Asymmetric time interval between evening and morning milking and its effect on the total daily milk yield

Samples of milk obtained in the course of evening and morning milking performed in variable time intervals of either 11 and 13 hours (n = 1,282) or 10 and 14 hours (n = 370) were collected with the aim to quantify the effect of the length of a variable (asymmetric) time interval between evening and morning milking on the total amount and composition of daily milk production of dairy cows. Milk samples were analysed in an accredited (EN ISO 17025) laboratory in Brno-Turany (Czech Republic) and the following contents of individual milk components were estimated: fat, total protein, lactose, and somatic cell counts. It was found out that with the increasing total daily milk production the shares of evening and morning milk yield increased as well; however, the percentages of evening and/or morning yields in the total yield remained practically unchanged and represented 43.5 % and 56.5% or 40.4 % and 59.6 % in variants with intervals of 11 and 13 hours and/or 10 and 14 hours, respectively. In the variant with the milking interval of 11 and 13 hours, values of correlation coefficients between the studied components of evening and morning milk yields on the one hand and the total milk performance on the other hand ranged from the minimum r = 0.896 (fat) to the maximum r = 0.980 (total protein). In the variant with the interval of 10 and 14 hours, the corresponding values of correlation coefficients were r = 0.848 (fat) and r = 0.983 (total protein). These correlations were significant in all cases. Further, linear regression equations enabling the estimation of milk characteristics of the total milk yield on the base of results obtained in evening and morning milking was calculated as well. The values of coefficients of determination of these equations ranged from 0.803 (fat) to 0.960 (total protein) and from 0.718 (fat) to 0.966 (total protein) for intervals 11:13 hours and 10:14 hours, respectively.