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Muscle surface capillary blood flow was measured in the biceps femoris and lateral head of the triceps brachii muscles in six horses before and during halothane anesthesia by using laser Doppler flowmetry. During 90 minutes of anesthesia, muscle surface capillary blood flow was reduced to 20% to 40% of preanesthetic values. Muscle surface capillary blood flow tended to be lower in dependent muscles than in nondependent muscles, and this disparity was greater in the forelimbs than in the hind limbs.

The vascular and microvascular anatomy of normal equine superficial digital flexor tendons was studied by dissection of vinyl-perfused specimens and by microangiography on high detail film. The presence of an extensive intratendinous vascular latticework was confirmed, and a 'nutrient artery' described closely associated with the accessory ligament of the superficial digital flexor tendon (proximal check ligament). Circumferential stripping of the paratenon from the tendon to eliminate afferent vessels was performed bilaterally in three horses and unilaterally in a fourth, followed by a treadmill training regimen. No resulting intratendinous lesions could be documented on gross post mortem and histological examination at three, 10, or 35 days post operatively. There was mild paratendinous proliferation in all instances. In one horse, four intratendinous ligatures were placed within the medial and lateral borders of the contralateral tendon to isolate further from its blood supply a 10 cm segment. Gross lesions at 35 days post operatively included a marked paratendinous response involving the entire 10 cm segment, and a darkened, soft focus within the core of the tendon. Histopathology and electron microscopy demonstrated focal degeneration. It was concluded that the blood supply of the normal equine superficial digital flexor tendon is primarily intratendinous, rather than paratendinous as previously thought. The lesions in one horse similar to those in naturally occurring tendinitis supported a vascular aetiology of the disease, and set the groundwork for studies aimed at the development of a clinically relevant tendinitis model.

In a double-blind study under simulated racing conditions, six Standardbred horses, which had been trained for 12 weeks, were given 1 mg of furosemide/kg of body weight or saline solution IV 15 minutes before the first of two warm-up workouts (1.6 km at 60-minute intervals). Sixty minutes later, 135 minutes after drug or placebo injection, these horses were driven 1.6 km at maximum speed. Heart rate, respiratory rate, cardiac output, pulmonary trunk pressure, body temperature, PCV, arterial oxygen, and plasma lactic acid were recorded during and after the first warm-up workout and after a simulated race (1.6 km). Values increased compared with values determined at rest whether saline solution or furosemide was given. There were decreases in arterial CO2 and pH. When furosemide was given, the pulmonary trunk pressure was significantly lower (P < 0.05) during the first warm-up workout (1.6 km). There were no significant differences in the other values. The average times of the simulated races were not significantly (P < 0.05) different after the use of furosemide compared with average times after use of saline solution.

Measurements were made by real-time ultrasonography in 14 healthy mares to assess fetal growth and estimate newborn foal weights. Intrauterine fluid volumes were estimated and the placenta was measured and observed for maturational changes. The onset and incidence of echogenic particles in the allantoic fluid were recorded. In the second approach, baseline fetal heart rate, physiological rate variations and number, amplitude and duration of recorded accelerations were measured. Estimates of birth weights were within +/- 3.49 kg. Allantoic fluid was evident in all sonographic planes within the uterine cavity. Average vertical axis was 1.9 +/- 0.9 cm. The mean thickness of the ventrally located gravid uterine horn and allantochorion was 1.26 +/- 0.33 cm. No placental maturational changes were noted. Echogenic particles were observed in the allantoic fluid of all mares recorded within 10 days of foaling. Baseline fetal heart rate was 76 +/- 8 beats/min. Spontaneous fetal activity resulted in accelerations in fetal heart rate from 25 to 40 beats/min in amplitude and of 23-36 sec in duration. About 10 accelerations were observed in a 10-min period. In 17 clinical case mares, abnormal records included decreased fetal activity; lack of fetal growth; haemorrhage and fibrin-like tags in the allantoic fluid; fetal tachycardia, bradycardia, arrhythmia, and cardiac deceleration. We suggest that ultrasonic fetal measurements provide useful information with regard to the fetal condition, but additional variables are required for more reliable assessments of fetal stress and distress.

