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1.
Plasma lipoproteins were isolated from eight Thoroughbred horses and eight Shetland ponies on the basis of particle size by gel filtration chromatography and according to density using rate-zonal ultracentrifugation. Three major classes corresponding to very low density lipoproteins (VLDL), low density lipoproteins (LDL) and high density lipoproteins (HDL) were identified and characterised by their lipid and apolipoprotein compositions. The particle size distributions of each class were determined by electron microscopy and non-denaturing polyacrylamide gradient gel electrophoresis. HDL was found to dominate the equine lipoprotein spectrum, accounting for 61 per cent of the total plasma lipoprotein mass (VLDL 24 per cent, LDL 15 per cent). The VLDL class was isolated as a single population of particles that were triglyceride rich and cholesterol, phospholipid and protein poor. Equine LDL was characteristically cholesterol rich and was found to be polydisperse comprising three subfractions that were discrete with respect to particle size and lipid composition. The HDL class was composed of homogeneous particles that were typically protein rich. Apolipoprotein (apo) B was the major protein of VLDL and LDL, and presented two components on polyacrylamide gel electrophoresis with molecular weights in the region of human apoB-100 and a third in VLDL similar to that of apoB-48. ApoA-I was the predominant protein in equine HDL. Although there were no breed differences in the physical or chemical properties of each lipoprotein class, the Shetland ponies had higher plasma triglyceride and VLDL concentrations than their Thoroughbred counterparts.  相似文献   

2.
The effect of dynamic exercise on complete blood cell count, lymphocyte β-adrenergic receptor and plasma catecholamine (adrenaline and noradrenaline) levels in horses performing different disciplines were investigated during rest and after exercise. Blood samples were collected from jumping horses (n=6), Arabian Endurance horses (n=6) and Standardbred trotters (n=6) before and immediately after competition. Dynamic exercise caused a significant increase in red blood cell count (Standardbred trotters: P=0.0012), haemoglobin concentration (jumping horses: P=0.001; Standardbred trotters: P=0.01), haematocrit percentage (Standardbred trotters: P=0.005), neutrophil percentage (jumping horses: P=0.0003), lymphocyte percentage (jumping horses: P=0.0003), monocyte percentage (Standardbred trotters: P=0.0008), lymphocyte β-AR numbers (jumping horses: P=0.01; Arabian Endurance horses: P=0.016; Standardbred trotters: P=0.05), plasma adrenaline concentration (Standardbred trotters: P=0.0001) and plasma noradrenaline levels (Standardbred trotters: P=0.003). It is concluded that acute increases in plasma catecholamine concentrations depended on the exercise performed and may induce up-regulation of β-AR in equine lymphocytes. However, the exact mechanism of β-AR up-regulation still remains unclear.  相似文献   

3.

Background

There are conflicting reports of plasma lipoprotein lipid content in dogs with diabetes mellitus (DM).

Objectives

To determine lipoprotein lipid content of plasma of dogs with DM by spectrophotometry and ultracentrifugation; to compare lipoprotein lipid content in diabetic and healthy dogs; and to quantify apolipoprotein B‐100 (ApoB) in dogs with DM.

Animals

22 dogs with DM and 9 healthy dogs.

Methods

Cross‐sectional study. Triglyceride (TG), total cholesterol (TC), and high‐density lipoprotein cholesterol (HDL‐C) concentrations were measured by spectrophotometry. Very low‐density lipoprotein cholesterol (VLDL‐C) and low‐density lipoprotein cholesterol (LDL‐C) concentrations were calculated after ultracentrifugation. Non‐HDL‐C cholesterol was calculated by subtracting HDL‐C from TC. ApoB was quantified by ELISA. The Mann‐Whitney test was used for comparison of median lipoprotein concentrations, and Spearman's correlation was used to assess associations between ApoB and lipoprotein fractions.

