The aims of this study were to determine the relationship (1) between oxytocin release during parturition especially during the third stage of labor and placental retention time, and (2) between hand-milking or suckling and oxytocin release after foaling. Blood was sampled every 5 min from foaling to expulsion of the placenta in 9 heavy draft mares to evaluate circulating oxytocin. The relationship between the oxytocin concentration and recorded placental retention, hand milking and suckling times were investigated. Results: (1) High peak of oxytocin concentration observed around foaling in 7 mares. (2) Peaks of oxytocin were observed after expulsion of the placenta and suckling or after hand-milking about 2 hr after foaling in 2 mares. (3) The mean oxytocin concentration in mares which, had a shorter placental retention time (i.e.<1 hr) was significantly lower than that of mares which had a longer placental time (i.e.>1 hr). (4) A significant negative correlation was observed between oxytocin concentrations immediately after foaling and placental retention times. (5) Oxytocin increased distinctly after hand-milking and suckling in 2 mares. The response was most extensive in the mare, which had the lowest oxytocin concentration immediately after foaling and the longest placental retention time. In conclusion, the oxytocin concentration immediately after foaling is negatively related to the placental retention time. Low circulating oxytocin immediately after foaling may result in placental retention.
We examined total sweating rate (SR) and the amount of mineral (Na, K, Ca, Mg, Fe, P, Zn and Cu) loss through sweat in 2-year-old horses during exercise for approximately 2,000 m at a speed of 700 m/min, at cool ambient temperature. The total SR was estimated by the unit area SR on the neck by filter paper within a capsule. Mean total SR was 1.55 ± 0.47 (SD) kg. The ratio of sodium loss to the requirements reported by National Research Council reached 23% and that of potassium was 7%. The ratio of other mineral losses to the requirements reported by National Research Council was 2% or less. These results suggested that sodium had to be supplemented to the horse, but there was no need to add extra minerals to the diet to compensate for mineral losses of calcium, magnesium, iron, phosphorus, zinc and copper through sweat during exercise with light intensity and at a cool ambient temperature.
The objective of this preliminary study, conducted before a study to determine the total sweating rate (SR) of a horse during exercise, was to estimate the differences in the SR through unit area among different areas of the body of a horse during exercise, and to determine the existence of correlations, if any, among the values. The unit area sweating rate on the neck, shoulders, back, loins and flanks was monitored using filter paper layers fitted within a plastic capsule. The values of the SR through unit area on the neck and shoulders were found to be higher than those in other areas of the body. The varying sweat rates in different areas of the body indicates that it is difficult to estimate the total SR of an exercising horse by multiplying the SR through unit area in one area of the body by the total body surface area. On the other hand, the SR through unit area on the neck was correlated significantly with that in other areas of the body, suggesting the potential possibility of estimating the total SR from the SR through unit area determined on the neck region. In addition, measurement of the SR on the neck was also thought to be appropriate from the point of view of ensuring absence of interference with the rider.
In track testing of aerobic fitness in the racehorse, the measurement of heart rate and running speed is essential. In this study, we examined EquiPILOT®, an automated recording system which measures those two variables, for its reliability during the racehorse training. After some adjustment for fitting, it has been shown that the speed measured by this system is very accurate, and that its measurements of heart rate and running speed are stable. Based on our data, the EquiPILOT® has been proved reliable for assessing aerobic capacity of running racehorses on the track.
We conducted this study to determine the influence of bolus injection of thiopental sodium on cardiovascular function under general anesthesia in the horse. Thiopental sodium was administered to three horses as a bolus injection at the dose of 1 or 2 mg/kg, while anesthesia was maintained by continuous infusion of a mixture of guaifenesin, xylazine and ketamine. One minute after bolus administration of the drug at 2 mg/kg decrease in the respiratory frequency and mild decrease in mean arterial pressure was noted, although no change of tidal volume, the heart rate, stroke volume and cardiac output were present. These results indicate that bolus injection of thiopental sodium does not produce any serious cardiovascular changes for clinical use under general anesthesia in the horse.