|Spiers, Don - UNIV OF MISSOURI|
Submitted to: Journal of Thermal Biology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 2, 2008
Publication Date: June 14, 2008
Citation: Kirch, B.H., Aiken, G.E., Spiers, D.E. 2008. Temperature influences upon vascular dynamics in cattle measured by doppler ultrasonography. Journal of Thermal Biology. 33(7):375-379. Interpretive Summary: Two studies were performed using cattle to look at the ability of ultrasound to detect changes in blood vessels and flow of blood in cattle living in hot or cold environments. This study has been initiated to look at the feasibility of using ultrasound to detect blood vessel changes in cattle eating tall fescue grass. When cattle consume tall fescue grass the blood vessels of the animal will constrict and restrict blood flow to the appendages of the animal. Cattle grazing tall fescue grass can develop high body temperatures and will not graze and grow as desired. To validate the use of ultrasound, we needed to verify that it would detect even subtle changes when looking at blood flow in the tail of the cow. In these studies cattle were place in housing at 46 or 90oF for 24 hours. The changes in blood flow were check throughout the study. Changes were detected by ultrasound in cattle housed in cold and hot temperatures. In the cold, the artery of the tail decreased in diameter and flow also decreased to conserve internal body temperature. In the hot temperature, the artery of the tail expanded in diameter and flow increased to dissipate excess heat from the animal. This verified that the ultrasound technology had the sensitivity to identify changes in the blood vessels of the cow’s tail when placed under moderate temperature changes for short periods of time. Ultrasound will make a very good tool to study the changes due to toxicosis, such as tall fescue grass toxicosis, in the vessels of the cow. This will give the researcher a tool to further study the effects of such toxicosis and to develop strategies to manage animals under such conditions. It will allow producers and veterinarian to identify cattle that are stressed from fescue grass toxicosis and to evaluate management strategies to avoid lost production when utilizing tall fescue grass in their grazing programs.
Technical Abstract: Two preliminary studies were performed to determine if Doppler-image ultrasonography can be used to document vascular changes of cattle under hot and cold conditions. Three calves per study (320 ± 38 kg) were acclimated to thermoneutrality (17.5oC). Ultrasound measurements were taken of the median caudal artery at the 4th coccygeal vertebrae (Cd4) using a 13 MHz transducer. Animals were exposed to temperatures above (32oC) and below (8oC). Animals were maintained for 24h and returned to thermoneutrality. Ultrasound scans were repeated at -2 (2h prior to temperature change), 5, 23, 24 and 28h (4h after returning to thermoneutrality). Blood flow rates of 32oC cattle significantly increased (P<0.06) from 27.84 (-2h) to 43.42 mL/min at 23h of exposure. The vessel diameter tended (P>0.10) to increase (0.047 to 0.063 cm2) with stress. Heart rate was unchanged, but respiration rate increased (82 to120 breaths/min) during stress (P<0.05). Cattle at 8°C showed lower (P<0.05) caudal artery flow rates after 23h exposure (29.29 at -2h to 13.79 mL/min at 23h), following an increase after the challenge. At 5h, flow rates were 44.11 mL/min, increasing (P<0.05) over the baseline 29.28 mL/min. At 8°C, heart rate was unchanged (79 beats/min) across five time periods, while respiration decreased (P<0.05) (62 to 36 breaths/min) under stress. Arterial area increased (P<0.07) from 0.057 to 0.072 cm2 at 5h of 8°C then decreased to 0.043 cm2 at 23h. The ability of Doppler-image ultrasound to detect vascular changes due to environment demonstrates its use as a tool for assessing environmental stress on hemodynamics.