ON THE MATTER OF MILK SECRETION INTENSITY BY COW’S MAMMARY GLAND
Authors: Kostenko V. I. 
Published: April 2021

The secretion of milk in the intervals between milkings has its own patterns, and therefore researchers have different opinions about the intensity of the secretory process. Some scientists believe that the secretion of milk is uneven. Immediately after emptying the udder, it is higher, and with increasing interval, the intensity of the secretory process decreases, i.e. it is curved. This issue is still not clarified scientifically. The aim of our research was to study the change in the intensity of milk secretions during lactation under the condition of "voluntary", physiologically motivated emptying of the mammary gland and its frequency. The study of changes in the intensity of milk secretion during lactation under conditions of "voluntary" emptying of mammary gland in Holstein cows of different ages and levels of milk productivity was evaluated by using automatic milking control system based on electronic meters "Fullflow", which is mounted and functions in the milking unit VMS - 2012. Analyzing the nature of the secretory activity of the mammary gland of the first-born cow during lactation, we found that even under the condition of "voluntary" emptying, the intensity of the secretory process decreases. The average value of the intensity of milk secretion per hour during the first five months was quite close (1192.1 ± 33.51… 1105.6 ± 24.63) and only starting from the sixth month, it decreases initially by 17.3%, in comparison to the first month of lactation, and for the ninth month of lactation - by as much as 31.0%. In addition, there were significant fluctuations in the intensity of milk secretion for individual milkings during each month of lactation. Thus, the difference between the minimum and maximum values of the intensity of milk secretion by the mammary gland was the largest in the first month of lactation – 4.65 times, and the smallest - in the sixth month – 2.22 times. This indicates that the intensity of milk secretion even in the condition of "voluntary" emptying of the mammary gland is influenced by both internal and external factors, and above all – the conditions in which cows are fed, kept and exploitated. All this did not allow the animal to realize the functionality of the secretory epithelium of the mammary gland to the maximum possible secretory process for each day of lactation. Thus, under the relatively optimal parameters of these conditions, the average daily milk yield in the first month of lactation should be more than 65.0 kg of milk, with the actual – 25.7 kg, or 2.56 times higher. A similar pattern is observed during all months of lactation, where this difference ranges from 1.67 to 1.93 times. No less important, in our opinion, is the question of the time of emptying the mammary gland during the day. We found out that during lactation, mammary gland emptying occurs at all hours of the day without exception, although with varying frequency. Thus, more than 5.0 % of mammary gland emptying occurred: from 0 to 1 o’clock, from 7 to 8, from 10 to 12, from 17 to 18 and from 21 to to 22 o'clock. The rarest (1.74 %) mammary gland emptying occurred from 9 to 10 o'clock. Also, less than 3.0 % of emptying were observed from 4 to 5 and from 19 to 20 o’clock. On average per day, the emptying of the mammary gland in first-born cows occurred 3.5 times, and depending on the month of lactation ranged from 4.2 to 2.7 times. So the assessment of the intensity of the secretory process in the mammary gland can be a criterion for establishing genetic capabilities to the productivity of each animal and the time of milking during the day practically has no effect on the secretory process in the cow's mammary glands.