Özet:

The results of studies of biological features of 66 cows of Holstein breed with different reaction levels to stress have been quoted. The stress factor was the planned blood taking from them. In an hour after this procedure, blood was taken again from the jugular vein with the aim to determine the concentration of cortisol in experimental animals. Based on the different cortisol concentration in blood, the cows have been differentiated into three groups: I – with high stress resistance, II – with medium stress resistance and III – with low stress resistance. The aim of the studies was to establish the relationship between the different stress resistance in animals and the development and function of the udder, the milk productivity and the heat resistance of the organism under summer temperature loading in the conditions of Ukraine. It has been established that the animals of group I were milked in double-quick time (P <0.001), and their milk-ejection rate was 1.4 kg/min (P <0.001) compared to the third group. They also had a higher reaction rate at the beginning of milking (P <0.001). The parts of the udder in the cows of this group are more evenly developed, which serves as the best precondition for the implementation of the milk flow reflex by machine milking. Cows with low stress resistance have a well-defined prolonged latent period at the beginning of machine milking. This is explained by the delay in the reaction of their mammary gland in response to the beginning of milking. It has been suggested that this disadvantage can be mitigated by using a more improved milking equipment, with an udder massage regime, which is capable to compensate the disturbance of the milk yield reflex in cows, which are more sensitive to stress. The influence of different stress resistance on fat and protein content in the milk of Holstein cows has not been properly defined. But in comparison with low stress-resistant animals, milk yields for 305 days of the first lactation were higher in highly stress-resistant animals – by 639 kg (P <0.001), in cows of the middle group – by 216 kg (P <0.05). The lower resistance of cows to stress makes them vulnerable in conditions of temperature load during the hottest months (July, August) of the summer period in Ukraine. Their body reacts to such a load with sharper fluctuations in body temperature, pulse, respiration rate and thermal sensitivity index as compared to their peers with high level of stress resistance (P <0.01...0.001). To solve this problem with trans-humance grazing it is possible to use mobile canopies.

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