current study showed that most exercise was performed at walk, which is much slower and less intense than the exercise regimen given to the foals [in that study].
"Therefore, there may be an opportunity to modify or adapt sales preparations, without doing harm, in order to minimise the risk of musculoskeletal injuries in the future.
"However, implementations with the industry may prove difficult unless associations between early exercise programmes and future racing success and long-term musculoskeletal health can be shown through epidemiological studies, and buyers start to place a premium on yearlings prepared in this manner.
"There may be an opportunity to modify yearling sales preparation if the value of exercise in reducing future musculoskeletal injuries and enhancing racing careers can be shown."