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Getting cows rebred quickly.
The goal of every beef producer is a
high rate of pregnancy, with as many cows as possible becoming
pregnant early in the breeding season. Young cows are hardest to
get rebred quickly, since they are still growing and need a
higher plane of nutrition in order to cycle while nursing a
calf.
Importance of Nutrition
Nutrition is probably the most important key in getting cows
rebred on time. Ranchers who are most successful in attaining
high pregnancy rates with few late calvers are those who manage
their herds closely, sorting the cows into groups (before and
after calving) for different feeding programs in order to obtain
optimum body condition for breeding. Unless they are all on good
pasture, with no extra feed being given, heifers should be
managed as a separate group—from weaning through calving and
rebreeding—since they can’t compete with older cows to get their
share. Their nutritional needs for protein and energy are also
greater, since they are still growing. A heifer that does not
have adequate body condition at calving time will not breed
back.
Pregnancy rate in yearling
heifers is a combination of genetics and nutrition (heifers
should be selected for fertility and early puberty, keeping only
the ones that breed early) but rebreeding rate (breedback after
calving as a 2 year old) is highly dependent on nutrition. A
thin 2 year old nursing her first calf may not cycle at all. A
1990 study at Texas A&M showed hormonal changes associated with
return to estrus after calving are closely linked to nutrition
during pregnancy. Two year olds with higher body condition score
at calving will cycle sooner, with a higher percent pregnant by
40 days into the breeding season.
Three year olds are generally run
with mature cows, but there are some advantages to keeping them
with the 2 year olds after calving, on a higher plane of
nutrition. The best young cows (2 year olds and some 3 year
olds) often come up open just because they are raising a good
calf and don’t have enough feed to meet the demands of lactation
while still growing.
Mature cows can get by on plainer feeds and less protein before
and after calving, but must have adequate nutrition to stay in
good body condition for rebreeding—especially if weather is cold
or wet. Cows can lose condition rapidly when subjected to
nutritional and environmental stress. If a cow must rob fat
stores to keep warm, she will lose weight and may not cycle as
early in the breeding season. If you are trying to use an AI
program or synchronize cows for earlier calving, it is even more
important to closely watch body condition since you want as many
cows as possible to be cycling at the beginning of the breeding
season.
Old cows, thin cows, heavy
milkers, or cows in drought conditions or wintering in severe
weather may need extra feed. In some situations a rancher might
want to change calving season to enable cows to be on green
pasture after calving—so they have a higher plane of nutrition
before and during breeding. Cows in good condition can rebreed
in 30 to 40 days after calving, but a thin cow may not rebreed
for 100 days or more. Lactation accentuates the effects of poor
nutrition and can slow the return to estrus.
Challenges of 2 Year Old
Breedback
Since 2 year olds are the hardest group to get rebred, some
ranchers program their heifers to start breeding a few weeks
ahead of the cows, to give them a longer chance to recover and
rebreed after calving. This only works if heifers are well grown
and receiving adequate nutrition to cycle early for their first
breeding. And the cost of feeding an early calving lactating 2
year old from calving til green grass is a factor to consider,
along with the labor of a longer calving season (starting
several weeks early for the heifers). Whether it works will
depend on the individual operation and labor availability.
More important, perhaps, is
making sure heifers have little or no calving difficulty—by
selecting moderate framed individuals and breeding them to
moderate framed, short gestation (easy calving) bulls. A small
calf that can be quickly and easily born puts the least
reproductive stress on the heifer; her reproductive tract will
recovery more quickly and she’ll breed back on schedule.
If she does require assistance at
calving time, help should be given no later than an hour after
she starts active later—to minimize stress on her and the calf.
A Montana study showed that 87 percent of heifers given early
assistance came into heat by breeding season, compared with only
70 percent of heifers that were not helped until late in labor;
and 88 percent of early-helped heifers were pregnant at the end
of breeding season, compared with only 68 percent of heifers
given late assistance.
Heat Synchronization
Some ranchers choose to use hormones to synchronize estrus in a
group of cows, especially when using AI (to eliminate the time
consuming chore of heat detection and having to inseminate cows
all through the breeding season). At present there are more than
15 different synchronization methods available, and research
continues to find ways to fine tune them.
The goal is to find ways to
synchronize and inseminate cows and increase pregnancy rates
while minimizing costs and labor (less trips through the chute).
A number of prostaglandin products are used, including Lutalyse,
Insynch, ProstaMate and Estrumate. Some methods use GnRH (Gonadotropin
Releasing Hormone) along with prostaglandin. Another protocol
uses a CIDR (controlled intravaginal drug releasing device) that
delivers prostaglandin into the bloodstream. CIDRs, used with
Lutalyse, can be used to synchronize heat.
The basic principle for most of
these methods is use of GnRH to induce follicles within the
ovary to ovulate. After ovulation, a corpus luteum (CL) forms in
the area where the follicle ovulated. The CL produces hormones
that keep the cow out of heat until her next cycle. But the CL
can be regressed early by giving the cow prostaglandin,
triggering a new wave of follicular activity to bring her back
into heat quicker. At this point, a resulting follicle can be
induced to ovulate if the cow is given an additional injection
of GnRH, and the herd can all be inseminated at the same time,
or bred by bulls within a short time frame.
Or, the cows can be allowed to
ovulate naturally after the first injection, and bred AI after
heat detection. One advantage of using the additional injection
of GnRH is that some of the non-cycling cows that have not yet
shown heat after calving will be induced to cycle, shortening
the time period between calving and rebreeding. This method
works better for cows than heifers.
