खरगोशों में प्रजनन: शुरुआती खरगोश पालकों के लिए मूल बातें
Rabbitrearing is an enterprise which has limitless scope in a developing country like India where large population is involved in subsistence farming. Being a second most populous country in the world, feeding the population with a nutritious food remains a priority for the governments.
Rabbit, a small plant-eating animal, has tremendous potential to convert the inedible plant material to high protein meat. Rabbit is the highly prolific domesticated species gaining popularity in the recent decades. Rabbit meat is consumed in certain parts of world and India traditionally. But majority of the population is yet to taste the rabbit meat.
Rabbit rearing is not so popular like that of cattle, sheep, goat, pig and poultry. But the scope is high as they reproduce rapidly and every time they give birth to more number of kits.
Rabbits require cheap roughages for their normal productive life.
Advantages and scope of Rabbitry
- The reproduction potential of rabbits is unmatched. With a short gestation period, a rabbit can give birth 6-8 times in a year with an average litter size of 4-6. Theoretically, 80 kits/doe/year.
- Rabbits are noiseless animals; hence, they can be maintained in urban or suburban localities also without creating nuisance to the neighbors.
- Rabbits are suitable for small-scale colony to large- scale rearing.
- Rabbits adapt very well with cool temperate climates. Hot environment is disastrous for successful rabbitry.
- Rabbit rearing is used as occupational therapy to many patients who has special needs
- Rabbit meat is wholesome, tasty, and low in fat, low in cholesterol, low in sodium and calorie.
- They are analogically called as “living refrigerators” as one rabbit’s meat can be consumed at once; There is no issue excess cut-parts which need refrigeration for subsequent use
- Fur and pelt are high value byproducts; Rabbits produce more fur than sheep on body weight basis. 0.2kg fur per kg body weight is the average yield from Angora rabbits
- Rex fur has high demand and fetches more price
- Rabbit meat could be an opt alternative for sheep and goat meat. Mutton and chevon production is not sufficient to meet out the demand of growing population.
- Rabbit is good and promising alternative meat source to fulfill the nutritional security of developing countries where resources are limited and deficient.
Physiology of Reproduction
Male rabbit (Buck)
Male rabbits mature at 4 – 8 months of age. The age at maturity varies between breeds. Smaller breeds mature earlier than large giant breeds. Sexing is difficult until two months of age. The external genitalia of female are like a slit.
Male has a projection. These features are appreciable only after two months of age. Buck produces 0.4 to 1.5 ml semen per ejaculate with an average of 0.7ml. Level of nutrition is strong determinant for semen quality and volume. Sperm concentration is 10 to 300 million / ml (average: 150 millions / ml).
Semen collection and artificial breeding are also practiced in limited number of establishments. Although those procedures are similar to cattle, an hour before insemination, a shot of hormonal (busrelin) injection is mandatory for ovulatory response. It takes six hours for sperm capacitation before moving to site of fertilization.
Female rabbit (Doe)
Female rabbit (Doe) attains puberty and allow the male to mate in 3 ½ months of age. They are capable to get conceived in 4 to 4 ½ months.
It is not advisable to breed in the first month of puberty and it is wise to wait until doe attains optimal body weight. Undue delay is also not advisable as the doe turns fatty and unfit for breeding. Delayed breeding precipitates hairball formation in does.
Does do not have precise estrous cycles. Follicles are formed in wave pattern with 5-10 follicles each time. These follicles produces estrogen which induces receptive behavior (extends for 12-14 days).
After that, 4 days of sexual non-receptivity prevails before next phase of reception. Thus, the doe has a cycle of 16-18 days with about 12 to 14 days of receptivity and 4 days of non-reception.
Sexual behaviour of rabbits
All animals display different kinds of sexual behavior. Sexual behavior is pronounced in wild rabbits but inconspicuous in domestic rabbits.Territorial marking behavior with feces is observed both in males and females. Chinning is a unique receptive behavior exhibited by does in which she rubs her chin against water bowl, feeder, tap nozzle etc.
If the doe is receptive, copulation takes place almost immediately. Receptive doe raises her hind quarter to allow copulation. The buck mounts and performs rapid copulatory movements followed by intromission and ejaculation.
Just after the ejaculatory thrust, the buck falls off backwards and sideways with a peculiar cry. Thus indicates the completion of mating.
Rabbit Breeding - General Considerations
Does have the reproduction of potential of producing 80 kits per year at least in theory. For an economically viable rabbit fryer production unit, 35 kits / doe / year is the ideal target. Most of the rabbit farms set their target between 35 to 50 kits/doe/year. Before selecting rabbits for breeding, conditions like sore hock should be screened because they are heritable.
Venereal infections like syphilis (Treponemacuniculi infection) should also be checked. While selecting a rabbit for breeding, limited aggressiveness is admissible as they indirectly indicate mothering instinct. But presence of overt aggression in a doe may be deemed unfit for breeding.
Moist, swollen reddish-pink vulva in a young doe of 4 months is indicativeof sexual maturity. Small , whitish, immature vulva with less moisture will be non-receptive and juvenile.
