AJP - Regulatory, Integrative and Comparative Physiology, Vol 257, Issue 6 1303-R1306, Copyright © 1989 by American Physiological Society
Heart rate spectral analysis of fasting-induced bradycardia of cattle
D. L. Clabough and C. R. Swanson
Department of Food Animal and Equine Medicine and Surgery, College of Veterinary Medicine, North Carolina State University, Raleigh 27606.
The autonomic mechanisms of fasting-induced bradycardia of cattle were
studied using heart rate spectral analysis. This was performed on
digitized, lead II, surface electrocardiograms from conscious, fed, and
48-h-fasted adult cows. Fasting resulted in a significant (P less than
0.05) decrease in resting heart rate and a significant (P = 0.0041)
increase in low frequency (0-90 mHz) power spectral area. Administration of
atropine sulfate (0.02 mg/kg iv) in either the fed or fasted state resulted
in a significant (P less than 0.001) decrease in both low-frequency and
high-frequency (100-400 mHz) power spectral areas. Significant (P less than
0.05) increases in serum total bilirubin, inorganic phosphorus, and total
protein were associated with fasting. Significant decreases were seen in
fasting serum aspartate aminotransferase and potassium values. Manual
evacuation of the rumen of seven steers with chronic rumen fistulae
resulted in a mean percent decrease in heart rate of 22 +/- 0.9% (mean +/-
SE). These results indicate that in normal cattle a decrease in
ruminorecticular fill results in a reflex slowing of the heart rate, due
predominantly to an increase in parasympathetic tone.