Results

All values are reported in mg/dL. Median TG (122), TC (343.5), HDL‐C, (200), VLDL‐C, (27) LDL‐C (68), non‐HDL‐C (114), and ApoB (320) were significantly higher in dogs with DM, compared to healthy dogs (57, 197, 168, 12, 16, 31, and 258, respectively, P‐values 0.0079, <0.001, 0.029, 0.011, <0.001, <0.001, 0.025, respectively). A significant association was found between ApoB and LDL‐C (Spearman's rho = 0.41, P = 0.022) and between ApoB and non‐HDL‐C (Spearman's rho = 0.40, P = 0.027).

Conclusions and Clinical Importance

Dyslipidemia of dogs with DM is characterized by pronounced increases in LDL‐C and non‐HDL‐C concentrations, although all lipoprotein fractions are significantly increased. Knowledge of specific lipoprotein fraction alterations in dogs with DM can enhance treatment options for diabetic dyslipidemia in dogs.  相似文献   

4.
This study examined the influence of sex steroid hormones on lipid metabolism in horses. The group of 34 clinically healthy Standardbred trotters aged 2 to 4 years was studied during an exercise test. The horses were divided into groups according to their sex. These groups were: 11 stallions, 16 mares, and seven geldings. Concentrations of testosterone, 17-β-estradiol, leptin, ghrelin, glycerol, free fatty acids (FFA), and triacylglycerols (TG) were measured in plasma obtained from blood samples taken at rest and after the end of the exercise. At rest, plasma ghrelin concentration was significantly higher in geldings than in stallions and mares (1,541 ± 206 vs 1,280 ± 288 and 1,310 ± 267 pg/mL, respectively; P = .012). Leptin was lower in geldings than in mares (2.65 ± 0.93 vs 4.70 ± 2.31 ng/mL; P = .036). The post-exercise rise in plasma ghrelin and TG concentrations was significantly higher in mares than in geldings (+220 ± 330 vs -25 ± 206 pg/mL; P = .049 and 0.31 ± 0.14 vs 0.13 ± 0.15 mmol/L; P = .016, respectively). The increase in plasma FFA level was higher in geldings than in stallions (535 ± 178 vs 334 ± 191 μmol/L, P = .046). In conclusion, lipolysis rate in geldings is higher than in noncastrated trotters.  相似文献   

5.
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6.
A common sign of obesity, in dogs, is hyperlipidemia, which is characterized by hypercholesterolemia and/or hypertriglycemia. Hyperlipidemia can be caused by a quantitative increase in circulating lipoproteins (LP) or by a higher lipid concentration in the various LP classes. In this study, we sought to determine whether aberrations occur with cholesterol lipoprotein profile, especially with sub HDL-cholesterol fraction % in obese dogs. Using clinically healthy and disease free (no overt signs) body condition score classified obese dogs, of all ages, we attempted to determine the influence of age, gender and obesity status on cholesterol lipoprotein profiling. Overall, no aberration in pattern was observed in obese dogs <8 years of age. However, in older obese animals (≥8 years of age), the general aberration pattern to cholesterol lipoprotein observed was that a significant decrease in HDL2 and 3 fraction % occurs with a concomitant increase in either HDL1-Cho or VLDL and LDL -Cho fraction % depending on gender. Linear regression analysis indicated that obesity status appears to significantly affect total cholesterol, HDL2 and 3-Cho, VLDL and LDL-Cho levels (P = 0.02, 0.046, and 0.045, respectively), whereas it is borderline with HDL1-Cho (P = 0.062). On the other hand, age significantly influenced TG, Total cholesterol, and HDL1-Cho levels (P = 0.009, 0.006, and 0.002, respectively), while gender influenced VLDL and LDL-Cho (P = 0.024) level. Therefore, aberrations in cholesterol lipoprotein profile pattern might be of potential use to assess and diagnose obesity status, in conjunction with BCS, especially of older overweight animals which might be considered borderline obese.  相似文献   

