B136 Estrus Synchronization & Heat Detection
Name ___________________________
Date ________________
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Scroll down to A714 Estrus Synchronization & Heat Detection
Estrus Synchronization:
1. If a decision is made to artificially inseminate (AI) animals in the herd, a
significant effort needs to made in what two areas?
2. Define Estrus synchronization:
3. What are two important purposes of estrus synchronization?
A.
B.
4. Because the estrous cycle is ________ days long, only about ________ of the
cycling animals are in heat during the first week of the breeding period/season if
estrus synchronization is not used. Regardless of whether the animals are
inseminated naturally or artificially, only 65 to 70% of them will conceive to a
given insemination or breeding. Thus, after a week of breeding to natural heats,
only about ___________% of the eligible animals may be pregnant (33% in heat
x 65% conception rate). Because many animals may not have resumed normal
cycling activity, the actual pregnancy rate during the first week of the breeding
period may often be considerably less.
5. Many of the estrus synchronization protocols can induce ________ to
________% of the cycling animals to display estrus within a 5 day period.
Additionally, many protocols can induce a fertile heat in as much as 50% of the
anestrous (non-cycling) cows. Thus it is typical for many of these synchronization
protocols to result in _______ to _______ % of the animals being pregnant by
the end of the first week of the breeding period. Several fixed-time Al options can
result in 40 to 50% of the cows becoming pregnant following one single day of
breeding with zero hours spent for heat detection.
6. Cows that display estrus during the first week of the breeding period will have
________ opportunities to conceive during the first 45 days, while those who do
not cycle early will only have 2 or less. Also, cows that do not respond to estrus
synchronization may be _______________ animals. Early identification of
problem cows allows appropriate veterinary therapy to be administered in a
timely fashion and reduces the potential for excessive days open.
7. Additional Benefits of Estrus Synchronization: Beef cows that conceive
early in the breeding season will produce calves that
___________________more at weaning simply because they are older. A calf
conceived on the first day of a 60-day breeding season will be worth more than
one conceived on the last day. Economic returns like these can more than pay
the cost of the average synchronization program.
8. Cows require time (60 days) to __________________ from the stress of
calving before they can be expected to rebreed. Cows that calve early will have
more days postpartum before the beginning of the next breeding season. Thus,
compared to late calving cows, more early calving cows will have resumed
normal estrous cycles and fertility by the beginning of the next breeding season.
Estrus synchronization programs help to keep cows conceiving early in the
breeding period, which helps to _________________________ reproductive
performance during the next year’s breeding season as well.
9. Replacement heifers kept from early calving cows will be _______________ at
the beginning of their first breeding season and more likely to have reached
puberty and targeted breeding weights. Heifers kept from late calving cows will
be younger and smaller at the beginning of their first breeding season and are
predisposed to reproductive problems. Even in the best management scenarios,
first-calf heifers can present problems getting bred. Estrus synchronization allows
virgin heifers to be bred 3 weeks prior to the cow herd. This allows the first-calf
heifer additional ______________________ time after calving before the next
breeding season begins. Also, synchronization of virgin heifers facilitates the use
of semen or bulls with a lower calf birth weight and a high calving ease. Calving
assistance labor is also more efficiently utilized because the heifers will calve
within a narrow window of time. Thus, estrus synchronization of virgin heifers is
particularly important to reduce __________________ problems, subsequent
_________________ problems, and ____________ ________________ rates.
The economic benefits of estrus synchronization apply to every herd, regardless
of how the animals are bred (Al or natural service).
10. Why is natural service with estrus synchronization cost prohibitive?
Estrus Synchronization Programs:
11. What are three prostaglandins that are commercially available?
A.
B.
C.
12. Explain how a shot of a prostaglandin causes an animal to come back into
heat?
13.What is the biggest limitation to a prostaglandin shot?
14. The most common method of synchronization with prostaglandin is to inject
_________ animals, and breed those that come into heat over the next ____ to
____ days. Animals not detected in estrus after the first injection are reinjected
_____ days later and bred over the next 5 to 7 day period (Figure #1). Animals
detected in standing heat should be inseminated ____________ hours later.
PGF2α Limitations: Fixed-time insemination after single or double injections of
PGF2α alone seldom yields acceptable results. Because of this, it is usually not
recommended.
