A Complete Guide to Dog Estrus and Mating
Estrus and mating in female dogs is an important part of breeding work. Only by correctly understanding the cyclical changes in a female dog's sexual cycle and the timing of ovulation can mating be carried out at the right time, improving conception rates and reproductive capacity.
I. The sexual cycle of the female dog
In reproductive science, based on the different sexual physiological changes in dogs, the canine sexual cycle is divided into four stages: proestrus, estrus, diestrus, and anestrus.
1. Proestrus: from the beginning of bloody mucus dripping from the vulva until acceptance of the male dog mounting, about 8 days (8.2 ± 2.5 days). During this period, the corpus luteum produced in the previous estrous cycle gradually atrophies, and new egg cells begin to grow; the uterine glands grow slightly, the reproductive tract becomes mildly congested and swollen, and glandular tissue gradually increases. External signs include gradual congestion and swelling of the vulva, increased frequency of urination with small volumes, and urine that attracts male dogs to sniff. The female dog is restless and excited, likes to approach male dogs and play with them, but shows no sexual desire (does not accept mounting by male dogs). Vaginal smear examination mainly shows nucleated epithelial cells, numerous red blood cells, and a small number of neutrophils.
2. Estrus: from the beginning of acceptance of male dog mounting until acceptance ceases, that is, from day 8 to day 18 of vulvar bleeding. The female dog's vulva shows congestion and swelling, and as time progresses, the degree of congestion and swelling gradually intensifies, reaching its peak at the height of estrus; the uterine horns and uterine body are congested, muscle layer contractions strengthen, and glandular secretory activity increases; the cervical canal relaxes; ovarian follicles develop rapidly, with most ovulating in mid-estrus. Externally, the vulva is swollen in the early stage and somewhat subsides in the late stage, the bloody mucus discharge decreases, and its color changes from bright red to pale red. The odor emitted by the female dog significantly entices male dogs to chase and mount. When a male dog licks her vulva or mounts, she stands still on all fours, raises her tail to one side, repeatedly lifts her vulva, shows sexual receptivity, and mating is easily successful. Vaginal smear examination mainly shows keratinized epithelial cells, lacking neutrophils, with more red blood cells in the early stage and fewer in the late stage.
3. Diestrus: after estrus ends, diestrus begins, lasting about 10 days. The female dog gradually transitions from the sexually excited state of estrus to a quiet state; the cervical canal gradually contracts, glandular secretory activity gradually decreases, and mucus secretion is scanty and viscous; the endometrium gradually thickens, the surface epithelium becomes taller, uterine glands gradually develop, follicles rupture, and the corpus luteum begins to form after ovulation. External signs include further reduction of bloody mucus from the vulva, with color changing from pale red to dark red or colorless, subsidence of swelling, and most dogs not accepting mounting. Vaginal smear examination shows the reappearance of nucleated epithelial cells and neutrophils, lacking red blood cells and keratinized cells.
4. Anestrus: refers to the period from the end of diestrus to the beginning of the next proestrus, about 6 months (7.0 ± 1.5 months). At this time, the female dog's sexual desire has completely stopped, and her mental state has fully returned to normal. In the early stage, the endometrium thickens, the surface epithelium is tall columnar, uterine glands are highly developed, enlarged and curved, and glandular secretory activity is vigorous; in the late stage, the thickened endometrium retracts, becoming low columnar, glands become smaller, and secretory activity stops; the ovarian corpus luteum has fully developed, so this period is the luteal activity phase. External signs include a dry, shrunken vulva, no bloody mucus discharge, unwillingness to approach male dogs, not allowing male dogs to mount, and male dogs showing no interest in her urine or body odor. Vaginal smear examination mainly shows nucleated epithelial cells and a small number of neutrophils, lacking red blood cells.