7.
To test the hypothesis that the pulmonary vascular pressures of Thoroughbred and Standardbred horses behave similarly during exertion. Measurements were made on 5 Thoroughbred and 5 Standardbred horses on a treadmill at rest and during 3-minute exercise intervals at speeds predicted to produce 75%, 90%, and 100% maximal heart rate. Left forelimb acceleration, heart rate, esophageal pressure, and pulmonary artery pressure were measured continuously. Pulmonary capillary and wedge pressures were measured during intermittent occlusion of the pulmonary artery. Breathing rate and gait frequency were the fundamental frequencies of the esophageal pressure and limb acceleration signals respectively. The ratio of speed:gait frequency gave stride length. The effects of exertion and breed were evaluated using two-way analysis of variance. Exertion produced significant increases in pulmonary artery (P = 0.001), capillary (P= 0.002), and wedge (P= 0.005) pressures. No significant effect of breed was detected on pulmonary artery pressure, but at exertion pulmonary capillary and wedge pressures were 15% (P= 0.03) and 23% (P= 0.04) greater in Thoroughbreds, respectively. Treadmill speed was ~12% greater (P= 0.04), stride length was ~25% greater (P= 0.0003), gait frequency was ~10% less (P= 0.006), breathing rate was ~10% less (P= 0.001), and heart rate was ~6% less (P= 0.06) for Thoroughbreds. There was no effect of breed on inspiratory or expiratory esophageal pressure although mean esophageal pressure was ~2 mmHg greater (P= 0.03) in exercising Standardbreds. In conclusion, pulmonary capillary and wedge pressures are greater in Thoroughbreds than in Standardbreds at similar fractions of maximal heart rate. This is compatible with the higher incidence of exercise-induced pulmonary hemorrhage observed in Thoroughbreds.  相似文献   

8.
Twenty horses with central and third tarsal bone slab fractures, were treated internal fixation. Eighteen of the 20 cases were Standardbred trotters, one was a Thoroughbred racehorse and one a Swedish Warmblood. The central tarsal bone (CT) was involved in 12 cases and the third tarsal bone (T3) in 8 cases. The fractures were treated by lag screw fixation with one (18 cases) or two (2 cases) 3.5 or 4.5 mm cortical screws. Horses were confined to stall rest for one month and then put on a gradually increasing exercise programme. Convalescence time was 3-8 months until the fracture had healed and training could be resumed. Fifteen of the horses regained athletic soundness. Thirteen of the horses (72%) raced after surgery (12 Standardbreds and 1 Thoroughbred). Nine (69%) of these 13 horses won races after surgery.  相似文献   

9.
Utilising a face-to-face interview of stud managers, a survey was conducted to investigate the movement patterns around, and biosecurity practices on, Thoroughbred and Standardbred stud farms. Eligible stud farms (n = 60) were identified from the 2009 Thoroughbred stallion register and 2009 Standardbred stallion register, and stud managers were asked to participate in the interview. In total, 27 stud managers agreed to participate in the study, and participating stud farms included 38% of Thoroughbred and 60% of Standardbred mares bred in 2009. All stud managers reported the movement of horses to and from their stud farm. The median number of movement events per year was 127 (interquartile range 83–300). The frequency of movement events from a stud farm was not associated with the breed of horse managed on the stud farm, however Thoroughbred horses travelled further than Standardbred horses during these movement events (P < 0.001). The movement patterns of horses around stud farms showed a strong seasonality associated with the commercial breeding season of each breed. While 26 (96%) of stud managers reported having procedures in place for checking newly arriving horses, only 6 (22%) stud managers reported isolating horses on arrival as a standard protocol. The main reason for isolating horses on properties, where isolation was not a standard procedure, was in response to strangles outbreaks on other stud farms (n = 10). Only 2 (7%) stud managers reported implementing visitor protocols, and these protocols only applied to visiting veterinarians, but not to farriers. These findings have important implications for the control of both endemic and exotic infectious disease outbreaks within the New Zealand breeding population as the high frequency of movement around stud farms, the high number of visitors to stud farms and the lack of effective biosecurity practices or visitor protocols will be critical factors in the spread of equine influenza during an outbreak.  相似文献   