To establish the feasibility of utilizing high-frequency ultrasound to image equine fetal development transabdominally, in vitro and in vivo observations were made. Three fetuses retrieved from mares that died from various causes were scanned in vitro to establish fetal images from various orientations. A total of 50 mares ranging in age from 4 to 16 years and representing various breeds were scanned intermittently from 100 days of gestation to parturition. Fetal parts, amniotic fluid, placental membranes, and motion patterns could be reliably identified. Fetal heart rates decreased from 180 beats/min at 100 days' gestation to 60 to 80 beats/min from 2 weeks before parturition to term. Detection of fetal orientation, viability, and twin recognition represented practical applications of the technique.

The distal radial physes of 113 two-year-old Standardbreds were radiographed an average of 2.6 times each during an average of 4.72 +/- 1.7 months, beginning May 1, 1975. The radiograph of each physis was graded C, B-, B, B+, or A (closed), and the date of closure was determined by a method that proved to be reliable. The average age of closure of the distal radial physes was 29.8 +/- 1.6 months, with age of closure ranging from 26 to 35 months. There were no statistical differences between age of physeal closure of colts, geldings, or fillies; pacers or trotters; "well-bred" or other horses, or between horses by the same sires or from mares by the same sires. Most of the 2-year-old racing was done before physeal closure, the average date of closure being approximately Sept 25, 1975. The average birth date of the horses was March 30, 1973. Eighty of the horses raced an average of 10.5 times, and 46 of them won an average of 2.6 races. There was progressive increase of the number of horses in the more mature classifications (B-, B, B+, to A) as they; first raced, won their first race, went their fastest mile, won their fastest mile, and attained more spped. There was no correlation between age or month of closure of the physes and money won, races won, fastest mile, or fastest win mile during the 2-year-old year. Of the 113 horses, 62 (55%) had injuries--19 major and 57 minor injuries. A significant relationship was not found between physeal classification and the incidence of injury. The number of injuries was also found not to be related to the number of races, number of races won, money won, or to the fastest mile. There was a weak indication that horses with physes classified as C or B- (very immature) may not have raced quite as well as the more mature horses and may have had a slightly higher incidence of injury.

Ultrasonographic detection of pregnancy was performed in 952 Thoroughbred mares. Characteristic images were obtained between 12 and 55 days after breeding. Twins in the same uterine horn as well as twins in opposite horns were imaged, and for the first few months of gestation appeared similar to single pregnancies. Growth curves as a function of time were developed, utilizing horizontal diameters of the blastocysts versus breeding dates. Comparisons between horizontal and vertical diameters demonstrated no appreciable differences when observed as a group. Growth curves derived from twins did not differ significantly from those for single pregnancies during the period we observed them. Ultrasonographic evaluations were valuable in substantiating mechanical destruction of one of the twin blastocysts immediately following the maneuver. Uterine artifacts such as endometrial and lymphatic cysts also were visualized and portrayed. Although these structures represented a source of false-positive results, they usually could be properly identified on the basis of their morphometric and growth characteristics.

Echocardiograms were obtained from 25 standing, clinically normal horses, using an ultrasonic recording device. The echobeam penetrated the right thoracic wall in the area of the 4th to 5th intercostal space, with a frequency of 2.5 mHz. Measurements of left ventricular wall thickness generated a mean value of 3.2 +/- 0.18 (SEM)cm, whereas the left ventricular chamber diameter in diastole was 9.3 +/- 0.30 cm and in systole was 5.7 +/- 0.23 cm. The aortic root dimensions had a mean of 7.7 cm, with a SEM of 0.16. Mitral valve closing slope (E-F) was calculated to be 17.7 +/- 0.87 mm/second, and percentage of delta D, a correlate of ejection fraction, was 38.6 +/- 1.6%.