Equine veterinary journal. Supplement最新文献

The objects of this study were to monitor the development of the cumulus complex and nuclear maturation in oocytes recovered from preovulatory follicles following treatment to induce ovulation and to investigate the in vitro maturation competence of oocytes recovered from smaller nonpreovulatory follicles of varying size. All follicles > or =5 mm in pony mares were individually punctured at 0, 6, 12, 24 and 35 h after an injection of LH to induce ovulation. The recovery rates of oocytes were 64% from 55 preovulatory follicles, 22% from 32 subordinate follicles and 52% from 227 small follicles. Cumulus expansion of the preovulatory oocytes occurred at 12 h post LH treatment while the metaphase I and II components of nuclear maturation were not completed until 24 and 35 h post LH respectively. For nonpreovulatory follicles, the frequency of atresia and oocyte competence for in vitro nuclear maturation both increased with increasing follicular size.

The mammalian fetus is maintained hypercalcaemic relative to its mother primarily by the action of a placental calcium pump located in the basal plasma membrane of the trophoblast. It is suggested that the activity of this pump is stimulated by a mid-molecular fragment of parathyroid hormone-related protein [PTHrP(38-94NH2)], produced in the placenta (and also in the parathyroid glands of fetal lambs and calves) as a result of post translational processing. In the sheep, calcitriol is an important determinant of fetal calcium homeostasis and it, too, stimulates the transport of calcium across the placenta. Fetal bone resorption is under the control of calcitriol, parathyroid hormone (PTH) and PTHrP. This resorption is modulated by the inhibitory effect of calcitonin. PTHrP also plays an important role in the regulation of endochondral ossification and chondrocyte maturation.

The aim of the present study was to determine the effect of different environmental conditions on physiological response to exercise. Four winter acclimatised, nonheat acclimated horses of different breeds were exercised at 20 degrees C/40% RH (CD), 30 degrees C/40% RH (HD) and 30 degrees C/80% RH (HH). The exercise test was designed to represent the structure and intensity of a One star Speed and Endurance test (competition exercise test [CET]). All 4 horses were able to complete the full CET (60 min + 30 min active recovery) in CD and HD, but only one horse completed the CET in HH. Two horses were stopped because of pronounced general fatigue and one because of a right atrial temperature (TRA) of 43 degrees C. Oxygen uptake on each phase was not different between CD and HD, but was higher during Phases B, C and D in HH. Mean peak TRA at the end of Phase D was 40.3 +/- 0.2, 41.6 +/- 0.4 and 42 +/- 0.3 degrees C for CD, HD and HH, respectively. Corresponding, mean peak rectal temperatures (TREC) following Phase D were 39.5 +/- 0.1, 40.6 +/- 0.1 and 41.5 +/- 0.1 degree C for CD, HD and HH, respectively. Mean time to peak TREC was 9.3 +/- 1.1 (CD), 7.3 +/- 1.8 (HD) and 10.8 +/- 2.3 (HH) min and was not significantly different between conditions (P > 0.05). Heat dissipation amounted to 83 +/- 1, 73 +/- 2 and 70 +/- 1% of heat production in CD, HD and HH, respectively. Weight loss was significantly correlated with both body surface area (CD r = 0.85; HD r = 0.87; HH r = 0.81) and bodyweight (CD r = 0.97; HD r = 0.93; HH r = 0.94). The greatest weight loss recorded was 4.6% bodyweight in one horse in HD. The mean increase in exercise intensity over the whole CET (in terms of VO2) of HD and HH and HH compared with CD was 5 +/- 3 and 14 +/- 3% higher, respectively. The exercise induced hyperthermia and the reduced capacity for heat dissipation produced partial compensatory responses in minute ventilation (VE), particularly during Phase C, when the horses were trotting. In HD, the increase in VE was achieved mainly through an increase in frequency, whilst in HH it was achieved through an increase in tidal volume (VT). The horses demonstrated a high degree of tolerance to environmental heat load, suggesting a high thermoregulatory capacity. However, for unacclimatised animals exercising in severely hot and humid conditions, performance may be limited.