10.
This study was performed to estimate the prevalence of gastric ulcers in Standardbred racehorses, to describe the lesion score and location, and to identify potential risk factors. Two hundred seventy-five (275) Standardbred horses from 5 training centers and 2 racetracks in Quebec, Canada, were studied. Historical data for the 2 months before examination were recorded for each horse, and the presence of gastric ulcers was determined by gastroscopy. A previously reported scoring system that used grades 0-3 for gastric lesions was used. Overall, 121 horses (44.0%; 95% CI, 38.1-50.1%) had gastric ulcers. The prevalence of gastric ulcers was significantly higher (P < .0001) in actively racing horses (63.3%; 95% CI, 54.7-71.2%) than in horses at rest. Multivariate analysis defined that horses in racing (OR = 9.29; 95% CI, 3.55-24.3) were significantly more likely to have gastric ulcers than horses at rest and that trotters (OR = 2.23; 95% CI, 1.28-3.86) were more likely to have gastric ulcers than pacers. The number of lesion sites (P < .0001) and poor body condition (P < .0001) were significantly associated with lesion scores. Gastric ulcers are highly prevalent in Standardbred racehorses. Furthermore, actively racing horses and trotters are more likely to have gastric ulcers. Also, poor body condition in Standardbred racehorses may be an indication that gastric ulcers are present and that lesion scores are high. The cause-and-effect relationship between poor body condition and the presence of gastric ulcers is unclear.  相似文献   

11.
To assess the significance of radiographic signs of sclerosis of the third carpal bone (C3) in young Standardbred trotters in relation to performance, lameness and bone turnover both carpi in 14 Standardbred trotters were radiographically and scintigraphically examined 6 times, from the beginning of speed training until the beginning of racing, between the mean ages of 20 and 42 months. At the end of the study 8 horses had raced in official qualifying races and 14 limbs in 11 horses had been diagnosed with carpal lameness. All horses but 2 developed sclerosis and all but one had increased bone turnover in the C3 area by scintigraphy. C3 sclerosis increased continuously over time and with increased performance. Carpal lameness was significantly associated with progression of sclerosis but in most cases sclerosis developed without concomitant signs of carpal lameness. No association between carpal lameness and increased scintigraphic uptake was found, but horses that had qualified for racing had significantly higher C3 to carpus ratio of radiopharmaceutical uptake. We conclude that there is a continuous increase in C3 radiographic sclerosis with time in young Standardbred trotters in professional training, but radiographic sclerosis appears to be of limited value as an indicator of clinical carpal disease or level of performance in Standardbred trotters.  相似文献   

12.
OBJECTIVE: To measure and compare concentrations of selected blood lipids before and after thyroidectomy in horses. ANIMALS: 5 healthy adult mares. PROCEDURE: Mares were confirmed to be euthyroid. Thyroidectomy was performed, and hypothyroidism was confirmed. Selected blood lipid variables were measured before hypothyroidism was induced and weekly for 4 weeks after induction. Plasma concentrations of very low-density lipoprotein (VLDL), low-density lipoprotein (LDL), serum triglyceride (TG), total cholesterol (TC), and nonesterified fatty acid (NEFA) were measured. The composition of VLDL and LDL also was examined. RESULTS: Mean plasma concentrations of VLDL and LDL increased significantly after thyroidectomy. By 4 weeks after thyroidectomy, a ninefold increase in mean plasma concentration of VLDL and a threefold increase in LDL, compared with baseline values, were detected. After thyroidectomy, mean percentage of TG in VLDL increased significantly, whereas free cholesterol and cholesterol ester content decreased. Mean percentage of TG in LDL also increased by 3 to 4 weeks after thyroidectomy. Serum concentrations of TG and TC increased, whereas serum NEFA concentration decreased. CONCLUSIONS: Hypothyroidism significantly alters blood lipid concentrations of horses. After thyroidectomy, markedly high VLDL concentration, appearance of TG-rich VLDL, increased serum concentrations of TG and TC, and decreased blood concentration of NEFA were evident. CLINICAL RELEVANCE: Examination of blood lipid concentrations of horses may be useful for detecting naturally acquired hypothyroidism.  相似文献   

