How to Tell when a Cow or Heifer is in Estrus

Co-authored by Karin Lindquist

Last Updated: December 10, 2024 Approved

Estrus is defined as the period where a female (in this case, a cow or heifer) is receptive to a male (or, the bull). Estrous, on the other hand, is the whole reproductive heat cycle that a female goes through, from heat period to no heat period (Proestrus, Estrus, Metestrus, and Diestrus).^{[1]
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Estrus is actually a result of the release in estrogen from a maturing follicle in the cow's ovaries prior to ovulation. Secretions from the reproductive tract act as lubricant for breeding and help sperm travel to the uterus.

Below are the steps that describe the physiological steps of how estrus occurs in female bovines, and how to detect a cow or heifer that is in heat.

Steps

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Cows and heifers typically go into heat or estrus every 17 to 24 days (average is 21 days). A bred cow or heifer will usually not go into heat until a few weeks after giving birth.^{[2]
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Compare how a female in heat behaves differently than if she were not in heat.

Method 1

Method 1 of 2:

Physiology of the Bovine Estrous Cycle

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Increased levels of estrogen are produced by a maturing follicle in the cow's ovaries. Secretions along the reproductive tract allow for easier breeding and aid for sperm to travel through the uterus to the ovum. Standing heat usually lasts for 12 to 24 hours, after which ovulation occurs.
The mature follicle ruptures and the ovum travels through to the fallopian tube where it awaits the arrival of the sperm. Ovulation occurs in response to a surge of Luteinizing Hormone (LH) from the pituitary gland in the cow's brain. Ovulation occurs 12 hours after the cow goes out of heat.
These cells regenerate and grow to create the corpus luteum (CL) in the area where the mature (now dead) follicle had ruptured and release the ovum.
The growing CL produces high levels of progesterone which causes other follicles to regress and prevent from further maturation. During the early part of this phase, a portion of the lining over the caruncles (which are small protuberances on the inner uterine wall which the placenta attaches itself during the gestation period) becomes engorged with blood and bleeding from smaller capillaries may occur. Bloody discharge may be seen 2 or 3 days after the female has experienced estrus, which is caused by the sudden decrease in estrogen in her system. If you haven't seen the cow in heat, this is as good an indication as any that she had just been in heat a few days ago.
The CL usually maxes out growth by the time days 15 or 16 arrive. This period is called Diestrus (or, "between estrus") because it is the longest phase of the estrous cycle. Progesterone secreted by the CL block any LH release from the pituitary gland, resulting in the ovaries being relatively inactive. No follicles are able to mature or ovulate. The cervix is closed up tightly and there are also no secretions from the reproductive tract during this time.^{[3]
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Estrogen secretions stimulates the uterus to secrete prostaglandins, causing rapid regression of the CL.
Very little progesterone is released, which means that progesterone and other reproductive hormones are no longer able to have any blocking effect on anything else. Several follicles on the ovaries begin to grow; one becomes dominant, secreting increasing levels of estrogen as it reaches maturity.
An increase in estrogen and corresponding decrease in progesterone brings the cow back into heat again, starting the cycle back to 0.

Method 2

Method 2 of 2:

