Breeding efficient cows is usually measured by a cow’s ability to calve each year and maintain a yearly calving interval.
As an example, a cow who provided a calf on Feb.14, 2023, and turned around and provided another one on Dec. 20, 2023, has reached the pinnacle of reproductive efficiency.
Normal beef cow gestation length is 283 days; subtracting those number of days from the latest calf puts conception for March 12. Subtracting this conception date to the Valentines’ Day calf’s birth only allows for 26 days of uterine involution and recovery from the previous birthing process.
This is quite unusual. In the example, management has bulls exposed to the cows during a limited breeding season resulting in a defined calving season, so apparently there was a visitor during the night to allow this immaculate conception to occur.
This example shows that selecting for reproductive efficient cows can be achieved. A recordkeeping goal could be to keep track of birth dates and target for the start of calving season around March 1, which has a corresponding Julian day of 60.
Breed differences in gestation length and age at puberty
| Breed | Gestation Length (Days) | Age at puberty (Days) |
Angus | 282 | 359 |
| Hereford | 284 | 366 |
| Holstein | 281 | 345 |
| Jersey | 283 | 300 |
| Brahman | 293 | 426 |
| Simmental | 289 | 372 |
| Charolais | 290 | 398 |
| Limousin | 291 | 398 |
USDA-MARC Germ Plasm Evaluation Project Cycles I, II and III.
Some cows will not read the book and can have unique gestation lengths. The easiest way to find these cows is through artificial insemination because then you know the day of hopeful ovulation/conception and once the calf is born then gestation length can be calculated within an individual or breed differences. — Brian Freking, Oklahoma State University Extension livestock specialist