13.
Sodium bicarbonate administration in the hours prior to exercise has been used as a performance-enhancing substance in horses since the late 1980s. Although sodium bicarbonate administration to racehorses 24 hours before racing is a banned practice in most racing industries, whether or not it improves running performance in racehorses is currently unclear. The aim of this systematic review and meta-analysis was to establish whether or not acute sodium bicarbonate administration improves running performance in trained Standardbred and Thoroughbred horses. Seven randomized controlled trials, including eight experimental (exercise) trials and 74 horses, were included after a comprehensive search for relevant studies that met the inclusion criteria. Results indicated that sodium bicarbonate administration at 2.5–5 hours prior to a standardized treadmill test to exhaustion or simulated race (time-trial) does not influence running performance (number of horses, the overall effect [95% CI]: 32, –0.13 [–0.64 to 0.37] and 42, 0.01 [–0.42 to 0.44], respectively, both P > .05). The included studies demonstrated minimal heterogeneity (I2 = 0%–2%), low risks of bias according to the Cochrane Risk of Bias Tool and a lack of publication bias. On the basis of these findings, there is high-quality evidence to suggest that sodium bicarbonate administration does not improve running performance in trained Standardbred or Thoroughbred horses.  相似文献   

14.
The objectives of this study were to survey clinics’ guidance about recommended fasting duration (FD) prior to lipoprotein analysis, and to characterize lipoprotein cholesterol and triglyceride concentrations in obese and overweight dogs categorized on the basis of the 5-point body condition score (BCS) scale. A dataset was created from lipoprotein analysis medical records of 1,538 dogs from 75 breeds in 354 clinics from 2012 to 2013. A phone survey was conducted to obtain the clinics’ FD. Two-level linear mixed-effects models were applied to the data. Over 50% of the clinics said they recommended fasting for 12 hr or more. Dogs in clinics with FD 12 hr or more had lower chylomicron triglyceride concentrations than those in clinics with FD less than 8 hr (P=0.05). Mean (± SEM) BCS at sampling was 3.7 ± 0.02. Obese and overweight dogs had higher very low density lipoprotein (VLDL) and high density lipoprotein (HDL) cholesterol and triglyceride concentrations than ideal dogs (P<0.05), but no such difference was found for low density lipoprotein cholesterol and triglyceride concentrations (P≥0.07). Across all BCS, as dog age rose from 0 to 8 years old, HDL cholesterol concentrations decreased by 13.5 mg/dl, whereas VLDL triglyceride concentrations increased by 81.7 mg/dl (P<0.05). In conclusion, FD of 8 hr or less may affect lipoprotein lipid concentrations. Obese and overweight dogs were characterized as having high VLDL and HDL cholesterol and triglyceride concentrations.  相似文献   

15.
Muscle biopsies were obtained from 17 Standardbred trotters (S) and 22 Thoroughbred racehorses (T) after races which varied in length from 1200 to 2840 m. Biopsies were taken between 2 and 14 minutes from the conclusion of the race. Histochemical and biochemical analyses were performed on all muscle samples. Standardbred horses possessed fewer Type II fibers, especially Type IIB fibers, and demonstrated a higher oxidative and lower glycolytic capacity in muscle than Thoroughbred horses. Intramuscular glycogen and lac-tate concentrations were lower in Standardbred horses after racing (mean 420 and 82 mmol/kg d.w. respectively) com-pared to Thoroughbred horses (mean 545 and 148 mmol/kg d.w. respectively). Low levels of intramuscular adenosine triphosphate (ATP) (mean S 17, T 15 mmol/kg d.w.) and creatine phosphate (mean S 28, T 42 mmol/kg d.w.) were recorded in both breeds after racing. Differences in muscle enzyme activities and metabolic response to exercise between breeds were related to the different muscle fiber compositions of Standardbred and Thoroughbred horses. Within both breeds, a high percentage of Type IIB fibers was associated with a low oxidative and high glycolytic capacity in muscle and a greater lactate accumulation after racing. In Standardbred horses low intramuscular ATP concentrations post-race were associated with a high percentage of Type IIB fibers and high lactate levels. No relationship was found between placing or speed of racing and intramuscular lactate and ATP concentrations post-race. This may have been due to many other factors which affected the outcome of a race and also due to the fact that it was not known when during a race lactate accumulation and ATP depletion occurred. Since the properties of fiber types appeared to be very different, the metabolic response within individual fiber types may be more closely related to fatigue than the metabolic response measured in whole muscle.  相似文献   

