My first use of timed artificial (AI) insemination came immediately after veterinary college. A prostaglandin product had
been approved for horses, but it was expensive. By infusing a fraction of the equine dose into the uterus of a cow with a
corpus luteum, it usually could be brought into estrus. Timed insemination has come a long way.
Figure 1: A color-coded breeding calendar is a helpful client tool to explain the benefits of an aggressive program of timed
insemination. It allows producers to see what happens rather than interpret the results based on numbers alone.
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Now I visit many farms where reproduction is a limiting factor. Herd records often reveal conception rates between 25 percent
and 35 percent with heat detection between 35 percent and 50 percent. In past years, these levels would have been seen as
unacceptably low, but today they are common, even in well-managed herds. While there might be steps we can take to improve
conception rates, we often can make faster progress by using an aggressive timed insemination program to raise the number
of inseminations.
I find it helpful to create a calendar showing producers how to group cows to get the maximum benefit from timed AI. When
clients can see days to first service and days to conception visibly moved closer to freshening, they seem to respond better
than if I just show them numbers. I also use their own records to show them the potential impact.
Laying out detailsFigure 1 depicts a calendar developed on a spreadsheet using color to clarify actions and events. I begin by explaining terminology:
"P" represents prostaglandin, "G" is GnRH, and "B" stands for breed. Natural estrus occurs 21 days after the first breeding.
The "Preg/P" means pregnancy exam and prostaglandin to open cows. Pre-sync refers to prostaglandin injections used prior to
the desired breeding time, designed to synchronize the estrus cycle to garner better response to the Ovsync program.
Ovsync is the program using GnRH and prostaglandin to induce ovulation for breeding. Finally, Re-Sync is used on cows prior
to pregnancy exam, so that open cows can quickly be re-inseminated.
Consider a herd where records show a 40-percent heat detection rate and a 35-percent conception rate. They do pregnancy exams
every four weeks. If this is the case, I suggest they group cows according to calving date, and that every four weeks they
begin a new group on a fully timed AI program. The calendar in Figure 1 shows when injections would be given to this group.
All cows that freshen in a given color range become part of one group. The ones in the first band, from June 5 to July 2,
receive prostaglandin on July 27 and Aug. 10. These injections get cows into the best stage of their cycle to start synchronization
with gonadotropin-releasing hormone analogue (GnRH ) on Aug. 22. Prostaglandin will be given on Aug. 29, GnRH is repeated
two days later, and all cows are bred the morning of Sept. 1. This means that days to first breeding for this group will vary
from 61 for a cow that freshened on the last day of that group (July 2) to 89 for one that delivered on the first day (June
5). We will breed 100 percent of the eligible animals.
The math
The next set of injections is the re-synchronization program. Cows not found in natural heat 21 days after breeding are given
GnRH at day 32. This is when open cows will be at the best stage of their cycles. Pregnancy checks can be done at 39 days
post breeding when you can be confident to correctly identify the non-pregnant animals. These are immediately given prostaglandin
followed in two days by GnRH and rebreeding. Thus, the second breeding will occur 42 days after the first. Adding that to
the days at first breeding (ranging from 61 to 89), we see that all cows that failed to conceive on first service are re-bred
between 103 days to 131 days in milk.
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