Estrous Cycles in doodles

In female dogs, the breeding cycle, also known as the estrous cycle, is the regular natural change that occurs in the reproductive system of female mammals. This cycle prepares the body for pregnancy and birth.

The estrous cycle occurs in most female mammals, including dogs, and is characterized by hormonal changes and physical signs that indicate the animal is sexually receptive, or "in heat."

The estrous cycle in dogs typically occurs every six to eight months, although this can vary depending on the individual dog and its breed. The cycle is usually shorter in small breeds and longer in large breeds.

The estrous cycle is divided into four stages:

Proestrus: This is the first stage of the estrous cycle, and it is characterized by swelling of the vulva and a bloody discharge. The female dog may also be more affectionate and attentive to male dogs during this stage.
Estrus: This is the second stage of the estrous cycle, and it is characterized by a significant drop in estrogen levels. The female dog becomes receptive to male dogs and may allow them to mount and breed. Ovulation (the release of eggs from the ovaries) usually occurs during this stage.
Diestrus: This is the third stage of the estrous cycle, and it is characterized by a rise in progesterone levels. The female dog is no longer receptive to male dogs and pregnancy can be determined during this stage.
Anestrus: This is the fourth and final stage of the estrous cycle, and it is characterized by a lack of estrogen and progesterone. The female dog is not sexually receptive during this stage, and the body is preparing for the next estrous cycle.

It is important to note that not all female dogs will go through the estrous cycle at the same time or with the same regularity. Some dogs may experience irregular cycles or may not go into heat at all, especially if they have been spayed (had their ovaries and uterus removed). Spaying a dog can also help prevent certain health problems and unwanted pregnancies.

The Estrous Cycle in Doodles

The estrous cycle is divided into three parts: proestrus, estrus, & diestrus.

Proestrus starts when the bitch shows her first signs of heat: swelling of the vulva, a blood-tinged vaginal discharge, and attractiveness to male dogs. During this time her estrogen level is rising, and her body is preparing for ovulation. This period lasts 9 days on average, with a range of 2 – 22 days.

Estrus starts when the bitch solicits and permits mating. You may see her flagging (holding her tail to the side) or showing lordosis (arching her back to raise her hind end and vulva up for the male). During this time her estrogen is dropping, her progesterone is rising, and her LH (luteinizing hormone) peaks and falls. This period lasts 9 days on average, with a range of 4 – 21 days.

Diestrus starts when the bitch aggressively prevents mating. During this time her progesterone level is slowly falling. This period lasts 120 days on average in the non-pregnant bitch.

Anestrus is the inactive period until the start of the next estrus.

What Hormones Play a Role in Ovulation?

The first hormone of significance is estrogen. Estrogen prepares the reproductive tract for breeding. It causes the vagina to thicken and diapedesis of red blood cells to occur. This is the part of the estrous period that is highly variable dame to dame — it may be as short as 1 day or as long as 21 days or even longer.

After the estrogen period, the next hormone of significance is the Luteinizing hormone or LH. LH is the biological trigger for ovulation in mammals, which we denote as “Day 0.”

Progesterone is baseline prior to the LH surge, begins to rise at the time of the LH surge, is in the 4-8 nanograms-per-milliliter range by time the dame ovulates, and is greater than 20 nanograms per milliliter (often 30-40 ng/ml) range by the time the dame is in her peak fertile period.

Timing Breeding - ovulation timing (OVT)

Natural mating: If you plan to breed by natural mating, you can either put the male and the bitch together for the entire estrous period, or allow them to mate every other day as long as the bitch allows.

Preferably there should be at least three breedings in the first 6 days after ovulation.

Breeding by following hormones: following the bitch’s hormonal changes allows you to know precisely when she ovulates, and therefore when her best breeding times are, and when she is likely to deliver. This allows you to breed using fresh chilled semen, frozen semen, or by giving the pair limited access to one-another. It also allows for accurate calculation of the due date, which is especially important if a caesarian section is expected. Fresh chilled semen breedings are expected to produce puppies 80% of the time. This means that 20% of the time even if everything goes as planned puppies may not result.