16.
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17.
OBJECTIVE: To determine the lipid composition and electrophoretic pattern of plasma lipoproteins in samples obtained from healthy 1-humped camels (Camelus dromedarius). ANIMALS: 34 healthy camels raised under similar farming and dietary conditions. PROCEDURES: Plasma samples were subjected to density-gradient ultracentrifugation for separation of plasma lipoproteins, including very-low-density lipoproteins (VLDL), low-density lipoproteins (LDL), and high-density lipoproteins (HDL). Purity of the separation was assessed by use of polyacrylamide gel disk electrophoresis. Concentrations of triglycerides, cholesterol, and phospholipids were measured in each lipoprotein fraction, and lipoprotein electrophoretic patterns were determined in plasma samples. RESULTS: Phospholipid was the major constituent of VLDL (mean +/- SD concentration, 10.62 +/- 1.2 mg/dL), LDL (24.66 +/- 3.12 mg/dL), and HDL (38.08 +/- 0.76 mg/dL). Low-density lipoprotein, VLDL, and HDL were important plasma lipoprotein carriers for cholesterol (67.94 +/- 9.51%), triglyceride (55.83 +/- 7.81%), and phospholipid (51.91 +/- 1.55%), respectively. On the basis of electrophoresis results, relative percentages of alpha- and beta-lipoproteins were 31.72 +/- 4.88% and 68.3 +/- 4.68%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE: The lipoprotein profile in 1-humped camels differed substantially from that of other ruminants. Results may be useful in the evaluation of metabolic disorders in camels.  相似文献   

18.
Genetic correlations for body measurements and subjectively scored traits between foals and studbook horses were estimated using bivariate linear mixed models. Observations for nine foal and eleven studbook traits in Finnhorses on 6529 foals and 6596 studbook horses and in Standardbred trotters on 3069 foals and 2112 studbook horses were available from the Finnish horse breeding shows. The number of sires with progeny in both foal and studbook data was 203 in Finnhorse and 145 in Standardbred trotters. Estimates of heritability for body measurements in foals and studbook horses using univariate models were high in both breeds (0.41-0.84). Heritability estimates for subjectively scored traits using univariate models were generally higher for foals (0.08-0.46) than for studbook horses (0.06-0.21) in both breeds. Genetic correlations between foals and studbook horses for body measurements were highly positive ranging from 0.74 to 0.96 in Finnhorses and from 0.79 to 0.99 in Standardbred trotters. Low to highly positive genetic correlations between foals and studbook horses for subjectively scored traits were obtained in Finnhorse trotters, whereas in Standardbred trotters genetic correlations for subjectively scored traits varied from moderately negative to highly positive. Higher estimates of heritability for foal traits and generally high genetic correlations between the foal and studbook traits indicate that an early selection for conformation traits would be efficient in the breeding programmes.  相似文献   

