The period from the breeding of a cow to the birth of a fetus is called pregnancy. The average period of dairy cows is 280 to 285 days. The length of pregnancy period is related to the breed, age, gender, number and environmental factors. The period of early maturing breeds is generally slightly shorter, while the period of late maturing original breeds is generally slightly longer. In addition, the period of youth cows is 3 days shorter than that of multiparous cows, cows with female calves have 2 days shorter than cows with male calves, and with twins have 4 days shorter than single. In the case of insufficient nutrition, the cow's period is slightly longer.
The calving period of the cow is calculated from the last day of artificial insemination, plus the average number of days of pregnancy, which is the expected delivery period of the cow; it can be calculated by the method: expected month=breeding month minus 3(-3); expected date=breeding date plus 6 (+6). That is to say, the pre-production month is the breeding month minus 3; the pre-production date is the breeding date plus 6.
For example, a cow was bred on June 18. The expected date is:
Pre-production month = 6-3 = 3 (month)
Pre-production date = 18 + 6 = 24 (date)
Means that the cow is expected to calve on March 24 of the following year.
When the breeding month is less than March (3), the calculation method of the pre-production month is: the breeding month plus 12 and then minus 3; when the breeding date plus 6 is greater than the number of days in the month, then the number of days in the month is subtracted, the remainder is the date of next month.
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