Heat (estrus) is simply the period of time when a cow or heifer is sexually receptive and signals that an egg, ready to be fertilized, is about to be released. It normally occurs every 18 to 24 days. In a natural breeding program, the bull is the one that determines when a cow is in heat. In an AI program, you make the decisions.
Heat detection is just another step in the more intensive management system that is part of artificial insemination. It is not difficult, but it does demand both time and attention. If you want your AI program to be successful, you cannot cut corners here.
You have to learn what the bull knows instinctively, but once you have that knowledge, you can easily get the equipment needed for detection eyesight, a pencil and a notebook. Your cows must be identified, too. Ear tags, neck chains or number brands will work, just as long as they are easy to read and can be read from a distance.
Essentially, successful heat detection begins with understanding one simple fact: there is only one sure sign of heat -- a cow stands while other animals mount her. This is appropriately termed standing heat.
It is recommended that one person be responsible for heat (estrous) detection. For the sake of discussion, we are going to assume that that person is you.
During the time you are detecting, neither you nor the cows should be distracted in any way. Heat detection periods should not be scheduled to coincide with feeding. Success requires absolute, and total attention.
Because cows' responses can be modified by disease, hunger, thirst, fatigue, or fear, it is up to you to make sure the cows are healthy and content and in a familiar environment. They should be given time to get used to the breeding pasture before the breeding season. The cows should be familiar with you and not afraid of your presence. When you detect, it is important to move through the herd quietly.
Adequate facilities vary from operation to operation. The area for detection should be large enough to allow the cows to mingle freely, but small enough so that all of them can be watched at once.
Of course cows have to be cycling, which means they must be healthy and have been receiving a good level of nutrition. Age and weight determine when heifers first cycle, but 13 to 14 months of age is a good rule of thumb. Cows need about 60 days after calving before rebreeding; first calf heifers may require a longer period of time, particularly if the nutrition program is less than optimal.
Be aware that weather changes and temperature extremes can cause cows to exhibit estrus differently (or less noticeably). You can't do much about either of those factors, but you should watch even more carefully at those times.
All told, about five percent of a normal cycling beef herd should be showing heat (estrus) on any given day.
You will need to spend at least one hour, twice a day, every day, heat detecting. Ideally, you will heat detect first thing in the morning and then again late in the evening. Both research and practical experience indicate this pattern of visual heat detection is well worth the time invested.
Data collected at the Meat Animal Research Center in Nebraska show that 58 percent of the cows in heat were spotted with one morning observation. Only 28 percent were found if the daily check was at noon; 49 percent were detected by checking only in the evening. With two checks, one first thing in the morning and the other late in the evening, 94 percent were detected.
A Cornell University study yielded similar patterns: from 6 a.m. to noon, 22 percent of the cows showed heat; from noon to 6 p.m., 10 percent did; from 6 p.m. to midnight, 25 percent; and from midnight to 6 a.m., 43 percent.
Accuracy of detection increases with frequency of observation, but the twice-a-day routine is practical and produces acceptable results.
Incidentally, technology does exist to heat detect electronically all day, every day. In a study at Colorado State University, researchers were able to identify more cows in estrus with the HeatWatch Electronic Heat Detection System (HW) than with twice-a-day visual heat detection.
In a nutshell, the HW system is an integrated electronic hardware and software system designed to detect, transmit, and record each time a cow is mounted during behavioral estrus. A transmitter mounted to the tailhead of cows records the frequency, time and duration of each mount. Using these real time observations, researchers discovered more cows in the study (235 head in two different herds) initiated standing estrus between 6 a.m. and noon than during any other six hour period of the day. Moreover, 28 percent of the unsynchronized cattle in the study displayed mounting behavior only in the darkness between 9 p.m. and 5 a.m.
All of this essentially means that timing is of great importance in a successful AI program. The average time a female is in standing heat is about 12 to 18 hours; cows usually ovulate 25 to 30 hours after first standing. The life of an egg, once released, is six to 10 hours.
On the other side of the fertilization equation, sperm cells have to be in the reproductive tract for about five to six hours before they are capable of fertilization. So, in an ideal world, insemination should take place six to eight hours before ovulation.
Traditionally, cows and heifers are inseminated about 12 hours after they are first observed standing. Those standing in the morning are bred that night; those standing in the evening are held over and then inseminated first thing the next morning. It works well with the twice-a-day routine established for detection.
