A Detailed Guide to the Correct Methods of Mating and Breeding Rex Rabbits
Mating of Rex Rabbits:
① Estrus identification. Correctly identifying the estrus status of the doe and arranging the mating time promptly is the key to improving the conception rate.
Estrus identification in does is carried out by observing behavior and examining the vulva. During estrus, the rabbit reduces its feed intake, becomes lively in temperament, and jumps restlessly in the cage, sometimes rubbing the cage fixtures with its chin. During peak estrus, it mounts its own young or other does in the same cage. When placed together with a buck, it actively flirts with the buck, chases and mounts the buck, raises its hindquarters, and lifts its tail to accept mating from the buck. At this time, examination of the doe's vulva reveals swelling, moisture, and congestion. In production, the estrus state is judged based on the color of the doe's vulvar mucosa, and the mating time is selected accordingly. In early estrus, the vulvar mucosa is pink; in mid-estrus, dark red; in late estrus, dark purple. During mid-estrus, when the vulvar mucosa is bright red, the conception rate of mating is highest. There is a saying: “Pink is too early, dark purple is too late; bright red is exactly the right time to mate.”
② Mating methods. There are three mating methods for Rex rabbits. First, free mating, in which bucks and does are kept together in a certain ratio and allowed to mate freely; second, manually controlled mating, in which bucks and does are normally kept separately, and when the doe is in estrus, she is placed in the buck's cage for mating, and after mating the buck and doe are separated; third, artificial insemination, in which certain instruments are used to collect the buck's semen, and with the aid of an insemination device, the semen is deposited into the vagina of the estrous doe, so that the buck and doe do not directly come into contact with each other's reproductive organs.
Free mating, namely natural mating, is a primitive and backward mating method. It saves labor and effort, but the buck's mating frequency is high, which easily leads to physical decline and affects the conception rate, and it also easily spreads reproductive organ diseases. When using this method, breeding rabbits should be constantly checked, sick rabbits isolated promptly, bucks rotated regularly, and special attention paid to the blood relationship between bucks and does to avoid inbreeding; manual assisted mating allows accurate knowledge of the mating date and the pedigree of the young rabbits, controls the mating intensity of bucks, and can also reduce the transmission of reproductive organ diseases. However, manually controlled mating is labor-intensive and effort-consuming, with high labor intensity, and requires experienced breeders to promptly detect doe estrus and arrange mating. This method is commonly used in rabbit farms across China; artificial insemination can make full use of excellent breeding bucks, accelerate the spread of improved breeds, reduce feeding costs, control certain diseases transmitted through direct contact of the reproductive organs of breeding rabbits, and can synchronize the reproductive production of rabbits. Artificial insemination requires certain equipment and techniques, and is suitable for larger rabbit farms and organized promotion of improved breeds.
③ Manual assisted mating. When the doe is in estrus, according to the mating plan, the estrous doe is introduced to a certain breeding buck for pairing and mating. Before pairing, the dirty hair around the doe's external reproductive organs should be clipped off, the dirt around the vulva cleaned away, and disinfected. The feed trough and water basin in the buck's cage should be removed. If the floor slats are uneven or the gaps are too large, first place a wooden board or fiberboard of appropriate size (not too smooth), and then put the doe into the buck's cage. At this time, the buck mostly follows over, first sniffing the scent with its nose, and then mounting the doe. Most does move forward a few steps, then brace their hind legs and raise their tails to accommodate. After the buck's penis is inserted into the doe's vagina, it thrusts back and forth several times and immediately ejaculates. The buck emits a “gu-” sound, then curls its hind legs, slides off the doe's body, and falls to one side, and mating is concluded. At this point, grasp the doe and give a sharp slap on its rump to make the muscles tense, preventing backflow of semen, and return the doe to its original cage. Manual assisted mating has been widely adopted in rabbit farms (households).
Breeding of Rex Rabbits:
The age of sexual maturity in Rex rabbits is related to the individual, feeding management, climate, and so on. Generally, sexual maturity occurs at 4 months of age. They have the ability to reproduce offspring, but are not yet physically mature, and breeding too early will affect their own development. Therefore, after sexual maturity, it is appropriate to delay somewhat, that is, to 5-6 months of age, when body weight reaches 3-4 kg, before starting mating.
(I) Estrus
Rex rabbits are year-round estrous animals; after sexual maturity, they are often in a state of estrus and can mate at any time. Some scholars also believe that does are periodically estrous, coming into estrus once every 8-9 days, with estrus lasting 3-5 days. The estrous behavior of does is mainly manifested as restlessness, stepping on the floor slats with the hind legs, scratching the ground with the claws, reduced appetite, rubbing the jaw against equipment, and does with strong libido may also mount other does. In estrous does, the vulva is swollen, appearing light pink or purplish red; those appearing pink are most likely to accept mating, those appearing purplish red are next, and those without the above symptoms can mostly also accept mating, but the buck must chase in the cage for a longer time or mating can only succeed on the next day.
(II) Mating
Bucks have mating ability year-round. However, nutritional status, the molting season, or the hot summer can reduce libido and lower the conception rate. A buck's ejaculate volume per mating is 1-3 milliliters. After mating, sperm enter the oviduct within 15-20 minutes.
(III) Ovulation
Rex rabbits are induced ovulators; mature follicles in the ovary must undergo mating stimulation before ovulation can occur. Ovulation generally occurs 10-13 hours after mating. After the egg is released, it loses its fertilizing ability after more than 6 hours. Without mating stimulation, mature follicles repeatedly develop over about half a month.
(IV) Pregnancy and Pseudopregnancy
The gestation period of Rex rabbits is between 30-35 days, generally 30 days; when litter size is small, gestation is often extended by 1-2 days, and when gestation exceeds 35 days, it is mostly stillbirth. After the doe becomes pregnant, the uterus enlarges several times, pushing the abdominal organs forward, even pressing against the diaphragm, so breathing accelerates, and digestion and circulation are both affected to a certain degree, often causing constipation and hindlimb venous stasis. Pseudopregnancy refers to when the doe accepts mating and ovulates but is not fertilized, or ovulates due to group housing mutual teasing as well as mounting stimulation, forming a corpus luteum. The corpus luteum secretes luteal hormone and causes pseudopregnancy. Pseudopregnancy also has pregnancy symptoms, such as refusing mating, abdominal enlargement, pulling hair to make a nest, lactation, and so on. After about 17 days, the corpus luteum degenerates, progesterone secretion decreases, and pseudopregnancy stops.
(V) Parturition and Lactation
After the fetus develops to maturity, parturition occurs. A few hours before giving birth, the doe pulls hair and prepares the kindling box. At this time, the uterine muscles undergo paroxysmal strong contractions; the doe stands slightly, licks the vulva with its mouth, and emits a “gu gu” sound; the fetal membranes rupture, amniotic fluid flows out, and the fetus is delivered together with the placenta, one every 1-2 minutes, with all delivered in 15-20 minutes. For the delivered young rabbits, the doe bites open the amniotic membrane, eats the amniotic membrane and placenta, licks clean the amniotic fluid and blood on the body surface of the young rabbits, then covers the young rabbits with rabbit hair, and immediately leaves the box to drink water. One hour after parturition, the doe can nurse the young rabbits. Doe lactation can last 2 months. Within 5 days after parturition, daily milk yield is 100-120 grams, then increases day by day, reaching a peak at 21 days after parturition, with daily milk yield reaching about 700 grams, and after 28 days postpartum, lactation also declines rapidly.