Factors for successful estrus synchronization
June 5, 2014
This is a busy time of year for ranchers — planting in the fields, fixing fence for summer grazing, and getting cows bred. If artificially inseminating (AI) heifers and cows, there are many options for getting the job done. Ranchers can choose between breeding the cows as they naturally come into heat through heat detecting or timed breeding may be a better option for those who don't have time to sit and detect cycling heifers and cows.
"If you don't have time to heat detect, then we go to timed AI protocols, which some studies show will yield better results," said George Perry, South Dakota State professor and Extension beef reproductive management specialist, who offered some tips on estrus synchronization protocols and warned ranchers about some common pitfalls that prohibit cows from getting bred.
"Factors that impact success for synchronizing cows include the percentage of animals detected in heat and inseminated, inseminator efficiency, fertility level of the herd, and semen fertility level," Perry explained. "If you are at 100 percent for all of these factors, you will have a 100 percent success rate; however, if you are at 70 percent for those four factors, suddenly your success rate drops down to 24 percent. There is no difference between the success of a bull and the success of artificial insemination if all factors are done correctly."
The success of a bull is pending a passed breeding soundness examination (BSE), along with the fertility level of the herd.
"When we look at the fertility level of a cow herd, we have to consider cycling status, protocol compliance, body condition, nutrition level, disease, embryonic mortality and stress," Perry said.
Meanwhile, a BSE looks at semen fertility levels, motility, morphology, soundness of the bull, and scrotal measurement.
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Looking at artificial insemination, it's important to have a reputable source for certified semen services. Once a rancher understands the factors for success, it's time to look at the practical application of breeding cattle.
"A cow shows estrus every 21 days, with a range of 17-26 days," Perry said. "All we do with synchronization is to try and control that to make it more convenient for us. When we synchronize in the U.S., we use hormones that the cow already has in her body naturally. We use three different hormones in the United States including Prostaglandin (PG), Gonadotropin Releasing Hormone (GnRH), and Progestins. There is nothing we use that doesn't already occur naturally in a cow's body. Our goal is get the cattle to come into estrus when we want them to."
Perry said if a rancher takes the time to understand these hormones, he can better manage what to do in his own breeding program.
"My recommendation to folks who are just learning how to AI is to use a single shot of PG because you can breed a few each day to allow you to gain some confidence and not have to face breeding a whole group at once," Perry recommended. "It's simple and affordable but only works if a heifer is already cycling."
The next option is GnRH, which causes a luteinizing hormone (LH) surge during ovulation, if there is a follicle present. (Ovarian follicles contain a single immature egg, and are developed every menstrual cycle.)
"Using GnRH is simple as it syncs follicular waves, works in cycling anestrus (non-cycling) cows, and can induce estrus cycles," he said. "However, it only works about two-thirds of the time. There must be a dominant follicle present."
Progestins can be administered through Melengestrol Acetate (MGA) protocols, as a feed additive, or through a Controlled Intra-vaginal Drug Release (CIDR), implanted into the vagina.
"The advantages of MGA protocols are it's simple to feed, inexpensive and works in both cycling or anestrus cows," he said. "The disadvantages are it's a labor to feed the animals, the protocol takes an extended period of time, and there is decreased fertility at first estrus after treatment."
"The advantages of CIDR protocols are it works in cycling or anestrus cows and induces estrus cycles in anestrus cows," he addd. "The disadvantages are the cost and labor to catch each animal."
No matter which protocol a rancher chooses to use, Perry said that, "The number one reason people don't synchronize their females is due to a prior bad experience. They tried a protocol once, and things went wrong."
So what can go wrong and how can ranchers avoid these common pitfalls? Perry shared some words of wisdom.
"Low body condition scores in females is a big factor that leads to failure in getting cows bred," Perry said. "Their bodies don't have the energy to signal breeding. On the other hand, if you have heifers that are too fat, their bodies won't cycle because her body won't recognize the hormones."
Another factor that can be a detriment to breeding success is stress.
"Any stressors can cause a loss in an estrus cycle," he said. "A cow knows she's pregnant at 16 days, but if she experiences shipping stress or nutritional decline, this can cause her to lose that pregnancy. Then you can lose a whole cycle before she can get bred again."
Cattlemen can also consider combination protocols, which take advantage of multiple options for synchronizing and breeding cows.
"The advantages of combining protocols are that it works in cycling and anestrus cows, can induce estrus cycles in anestrus cows, and offers tighter synchrony of estrus," he said. "The disadvantages are it's more complicated, more labor intensive and more expensive."
Before selecting an estrus synchronization protocol, it's important to consider the following factors: condition of cows, whether or not cows are cycling or anestrus (post- calving pubertal or prepubertal heifers), length of time to start the breeding season, cost, labor, facilities and experience with synchronization and artificial insemination.
"Make sure to give the correct injection on the day specified in the protocol," Perry advised. "Use at label dose, and follow Beef Quality Assurance (BQA) guidelines for all injections."
Even if a rancher doesn't want to AI, synchronization can offer a tighter calving season when breeding naturally.
"For natural serve when synchronizing cows using these protocols, you can plan on one bull being able to handle 20 cows," Perry said. "The benefits of this is there is no estrus detection; however there are limitations on the serving capacity of the bull because he can only do so many in a short period of time."
"I'm often asked why there are so many protocols out there," added Perry. "I always return these questions with some of my own. What are your goals? Are the animals cycling? Some protocols work to get cattle cycling and others don't. How long until you want to AI? Answer these questions to help you choose the best protocol for your breeding needs."
Perry recommended that ranchers take advantage of online applications to help answer the many questions that come along with breeding cows. The Iowa Beef Center offers an Estrus Synchronization Planner, with an updated 2014 version available for a free download, at iowabeefcenter.org/estrus_synch.html. The features include recommended systems for cows and heifers, select systems by protocol and breeding program planned, list of daily activities, barn calendar generator, cost/AI pregnancy, and support materials.