Gestation length varies by age of dam, breed, and sex of the calf. Gestation length ranges from 279 to 287 days. For most breeds, 283 days is common. Cows carrying bull calves tend to have a slightly longer gestation compared to cows carrying heifer calves. First-calf females tend to have a shorter gestation than mature cows, but that may be due to their being bred to calving-ease bulls, and they may be calving easier because they sire calves that are in utero for a shorter length of time.