II. Factors affecting the sexual cycle of female dogs
1. Season: Dogs have seasonal breeding characteristics. Generally, female dogs come into estrus twice a year, with an interval of about 6 months between each. Individually kept dogs mostly come into estrus in spring and autumn (March-May, September-November); group-kept dogs (such as Beagles) come into estrus in all four seasons with no obvious seasonality. In addition, according to Marshall (1906) and Heape (1900), wild dogs in South America and dogs kept within the Arctic Circle also have one estrus per year, with no obvious seasonality.
2. Age: As age increases, the metabolic function of older dogs declines, and the estrous cycle becomes irregular, often prolonging anestrus while shortening proestrus and estrus.
3. Puberty: Generally, small breeds reach puberty earlier (e.g., Beagles reach puberty at 6-7 months of age), while large breeds reach puberty later (e.g., German Shepherd Dogs reach puberty at 8-10 months of age). Dogs at first estrus have longer proestrus and estrus. In addition, nutrition and environmental temperature also affect puberty; those with higher nutritional levels reach it earlier than those with lower levels, and those in tropical zones earlier than those in cold or temperate zones.
4. Nutrition: Nutritional deficiency or excess (obesity) can also prolong anestrus or cause abnormal estrus.
5. Disease: Reproductive organ diseases such as ovarian cysts and pyometra often lead to excessively long anestrus or absence of estrus. In addition, if the previous litter was too large or several litters were produced consecutively, the female dog's body cannot adjust and recover properly, which can also lead to excessively long anestrus.
6. Abnormal estrus in female dogs: (1) Silent estrus. The female dog lacks signs of estrus, but her ovarian follicles still develop to maturity and ovulate. Generally, when the interval between two consecutive estrous periods is 2 or 3 times the normal interval, silent estrus in between can be suspected. The cause of silent estrus may be an imbalance of related reproductive hormones. For example, when estrogen secretion is insufficient, signs of estrus are not obvious. Insufficient or absent prolactin secretion causes early atrophy of the corpus luteum, resulting in insufficient progesterone secretion, which can also cause silent estrus, because insufficient progesterone secretion reduces the sensitivity of the hypothalamic center to estrogen. (2) Short estrus. The female dog's estrus is very short, and if not carefully observed, the mating opportunity is often missed. The cause may be that developing follicles mature and rupture quickly to ovulate, thus shortening the estrus period, but it may also be caused by arrested follicular development. (3) Interrupted estrus. The female dog's estrus is intermittent and lasts a very long time (some female dogs mate and become pregnant even at 30 days of estrus). This is caused by alternating follicular development: the first developing follicle degenerates midway, while another new follicle develops again, thus producing the phenomenon of interrupted estrus. (4) Post-pregnancy estrus. A female dog still shows signs of estrus during pregnancy, called post-pregnancy estrus or false estrus. The main cause is hormonal dysfunction, namely insufficient progesterone secretion by the corpus luteum and hyperfunction of estrogen secretion by the placenta.
III. Ovulation timing and number of ovulations
1. Ovulation timing. During the female dog's estrus period, that is, starting from acceptance of mating, at 39-48 hours, the majority of dogs have not yet ovulated; after 90 hours, only a minority have not ovulated; the ovulation process continues until 96 hours, when it is completely finished. There is no time difference between the left and right ovaries during ovulation. In summary, the female dog's ovulation period begins from the early stage of estrus, and is generally judged by the following two points: (1) ovulation begins on days 8-14 of estrus bleeding (11.2 ± 3.0 days); (2) ovulation begins on the 2nd or 3rd day after the female dog accepts male mounting.
2. Number of ovulations. Dogs are polytocous animals; in one estrus, the left and right ovaries can release from a few to over a dozen eggs (6.0 ± 1.7). Small breeds ovulate fewer, large breeds ovulate more; older dogs and overweight dogs ovulate fewer, while young adult dogs ovulate more. The number of ovulations in dogs can be inferred from the number of fetuses born, or accurately determined by examining corpus luteum sites in the ovaries during necropsy. Under normal circumstances, about 89% of ovulations result in conception and pregnancy, with embryonic death or resorption after conception being rare.