Although conception rates will not drop significantly if insemination times aren't exact, programs with consistently good results tend to inseminate close to the prescribed times. However, there is research to support that some flexibility in the breeding schedule can be economically feasible, especially if you hire an outside inseminator. In that case, many producers achieve success with once-a-day breeding. We suggest you have an AI professional advise you and that you consider all factors when making this sort of decision.
Secondary Heat Signs
When you are detecting for estrus, remember the primary sign is standing heat. There are, however, secondary signs you should know and note. They can appear as early as 48 hours before standing heat.
A cow coming into heat may mount other cows, and she may urinate frequently. She may also lay her head over the backs of her herdmates. Nervousness, walking the fence, bawling, spooking, butting other cows and standing while others are lying down are other possible signs. In addition, a cow coming into heat can be off her feed. She may not let her milk down, and her calf may be protesting. The lips of her vulva can also be red and slightly swollen; she may have watery mucous hanging in strings from her vulva. She may pass a lot of mucous, which is most obvious when she is mounting another cow.
Cows in heat, or about to come into heat, tend to congregate. Because mounting activity increases when more than one cow is in heat, it is not a bad idea to keep a cow in the herd that is standing until it's time for her to be inseminated. If you do that, keep in mind that footing must be good.
When a cow is in heat, she's likely to have mud on her rump and sides, courtesy of the cows that have been riding her. For the same reason, the hair on her tail-head can be rough and matted (this will be most noticeable after heat - too late to be effective). Often you will have bull calves in the herd attempting to mount her as well.
After heat, her vaginal mucous will be thick and rubbery; one to three days after heat, you may notice a bloody discharge. This is no indication that she is or is not pregnant; it only means she's been in heat. If you failed to observe heat and see a bloody discharge, write down the cow's number and the date in your notebook so you can pay special attention to her in about 15 days.
Remember that the cow that rides may or may not be in heat and that the secondary signs vary so much in length and intensity that they are not reliable in determining when an animal should be inseminated. They are helpful, though. Once you've observed any of these secondary heat signs, make it easy on yourself by using your pencil and notebook to record them. Don't trust your memory, write it down.
By the way, records also help in heat detection. Accurate information compiled and written on heat expectancy charts helps you anticipate when cows are most likely to come into heat.
In heat detection, observation is essential but there are times when a cow either will not stand or will stand for such a short period of time that you miss her. That's when heat detection aids come in handy. Just remember they do not replace careful observation.
The chin ball marker is one such aid. It is a device worn beneath a detector animal's chin that works like a large ball point pen, leaving a mark on the back of the cow that has been mounted.
Detector animals were originally bulls that had been altered to prevent their ability to breed. Alterations include removal of the penis, relocating the penis to the side, suturing back the penis, and blocking the tip. These bulls retain their sexual drive but can't have sexual contact. Vasectomized bulls also can be used. They are sterile; however, because they can have sexual contact, they can spread disease.
In terms of numbers, herds with high cycling activity need a detector animal for every 30 breeding females. In less frequently cycling herds, a 1:40 or 1:50 ratio is acceptable.
Another popular aid, KaMar Heat Mount Detectors, are used successfully in a number of AI programs, particularly when they're used in conjunction with detector animals. It is a white plastic device that is glued to the tailhead of any cow eligible for breeding in the next 21 days. Prolonged pressure from a mounting animal's brisket turns the device red.
The KaMar detector must be completely red, not just partly red, to give an accurate indication that a cow stood to be mounted. Keep in mind that the KaMar detector is not recommended when cattle are pastured in lots containing low tree branches or heavy brush since rubbing could cause a false reading or tear the KaMar detector off.
A more recent development is a similar system that goes by the name of Bovine Beacon. It is also applied to the tailhead. The design and technology behind it mean that a single mount will break the chemiluminescent ampule contained inside, giving off a bright red glow that can be seen in daylight or darkness.
As mentioned previously, electronic heat detection systems are also taking root in some programs as an effective heat detection tool.
Once you have done your detecting, the cows you have determined to be in heat can be quietly moved from the herd to the holding area near the breeding facilities.
Much of the information in this article is based on the Artificial Insemination Handbook, available in English, Spanish and Portuguese versions and is produced and distributed by the National Association of Animal Breeders. To order a copy of the handbook, contact NAAB at 573-445-4406.