A Detailed Guide to Practical Methods for Identifying Estrus in Foxes, Raccoon Dogs and Mink

I. Estrus identification in foxes: For the fox estrus period, the silver fox (silver-black fox) is generally from mid-January to mid-March; the Arctic fox (blue fox) is from mid-February to late April. Estrus in male foxes is easy to determine. A male fox entering estrus is active, drawn toward the opposite sex, has reduced feed intake, urinates frequently, and the "fox scent" in its urine becomes stronger. When a female fox is placed with it, the male shows great interest, continually mounting the female, and if the female is in estrus, mating is successfully achieved. Estrus identification in female foxes is relatively complicated; commonly used identification methods include the vulva observation method, the pair-pen teasing method, the vaginal smear method and the estrus detector method. Estrus symptoms: the female fox shows reduced appetite and climbs at the cage door. In peak estrus the vulva is oval, highly swollen and pink in color; at the same time, the labia turn outward and the color deepens, slight wrinkles are visible at the vulva, and in some individuals a curd-like secretion flows from the vulva. The female is active, urinates frequently and is docile in temperament. If at this time the female is placed in the male's cage, she will automatically raise her tail and accept the male's mounting; this is the optimal estrus mating period.

II. Estrus identification in raccoon dogs: Raccoon dogs generally come into estrus and mate in February to March. Depending on latitude, the start of estrus is slightly earlier or later in different regions. In Heilongjiang Province some come into estrus and are mated as early as late January; in Jilin and Liaoning estrus begins in early February, and the peak period of estrus and mating is in late February (accounting for more than 80%). Estrus identification in female raccoon dogs is generally carried out in three aspects: behavioral observation, external genital organ examination and pair-pen teasing. Where conditions permit, examination of the cell picture of vaginal secretions can be carried out. The above methods should be combined with one another for comprehensive judgment, but external genital organ examination should be the main basis, with pair-pen teasing as the final criterion. At the start of the mating period, the raccoon dog farm should carry out one estrus identification of the whole group, recording the vulva morphology, color and amount of secretion of each animal. Thereafter, checks are made according to the estrus progress of each animal. Generally "+" can be used; such females can be checked again after 5-6 days; those with obvious estrus changes (the hair basically separated, increased swelling of the vulva, color beginning to darken, a relatively large amount of pale yellow mucus) are marked "++", and such females can be checked again after 2-3 days; if the female already has typical estrus signs (the vulvar hair completely separated, the vulva turned outward and highly red and swollen, dark red in color, with a large amount of creamy yellow mucus), it is marked "+++". At this point the female has entered or will soon enter estrus, and pair-pen teasing should be carried out immediately; if she accepts mating, the male can be replaced for formal mating, or she can be paired directly with the selected male. If she refuses mating, she must be checked and paired every day until she accepts mating. Apart from the geographical location mentioned above, factors affecting the timing of estrus in raccoon dogs also include nutritional conditions, the age of the female and stimulation by the opposite sex. If rearing before the mating period is extensive and the normal development of the reproductive organs cannot be ensured, estrus is generally later or does not occur at all. If the nutritional level is too high and the female becomes overweight, normal estrus can likewise be affected. Therefore, during the preparation period before mating, the feed must be guaranteed to be complete in nutrients, and the nutritional level need not be too high. Age is an important factor affecting early or late estrus in female raccoon dogs. One-year-old females come into estrus latest, concentrated in late February and early March; 2-year-old and 3-year-old females come into estrus earlier, concentrated in mid-February; females over 4-5 years old come into estrus later than 2-3 year olds, concentrated in late February. During the mating period, if females in proestrus come into frequent contact with males, this can also promote their earlier entry into estrus.

III. Estrus identification in mink: The estrus pattern of mink. Mink generally come into estrus between February and March. In March

early and mid-month is relatively concentrated. There are 2-3 estrus cycles (a few have 4-5). Each estrus cycle is usually 6-10 days (estrus duration 1-3 days, interval 5-7 days). Population structure, changes in the light cycle and nutrition and other factors affect estrus in mink. Females that have given birth before come into estrus early, while females born that year come into estrus later; among the new females, those born early come into estrus earlier than those born late. Low-latitude regions (south) are slightly earlier than high-latitude regions (north). Introduced breeding stock comes into estrus later than self-bred stock. Estrus identification in mink. Estrus identification in mink is mainly based on examination of the external reproductive organs, with pair-pen teasing as the final criterion, combined with activity performance for comprehensive judgment, and is mostly carried out in the form of "look, examine, pair". (1) Observe the signs of estrus: a female mink in estrus has reduced appetite and increased activity, showing an excited state. From time to time she licks the vulva, urinates frequently, the urine is dark green, and some emit a "gu, gu" courtship call. When a male mink is in the neighboring cage, there is an obvious tendency toward the opposite sex. (2) Examine the external reproductive organs: see Table 1-7. The second stage, namely the estrus duration, is the suitable period for mating. Both the first stage and the third stage make mating difficult to achieve. (3) Pair-pen teasing: a female mink in estrus shows courtship behavior when paired; although some are afraid and avoid the male, they do not bite at the male. A female not in estrus shows a hostile attitude, resisting the male's mounting and biting at the male's head, often hiding in a corner of the cage net or in the small chamber and emitting piercing screams. When pair-pen teasing, a male of gentle temperament should be chosen and the time should not be too long; even if the female is not yet fully ready for estrus, it can still serve as stimulation by the opposite sex. If a male of violent temperament is chosen, the female will be frightened, and not only will the teasing fail, but it will also affect subsequent estrus.

Note: Some female mink show no obvious morphological changes in the external reproductive organs during estrus, but can still mate and conceive; this phenomenon is called hidden estrus or silent estrus. Generally, if no changes in the external reproductive organs can be seen after entering peak estrus, attention should be paid to the possibility of hidden estrus. A male mink of mild temperament can be chosen for teasing, or the female's vaginal secretions can be taken and observed under a microscope; if large numbers of keratinized epithelial cells are found, this indicates estrus.