Age at first start and racing career of a cohort of Australian Standardbred horses

OBJECTIVE Compare the career profiles of a cohort of Standardbred horses that first raced as 2-year-olds with those that started their racing careers at a later age. METHOD Retrospective analysis of the racing records of all foals born in New South Wales in the 2000 foaling season. RESULTS The career records of 999 horses were analysed. Almost half (43.9%) first raced as 2-year-olds and one-third (33.9%) as 3-year-olds. The median career duration for horses that first raced as 2-year-olds was 2.93 years (interquartile range (IQR) 2.70-3.16), which was significantly greater than the median for horses that first raced at 3, 4 or ≥5 years old (P < 0.001). Males, and horses that first raced as 2-year-olds, earned significantly more prize money than females or horses that started racing aged ≥3 years (P < 0.001). The population median number of career starts was 28.0 (IQR 8-64). Males, and horses that first raced as 2-year-olds, had significantly more career starts than females or horses that started racing aged ≥3 years (P < 0.001). CONCLUSION This study found no evidence suggesting that racing as a 2-year-old had a deleterious effect on a horse's racing career.     

Effect of tracheal mucus and tracheal cytology on racing performance in Thoroughbred racehorses

REASON FOR PERFORMING STUDY: Accumulations of mucus within the trachea are often found during endoscopic examinations of the airways of poorly performing racehorses, but the clinical importance of this finding is unknown. OBJECTIVES: To determine the effect of tracheal mucus, pharyngeal lymphoid hyperplasia (PLH) and cytological indices of tracheal aspirate on racing performance in Thoroughbred horses assessed by race place and whether the horse was raced. METHODS: Endoscopic examination of the nasopharynx, larynx and trachea was performed, and a tracheal aspirate obtained monthly at Thistledown racetrack from April to December, 2002 and 2003. Horses received a score of 0-4 for the degree of PLH and 0-4 for the amount of mucus visible in the trachea. The tracheal aspirate was assessed for turbidity, and total and differential cell counts. Generalised estimating equations models were used as repeated measures models for each risk factor and the level of association assessed through the risk factor's P value in the model. RESULTS: Moderate to severe tracheal mucus (2-4) was a risk factor for poor racing performance. There was no association between degree of PLH, cell counts or turbidity of tracheal wash fluid and racing performance. However, horses that raced had higher total neutrophil counts in tracheal wash aspirates than horses that did not race. CONCLUSIONS: Grades 2-4 tracheal mucus should be considered a potential cause of poor racing performance in Thoroughbred horses. CLINICAL RELEVANCE: Because moderate to severe tracheal mucus accumulation, and not increased tracheal neutrophils, was a risk factor for poor racing performance, functionally significant airway inflammation may best be confirmed by the presence of mucus rather than increased number of neutrophils in the trachea.     

Association between the purchase price of Thoroughbred yearlings and their performance during the 2- and 3-year-old racing seasons

OBJECTIVES Describe the association between the purchase price of Thoroughbred yearlings sold in Australia and racing performance as 2- and 3-year-olds. METHODS Race performance data of 2773 Thoroughbred yearlings sold at auction during 2003 were collected. Associations between purchase price and the probability of starting, the number of race starts and the prize money earned were examined. RESULTS In total, 2206 (79.6%) horses started a race. The mean number of race starts was six and the mean prize money earned was A$24,420. A total of 1711 (61.5%) horses earned prize money, 402 (14.4%) earned more than their purchase price, 312 (11.2%) earned more than A$40,000, the estimated cost of training, and 142 (5.1%) earned A$40,000 more than their purchase price. There was a positive association between purchase price category and the probability of starting, number of starts, earning prize money and earning greater than A$40,000 (P < 0.001). Purchase price category was negatively associated with the probability of earning greater than the purchase price (P < 0.001). The proportion of horses earning greater than the purchase price plus $40,000 was significantly different (P = 0.03) among the five price categories. CONCLUSION Yearling purchase price was positively associated with all race performance outcomes measured and researchers examining the race performance of yearlings purchased at sales should consider including purchase price when modelling. The Thoroughbred yearling market in Australia behaves in a similar manner to the United States market; owners pay a premium to enter the sport of racing and an additional premium in the quest to own a champion.     

