A Reproductive Moment With MEL
Get 'Em Bred and Keep 'Em
by Mel DeJarnette, Reproductive Specialist
A.I. breeding problems can be
classified into two fairly broad
categories: fertilization failure
and embryonic death. Most of my
articles focus on semen handling,
heat detection and estrous synchronization
to improve fertilization
rates. However, research suggests
that with normal semen quality and
appropriate timing of inseminations,
fertilization rates will exceed 80%.
The difference between the fertilization
rate and your pregnancy rate is
due to early embryonic death. It’s
time to dedicate an article to keeping
cows pregnant once fertilization
occurs.
When you mention embryonic
death, most people immediately
think of abortion and aborted fetuses.
However, embryonic mortality
rates are highest in the first few
weeks after breeding; before a recognizable
fetus is fully developed. Data
compiled by Sreenan and Diskin
(1986) suggests fertilization rates
approach 90% while actually pregnancy
rates will decline to 60% by
day 19 after insemination (Figure 1).
During the period of maternal
recognition (days 16-19 after estrus),
hormonal communication between
the developing embryo and the
uterus is essential for recognition
and maintenance of the pregnancy.
When the embryo and uterus fail to
communicate, the corpus luteum
(CL) is regressed resulting in the
animal returning to estrous. While
embryonic death is often associated
with an extended inter-estrus interval
(25-35 days), this may not always be
the case. If embryonic death occurs
early enough (≤ 7 days), the animal
will likely return to estrus at a normal
18-24 day interval.
The potential reasons for very
early embryonic death (≤ 3 weeks)
are numerous, difficult to define and
often not clearly understood. In general,
it appears that any type of
stress on an animal can increase
rates of embryonic mortality. Typical
sources of stress that can affect
reproduction include high milk production,
poor nutrition, heat, disease
and fear.
PRODUCTION STRESS
Obviously it would not be economically
advisable to decrease milk
production in
order to get better
pregnancy rates.
However, it’s
important to keep
in mind that there
may be interactions
among different
sources of
stress. Thus, the
high producing
cows in a herd
will be more sensitive
to stress
arising from other
sources.
Minimizing stress
from all sources is
essential to maintenance
of high levels of production
and reproduction.
NUTRITIONAL STRESS
Animals on a poor plain of nutrition,
as reflected by low body condition
scores, have been shown to have
reduced pregnancy rates and altered
levels of several important reproductive
hormones including LH and
progesterone. Progesterone is essential
to maintenance of the pregnancy
and may be closely associated with
the ability of the embryo and uterus
to communicate. Use body condition
scoring on a routine basis to monitor
the effectiveness of your nutrition
program. Cows should calve in at a
body condition score of about 3.5.
Energy dense postpartum rations
should be used to minimize negative
energy balance and body condition
loss. Cows should lose no more than
one point of body condition after
calving before they start to regain
weight. Work with your nutritionist
to develop a complete nutrition program
tailored for cows at various
stages of lactation and production
levels.
HERD HEALTH
Work with your veterinarian to
establish a sound herd health program
addressing all diseases of relevant
concern in your geographic
region. Remember, to be effective, all
vaccines require time to work before
they can establish
immunity.
Also, many vaccines
can cause
an elevation in
body temperature
which can
result in
reduced fertility.
Thus, make
sure all vaccinations
are
completed at
least three
weeks prior to
the VWP.
When vaccinating
pregnant
animals, make
sure all vaccines are approved and
recommended for use in these animals.
Mastitis and high somatic cell
counts are signals of a reduced
immune system and have been associated
with reduced reproductive
performance. In addition to production
of a high quality dairy product,
proper hygiene and sanitation procedures
in the milking parlor may go a
long way in improving reproductive
performance as well.
HEAT STRESS
Heat stress can have extreme
effects on early embryonic development.
Your first line of defense
against heat stress is to focus on
estrous synchronization and heat
detection in the
spring to get cows
pregnant before
hot weather
arrives. A more
advanced fetus is
less sensitive to
heat stress.
