Abstract
1. The average length of gestation in Friesian cattle under Egyptian conditions was found to be 282·28 ± 10·7 days. 2. Neither the sex of the newborn calf nor the season of the year affects the gestation period significantly. 3. The average interval between calving and the first post-partum heat was found to be 85·52 ± 2·15 days. 4. The sex of the newborn calf does not affect significantly the interval of heat after calving whereas the month and the season of the year of calving affect this interval significantly.