Heart rate, activity periods and blood measures in pregnant, non lactatingcattle kept on pasture

Long term heart rate recordings (Polar Sport tester) were made repeatedly a t the middle and at the end of a period at grass on 65 pregnant, non-lactat ing cattle. Venous blood samples were taken at the end of the pasture perio d and analysed for acid-base balance status, gas content and pressure, haem oglobin, haematocrit, total protein, albumin, blood urea and creatinine con centrations. Two complete 24 hour rate recordings were obtained for forty-o ne animals, of which five proved to be non-pregnant. Heart rate recordings ere used to identify activity and rest periods of the animals and to establ ish characteristic HR values, which were classified by 3-hour day-time peri ods. Activity periods were prolonged by between 3 and 12 hours and were dim inished between 18 and 21 hours. Rest periods were shortened within the cor responding day time. Characteristic heart rate values exhibited great inter -animal variation and increased significantly between 15.00 and 21.00 hours , only, during the first run. HR values were significantly different betwee n activity and rest periods within all time periods and between the two run s at the middle and end of the period at pasture. A significant correlation was apparent between the estimated time to calving and the characteristic heart rate values, which were stronger when animals were resting. This effe ct was more marked in the second run. There was also a significant negative correlation between HR values and total plasma protein concentration. Moto r activity and functional adaptation to pregnancy proved to be the main det erminant of HR values in pregnant, non-lactating cattle at pasture.