Herzfrequenz, Aktivitäts- und Ruhezeiten sowie Wachstumsleistung von in Gruppen mit Tränkeautomatenfütterung gehaltenen Milchrindkälbern während der Aufzucht im Winter und Frühjahr

Abstract. Title of the paper: Heart rate, activity and resting times and growth in group reared feeder-fed dairy calves reared at transition from winter to spring
To characterize the food entrainable oscillator and/or light entrainable oscillator determined rhythmicity of physiological variables of feeder-fed dairy calves reared at transition from winter to spring (35 German Holstein Friesian, 2 German Red Pied, 17 male and 20 female) long term heart rate recordings were taken at 5 , 15, 40 and 60 days of age using Polar Sport Tester, from which the number and duration of activity (ZDA) and rest periods (ZDR) and the total activity (GZA) and rest times (GZR) could be established. For these periods characteristic heart rate values were calculated (HFA and HFR) and they were analysed for daytime periods of three hours duration at different life ages. HF of feeder-fed dairy calves showed substantial interindividual variation and a high individual specificity. Mean HFA and HFR were significantly smaller at 15 and 40 days then at 5 and 60 days of age. HFA and HFR showed a high correlation and the mean values of HFA and HFR were allways significantly different. More profound increases of HF (HFA-HFR) could be observed at feeding and service times. Individual level of HFA and HFR changed regularly with daytime, but mean values were significantly different between daytime periods only at some age points. Deviation of HFA and HFR from the mean of the individual daytime heart rate recording followed a circadian rhythm that became more obvious with advanced development and adaptation of the animals in case of HFA and HFR. For the means of the deviations of HFA and HFR significant differences between the daytime periods could be found. The mean ZDA and the quotient GZA/GZR were greater at 40 and 60 days of age then at 5 and 15 days of age. ZDA and ZDR showed great variation and presented rhythmic changes during the course of the day. The means of ZDA and ZDR were significantly different between the daytime periods of three hours duration at the age points excluding that of ZDA for 15 days of age. Results show the establishment and the prevalence of a circadian rhythm of heart rate at the early growth period in feeder-fed dairy calves reared at transition from winter to spring and how this was superimposed by feeding activity around the programmed daytimes of feed access at the start of rearing.