By Bethany Johnston and Aaron Berger,
University of Nebraska
Have you wanted to have more calves born earlier in your calving season, but did not want to deal with
the increase in labor, cost and facilities to utilize estrus synchronization and artificial insemination? The
protocol shown (Figure 1.) can increase the number of cows coming into estrus early in the breeding
season, with one time through the chute, one injection, and breeding using only natural service.
Protocol for Utilizing One Shot of Prostaglandin to Synchronize
Estrus with the Use of only Natural Service
Turn in bulls
with cows
Give all cows an injection
of prostaglandin
Natural Estrus
Day 0
Synchronized Estrus
Day 5 Day 6
Natural Service Continues
Day 10
Figure 1.
This protocol calls for bulls to be turned out
with the cows on Day 0. On Day 5, cows are
given a shot of prostaglandin (PGF2α) which
synchronizes a majority of the cows to be in heat/
estrus from Day 6 through Day 10. The injection
of prostaglandin causes any cows with a corpus
luteum present on one of their ovaries to regress,
ceasing progesterone production. This then
triggers the cows to come into heat/estrus.
If the cow conceives during Day 1 to 5, she will not
abort when given the prostaglandin injection on
Day 5 because the developing corpus luteum at the
108 | JUNE/JULY 2019
site of ovulation on the ovary has not yet reached
maturity and will not respond to prostaglandin.
Research conducted at the Fort Keogh
Research Center near Miles City, Montana
utilized this protocol over a three-year period,
achieving pregnancy rates over 85% in a
32-day breeding season. Research from the
University of Nebraska showed 75% of cows
calved in the first 21 days of the calving season
utilizing this estrus synchronization protocol