19.
This study was designed to compare the effects of a fat-supplemented diet versus a traditional diet on the lipoprotein (LP) content in horses. In the first of two trials, eight two-year old horses were fed a basal diet, in which 80% of the digestible energy was supplied as chopped alfalfa hay. One group of four horses (fat-supplemented group, FS) was fed the remaining 20% of the digestible energy as corn oil, while the other group of four horses (control) was fed rolled corn to complete their diet. Blood samples were collected at the start of the experiment and every 2.5 weeks thereafter for 10 weeks. Total serum lipids were measured in both groups of horses and the lipoproteins were fractionated into very low density LP (VLDL), low density LP (LDL), and high density LP (HDL) using ultracentrifugation and agarose-column chromatography. Each LP fraction was measured for protein, cholesterol (CH) and triglyceride TG) content. Total serum lipids were increased in the FS group above the control (9.16 vs. 4.65 mg/ml, week 5). Serum cholesterol and triglyceride concentrations were elevated in the FS group, but were highly variable. Variations in lipid concentrations may have been due to variation in time of sampling during the day. In the second trial, four of the eight horses were used and divided into the same two groups; FS vs. control. After an initial sample, postprandial serial blood samples (1 hour intervals for 8 hours) were drawn at 2, 4 and 6 weeks. Upon examination of the data, Hour 3 post-feeding was chosen to represent postprandial LP values. In both trials, the horses were able to adapt to the added dietary fat. Maintenance of body weight and increased speed of lipid clearance from the blood by the end of each trial in the FS group support this statement. In the FS group, there was an increase in VLDL TG concentration, but not in LDL. This indicates an increase in VLDL TG clearance from the circulation, presumably by increased lipoprotein lipase (LPL) activity. Cholesterol concentrations were also increased in the FS horses in the LDL and HDL. The rise in cholesterol may be attributed to endogenous recycling of liver products such as bile salts, which aid in digestion and absorption and are cholesterol based. In addition, there were greater quantities of LDL and HOL produced in the FS horses as supported by the increased protein concentrations as well as larger peaks for the eluate from the gel filtration column.  相似文献   

20.
Harness racing is a form of horseracing in which the horses race in a specified gait (trot or pace). In contrast to the Thoroughbred, the trotter is not an international breed. In this type, the horses are raced with trotting or pacing gait. Breeds specialized for racing at trot or pace are indigenous to many countries. Separate breeds of light harness horses, generally designated as trotters have evolved for racing purposes in several countries. The important horse breeds used for harness racing in different parts of the world are the Standardbred, French Trotter, Swedish Trotter, Orlov Trotter, Russian Trotter, Finnhorse, Icelandic Toelter, Dole horse and North-Swedish cold-blooded horses. The trotter ranks worldwide second to the Thoroughbred in popularity as a racehorse. Racing performance in trotters, in contrast to Thoroughbred is characterized by qualifying tests before entering the races, inclusion of more than one breed in international races only and greater duration of racing career. An intensive selection of stallions on the basis of phenotypic racing performance has been practised in many trotter populations for quite a long time. Unlike Thoroughbreds, improvements have been observed in different trotter populations and this is attributed to both genetic and environmental changes. Environmental changes include enhanced training methods, as well as improved tracks, harness and sulkies. As a result of selection, racing time of trotters has been reduced over the years. The estimated annual genetic progress in racing performance traits of Swedish Standardbred horses corresponds to 5% of the phenotypic standard deviation, 3.6% in French Trotters and 5% in Dutch Trotters. According to the recent selection for speed in trot, this trait remains heritable and genetic improvement is observed in most countries. Correlations between earnings and times are negative and high, and hence favourable. As a result, selection based on times and earnings are quite effective. A multiple trait approach avoids potential biases of one particular measure, even if the objective of all traits is much the same. Since racing performance may be evaluated in both males and females and repeated observations can be obtained on the same animal, mass selection based on performance tests would be the selection procedure of choice. In the future, interest in the possible use of marker-assisted selection (MAS) for enhanced genetic improvement in horses is likely to increase. MAS is likely to be a valuable complement to selection of horses based on estimated breeding values (EBVs) obtained by the Best Linear Unbiased Prediction (BLUP) method, rather than as a replacement for EBVs.  相似文献   

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