Heritability estimates for racing performance in Japanese Thoroughbred racehorses using linear and non-linear model analyses

This study evaluated the differences between linear and non‐linear modelled heritability estimates of racing performance based on lifetime earnings (LE) and lifetime ranking (LR) in Japanese Thoroughbred racehorses. The heritability estimate (h² = 0.25) obtained from a non‐linear model based on formal Japan Racing Association ranking was much higher than that obtained from a linear model based on the original trait phenotype (h² = 0.11). The linear models showed slightly higher heritability estimates under the trait categorizations than under the original phenotypes, while the non‐linear categorical trait models showed much higher heritability estimates than the linear models, especially for binary trait categorizations (h² = 0.34) with non‐winning and winning horses. The binary trait categorizations were consistent with the case and control classifications in the previous genome‐wide association study (GWAS), which identified possible sequence variants on ECA18 that affect racing performance in Japanese Thoroughbred racehorses. Those findings suggested that the different heritability estimates obtained from several trait categorizations would reflect the possible presence of susceptibility gene segregations in the analyzed population, indicating that heritability estimates from non‐linear models are useful for the selection of case and control populations in GWAS.     

Multivariate genetic analysis to account for preselection and disqualified races in the genetic evaluation of racing performances in German trotters

Abstract

The genetic associations between racing performance and preselection of horses considered as the binary trait racing status (trotters without or with at least one racing performance in life were classified as 0 and 1, respectively) as well as disqualified races (disqualified and non-disqualified trotters were classified as 1 and 0, respectively) were analysed in German trotters. Variance components for racing performance traits square root of rank at finish, racing time per km, and log of earnings with racing status were estimated based on an animal model using REML. Heritabilities of racing status, racing time and rank at finish were 0.30, 0.21, and 0.06, respectively. The genetic correlations between racing status and racing time or rank at finish were ?0.74 and ?0.32, indicating that horses started at least once showed a higher genetic potential in racing time or finishing ability than never started horses. This showed the high preselection of German trotters especially based on racing time. To account for this preselection, it was recommended for additional use of racing status in the German evaluation system. Breeding values of the three racing performance traits were estimated by two distinct models, in- or excluding racing status and compared by using three criteria. Racing time per km showed the highest correlation (r=0.98) between breeding values evaluated by these two distinct models. Therefore, incorrect selection rate of horses using breeding values from the model without racing status, was lowest for racing time per km (9.7%). Selection response increased about 1% for this trait after including racing status in the model. For the estimation of rank at finish, inclusion of racing status in the multiple trait model was much more important as indicated by a low correlation between breeding values (r=0.29) and high percentage of incorrectly selected stallions (97.5%). The trait disqualified races was first analysed using an univariate threshold model. Heritability of this trait was low (h ²=0.12) and repeatability (r=0.43) showed a moderate magnitude. Using a linear multiple trait animal model, disqualified races showed a low heritability (h ²=0.05) and a moderate favourable genetic correlation (r _g=0.43) with racing time per km. Consequently, selection on racing time per km is expected to improve indirectly the reliability of racing performance. Combined selection of reduction in disqualified races and racing time may even further improve the reliability of racing trotters.     

The association of 2‐year‐old training milestones with career length and racing success in a sample of Thoroughbred horses in New Zealand

Reasons 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.     

Profiling the careers of Thoroughbred horses racing in Australia between 2000 and 2010

Reasons for performing study: Research investigating trends in racehorse careers require a benchmark for accurate comparison. Currently little whole population data exists for horses racing in Australia. Objectives: To determine the range and variation in career length and number of career starts for horses racing in Australia. To document and provide evidence regarding the current differences between the sexes for career length and careers starts. Methods: Racing data were collected for Thoroughbreds over a 10‐year period. Career length, number of career starts and spells per year were evaluated. Statistical analyses were performed using the statistical package R. Results: A total of 2,782,774 performance records yielded career information for 164,046 horses. Median career length and number of career starts for the population were 14.7 months and 10 starts, respectively. Significant differences (P<0.001) were present between the sexes for all career outcomes. Between 2000 and 2010, the percentage of Thoroughbreds racing in Australia with careers longer than 12, 24, 36 and 48 months was 56.65, 32.35, 16.66 and 7.74, respectively. Conclusions and potential relevance: Clear differences in career outcomes exist between intact males, females and geldings racing in Australia. Future research should be conscious of these differences when analysing population data.     

