Calving Interval and Gestation Length

Brian Freking, Oklahoma State University SE Extension Livestock Specialist

 

Breeding efficient cows is usually measured by a cows’ ability to calve each year and maintain a yearly calving interval.  Recently, one of my cows provided a calf on February 14, 2023 and turned around and provided another one on December 20, 2023.  This cow has reached the pinnacle of reproductive efficiency.  Normal beef cow gestation length is 283 days therefore subtracting those number of days from the latest calf puts conception for March 12.  Now subtracting this conception date to the valentines’ day calf only allows for 26 days of uterine involution and recovery from the previous birthing process.  This is quite unusual.  My 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.  One of my main recordkeeping goals is 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.  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.

 

Here is a chart showing breed differences in gestation length and age at puberty:

Breed (Abev.)

Gestation Length

Age at puberty

Angus (AN)

282

359

Hereford (HP)

284

366

Holstein (HO)

281

345

Jersey (JE)

283

300

Brahman (BR)

293

426

Simmental (SM)

289

372

Charolais (CH)

290

398

Limousin (LM)

291

398

Source: USDA-MARC Germ Plasm Evaluation Project Cycles I, II, and III.


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