Measure a baseline progesterone at the first noticeable signs of heat. It usually measures < 1.0 ng/ml at this time.
About 4 days later, start measuring progesterone every other day. We save serum each time so that LH can be checked later, if needed. This frequency is necessary to ensure that ovulation is not missed.
When progesterone is > 2.0 ng/ml (or twice the baseline level), we measure LH. This rise in progesterone is the best indicator that the LH surge has taken place. Since the LH surge lasts only 12 – 24 hours, it can easily be missed if that was the only level you were following. By following the progesterone, you can narrow down the time of the LH surge very accurately.
The LH surge initiates ovulation
Eggs are released (ovulated) 44 hours (2 days) after the LH surge, on average. The eggs are viable for about 3 – 4 days after this (5 – 6 days after the LH surge)
Breeding the bitch on days 3 and 5 (or 4 and 6) after the LH surge ensures the maximum conception rate and largest litter sizes. If only one breeding is possible, do it on day 5 or 6 after the LH surge.
Gestation lasts 65 +/- 1 day from the LH surge (63 +/- 1 day from ovulation). If the hormonal information is not available, gestation lasts 63 +/- 8 days from mating.
In short, when female dogs are in heat, they release eggs for about 48 to 72 hours. These eggs can't be fertilized right away. It takes around 60 hours for the eggs to change in a way that allows them to be fertilized. Once this change happens, the eggs can be fertilized for about 48 hours. Male dog sperm can stay ready to fertilize the eggs for about 5 days inside the female dog's reproductive system. So, overall, the window for dogs to mate and conceive puppies lasts about 7 days from when the female dog goes into heat.

During the first 20 days, the embryos are free-floating in the uterus. They implant around day 20, and from then until day 40 is when the majority of development takes place. After day 40 the skeletons are mineralizing, and the puppies are steadily growing.

Timing and Frequency - Most dames have their first 'season' before they are twelve months old, although some can be as late two years, although this is irregular. Having a 'season' is also commonly called 'in heat'. The subsequent frequency of the 'heat' cycle depends on the breed but is usually every five to ten months.

Coming into season - There are a few tell-tale signs of when your bitch is about to come into season. Not all bitches show all the signs, but usually, some are present.

Physical and Behavioral Changes With LH Surges

Loss of appetite
Frequent urination
Licking around the vulva
Swelling around the vulva
Considerable edema, or swelling, and dark red bloody discharge
As estrogen drops and progesterone begins to rise at the start of the LH surge, the edema will go out of the vulva and vagina. You may observe softening of the skin around the vulva and a change in the discharge from a dark bloody red to a more serum straw color secretion
The day of the LH surge is often when there is a dramatic change in flagging behavior. For example, when a bitch wasn’t flagging in the evening but is in the morning. This abrupt change is often on the day of the LH surge (Day 0) or right around it. This is when fellow house mates will start mounting, but the male is not that interested yet. Male dogs will usually intensify their interest and go off feed and cry for the female on Days 4, 5, 6, and post LH surge.

The most obvious sign is spots of blood around the vulva, in this case, you need to make a note of the date and start making arrangements for the mating. Knowing when your bitch is ready - There are two stages of a season, pro-oestrus and oestrus, the length of each stage varies according to the breed, but it's usually around eight to ten days. During the pro-oestrus stage, the bitch will release a blood-stained discharge and her vulva will be enlarged, she will more than likely reject advances from a male dog at this time. During the oestrus stage, the vulva will swell further and the discharge will be pale yellow in color. It's during this second stage that the bitch will welcome the male dog. The most fertile period is two days after the onset of the second stage. This is the period of ovulation.

LH Controls Ovulation Timing and Prepares For Pregnancy

Luteinizing Hormone (LH) is one of several important chemical messengers (hormones) produced by the pituitary gland, which sits just beneath the base of the brain.

