Prostaglandins
Rumors and Facts
By Mel DeJarnette, reproductive specialist
Have you ever told a story at the coffee shop and heard it retold
several days later with the details completely changed? Have you had
first hand knowledge to an event for which friends or the media gave
bogus or exaggerated reports? It’s sad to say, but it appears to be
happening more and more these days. Sometimes, I wonder how much I
can believe of anything I hear over the news wire anymore. Rumors
and half-truths seem to travel faster than facts.
Such appears to be the case with prostaglandins (abbreviated PGF).
Introduced in the ‘60s, prostaglandins (marketed as Lutalyse,
Boralene and Estrumate) have been part of reproductive management
programs through the years. Recently, however, the development of
new methods of using prostaglandins in reproductive management
programs has resulted in a renewed interest in this hormone. Unfortunately,
rumors and myths based on previous experiences with prostaglandins seem
to be traveling faster and are receiving greater acceptance than the
actual facts. Prostaglandins themselves have not changed over the years,
however, the ways we are using them and the types of cows we are using
them on have changed dramatically.
It used to be that prostaglandins were only given to problem cows or
based on veterinarian recommendation. With current programmed breeding
protocols (target breeding, Monday Morning, etc.) all cows are receiving
prostaglandins within a few days of the voluntary waiting period.
Comparing results with prostaglandins in these two very different
reproductive management programs is like comparing apples to oranges.
Before we discuss the rumors surrounding prostaglandins, and what the
facts really are, let’s review what prostaglandin is and does.
Prostaglandin  is a naturally occurring hormone that is produced by
the uterus of nearly all mammalian species. Prostaglandin’s main action
is on the ovary to destroy the corpus luteum. The corpus luteum is a
structure that prevents animals from coming into heat or ovulating by
producing the hormone progesterone.
"Injecting cows with all these drugs and chemicals just ain’t natural."
Fact: As previously stated, prostaglandin is a naturally occurring hormone.
Normal cycling cows inject themselves with prostaglandin every 21 days
in order to return to estrus and propagate the species.
"Even if prostaglandin is natural, injecting cows at these odd times and
short cycling them will mess them up."
Fact: Messed up cows inject themselves at odd intervals. Many cows with
low grade uterine infections inject themselves with PGF to make
themselves cycle. This is Mother Nature’s way to clean up these problems.
It is also very typical for cows to release PGF early after the first
postpartum ovulation resulting in a short interval to the next estrus.
Fact is, cows short cycle themselves frequently.
Additionally, fertility tends to rise at each of the first three heats
after calving. Short cycling with PGF can help to get you to that third,
more fertile heat in fewer days.
"Prostaglandin heats are not as strong or as fertile as natural heats."
When you think about how we first used prostaglandins, it’s easy to see
how this rumor got started. In the past, we only used PGF on cows after
they were diagnosed as being problems. Thus, intensity and fertility of
heats in these animals could be less than optimal because the cows were
problems to begin with, but had absolutely nothing to do with the PGF injection.
Fact: Hundreds of controlled research trials involving tens of thousands
of animals overwhelmingly suggest that natural and PGF induced heats are
equal in fertility when animals are bred using the AM/PM rule after
observed standing heat. Problem cows will exhibit less than optimal
fertility regardless of whether the heat is naturally or artificially induced.
Intensity of estrous or mounting behavior is regulated by estrogen
production by the growing follicle and numerous environmental factors.
I am not aware of any controlled studies that would suggest PGF injections
have any effect on estrogen or estrous intensity.
"Cows don’t show heat when they are supposed to after PGF injections."
This rumor is true, but is a result of unrealistic expectations and not a
problem with PGF itself.
Fact: First of all, only cows with a functional C.L. will respond to PGF.
Non cycling animals and animals that were in heat within 5-6 days prior
to the injection are not going to respond. Secondly, even for cows that
do have a palpatable C.L., a certain percentage are not functional and
thus do not respond even after the vet says to give them a shot.
Thirdly, for those animals that do respond to PGF, estrous activity may
be at 36-+8 hours or may not start until 100 hours or more after the
injection. Thus, on average, many of the animals will be ready for
insemination at 80 hours. But an equal or greater number will be either
too early or too late for optimum conception at that time.
Although I’ve seen many animals stop, sniff and look a PGF bottle over,
I have no indication that one ever actually read the label and knew that
she was supposed to be in heat at 80 hours. If an animal responds, she
will be in heat between two and five days after the injection and
fertility will be normal if you catch her in standing heat and breed her
10-12 hours later. If you force the issue and time inseminate her at 80
hours, conception rates will be less than optimal due to the timed
insemination and not related to the PGF injection. Thus, the 80-hour
recommendation is another reason PGF has taken a "bad rap" with
respect to conception rates.
"Repeated injections with PGF will cause cows to go cystic."
This is another one that’s easy to understand how it got started when
you consider how PGF was used historically.
Fact: Problem cows (retained placentas, difficult births, metritis, etc.)
have a significantly higher risk of becoming cystic regardless of
whether or not they receive PGF.
No study has ever shown a direct relationship between PGF and cyst
formation. In fact, recent research suggests just the opposite. One
study in a large Florida herd found PGF injections to be more effective
for treating cysts than the more expensive GnRH injections. Also, many
testimonials are available from producers adopting PGF-based breeding
programs who say they have observed a decrease in the number of
animals diagnosed as cystic.
Normal animals do not receive repeated injections. If the animal is normal
and healthy, she should respond to the first or second PGF injection
(14 days later). She would then be inseminated and would not receive
PGF again until it’s time to breed her next year.
"PGF causes more twinning."
Fact: Twenty-five to thirty years of research using PGA has not even
hinted at a possible link to increased twinning rates.
These are but a few of many PGF rumors floating around. Unfortunately,
most of these rumors have blossomed from isolated circumstances where
more emotion and speculation was involved in forming opinions than
concrete data and research.
PGF based breeding programs have proven themselves to be cost effective
reproductive management in many herds. At the same time, they do have
their limitation. They can’t work miracles. Understanding how and why
PGF works to bring cows into heat will help you set realistic expectations
for your herd. Don’t let old wives-tales and grist from the rumor mill
clog the milk lines in your dairy.
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