at the start of breeding
- The most important factors
that determine if and when a cow returns to cycling activity were reviewed
by Dr. Jeff Stevenson of Kansas State University. Over the past
6 years, Kansas State 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. They then looked
at the previous data about each cow and determined the major factors that
determined the likelihood that she would have returned to heat by the start
of the breeding season. The research indicated that three main factors
were the most important determinants as to whether the cow would recycle
before the breeding season began. Body condition, age of the cow,
and the number of days since calving were the biggest influences on incidence
of cycling activity before breeding. Cows ranged in body condition
score from 1 (extremely emaciated) to 7 (very fleshy) . As body condition
score increased the percentage of cows cycling increased in a linear fashion.
The Kansas data reported that there was an 18% increase in percentage cycling for every 1 full condition score improvement.
The percentage of first calf two-year-olds cycling was about 10% less
than mature cows that were having at least their second calf.
The extra nutrient requirement for growth clearly limits the cycling
activity at the beginning of the breeding season of two-year-olds.
Cycling activity was also influenced by the number of days since
calving. For every 10 day interval since calving (from less than
50 days to 70 days) the percentage cycling increased by 7.5%. Cows
that calve together in a short calving season is important because it allows
more cows to be cycling by the start of the breeding season