Looking for Behavioral and Physical Signs of Estrus

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1
Walk out to the pasture or corral where you are keeping your cows and/or heifers.
- The best time to observe any behaviours is in the morning and the evening.
Find some place to sit where you can easily watch the behaviour of your cattle but at the same time, don't really attract the attention of your animals. Bring your binoculars and a notepad to do any recording of what you see.
3
Look for behavioral signs if estrus: (Note that the herd is highly sensitive to when even one female is in heat!)
- She may be acting restless and mooing a lot
- She will be wandering around the pasture or corral in search of a mate
- She may travel thrice or four times as much as she does when she's not in heat
- Sniffing or nudging may occur in the vulva region between her and other cows
- More vigorous interaction may be observed between that female in heat and her herd-mates, from excessive licking to even fighting.
  - Usually if you have a group of cows that are in heat at the same time, they will be sticking together, fighting and mounting each other.
- She may attempt to ride other cattle, and stand for them to mount her. Putting her chin on the back or rump of another cow to test whether that cow will stand for her may be seen. If the cow stands, she's also in heat. If she doesn't, and turns around to give her a good bunt with her head, she's not in heat.
- If there's a bull around, she will also mount the bull before she stands to let him mount and breed her. During her early heat period, she will often let other cows mount her before she lets the bull service her.
  - During this time, before she lets him mount her, the bull will be sniffing and nudging her vulva region, and doing a Flehmen response (where he curls back his nose, raises his head in the air as high as it can go, smelling the pheromones she's emitting in her urine and vaginal secretions). He will also rest his chin on her rump or loins to test if she'll stand for him or not.
4
Also note any physical signs of estrus:
- Clear discharge from her vulva; the discharge would be so viscous it has the consistency of egg white. You will see it hanging from her vulva in a long string.
- Her tail may be slightly raised and off to one side.
- Her vulva will also look enlarged and swollen red.
- If she's in with other cattle, the hair over her rump, hipbones and tailhead will look ruffled.
- She may also have a bit of dirt or mud on the rear part of her sides from other cattle mounting her. This may not be as evident if they are out on a clean pasture with no mud patches to speak of. However, during springtime when she is shedding, there may be hair that has rubbed off from other animals mounting her, and she may have abrasions and raw areas over her tailhead and hips if she was mounted quite frequently. This usually happens when you have more than one bull in the herd and there was a bit of competition going on.
- If she was actually bred, she will hold her tail out and her back will be arched for several hours or even days. This is because of the vaginal irritation she experiences from the bull thrusting his penis in her. This physical sign will usually last for 24 hours or more, especially if she's been serviced repeatedly by more than one bull.

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Can I use my bull to breed his daughters?

Karin

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It's not recommended, especially if you don't know the history of your bull and the dams of these heifers as far as genetic abnormalities are concerned. Inbreeding can bring out the ugly in terms of genetic defects and abnormalities, which can result in poor-doing or stillborn calves. Use a different, unrelated bull on the heifers to avoid this.

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So a heifer can only be bred in a 24 hour period and then she is out of heat?

Karin

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Yes, that's right.

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How is it safe to breed a cow after calving?

Karin

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It's not safe at all if you try to do it immediately after. You must wait 90 days after she's calved to get her bred again. This gives her uterus time to shrink back into normal shape and size, and allows her hormone cycles to get back to normal, where she is cycling regularly instead of irregularly.

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Tips

The tail-out sign is a definite sign that a cow has been bred, especially if you weren't around to see the bull[s] servicing her.

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A cow in heat is very obvious in her behaviour and mounting actions, especially in a large herd. This behaviour can be seen from a distance and is what will usually attract a bull.

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Mounting is a sure sign that a cow is in heat. You can usually quickly tell which female is in heat and which isn't by studying the actions of the herd and of that particular female that is causing all the uproar.

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Warnings

Cows in heat can be dangerous, especially if they are alone and have no other cows to interact with. You are obviously a part of her herd, and when she's in heat, she will try to mount you.

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Bulls can be very dangerous during breeding season, especially those who do not know how to trust nor respect a human or a human on horse-back. If they feel you are a threat and are competition to his harem, he will challenge you and, if worse comes to worse, charge you.
- Even if a bull respects your space and wants nothing to do with you even during breeding time, never let your guard down nor get complacent around a bull.
  - Always keep an eye out for trouble, and always have an escape route planned out if you get into a bit of a fix with a bull.
    - Carry a 2" diameter 3' to 4' piece of PVC pipe, an axe handle or a thick, stout stick with you if you suspect any bull may try to challenge you.
      Better safe than sorry.
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