The influence of temperature variation upon vascular dynamics in cattle as measured by Doppler-image ultrasonography

Abstract

Two studies were performed to determine if Doppler ultrasound can detect vascular changes in cattle exposed to hot and cold conditions. Three calves per study (320±38 kg) were acclimated to 17.5oC, and then exposed to 32oC and 8oC. Animals were maintained under these conditions for 24 h and then returned to the original thermoneutral level. Three replicated ultrasound measurements of the median caudal artery were performed. Scans were repeated at -2, 5, 23, 24 and 28 h. Blood flow rates of 32oC cattle ranged from 27.84 (-2 h) to 43.42 ml/min at 23 h (P<0.05). Heart rate was unchanged, but respiration increased from 82 to120 breaths/min at 32oC (P<0.05). Cattle exposed to 8°C showed lower flow rates after 23 h of exposure (P<0.10) (29.29 at -2 h to 13.79 ml/min at 23 h). Blood flow rates of these cattle initially increased after the challenge. At 8°C, the heart rate was unaffected. Respiration rate decreased from 62 at -2h to 36 breaths/min at 23h (P<0.05) when housed under cool conditions. Arterial cross-sectional area increased from 0.058 to 0.076 cm2 at 5 h (P<0.05) exposure to 8°C then decreased to 0.043 cm2 at 23 h. The ability of the Doppler-image ultrasound to detect vascular changes demonstrates its use as a tool for assessing environmental stress effects on haemodynamics. Keywords: tall fescue, Doppler-ultrasound, cattle