Effects of 7.2% hypertonic saline solution on cardiovascular parameters and endogenous arginine vasopressin secretion in euvolemic isoflurane-anesthetized horses.

OBJECTIVE: To compare the effects of 7.2% hypertonic and 0.9% isotonic saline (sodium chloride) solutions on cardiovascular parameters and plasma arginine vasopressin (AVP) concentrations in healthy, isoflurane-anesthetized horses. ANIMALS: 8 healthy horses. PROCEDURES: In a prospective, randomized, crossover study, horses were anesthetized with isoflurane twice with a 14-day washout period between anesthetic episodes. While anesthetized, horses received a bolus (4 mL/kg) of 7.2% hypertonic saline solution (HS) or 0.9% isotonic saline solution (IS). Heart rate; systolic, mean, and diastolic arterial blood pressures; and central venous and pulmonary artery pressures were measured every 5 minutes; cardiac output was measured by means of thermodilution every 15 minutes. Systemic vascular resistance (SVR) was calculated. Blood samples were collected before and during anesthesia, and plasma AVP concentrations were determined with a validated ELISA. Data were analyzed with repeated-measures ANOVA and Pearson correlations. RESULTS: HS caused an increase in systolic (P = .003) and mean (P = .023) arterial blood pressures that lasted for 30 minutes. The SVR was increased (P < .001) for 45 minutes with HS compared with the SVR after IS administration. Mean plasma AVP concentration increased (P = .03) 15 minutes after HS administration, with the increase lasting 90 minutes. CLINICAL RELEVANCE: A bolus of HS resulted in a clinically relevant increase in blood pressure in healthy, isoflurane-anesthetized horses. This effect was attributed to volume recruitment and an increase in SVR. Administration of HS offers an option for improving arterial blood pressure in anesthetized horses.

Effect of exercise and environmental terrain on development of the digital cushion and bony structures of the bovine foot.

OBJECTIVE: To determine whether exercise on alternative terrain affects the development of the digital cushion and bony structures of the bovine foot. ANIMALS: 20 weaned bull calves. PROCEDURES: Two-month-old calves were randomly allocated to an exercise or control group. For 4 months, the control group was maintained in grass paddocks, and the exercise group was maintained in a 0.8-km lane with a mixed terrain of dirt, stones (0.32- to 0.95-cm pea gravel and 5-cm crusher run), and grass. Water and food for the exercise group were located at opposite ends of the lane; calves were fed twice daily, which ensured they walked 3.2 km/d. Pedometers were applied to all calves to measure distance traveled. All calves were slaughtered at 6 months of age. The right forefeet and hind feet were harvested for MRI and CT evaluation. RESULTS: Control calves walked a mean of 1.1 km daily, whereas the exercised calves walked a mean of 3.2 km daily. Mean digital cushion volume and surface area were 25,335 mm(3) and 15,647 mm(2), respectively, for the exercised calves and 17,026 mm(3) and 12,745 mm(2), respectively, for the control calves. When weight was controlled, mean digital cushion volume and surface area for the exercise group were increased by 37.10% and 18.25%, respectively, from those for the control group. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicated that exercise on alternative terrain increased the volume and surface area of the digital cushion of the feet of dairy calves, which should make them less susceptible to lameness.