Body condition, age and the number of days since calving are the most important factors determining if and when a cow returns to cycling activity after calving, according to Jeff Stevenson at Kansas State University.
Dr. Stevenson and other scientists have used more than 2,200 beef cows in estrous synchronization studies. As a part of these studies, they determined which cows were cycling before the start of the breeding season-both before and after synchronization treatments-and then looked at previous data about each and found the major factors determining the likelihood of a return to heat by the start of the breeding season. Here is what they found:
- Cows ranged in body-condition score from extremely emaciated (BSC 1) to very fleshy (BCS 7). As body-condition scores increased, the percentage of cycling increased.
- There was an 18 percent increase in cycling for every one full condition score improvement.
- The percentage of first-calf 2-year-olds cycling was about 10 percent less than mature cows having at least their second calf. The nutrient requirements for growth clearly limits the activity at the beginning of the season for 2-year-olds.
- For every 10-day interval since calving, the percentage of cycling increased by 7.5 percent.