Pre-breeding checkup for body condition, reproductive health, sore hock and hutch burn is essential. Body condition should be assessed by touching and palpating over the spine and ribs. Visual inspection alone could be deceptive and wrong assessment.
At any cost, doe should be taken to buck to avoid the conflicts precipitated by territorial behavior of does. Placing the bucks in doe’s cage is not advisable; Owing to territorial aggression, doe may turn violent and attack the buck and inflict serious injuries.
Traditionally, a sex ratio of 1:10 was used. In the recent decades, 1:25 or 1:30 ratio is used. Breeding three to four times a day by buck does not depress the semen quality or libido either. But, underutilized buck becomes lazy and fatty.
Fatty bucks become lethargic and unfit for breeding. Incremental feeding of bucks is advisable in the peak breeding season. High energy pellet feeding is necessary in the event of over-utilization of buck.
In a Rabbitry, number of bucks to be maintained is according to the rebreeding interval being practiced in that farm. In rabbitries wherein very intensive commercial fryer production is practiced, 1:20 is ideal.
Shortage of bucks will detrimentally affect the conception, litter size and consequently the fryer production. Maintenance of Excessive number of bucks without appropriate utility will increase the feed cost and space requirement.
Some does may not allow mating although in a state of reception. In those animals, assisting / restraining the doe may aid in successful breeding. Despite of assisted breeding, conception rate is lower than normal mating. Allowing the buck to mate again even after a successful mating increases the ovarian response and consequent increase in litter size.
Similar to their wild counterparts, domestic rabbits can also breed immediately after few hours of kindling. In fact, in this period, does are more receptive and fertile. The practice of breeding immediate 24 hours of kindling is widely practiced in very intensive large-scale rabbitries.
It should be kept in mind that success of this practice is largely dependent on appropriately modified feeding management. Another mandatory management action is that stock replacement / culling should be frequent in order to maintain productivity in intensive fryer production systems.
Less intensive fryer production farms can aptly breed-back after 14-21 days of kindling. Ideally, a beginner is advised to rebreed 35-42 days after kindling. It can be shortened later according to the standard of feeding and housing management. Research findings suggest 42 days breed-back policy is successful and profitable.
Apart from all, rebreeding a just kindled doe should be based on the body condition of the doe and litter size. If a doe has few litters (1 to 4) and good body condition, she can be rebred in 7 days. Does with large litter size and wasting body condition, rebreeding should be done after 28 days.
Physiology of pregnancy
As said earlier, rabbits are unique in reproduction. In them, ovulation (release of ova) from the ovary requires stimulation of vagina. In natural mating, intromission induces the ovulation. Ovulation takes place 10 hours after mating.
The released ova can survive only for 6-8 hours in the oviduct. Semen is deposited in the anterior vagina and sperm capacitation requires 6 hours. Fertilization (union of ova and sperm) takes place in the middle third of oviduct.
Embryo (united ova and sperm) migrates to uterine body after 72 hours of syngamy (8 or 16 cell stage). Differently, there is no uterine body in rabbits. Cervix is bifurcated and connected with ipsilateral horns. There is no movement of embryo across horns in rabbits.
Pregnancy period- ranges from 29 days to the maximum of 35 days. Very commonly, kindling takes place between 31 to 32 days. Birth weight ranges from 25 to 90 grams (average 60grams).
Delayed parturition may lead to birth of single kit weighing over 100g. If kindling did not happen on 31 days, 1-2 IU of oxytocin should be given subcutaneously. This will induce kindling.
Occasionally, mounting without intromission and ejaculation can also occur which predisposes the doe for pseudopregnancy. This condition lasts for 16 to 18 days. No conception take place during this period as the sperm capacitation process is disrupted. At the end of pseudopregnancy, nest building and lactation behaviors occur invariably as that of kindling.
In the last few days of pregnancy, progesterone level reduces and an elevation of prostaglandin in the serum which was produced from endometrium. PGF2α lyses the corpus luteum. At the same time, increasing blood levels of prolactin induces nesting behavior.
Maternal behavior in Rabbits
Approaching kindling is characterized by nest making behavior. Firstly, pregnant doe select site for nest. In commercial and research rabbitries, nest boxes are specially designed, constructed and provided in the last week of pregnancy.
Pregnant does build the nest with hay, straw and other similar materials provided for that purpose. They pluck the fur from dew lap, ventral abdomen, breast and inner thigh. and interweave with the straw / hay to construct the nest. Bringing up the kits from kindling to weaning at 28 days
Nest building for Rabbit rearing
Increasing blood levels of prolactin induces nesting behavior in pregnant does. Usually, nest is built with straw, hay or any other material provided in the nest box. Nest box is preferably a wooden box which gives warmth.
The dimensions of 30 x 30 x 20 cm is suitable of medium sized rabbits. being an animal living in burrow, rabbits likes to kindle at least 10 cm below the its cage floor level. So the nest boxes are ideally kept in such a way.
Large- sized nest boxes are not preferred as does may extend their stay inside the nest box. In such a case, defecation and urination inside the nest box (nest watering) will adversely after the survival of kits.