Effects of collecting serial tracheal aspirate and bronchoalveolar lavage samples on the cytological findings of subsequent fluid samples in healthy Standardbred horses

Objective To evaluate the effect of collecting serial tracheal aspirate (TA) and bronchoalveolar lavage (BAL) samples on the cytological findings of subsequent fluid samples obtained from horses without clinical signs of respiratory disease. Study design Experimental. Study population Six healthy Standardbred horses. Methods Endoscopically‐guided TA samples, and BAL samples collected using the blind field technique were obtained from the six horses on days 1, 2, 3, 4, 5, 12, and 17. On day 17, horses were sampled three times: at baseline and at 2.5 h and 4 h apart. The differential cytology of the fluid samples collected at each time point was expressed as percentages and compared statistically. Results There was a significant increase in neutrophil percentage in the TA samples taken at day 17 (at 2.5 h but not at 4 h apart). There was no significant change in the neutrophil percentages in the TA samples when repeated samples were taken ≥24 h apart. There was no significant change in the neutrophil percentages in the BAL fluid at any collection point. There were inconsistent changes in the percentages of lymphocytes and macrophages in the BAL fluid over time, but these remained within normal reference ranges and were considered clinically insignificant. Conclusions Serial TA and BAL samples can be taken at 24 h intervals without affecting the cytological findings of subsequent fluid samples collected using the techniques described.     

Pulmonary function measurements immediately after exercise are correlated with neutrophil percentage in tracheal aspirates in horses with poor racing performance

Inflammatory airway disease (IAD) is common in racehorses, and is a cause of wastage in the industry. IAD has been diagnosed by measurement of percent neutrophils (N%) in tracheal aspirates (TA). The aim of this study was to investigate whether spirometric indices of pulmonary function were correlated with N% in TAs. Limits to breathing were measured by analyses of relationships between relative times and relative respiratory gas flows during inspiration and expiration in individual breaths recorded after exercise. Horses with higher N% had significantly lower relative gas flows at the same relative times during inspiration and expiration, suggesting a limit to breathing. These findings confirm a physiological basis for the measurement of N% in TA after exercise for diagnosis of IAD. Spirometric pulmonary function testing using analyses of individual breaths after exercise has application for assessment of pulmonary function and poor exercise performance.     

Association of racing performance with specific abnormal radiographic findings in Thoroughbred yearlings sold in Texas

The objective of this prospective study was to determine the association between presence of abnormal radiographic findings attributed to orthopedic disorders of development (ARF) with subsequent performance among yearlings in Texas. The study population was 348 yearlings offered for sale at the Texas Summer Yearling Sale during 2002 and 2003 for which presale radiographs of limbs were available for review. Radiographs of yearlings were reviewed and presence of ARF were recorded. Additionally, the following data were recorded for each horse: identifiers [name of dam, name of sire, hip number, and name (when available)], year of sale, state of birth, and sales price. Subsequent performance data were obtained for each horse at the conclusion of their 2^nd and 3^rd years of life. Results indicated that no ARF was significantly associated with performance outcomes. Lesions of the proximal dorsal aspect of the sagittal ridge of the 3^rd metacarpus/metatarsus resulted in significantly lower sales prices than either horses without this ARF or horses without any ARF. In conclusion, multiple radiographic abnormalities of Thoroughbred yearlings were not associated with reduced performance during the first 2 years of the racing careers of horses studied. Presence of some abnormalities, however, may be associated with reduced sales price.     