IV. Timely mating
After a female dog comes into estrus, to achieve timely mating, one must grasp the optimal period for ovulation and conception. According to reports, mating 54-41 hours before ovulation yields a conception rate of 79%; mating between the start of ovulation and 120 hours yields a conception rate of 83%, which is the optimal time for egg fertilization. Therefore, mating timing should not be too late or too early. If too late, the eggs lose their fertilizing capacity; if too early, the sperm lose vitality or die. Mating between 2-4 days after the female dog accepts mating (i.e., 60-108 hours after acceptance) yields the highest conception rate and litter rate.
V. Points to note when a female dog is in estrus
1. Strengthen feeding management; do not allow free roaming, and strictly prevent indiscriminate mating that leads to breed mixing.
2. Strengthen hygiene and disinfection work; ensure the cleanliness of the surrounding environment and the vulva to prevent reproductive tract infections.
3. If a female dog in training comes into estrus, training should generally be suspended for about half a month. This is because a female dog in estrus is restless and seeks male dogs, easily developing external inhibition, and her obedience also declines.
4. Carefully observe and record estrus signs daily, and accurately grasp the stage of estrus, so as to achieve timely mating.
VI. Points to note during mating
1. Female dogs at first estrus should generally not be mated, because at this time they are only sexually mature but not fully physically mature; otherwise, their own growth and development will be hindered, and their reproductive capacity will also decline.
2. Age for first mating. Generally, female dogs should be 1.5 years old (mating at the second estrus is preferable), and male dogs should be 2.0 years old.
3. Number of matings. A female dog should be mated 1-2 times in one estrus, with an interval of 48 hours between the two being ideal. A male dog should be mated 40-60 times per year, with no more than 2 times per week being optimal.
4. Time and place of mating. In the summer in the south, mating should be done in the morning and evening; in the winter in the north, it should be done in the morning or afternoon. The location should be a quiet environment, preferably a place familiar to both the male and female dogs, which is especially important for timid female dogs, to avoid crowds affecting mating.
5. Sexual experience. Female dogs mating for the first time, due to lack of sexual experience, especially those raised alone since puppyhood and having never contacted male dogs, will not allow mating even when in estrus. At this time, only the owner's assistance can help (one hand holding the collar, the other supporting the lower abdomen). Male dogs mating for the first time, due to lack of sexual experience, often become flustered and hesitant upon contact with a female dog, or mount without erection, or show incomplete sexual behavior, and only after several attempts can they perform normal sexual behavior. Therefore, they should be treated gently, otherwise sexual inhibition is easily caused. It is best to first let an experienced female dog mate with him.
6. Sexual inhibition in male dogs. Insufficient nutrition and exercise, lack of sexual experience, and a male dog mating several female dogs consecutively can all lead to sexual inhibition. In addition, it is usually caused by incorrect or rough management. Certain incorrect operations during semen collection can also cause sexual inhibition. This is because sexual inhibition is often caused by fear, pain, and interference during mating or semen collection, and can even develop into impotence.
7. Pre-mating sexual stimulation. Shortly before mating, sensory sexual stimulation is very beneficial for mating. Male and female dogs should be allowed to play together and chase each other for a period of time, and the male dog's sexual behavior should be appropriately restrained. Several empty mounts will not cause sexual inhibition; after 5-10 minutes and 4-6 such futile mounting attempts, the male dog's ejaculate volume and semen concentration can actually be improved, and sperm motility is also good. Pre-mating sexual stimulation can not only increase ejaculate volume and improve sperm density and motility, but also trigger the release of luteinizing hormone, subsequently raising the testosterone concentration in the blood.
8. Three mate and three do not mate, and one early and one late: mate those with the same merits, between young dogs, and where the male dog's rank is higher than the female dog's; three do not mate: do not mate those with the same or opposite defects, between old dogs, or where the male dog's rank is lower than the female dog's; one early and one late: older female dogs should be mated early (mating on days 8-10 of bleeding), and young female dogs should be mated late (mating on days 12-14 of bleeding).