Dr. Joe Ottobre, Associate Professor
Department of Animal Sciences
Data from DHI summaries of Ohio dairy herds indicate that the average estrous (heat) detection rate in Ohio is approximately 45%. Thus, Ohio dairy producers are missing 55% of the opportunities to breed cows, or are breeding at the wrong time, resulting in delays in conception and substantial economic loss. It is estimated that the calving interval in Ohio herds could be reduced by at least 40 days if more heats (>70%) were accurately detected.
Detecting dairy cows in heat is challenging because the duration of estrus in cattle is short. Estrus normally lasts from 10 to 18 hours, but could be as short as two to six hours - especially under hot environmental conditions. Even with twice-a-day heat checking, you may not observe heat in the cows with the shortest estrous periods. There is an advantage of the short estrous period of cows that should be appreciated, though. Estimation of time of ovulation and determining the best time to breed can be done more accurately in cattle than in some of the other domestic species.
An important point to remember about estrous detection in cattle is that the only definitive sign that a cow is in heat is that she will stand to be mounted. Cows mounted on the run are not displaying true standing estrus. Cows that mount other cows may or may not be in heat. It is true that estrous cows tend to be more active than herdmates, but to verify that they are in heat, you must see them stand.
There are secondary signs that you might use as clues that a cow is in heat, but these signs do not tell you for sure. Sometimes clear mucous secretions can be seen coming from the vulva. At the time of estrus, mucous secretions from the cows reproductive tract are more voluminous and less viscous than at other stages of the estrous cycle. The vulva may be swollen and pink. As mentioned above, cows are more active at the time of estrus. They may display an increase in vocalizations, nudging, and sniffing, and may attempt to mount other cows. Pedometers have been used to get an objective measure of their activity. Other secondary signs are decreased milk production and depressed appetite.
Occasionally, a small amount of blood may appear in the mucous secretions or a patch of blood may be observed on the tail. This is called metestrous bleeding and occurs about 35 to 45 hours after the end of estrus. This is not an indication of conception or failure to conceive. Observation of this phenomenon indicates that estrus and ovulation have already occurred. Therefore, if heat was not observed in a cow with metestrous bleeding, she should not be bred until her next detected heat.
To increase the rate at which cows are observed in heat, it is best to have cows in a situation where they are most likely to attempt to mount one another. Naturally, cows will be more inclined to attempt to mount when they have secure footing. Potentially slippery surfaces, such as concrete, and sloppy conditions, tend to discourage cows from mounting.
Cows that are distracted by other things, such as eating, are not very likely to investigate each other for estrous cues. As such, there is not much value in checking heat while cows are eating. Obviously, cows that are laying down will not mount other cows, nor will they be mounted. Therefore, cows should be encouraged to move around and interact during the observation period.
To optimize heat checking conditions, observations should be made while cows are in a clean area with good footing. A well-drained, dirt exercise lot works well, or a pasture if the cows are not too distracted by grazing. The cows feet should be properly trimmed. Cows with sore feet are less likely to mount other cows, or stand to be mounted. The cows should be grouped in reasonably close proximity, to encourage them to investigate one another. If they are spread out in a wide open space, group them so that they are closer together; however, they should not be grouped so tightly that their movement is restricted.
Observe the behavior of the cows for at least 20-30 minutes two times per day. Additional periods of observation would further improve detection rate. Since cows often come into estrus in the middle of the night, it is best to check as early in the morning and as late in the evening as possible. Take note of the animals that stand still and allow other cows mount. If the cows do not seem to be investigating one another, move them around to improve the opportunity for a cow to pick up the scent of an estrous cow.
It is important to keep good records of the occurrences of estrus, secondary signs of estrus, and even metestrous bleeding. Such records can be used to predict when the cow is due to return to heat. The estrous cycle of a cow ranges from about 18-24 days and averages 21 days. If a cow is showing estrus more frequently than this, she may have a cystic follicle that is stimulating estrous behavior repeatedly. In this case, the cow should be examined by a veterinarian.
There are various aids to estrous detection that the dairy producer could consider using. Aids, such as heat check patches, can be very helpful, but do not substitute for a conscientious program of regular observation for estrus. The electronic recording of mounts is an emerging technology that may prove to be effective. Methods for estrous/ovulation synchronization should also be considered for optimization of reproductive success. (See accompanying article entitled: Emerging Technologies for Estrous Synchronization.)
In summary, detection of estrus is critical for a successful breeding program. As such, the dairy producer should take this responsibility seriously and consider assigning this duty to a well-trained staff person. Higher estrous detection rates translate into improved fertility in the herd and ultimately result in greater economic benefits.