Recent research
(Drost et al., 1999) found embryo
transfer of frozen-thawed embryos
obtained from super-ovulated cows
may lend itself to improved summer
time fertility, however, frozen IVF
embryos failed to demonstrate any
positive effect on fertility. Keep cows
as cool as possible by use of shade,
sprinklers and plenty of cool clean
water. Some research suggests that
the 24 to 48 hours before and after
estrus are extremely important for
establishment of pregnancy. Any
preferential cooling animals in estrus
receive during this time will likely be
worth the investment.
FEAR/EXCITEMENT
Stress from fear or excitement
may also cause reproductive problems.
Keep animals as calm as possible
any time you handle them but
especially at breeding and for the
following several weeks. Avoid isolation
of individual animals. Cows are
social creatures that often get anxious
and excited when separated
from the herd. If a single animal
must be isolated for breeding, herd
health, etc., place another animal
with her to help keep her calm. If
animals must be transported after
breeding, research found that transport
at two weeks after A.I. reduced
pregnancy rates by 12% compared to
transporting animals within one to
four days after A.I.
GnRH AND PROBLEM BREEDERS
Gonadotrophin releasing hormone
(GnRH) has long been used to treat
problem breeding cows. Most commonly known as Cystorelin, injections
of GnRH to problem breeders
(>3 services) at the time of estrus
(±24 hours) appears to help these
animals develop a more competent
CL, higher levels of progesterone,
and may increase
conception rates
by 5-15%. GnRH
at estrus does
NOT appear to
have a cost effective
benefit in
first or second
service animals.
Beware that injections of GnRH at
the time of estrus has been associated
with an increased incidence of
twins. However, GnRH used in
estrous synchronization protocols
(Ovsynch or Select Synch), also
appears to be good therapy for problem
cows and does not appear to
increase the incidence of twinning.
DON’T SHOOT YOURSELF IN THE FOOT!
Prostaglandins (PGF) have
become an increasingly important
component of
dairy herd
reproductive
management
programs.
However, pregnant
animals
injected with
this hormone
will abort.
Accurate
recording
keeping systems
are essential
to ensure
that previously
inseminated or
pregnant animals
are not
inadvertently injected with
prostaglandin.
Oxytocin, which is often used to
encourage milk let down in slow
milkers, has been shown to stimulate
muscle contractions and PGF production
in the uterus. Recent
research (LeMasters et al., 1999)
found that 100 IU injections of oxytocin
at 8 hour intervals on days 5-8
after mating resulted in increased
PGF secretion, short estrous cycles,
and higher rates of embryonic mortality.
Although the level of oxytocin
use in this study is relatively high,
these data suggest it might be wise to
avoid oxytocin injections during the
first few weeks after breeding.
Reinsemination of pregnant animals
can wreak havoc on your conception
rates. In the study shown in
Figure 2, animals were inseminated
based on observed standing estrus.
Half of the animals were then reinseminated
12-24 days later without
regard to estrous expression. Animals
were palpated for pregnancy 40 days
after the initial A.I. Pregnancy rates
were 40% for control animals and
only 4% for the reinseminated cows.
These results suggests that reinsemination
of pregnant animals during
the first few weeks of gestation will
result in abortion/early embryonic
death 90% of the time. This may be
a major source of poor fertility in
herds that breed cows exclusively on
chalk markings
or other
secondary
signs of
estrus.
Extreme
caution must
be exercised
when interpreting
secondary
signs
of estrus in
repeat animals.
If a
thick
mucous plug
is encountered,
practice
mid-cervical
semen
deposition. Would you believe that
some herds may improve pregnancy
rates if they simply quit inseminating
so many cows?
Don’t ignore the possibility that
your hormone injection schedule or
your heat detection and breeding
program may be causing abortions in
your herd. To do so would be
"Shooting yourself in the foot".
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