Association of increased tracheal mucus accumulation with poor willingness to perform in show-jumpers and dressage horses

The objective of this study was to examine the association of pharyngeal lymphoid hyperplasia (PLH), recurrent laryngeal neuropathy (RLN), mucus accumulation (MA) score and tracheobronchial secretion neutrophil percentage (TBS-N) with rider-assessed performance in sport horses. Airway endoscopy scores, tracheobronchial secretion cytology, rider-assessed general impression and willingness to perform were investigated in 171 top-level sport horses. Increased MA appears to be associated with poor willingness to perform in sport horses. Older horses had decreased PLH scores and increased TBS-N. Mucus accumulation scores > or =3 were associated with increased odds (mean 9.92; upper and lower 95% confidence intervals: 1.5-64.6) of poor rather than excellent willingness to perform. A TBS-N of 20-50% compared with <20% was associated with decreased odds (median 0.11; upper and lower 95% CI: 0.02-0.66) of poor rather than excellent willingness to perform. In addition, horses with an RLN grade > or =2 had significantly higher odds for giving a poorer general impression and willingness to perform. This finding, however, must be interpreted with caution, since only two horses had significant RLN (grade > or =3).     

The use of race winnings, ratings and a performance index to assess the effect of thermocautery of the soft palate for treatment of horses with suspected intermittent dorsal displacement. A case-control study in 110 racing Thoroughbreds

REASONS FOR PERFORMING THE STUDY: There have been no reports of the efficacy of thermocautery of the soft palate (TSP) assessed objectively as a treatment of intermittent dorsal displacement of the soft palate (DDSP). OBJECTIVE: To compare: racing performance of horses that underwent thermocautery of the soft palate with matched controls; and 'Racing Post ratings' (RPR) with prize money won (RE) and a performance index (PI) for each of the horses in the study. HYPOTHESIS: Thermocautery of the soft palate has no beneficial effect on racing performance and the 3 measures of performance are significantly related. METHODS: The inclusion criteria were fulfilled by 110 horses and each was matched with 2 controls. Changes in performance were compared statistically. RPR, RE and PI were analysed using a regression model. RESULTS: The percentage of horses that improved in performance following the procedure was 28-51% for the 3 measures of performance, compared to 21-53% for the matched controls. There was no significant effect of the procedure on the changes in RPR or RE. There was a significant effect of the procedure on the change in PI (P=0.015) with more treated horses achieving an improved PI and fewer acquiring a worse PI than matched control horses. The measures of performance showed significant correlation. CONCLUSIONS: Thermocautery of the soft palate alone may not be the most efficacious treatment of DDSP. POTENTIAL RELEVANCE: Production of a reliable measure of racehorse performance may be possible.     

Frequency and severity of tracheal wash hemosiderosis and association with underlying disease in 96 cats: 2002-2003

BACKGROUND: Hemosiderophages may be found in feline tracheal wash specimens in association with various disease conditions, including heart failure, trauma, infection, foreign body migration, lung lobe torsion, pulmonary embolism or infarction, neoplasia, and bleeding diathesis. Based on observations in our laboratory, we hypothesized that tracheal wash specimens from cats with asthma also frequently contain hemosiderophages, even in the absence of other known causes of pulmonary hemorrhage. OBJECTIVES: The purpose of this study was to determine the frequency and severity of hemosiderosis in tracheal wash fluid from cats with various diseases, including asthma. METHODS: Feline tracheal wash fluid specimens submitted for cytologic evaluation between March 2002 and August 2003 were included in the study. One hundred and one specimens from 96 cats were examined with both Wright's-Giemsa and Prussian blue stains. Cats were assigned to 6 disease categories: feline asthma, pneumonia, pulmonary neoplasia, rhinitis, heart disease, and other disorders. Based on the percentage of Prussian blue-positive macrophages, hemosiderosis was categorized as negative (0%), mild (<20%), moderate (21-50%), or marked (>50%). RESULTS: The frequency of tracheal wash hemosiderosis in the study population was 63.5% (61/96); hemosiderosis was mild (29/96, 30.2%), moderate (22/96, 22.9%), or marked (10/96, 10.4%). Hemosiderosis was found in 85.7% (6/7) of cats with rhinitis, 78.6% (11/14) of cats with pulmonary neoplasia, 75.0% (27/36) of cats with asthma, 71.4% (5/7) of cats with primary or concurrent heart disease, 25.0% (5/20) of cats with pneumonia, and 66.7% (12/18) of cats with other disorders. In cats with asthma, hemosiderosis was usually mild to moderate and frequently was accompanied by increased eosinophils. CONCLUSIONS: The results of this study confirm that hemosiderosis is a common finding in tracheal wash specimens collected from cats with diverse disease conditions, including feline asthma syndrome.