Some of the most common protocols
for heat synch use various timings for hormone injections. One
method involves 2 injections of prostaglandin 11 to 14 days
apart, with heat detection and AI after each injection. About 60
to 70 percent of cows that have already started to cycle after
calving will come into heat within 5 days after the first shot
and can be bred 12 hours after being seen in standing heat. Any
that are not seen in heat are given a second shot 11 to 14 days
after the first. Good records are important (or cows from the
first breeding moved to another pasture) because a cow that was
bred after the first injection will abort if given a second
injection.
Another method is to give all
cows 2 injections 11 to 14 days apart, just breeding after the
second shot. If you don’t want to heat detect, all cows can be
inseminated 80 hours after the second shot, but this usually
results in a lower pregnancy rate than when heat detecting and
breeding 12 hours after standing heat.
Some ranchers inject all cows
once with prostaglandin and then just check heat and breed the
cows that show standing heat during the next 5 days. About 60 to
70 percent of cows will show heat after the injection. You can
also inject the remaining cows on day 6 and they should show
heat within the next 5 days. Using this method you can often
inseminate more than 90 percent of cows (that were cycling
already after calving) during the first 10 days of your breeding
season.
Another method, which takes 31 to
33 days to administer, uses MGA (melengestrol acetate) and
prostaglandin. The MGA suppresses estrus and can be given in
feed for 14 days. Most females show a sub-fertile heat within 2
to 5 days after you stop feeding MGA, but they should not be
bred. The CL resulting from this cycle is then regressed by
giving a shot of prostaglandin 19 days after MGA is withdrawn
from the feed. Most females will show heat 48 to 72 hours after
the prostaglandin shot. They can be bred at 72 hours after the
injection if you don’t want to spend time heat detecting.
A newer adaptation of this
system, which seems to give better results, is to give GnRH 12
days after halting the MGA, followed 7 days later with the shot
of prostaglandin. The cows can then be heat detected and bred,
and any that did not show heat can be inseminated 72 hours after
the shot, using an additional shot of GnRH at the time of
insemination. In cow herds that are not cycling very well yet at
the beginning of breeding season, this protocol may help get 10
to 15 percent more total pregnancies. It helps “jump start” the
cows that aren’t cycling yet, and also gives a tight
synchronization. The AI tenchnicians can basically be done in
about 2 days, cutting out the labor for heat detection. Giving
GnRH to cycling and non-cycling cows can improve synchronization
response to the prostaglandin.
Use of CIDRs
The CIDR insert has a T shaped nylon core with foldable wings
that allow for easy insertion, a layer of silicone that contains
progesterone, and a flexible nylon tail so you can pull it back
out of the vagina. While inside the vagina, this implant
continually releases progesterone into the bloodstream. This is
the same hormone released by the CL (to keep the cow out of heat
til her next cycle). The CL regresses at the end of her cycle
and when the progesterone drops below a certain level, the new
cycle begins.
By using CIDRs you can control
the hormone cycle and have all the cows decline in progesterone
at the same time (by taking out the CIDRs on day 7) and then
they’ll all come into heat at once. On day 6 or 7, an injection
of Lutalyse is given. If given on day 6, most cows show heat 1
to 3 days after removal of the CIDR. They may show heat slighter
later if the injection is given the same day the CIDR is
removed.
Avoid Stress
The conceptus is very vulnerable after it comes down the
fallopian tube—when it must attach to the uterine lining. A
number of factors that may disrupt this process include heat
stress, fever, or any other type of stress. Don’t transport cows
soon after breeding them. If cows are stressed at the time of
insemination (highly agitated at being worked and put through
the chute, etc.) this may also result in lower pregnancy rates.
Also pay attention to the timing
of vaccinations, especially when using modified live virus
vaccines. These are designed to be given to open cows, well
ahead of breeding, since the vaccine antigen replicates and
actually infects the body cells. Most animals develop a slight
fever following vaccination. This type of reaction is a stress.
Research has also shown that modified live virus BVD vaccine can
cause temporary ovarian inflammation. This is why it should be
given at least 30 days prior to breeding.
The timing of vaccination is very
important if you are doing estrus synchronization. These
programs require handling cattle to give the hormone shots, and
many ranchers give vaccinations at the same time, to save trips
through the chute. But the hormone drugs and vaccines should not
be given at the same time or you risk some ovarian inflammation
that may interfere with conception. It’s better to play it safe
and give these vaccines well ahead of heat synch protocols.
Tips for Early Breeding
One of the best ways to increase fertility and conception rates
is to shorten your breeding season to 45 days or less, to weed
out cows with fertility problems. Cows that breed in a short
season will all be recovering from calving about the same time
and coming back into heat again. If you have a long calving
season, there will always be some late calvers that can’t
recover fast enough to rebreed on time. Consistently using a
short breed season (on our ranch we put bulls with cows for only
32 days) and culling any open cows, selects for high fertility.
Heifers kept from fertile cows will also be more fertile. A
short breeding season makes for a short calving season, and can
group the calves almost as well as using heat synchronization.
For instance, in our herd, nearly 90 percent of our calves
arrive in the first 3 weeks of calving, without having to use
heat synchronization.
Another way to encourage cows to
cycle more quickly after calving is to put a sterile teaser bull
with them ahead of breeding season. The presence of a bull will
stimulate some cows to come into heat sooner after calving. But
care should be taken in selecting a teaser bull to make sure he
is free of disease.
Safety Warnings for Hormone
Drugs
Care should be taken when handling prostaglandin products, since
this hormone is readily absorbed through the skin. It may cause
bronchial spasms (breathing problems), abortion in pregnant
women or disruption of the menstrual cycle. Women of
childbearing age, or anyone with asthma or any type of
respiratory problem should be extremely cautious. Direct contact
with skin should be avoided. Accidental spillage should be
immediately washed off with soap and water. Technicians working
with CIDRs should always wear protective gloves/sleeves to
prevent exposure. |
