|Spiers, Don - UNIVERSITY OF MISSOURI|
Submitted to: International Symposium on Fungal Endophytes of Grasses
Publication Type: Abstract Only
Publication Acceptance Date: September 5, 2006
Publication Date: March 25, 2007
Citation: Kirch, B.H., Aiken, G.E., Spiers, D. 2007. The influence of temperature variation upon vascular dynamics in cattle as measured by doppler-image ultrasound. Proceedings of the 6th International Symposium on Fungal Endophytes of Grasses. p 383-385. Technical Abstract: Two preliminary studies were performed to determine if Doppler-image ultrasound can be used to document the vascular changes of cattle under hot and cold conditions. At the Brody Environmental Center located at the University of Missouri, three calves per study (320 ± 38 kg) were acclimated to thermoneutrality (17.5oC). In each animal, three replicated ultrasound measurements of the median caudal artery were taken at the 4th coccygeal vertebrae (Cd4) using a 13 MHz transducer. The animals were then exposed to air temperatures above (32oC) and below (8oC) this neutral level. The animals were housed under these conditions for 24 h and then returned to the original thermoneutral level. Ultrasound scans were repeated at -2 (2 h prior to temperature change), 5, 23, 24 and 28 h (4 h after returning to thermoneutrality). Blood flow rates of heat stressed cattle significantly increased from 39.12 (-2 h) to 59.87 cm/min at 23 h of exposure (P < 0.05). The vessel diameter tended (P> 0.10) to increase (0.047 to 0.063 cm2) with the onset of the stress. Heart rate was unchanged throughout the study, but respiration rate did increase from 82 to 120 breaths/min during heat stress (P < 0.05). Cattle at 8°C showed lower flow rates to the caudal artery after 23 h of exposure (P < 0.10) (30.73 at -2 h to 18.44 cm/min at 23 h). Blood flow rates of these cattle initially increased after the challenge. At 5 h post-temperature reduction, flow rates were 53.9 cm/min, increasing over the baseline of 30.7 cm/min (P < 0.07). At 8°C, the heart rate averaged 79 beats/min and was unaffected across all five scan periods. Respiration rate decreased from 62 at -2h to 36 breaths/min at 23h (P< 0.05) when housed under cool conditions. Arterial area increased from 0.057 to 0.072 cm2 at 5 h (P < 0.07) exposure to 8°C then decreased to 0.043 cm2 at 23 h. The Doppler-image ultrasound was able to detect vascular changes due to slight environmental variation and demonstrated its usefulness as a tool for assessing environmental stress effects on hemodynamics.