For an effective, in determining the index „Calving Interval“ we take into consideration the two components of each interval: service period (SP) and duration of gestation (DG). In order to obtain the optimal interval between calving (365 days) the cow should become gestant at 81 days after calving, because along with 284-285 days, length of gestation, to provide 305 days for normal lactation and 60 days for the rest of the breast enough for the formation of the udder for the next lactation.
The frequency curve has a single peak, 43.5% placed around 361 days after which the frequencies fall along a period of time long enough. The probably average of „CI“ of 360 days, which corresponds to the class with highest frequency, shows that the fecundity is good and that it can provide a rest for brest for 55 days in the case of normal lactations of 305 days.
The 42 days difference between the arithmetic mean of the „CI“ (402 days ago) and the likely media (360 days) is caused by the presence of breeding disorders. The large values of the coefficient of variance is due to the very long ranges as well as very short intervals of calving interval.