Variations in Heart Rate of Dairy Cows

Abstract

Heart rates were observed on 42 cows for periods varying from 2 mo. to 3 yr. The heart rate of normally-fed cows showed an increase of about 30 beats per minute during the last 3 mo. of gestation. During lactation, there was a gradual decrease in heart rate, which was similar to the milk-production decrease. When nutrients were consumed at a level above requirement there was an increase in the heart rate. During short-time trials this increase was about 3.9 beats per minute for each 10 per cent increase in T.D.N. consumed above requirement. In studies over a complete lactation this figure was about 7.7. The increase in heart rate was not immediate but gradual when extra T.D.N. were fed, the maximum was not reached for about 30 days after increased feed intake occurred. However, when a decrease in T.D.N. consumption occurs there is a large and immediate decrease in heart rate. Heart rate is in direct proportion to the total metabolism of the dairy cow. The results reported here show the importance of standardizing conditions and eliminating factors known to affect heart rate, in order to properly evaluate the results when determining heart rate. © 1951, American Dairy Science Association. All rights reserved.