15. A major limitation of PGF2α is that it only works in ____________________
animals.
16. Research suggests as many as ________% of postpartum, suckled beef
cows may still be anestrus at the beginning of the breeding season.
17. In these situations, use of prostaglandin in combination with gondotropin
releasing hormone are much more _____________________ option.
18. Each GnRH-based protocol uses the same basic framework, which involves
an injection of GnRH, followed ______ days later with an injection of
prostaglandin.
19. Follicular Waves and GnRH: An injection of GnRH causes a release of
________________________ hormone (LH) from the pituitary gland in the brain.
This LH "surge" results in ______________________ or luteinization of most
large dominant follicles. A new "synchronized" follicular wave is initiated in these
animals 2 to 3 days later.
20. Are gonadotrophin injections recommended on virgin heifers?
21. MGA - PGF2α System: The MGA-PGF2α system (Figure #5) is a time tested,
proven method for synchronizing estrus in beef and dairy
______________________. Metengestrol Acetate (MGA) is a synthetic form of
the naturally occurring hormone, ____________________________. For best
results, mix MGA with 3 to 5 lbs of a grain supplement and feed at a rate of 0.5
mg/head/day for 14 days. Top-dressing or mixing MGA in a ration can work, but
intake (and thus results) tends to be more variable. Within 3 to 5 days after MGA
feeding, most heifers will display standing heat. DO NOT BREED at this heat
because conception rates are reduced. Wait ______ to ______ days after the
last day of MGA feeding and inject all heifers with a single dose of prostaglandin.
For the next 5 to 7 days, inseminate animals 8 to 12 hours after detected estrus.
Figure #5:
Success of the MGA system depends on adequate bunk ______________ and
proper feeding rates so the appropriate ___________________ is consumed by
each heifer on a daily basis. With good heat detection of well-managed heifers at
the proper age, weight, and body condition, synchronized pregnancy rates of
_______- ________% can be achieved.
22. CIDRs (The Eazi-Breed): The Eazi-Breed CIDR cattle insert, or CIDR as it is
most commonly called, is the newest synchronization product available in the
U.S. market. Developed and used extensively in New Zealand and marketed in
the United States by
Pharmacia Animal Health, the CIDR is a _______________________ insert that
delivers the natural hormone ___________________________ throughout the
seven-day implant period. This progestin stimulation helps to induce cyclicity in
anestrous cows and advances puberty in heifers.
In studies that used an injection of prostaglandin (Lutalyse) on day six after
insertion and implant removal on day seven, research has shown the CIDR to be
an effective means of synchronizing estrus in virgin beef and dairy heifers, and in
postpartum beef cows. The CIDR is not approved for use in lactating dairy cattle.
Heat Detection:
23. A cow in heat is one that is receptive to the bull or ready to be artificially
inseminated. This time usually occurs every ___________ days and lasts for
____________ hours. Most cows should be bred __________ hours after being
observed in standing estrus. The following table demonstrates part of a cow’s
estrous cycle and when the proper time to inseminate a cow occurs.
24. List the various signs a cow shows when she is in heat
1.
2.
3.
4.
5.
6.
25. It is important to physically observe the herd or group of animals at least
______________ a day. This is because most cows show signs of heat in the
morning (6 a.m. to noon), evening (6 p.m. to midnight), or during the night. In
fact, most animals (approximately 45%) show heat during the hours of midnight
to 6 a.m. Because heat detection is often difficult, the following are tools a
producer can use to help identify animals that are in heat:
1.
2. Androgenized cows - These are female cows that are given
testosterone to cause them to show male-like behavior. These animals are
great candidates for the chin-ball marker.
3. Surgically altered bulls - These animals are surgically altered in a way
that prevents the penis from entering the cow. These bulls still have the
sexual drive to mount, but cannot reproduce.
4. Tail-head devices (Kamar) and paint - These devices are
_______________ onto the tail-head of the cow. Pressure on the device
when the cow is mounted, causes the marker to change
_______________.
5. Paint sticks can also be used in a similar manner. The paint can be
applied in areas on the hooks, pins and tail-head. When the cow is ridden,
the paint will ______________ and ______________.