Four horses (H, J, N and M) undertook a treadmill competition exercise test (CET), designed to simulate the physiological and metabolic stresses of the Speed and Endurance phase of a 3-day-event, under 3 different environmental conditions: 20 degrees C/40% relative humidity (RH) (cool, dry [CD]: 2 sessions); 30 degrees C/40%RH (hot, dry [HD]) and 30 degrees C/80%RH (hot, humid [HH]) (Marlin et al. 1995). A number of subjective clinical observations were made at designated time points throughout the exercise test and initial recovery period including buccal mucous membrane colouration, capillary refill time, neck and point of shoulder skin pinch recovery time, grade of abdominal sounds; anal sphincter tone as well as the presence or absence of fatigue and ataxia. The aim was to investigate their value in predicting performance in the final canter phase of the CET equivalent to the cross-country or Phase D of a field competition. In addition, the use of a more objective assessment, the cardiac recovery index (CRI), was investigated together with the heart rate, rectal temperature and respiratory frequency at the end of Phase C and at the 8 min point of the 10 Minute Box (8'X). The CRI was calculated according to the formula CRI = P2-P1 where P2 = the heart rate in beats/min at the 8 min point of the '10 Minute Box' (Phase X) of the CET. P1 = the heart rate (beats/min) at the 7 min point just before the horse was made to trot over a distance of 80 m at a speed of 3.7 m/s (at a 3 degrees incline) before returning to a walk. The study suggested that the subjective tests carried out at the 'End-C' and/or '8'X' time points were not useful in predicting subsequent performance in the final canter phase (Phase D) and neither were heart rate, rectal temperature or respiratory frequency. However, the only horse (Horse H) to complete the full CET under HH conditions was the only animal to show a decrease in respiratory frequency between the End-C and 8'X time points. All others showed an obvious increase. Under HH conditions, Horse H also had the lowest CRI. For 3 of the horses the highest CRI value was found under the HH conditions, for the fourth horse an equally high CRI value was found with one of the CD sessions. However, under the HH conditions, both P1 and P2 values were > 100. The study suggested that it could be beneficial if a suitably modified CRI test, as well as a procedure to monitor the change in respiratory frequency during the 10 Minute Box, were evaluated further on the treadmill and in the field with respect to their potential usefulness as additional aids to the assessment of a horse's suitability to proceed to Phase D.

Four horses (H, J, N and M) undertook a simulated competition exercise test (CET), designed to simulate physiological and metabolic stresses of the Speed and Endurance (S & E) test of a 3-day-event, under 3 different environmental conditions: 20 degrees C/40% relative humidity (RH) (cool, dry [CD] 2 sessions); 30 degrees C/40% RH (hot, dry [HD]) and 30 degrees C/80% RH (hot, humid [HH]) (Marlin et al. 1995a). Venous blood samples for electrolyte and total protein (TP) determinations were collected from indwelling catheters at predetermined time points throughout each CET and initial 30 min recovery period. Venous blood samples were collected by jugular venepuncture at 2 h and 24 h after the end of the final 8 min canter (Phase D). The effects of exercise, environmental condition and horse on venous TP, sodium (Na+), potassium (K+), chloride (Cl-), calcium (Ca2+), magnesium (Mg2+) and phosphate (PO4(3-)) plasma concentrations were investigated. In addition, the effect of environmental condition on estimated cation loss was evaluated. All horses completed the full CET under the CD and HD conditions, but only one horse completed the full 8 min of the final canter Phase D under HH conditions. Exercise had a significant (P < 0.05) effect on all parameters similar to those reported previously in field competitions. There was a significant (P < 0.05) interaction between time and horse for TP, Na+ and Cl-. Overall, the environmental condition had a significant (P < 0.05) effect on all parameters, but the differences were not considered to be of any physiological relevance, other than for Cl- and TP. There was a significant (P < 0.05) interaction between time and environmental condition for Cl- and TP only. During much of the CET and recovery period, mean Cl- values were higher with the first CD session than the second CD session or under the HH or HD conditions. For TP after 2 min of Phase D and during the initial recovery period, concentrations were higher under the HH conditions and returned to the Pre- values less quickly. There were marked individual variations in the estimated cation losses and no consistent effect of environmental condition was found. Although estimated fluid loss was similar following both HD and HH sessions, restoration of bodyweight was slower following the CET studies under HH conditions.