The period pregnancy data were taken from 580 cows-mothers of bulls neb race after investigations it was ascertained that length of prenatal period has inflowed in postnatal period following elements: day increment of bulls (r = 0.10ˣ); using of feed on unit of increment (r = -0.13ˣˣ); hauch high (r = -0.17ˣˣ), and breast circumference (r = 0.33ˣˣˣ).
Analysis were embraced 1810 deliveries of calves neb race. Calf losses made by nearbydelivery mortality reached 8.73% and depended on origin of father (from 0 to 17%); age of first delivery cow in the delivery day; next delivery of mother (r = -0.26); length of pregnancy (first delivery cow r = 0.16, multiple delivery cow r = 0.26); sex of calves; course of delivery (from 5.2 to 65%); season of born; flock population (r = -0.12).