The effects of abrupt dietary transition on the faecal microbiota of forage-fed horses over a 3-week period were investigated. Yearling Thoroughbred fillies reared as a cohort were exclusively fed on either an ensiled conserved forage-grain diet (“Group A”; n = 6) or pasture (“Group B”; n = 6) for three weeks prior to the study. After the Day 0 faecal samples were collected, horses of Group A were abruptly transitioned to pasture. Both groups continued to graze similar pasture for three weeks, with faecal samples collected at 4-day intervals. DNA was isolated from the faeces and microbial 16S and 18S rRNA gene amplicons were generated and analysed by pyrosequencing. The faecal bacterial communities of both groups of horses were highly diverse (Simpson’s index of diversity >0.8), with differences between the two groups on Day 0 (P<0.017 adjusted for multiple comparisons). There were differences between Groups A and B in the relative abundances of four genera, BF311 (family Bacteroidaceae; P = 0.003), CF231 (family Paraprevotellaceae; P = 0.004), and currently unclassified members within the order Clostridiales (P = 0.003) and within the family Lachnospiraceae (P = 0.006). The bacterial community of Group A horses became similar to Group B within four days of feeding on pasture, whereas the structure of the archaeal community remained constant pre- and post-dietary change. The community structure of the faecal microbiota (bacteria, archaea and ciliate protozoa) of pasture-fed horses was also identified. The initial differences observed appeared to be linked to recent dietary history, with the bacterial community of the forage-fed horses responding rapidly to abrupt dietary change.

Bone responded rapidly to early training. The data provide reference values and sites for use in longitudinal studies of commercial training regimens.

SummaryReasons for performing study: There is increasing evidence that exercise early in life has a positive effect on musculoskeletal health. At present, there is little whole population research investigating the effect of racing as 2-year-olds on future racing career. Objectives: To investigate the association between attaining training milestones as 2-year-olds with length of career and racing success in Thoroughbred horses in New Zealand. Methods: Retrospective data were obtained of the 2001/02-born Thoroughbred foal crop. The 3 training milestones were: registered with a trainer, trialled and raced. The association of the training milestones with career length was measured using the outcomes: number of race starts and number of years raced, in a Cox regression model. Logistic regression models analysed the association of the training milestones with the outcomes: won or placed in a race. Linear regression was performed to assess the association of training milestones with total career earnings. Results: Of 4683 horses in the population; 3152 horses were registered with a trainer, 2661 horses trialled and 2109 horses raced. Horses that raced as 2-year-olds had significantly (P<0.001) more race starts than those first raced as 3-year-olds or older, this was also true when the 2-year-old year data were omitted. Horses that raced as 2-year-olds had significantly (P<0.001) more years racing. Horses registered with a trainer, trialled or raced as 2-year-olds were more likely to have won or been placed in a race than those that achieved the milestones as 3-year-olds or older. Horses that first trialled and raced as 2-year-olds had greater total earnings than those that first trialled or raced at a later age. Conclusions and potential relevance: Two-year-old training milestones had a strong association with positive racing career outcomes. Horses in training or racing as 2-year-olds may have better musculoskeletal health throughout life than horses that are first in training or racing at a later age.

This study supports the feasibility of imposing early conditioning exercise in horses and is a benchmark for its effects on the development of equine musculoskeletal tissues.

Only one third the Standardbred racehorses born in 2001/2002 registered with a trainer as 2-year-olds, but the results of this study indicate that horses that began training, trialling, or racing as 2-year-olds had longer and more successful careers than those that did not achieve the milestones as 2-year-olds. Further investigation is required to quantify the management practices of these horses to determine the factors that may be associated with a successful racing career.