When LH is released by the pituitary, it starts a chain reaction that ultimately results in the release of eggs (ovulation) from the ovaries into the fallopian tubes where fertilization normally takes place. The fertilized eggs pass down the tubes to the uterus (womb) where they implant and develop into the growing fetus, nourished and fed via the placenta and umbilical cord.

LH also stimulates the formation of the corpus luteum. This is a structure that develops in the ovary after ovulation and produces the pregnancy-maintaining hormone progesterone. Progesterone prepares the lining of the womb (endometrium) for pregnancy, and acts on the pituitary to prevent further ovulation.

Dog Heat Cycle Info

Week one: Once the vulva begins to swell, the bitch will begin to produce a bloody discharge. The amount will vary from one bitch to the next, so it may or may not be noticeable.
Week two: Sometime around nine to twelve days, the color of the discharge lightens to a pinkish-tan color, and it's usually around this time, referred to as estrus, that the vulva softens and eggs are released from the ovaries. At this point, you may notice your bitch flirting with other dogs; this is a sign she is ready to accept a stud dog's advances.
Week three: If the bitch's heat cycle is allowed to continue uninterrupted, by the third week, the discharge begins to look bloody again. The amount will trail off until the cycle has concluded with anestrus.

Yearly, Bi-Yearly or Quarterly Cycles

On average, a healthy bitch comes into season or heat every six months. However, this can vary, and some bitches only cycle once a year while others come into season on a quarterly basis. Quite often, bitches that come in quarterly are not fertile every season.

Signs That It's Time to Breed

Look for these signals that your bitch is ready to be bred:

General flirty/affectionate behavior
Tail held high and flagging
Pushing up rear when petted on the back
Willingness to stand and present vulva
Color change in discharge from red to pinkish-tan

How long is each cycle?

Heat usually lasts between 2-4 weeks. Early in the cycle, a female dog may not be receptive to male dogs, although some are receptive through the entire cycle. It can be shorter or longer and you’ll know the cycle is over when all her vulva returns to its normal size and there’s no more bleeding or discharge. There’s a relatively small window when your dog is most fertile during the heat cycle; it may begin about nine or ten days after she goes into heat and lasts about five days. However, she can become pregnant until the end of the cycle.

heat cycle abnormalities

Female dogs can easily have heat cycle abnormalities. It just happens. These can be prolonged heats, split heats, silent heats, or even absent heats. At times, heat cycles can also be irregular.

Most bitches follow the heat cycle pattern of their dams if they live together. But there are situations in which a young bitch might skip a heat period. In fact, many females tend to have silent or irregular heats as well. Their cycle will however regulate itself within a couple of years but the situation does differ from time to time.

In this comprehensive article, we’ll cover the main dysfunctions occurring in a bitch cycle, including:

Absent Heat — a missed heat
Silent Heat — an undetectable heat (from a human perspective)
Split Heat — a heat happening in two distinct periods of times split by a break
Prolonged Heat — a too long heat compared to the breed’s average
Prolonged Interestrus Interval — a too long window between two heats
Shortened Inter Estrous Interval — a too-short window between two heats
Premature Ovarian Failure — ovarian functions lessening or stopping at an early age

Split estrus

Split estrus is a disorder in which no or quite short estrous signs develop despite the presence of proestrous signs. In this situation, pregnancy usually does not develop even if copulation occurs; the bitch is observed to enter proestrus again within 3–4 weeks. In these bitches, the next cycle is usually a normal ovulatory cycle.

Split estrus is usually seen in young bitches that have shown first estrus. However, continuous or frequent split estruses should suggest chronic premature luteolysis or hypothyroidism. Split estrus may be confused with recurrent estrus (short interestrous interval). Ovulation will not develop in dogs showing split estrus but without the typical progesterone elevation. The condition usually recovers spontaneously [1, 7]. Source