B136 Estrus Synchronization & Heat Detection

Name ______Date ______

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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?

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?

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

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:

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 ______.