'Estrus' is defined as that period in which the female (in this case a cow or a heifer) is ready for the male (the bull). Estrus is actually the entire reproductive cycle, from heat to its end (Proestro, Estro, Metestro and Diestro).
At this stage, the ovaries release estrogen into the mature follicle before ovulation. Secretions from the reproductive tract act as a lubricant for mating and help sperm pass into the uterus.
Here are the physiological steps of estrus in female cattle and some tips on how to tell if a heifer is in heat.
Steps
Step 1. Reproductive cycle of cattle
Cows and heifers usually go into heat every 17-24 days (the average is 21). A cow that has been mounted will not go into heat until two weeks after giving birth.
Step 2. Behavioral changes
To learn these, compare the behavior of a female in heat versus one at a normal stage in her life.
Method 1 of 2: Bovine Estro Cycle Physiology
Step 1. Day 0 - Heat Phase
High levels of estrogen are produced by mature follicles in the cow's ovaries. The secretions from the reproductive tract allow for easier mating and help the sperm reach the egg. The heat lasts 12 to 24 hours after which ovulation occurs.
Step 2. Ovulation
The mature follicle ruptures and the egg reaches the fallopian tube where it awaits sperm. Ovulation comes in response to the luteinizing hormone (LH) surge from the pituitary gland in the cow's brain. Ovulation occurs 12 hours after exiting the heat.
Step 3. Day 1 and 2 - Alteration of cells in the follicle
These cells regenerate and grow to create the corpus luteum (CL) in the area where the mature (now dead) follicle has ruptured and released the egg.
Step 4. Days 2-5 - Corpus Luteum Growth
Growing CL raises progesterone levels which cause other follicles to regress, preventing them from ripening. During the first part of this phase, a portion of the lining above the caruncles (small protuberances in the inner wall of the uterus to which the placenta attaches during gestation) becomes engulfed with blood and small bleeding can occur. The blood loss could occur on the second or third day after the female has oestrus, due to the sudden decrease of estrogen in her body. If you haven't noticed the heat yet, this is a good indicator of dating as well.
Step 5. Days 5-16 - Further development of the corpus luteum
CL usually reaches its maximum magnitude by day 15 or 16. This period, called Diestro (or "between estrus") is the longest phase of the cycle. The progesterone secreted by CL blocks the release of the luteinizing hormone by the pituitary, with the result that the ovaries remain fairly inactive. No follicle reaches maturity or ovulation. The cervix is closed and there are no secretions from the reproductive tract.
Step 6. Days 16-18 - The follicles start growing again in the ovaries
The secretions of estrogen stimulate the uterus to secrete prostaglandins, causing the corpus luteum to regress.
Step 7. Days 18-19 - The corpus luteum stops working
Very little progesterone is released, which means that this and other reproductive hormones are no longer able to have any blocking effects. Many follicles in the ovaries begin to grow, one becomes dominant secreting ever-increasing levels of estrogen as it comes to maturity.
Step 8. Days 19-20 - New heat
An increase in estrogen and the corresponding decrease in progesterone brings the cow back into heat, restarting the cycle from day 0.
Method 2 of 2: Look for Physical and Behavioral Signs of Estro
Step 1. Go to the pasture or pen where you keep the cows
The best times for behavioral observation are in the morning and in the evening
Step 2. Find a place to sit and observe all the cows at the same time, don't try to get their attention
Bring binoculars and a notebook to write down everything you see.
Step 3. Behavioral signs of estrus (note that the herd is more sensitive to even a single female in heat!):
- The cow may be restless and moo a lot.
- It will go back and forth in the pasture or pen in search of the male.
- It may move three or four times more than it would when not in heat.
- Sniff or touch the vulvar region of other cows with your nose.
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More vigorous interaction can be observed between the female in heat and her mates, from excess licking to fighting.
Usually, if you have a bunch of cows in heat at the same time, they will stick to each other, fighting and mounting each other
- The cow may try to mount other members of the herd and allow itself to be mounted as well. He puts his chin on other cows' backs or lumps to see if they are standing still. In that case, the other subject is also in heat. But if he moves, turns and heads her, she's not in heat.
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If there is a bull around, the cow will mount it too before allowing itself to be inseminated. During the heat phase, she will often let other cows cover her up before indulging in the bull.
In this phase, before the cow lets itself be mounted, the bull will smell the vulva, touching it with its muzzle and giving it what is called the 'Flehmen response' (wrinkles his nose, raises his head towards the air, smelling the pheromones that emits with urine and vaginal secretions). The bull will also rest its chin on the cow's back and back to see if it stays still or moves
Step 4. Physical signs of estrus:
- Transparent discharge from the vulva they will be viscous and of the consistency of an egg white. You will see them hanging from the vulva like a long strip.
- The tail may be a little raised and sideways.
- The vulva will be enlarged, swollen and red.
- If the cow is together with others, the hair on the flanks, lump and tail will be matted.
- The cow may have some mud or grime on the back of her hips due to her attempts at riding. It may not be obvious if the herds are in the pastures and there is no mud. However, in the spring, when it has losses, there may be other animal hairs, the cow may have abrasions or wounds on the tail and flanks, especially if it has been mounted often. This usually happens when you have more than one bull in the herd and there has been some competition.
- If the cow has mated, it will hold its tail out and its back will remain arched for hours or even days. This is due to vaginal irritation following penetration. This physical sign usually lasts 24 hours or more, especially if the cow has been ridden by more than one bull.
Step 5. Record the nameplate number or name of the cow that is in heat or that has been impregnated in your registry
Advice
- Riding is a sure sign that the cow is in heat. You can quickly understand that the cow is in heat by studying the actions of the herd and that particular female causing the havoc.
- A cow is aware of its own behavior and being mounted, especially within a large herd. This behavior is noticeable from a distance and is what attracts the bull.
- The signal of the queue towards the outside is the definitive one that reveals to you the successful mount, especially if you were not present when the bull 'had fun'.
- Check the herd and heifers, once or twice a day, to see which ones have gone into heat. This is especially important if you want to artificially inseminate females and need to keep timing.
Warnings
- Cows in heat can be dangerous, especially if they are alone and have no one to interact with. You are part of the herd and in that case it will try to mount you too.
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Bulls can be very dangerous in the breeding season, especially those who don't know how to respect people alone or on horseback. If they perceive you as a threat and a competitor, they will challenge you and at worst they will charge you.
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Even if a bull respects your space and doesn't seem to want anything to do with you during mating season, never let your guard down or rest on your laurels when you are around him.
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Plan for problems and plan an escape route in case a bull targets you.
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Bring a 2-inch (5-cm) piece of PVC pipe, an ax handle, or a large, gnarled stick if you suspect a bull might charge you.
Better safe than sorry
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