| | Health and nutrition | Handling facilities | Will it pay to synchronize estrus?
Estrus synchronization of beef cows and heifers is a program in which an artificially induced hormone or chemical agent causes groups of sexually mature and cycling females to come into heat (estrus) and ovulate at approximately the same time. Estrus is the complete cycle which a sexually mature non-pregnant cow or heifer goes through about every 21 days. Estrus is that part of the estrous cycle during which heat or willingness to breed is exhibited. Cattle which are not reproductively cycling should not be included in an estrus synchronizing program.
Estrus synchronization with prostaglandins has the potential to improve and increase artificial insemination (AI) programs with cattle. The Upjohn Company has developed a prostaglandin product called Lutalyse. Estrumate, marketed by ICI Pharmaceuticals, is a synthetic prostaglandin. There may be other natural and synthetic prostaglandin products coming on the market in the future. Use of a particular prostaglandin product for estrus synchronization will be dependent upon cost and availability.
Prostaglandins regulate the female reproductive cycle by causing luteolysis. This is a term meaning destruction or forced regression of the luteal tissue or corpus luteum. The corpus luteum is sometimes referred to as the CL, and is commonly known as the yellow body on the ovary. The CL is a group of cells that persist on the ovary around the empty egg sac after an egg is released during ovulation.
About five days after ovulation, the CL begins producing appreciable amounts of progesterone. Progesterone is a hormone which prevents the immediate development of another egg on the ovary, and thus prevents the cow from coming into heat. Normally, in a healthy sexually mature non-pregnant female, the CL naturally regresses about 17 to 18 days after she ovulates. Ovulation occurs just after she is in heat.
An injection of prostaglandin causes the CL to regress earlier than normal. This eliminates the source of progesterone. Usually, in two to five days after receiving prostaglandin, the female comes into heat and is ready for breeding.
In order for the prostaglandin to destroy the CL and speed up the estrous cycle, there must be a CL present. This means the cow must be cycling. Prostaglandins will not affect the cycle of cows with an immature CL; that is, between day one and day five of the estrous cycle. Nor will prostaglandin affect cows after the CL has already started to regress, about day 17 or 18 of the cycle, as these cows are within about three days of coming into heat.
For these reasons, four prostaglandin programs are being used. Two of them require two injections of prostaglandin, and two require just one injection.
An estrus synchronizing program will not enhance overall pregnancy rates, increase conception, nor benefit reproductive performance in non-cycling or subfertile cattle, particularly when poor management is responsible for the condition of the cattle.
For the program to be successful there must be:
- Normally cycling cattle
- Healthy animals that are free from disease and on a good nutrition program
- A willingness by producers to learn how to use prostaglandins
- Availability of an experienced inseminator
- High quality semen
- A physical facility that can provide a small crowding corral, a holding alley and a breeding chute.
Health and Nutrition
The health and nutritional status of the cows and heifers in an AI program is one of the greatest factors contributing to successful breeding. Good nutrition before and after calving will help cows return to estrus after calving and increase rate of pregnancy.
Heifers of the British breeds should be fed so they are well grown and weigh 650 to 700 lb by breeding time, which is at 14 to 15 months of age. Heifers of the larger continental breeds should weigh 750 to 850 lb at that time. Most breeders using an AI program want to get as many cows as possible pregnant in the early part of the breeding season. Nutrition is the main factor involved in getting cows and heifers cycling before the start of the breeding season. Maintaining herd health at a high level is essential in obtaining a high rate of conception. Heifer calves should be given brucellosis vaccinations at the proper age. Veterinarians can advise on control of vibriosis, leptospirosis, trichomoniasis, IBR and other diseases. Continuous, year-round health programs should control lice, grubs, pink eye and related problems.
Program 1. Two injections of prostaglandin
Inject
Prostaglandin(l)
All Cows | Breed After
Detected
Standing Heat | Inject
Prostaglandin(2) to
Cows Not Bred | Breed After Detected
Standing Heat (or
breed all cows 80
hrs. after 2nd injection) |
Days |
0 | 2-5 | 11 | 13-15 |
| After one injection, 60-70% of the animals should be in heat between Days 2 and 5. These animals should be bred after being detected in standing heat. The animals which are not detected in heat after the first injection, should receive a second injection on day 11 and be bred after estrus detection on days 13 - 15. These females could be inseminated 80 hours after the second injection. |
Program 2. Two injections of prostaglandin
Inject
Prostaglandin(l)
All Cows | Inject
Prostaglandin(2)
All Cows | Breed After Detected Standing Heat (or
breed all cows 80 hours after the 2nd injection) |
Days |
0 | 11 | 13-15 |
| Two injections should synchronize estrus in most cycling cows within 2-5 days after the second injection. Twice daily or more frequent heat detection on days 13-15, followed by insemination of females in heat is recommended. Timed inseminations at 80 hours after the second injection without heat detection will generally result in lower pregnancy rate. |
Program 3. One injection of prostaglandin
Check Heat & Breed All
Cows After Standing Heat | Inject Prostaglandin
All Cows
Not Bred | Breed After Detected Standing Heat (or
breed all cows 80 hours after the 2nd injection) |
Days |
0 | 1-5 | 5 | 5-10 | 10 |
| Heat detection and insemination of animals in heat on day 1-5. On day 5 inject all cows not bred. Most cows not already bred should respond and be in heat on days 7 to 10. This program will use less prostglandin, but requires more days of heat detection than Programs 1 or 2. This program is preferred by many operators. |
Program 4. One Injection of Prostaglandin
Inject
Prostaglandin
All Cows | Check Heat & Breed After Detected
Standing Heat (or breed all cows
80 hrs. after prostaglandin injection) |
Days |
0 | 1-5 | 5 |
| This is a shortcut method, which will minimize cost and detection effort, but will result in fewer cows bred and conceiving. Probably less than 50% pregnancies will occur. |
Handling Facilities
Facilities for handling cattle should facilitate movement of cattle with a minimum of effort. It is helpful if these facilities are reasonably close to the heat detection pastures. The pens and breeding chute should be built high enough and strong enough to control the cattle. A breeding chute covered with a roof or building to protect semen, supplies and records from the elements is most desirable. Heat detection pastures should have enough grass and water to support the cattle during the time of detection and breeding. The size of holding pastures will be determined by the size of the herd, but pastures should not be so large
that heat detection becomes even more of a problem. Some cattle ranchers prefer a different set of breeding facilities than those ordinarily used for vaccinating, branding, dehorning and similar chores.
Will it Pay to Synchronize Estrus?
The cost of each prostaglandin injection is between $10 and $1 2 per prostaglandin injection. Add to this the cost of semen, the inseminator, and labor required to make the program run successfully. In most of these programs, cattle are going through the chute three or four times. Figure out what your cost will be.
Some authorities say you can't expect to get more than 45 to 50 calves per 100 cows out of synchronized heat. Some have seen better results, and many not that good. It is usually necessary to run cleanup bulls in order to get conception rates up to 90 percent or better during the breeding season. Producers not using AI may find some advantage in using prostaglandins, but bulls would need to be fertility-tested to ensure high quality and ability to handle many females coming into heat within a short period of time.
This information was prepared by Laura Rutter.
Adapted from Beef Herd Management Reference Binder and Study Guide 422-1 |
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