Estrus synchronization is the control of the reproductive process such that females can be bred with normal fertility during a short, predetermined period. This control facilitates breeding in two important ways: it reduces or eliminates the need to detect heat in cattle and allows the farmer to plan the breeding. If the majority of a herd can be induced to exhibit signs of heat or estrus at about the same time, the farmer can organize for a few days of intensive insemination.
However this technology generally requires skilled management and adequate facilities therefore estrus synchronization may not be for every farmer. Cows respond poorly if not fed properly or if body condition is less than adequate. The level of herd health is also a factor, as there are many causes of infertility in cows.
Your choice of system depends on cost, labor, facilities, and the amount of time you want to devote to detection of heat in cattle and breeding. Success requires a cow herd with a close calving interval, good nutrition, good facilities, high quality semen, an experienced inseminator, and accurate heat detection (if heat detection is used).
Estrus synchronization of cattle can be achieved by the use of
• Prostaglandin injections
• “progesterone-like” ear implants and estradiol/progesterone injections
• A combination of an orally active progestogen (MGA) and prostaglandin
Prostaglandins are highly effective in synchronizing estrus or heats in cattle. They act by causing the corpus luteum to regress, thereby allowing the cow to return to heat. This cannot be happen if cows are not having estrus cycles and functional corpus luteum which usually occur between five and 18 days of the cycle. Prostaglandins do not cause non-cycling cows to come into heat. Their only effect is to cause regression of a functional corpus luteum (CL).
Several prostaglandin products are available by prescription from a veterinarian. The labels should be read carefully and closely followed. These products will cause abortions in pregnant cattle and should not be handled by pregnant women. They must also be handled with extreme caution by anyone who suffers from asthma
There are three basic systems used with prostaglandins:
1. Cattle are detected for heat and inseminated for four days. On the morning of the fifth day, cattle previously detected as not in heat are injected with prostaglandin.
Heat detection and breeding continues for another six days. This method is less expensive in drug (prostaglandin) costs, but requires more time detecting heat and performing artificial insemination. This approach allows the farmer an opportunity to inseminate all cycling females within a ten to twelve day period.
2. Two injections of prostaglandin are given 11 days apart.
The first injection interrupts the cycles of those cows with mature (more than five days old) CL’s. Any normally cycling cow that did not have a mature CL at the time of the first injection will have one by the time of the second injection (11 days later). Those cows that responded to the first injection will now have seven to eight day old CL’s. Therefore, all cycling cows will be synchronized by the second injection. Cows are either bred upon the detection of heat or within 72 to 80 hours after the second injection, regardless of any signs of heat. Improved conception rates occur when the synchronized females are bred on detected heat rather than by appointment.
3. Cows are injected with prostaglandin and if detected in estrus during the next six days they are inseminated.
Cows in the first five days of their cycle at the time of the injection will not be synchronized. Therefore a proportion of cycling cows will not be eligible to respond to prostaglandin treatment and will not be detected in synchronized estrus. Heat detection should continue for three more weeks if those cows are to be bred artificially. The farmer can apply a second injection of prostaglandin to those cows not detected in heat. This injection should be given 11 days after the first one. If the farmer wishes to discontinue the heat detection efforts, these cows can be bred by cleanup bulls. If fewer than 50 percent of the cows or heifers are detected in heat after the first insemination, then the second injection will give very disappointing results.
Synthetic Progesterone and Estradiol (Syncro-Mate-B System)
This synchronization program is not approved for lactating dairy cows. A combination of synthetic progesterone and estrogen compound is used. An ear implant containing the compound Norgestomet is inserted under the skin on the back of one ear 12 days before the intended time of insemination. A two milliliter intramuscular injection containing Norgestomet and estradiol valerate is also administered at this time. Nine days later the implant is removed and all cycling females are expected to be in estrus within the next three days. Starting at the time of implant removal, nursing cows should be separated from their calves for 48 hours. This results in a greater percentage of cows exhibiting heat in a tightly synchronized pattern. Because this method causes cattle to come into heat more uniformly than those in the prostaglandin programs, it has become the method of choice by many A.I. technicians who wish to breed by appointment.
Orally Active Progestogen (MGA) and Prostaglandins
Another estrous synchronization technique is the combined use of MGA and prostaglandin. Melengestrol acetate is a feed additive commonly used in heifer feedlot rations to block the cycling activity of heifers. When fed for a short period of time and then removed from the diet, the absence of MGA tends to allow a large percentage of cattle to exhibit estrus together. Compared to normal estrus, fertility at the first heat after MGA removal is reduced but subsequent heats are normal.
This program entails feeding 0.5 milligrams of MGA per head every day for 14 days. After 14 days, MGA is removed from the feed. Most of the females will then exhibit heat. Seventeen days after the MGA feeding has stopped, each female is injected with prostaglandin to interrupt the next cycle. Two to five days later, females are bred following detected standing heat. All remaining females can then be inseminated by appointment within 72 hours after the prostaglandin injection.
An important consideration is that the MGA/prostaglandin synchronization program must be started precisely 35 days before the start of the breeding season. This means that prior planning must be done to make sure that the feed containing MGA is prepared and ready to feed five weeks before the breeding season begins.