The hormonal changes at the end of gestation include dominance of estrogen and reduction in progesterone concentration and surge of prolactin sets up the nest building behavior.
Nearing parturition, does exhibit restless and nesting behavior. They spend more time in nest box.Owing to hormonal changes occurring at the end of pregnancy, on the day or a day prior to kindling, there is loosening of hairs on the abdomen (breasts), thigh and dewlap.
The doe pulls the hair and interweave it with the straw or hay to build the nest. Presumably, the loosening of hairs around the breast, inner thigh and dewlap starts 6-8 days before kindling.
The behavior of digging and burrowing in rabbits kept as colonies is noticed at the same time. Interestingly, 1-3 days before kindling, these does carry hay and straw by their mouth. And just a day before kindling or on the day of kindling, hair pulling occurs. In commercial rabbit units, nest box should be placed in the cage on 28 or 29th day of gestation.
Placing the nest box well before 28th day of gestaion may lead to nest watering, a vice in some rabbits wherein they use the nest box as latrine. Sometimes, does start building their nest on the floor of the cage.
Kindling on the cage may harm the kits. Naked kits born on the floor of the cage are highly susceptible for hypothermia and death. It may sound silly but the nest quality impacts the litter survival.
One popular say is that “success of Rabbitry lies in the nest box”. We should understand the fact that nest building is seen in both normal pregnancy and pseudopregnancy. Pregnancy diagnosis by abdominal palpation and test mating should be done at 10-12 days.
Abdominal palpation is more accurate and reliable than test mating. Stillbirth is commonly noticed in rabbits but not the abortion. Rabbits tend to abort and reabsorb in utero.
Primiparous rabbit usually construct a nest of poor quality. But on third parity, does learn to construct near-perfect nest. Hence, special care should be taken for litters of primiparous doe.
KINDLING
Parturition occurs normally in the early morning. It takes about 30 minutes. Kits born at an interval of 1-5 minutes. Doe crouches in the nest and licks the newborn to dry them. Removes blood andtissue from the kits by licking. First born kit starts suckling before the completion of kindling.
If there is delay in delivery, 1-2 units of oxytocin intramuscularly will help to deliver all fetuses.When the parturition is completed, the doe eats up the placenta and dead fetus to avoid attraction of predators, avoid bacterial multiplication in waste tissue. This will further increase the survival of kits. Very commonly,8-10 kits are delivered in a litter. Small breeds may have 4 in one litter. Litter size usually small in the first kindling
Doe nurses only once a day. They give little attention to the kits in nest box. Doe usually comes to the nest box to feed the kits. Before the arrival of dam, the kits move in such a way that the remain in an elevated position.
There is no preference of teats by the kits at least in the beginning of their life. After completing the nursing, the doe voids fresh fecal pellets in the nest box. Because of the dampness of nursing, all kits urinate. They remain in the nest for 22 hours and prepare the mound and climb it before the dam to come for nursing.
Problems of kindling and litter
- Poor nutrition during pregnancy may result in birth of weak, small, dead kits.
- Cannibalism- although a herbivore, rabbits tend to eat up the kits / dead fetus. This behavior is not acceptable for breeding doe to continue in the breeding program.
- Low energy diet during pregnancy results in increased incidence of cannibalism. Handling by strangers, disturbed environment, change of cage can also precipitate cannibalism and neglect of litter.
- Stressors like change of cage, nutritional stressors, weather stress, social stressor-mixing of strange animals; rough handling can affect litter survival.
- Rabbits are non-retrieving animal unlike cats. In any case, kits crawled out of nest box will never be taken back in the litter. Escaped kits will have to be considered as orphans.
- Scattering- an act of mismothering or poor mothering in first kindling lead to delivery of kits in different sites outside the nestbox. If this behavior continues, culling should be done.
Winter breeding depression
Rabbits are seasonal breeders. Breeding takes place in spring and early summer. They are sexually inactive in late fall and winter. The reproductive performance of rabbits gets depressed during the peak winter season. This has become universal problem in rabbitries. Winter breeding depression is characterized by
- Firstly, does will not breed
- Even if bucks are willing, does remain non-receptive
- Vulva is pale and dry. Thissign is usually missed by the rabbit raiser. He/she may not recognize abortion / resorption of litter, small litter size (3-4), stillbirth, weak kits.
- Weak kits are not capable to nurse by their own.
Winter breeding depression can be managed to certain extent by offering energy-rich diet and increasing the lighting upto 16 hours.
Factors that prevent conception
- Sterility-winter breeding depression and high environmental temperature
- Poor physical condition- inadequate feeding
- Pseudopregnancy- placing breedable does together can also result in pseudopregancy
- Poor genetic quality
- Sore hock / injuries- almost all breeds are susceptible; thin skin cover of paws is very vulnerable for abrasions, bruises and lacerations.
- Retained fetus
- Diseases
Authors:
Jegaveera Pandian and P.Thirumurugan
ICAR- Central Sheep and Wool Research Institute,
Avikanagar, Rajasthan-304 501
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