How to improve the fecundity of sheep

Fertility directly affects the development of sheep number and the improvement of production performance. In order to improve the fecundity of sheep, scientists and technicians at home and abroad have made great progress by studying biotechnology such as genetics, nutrition, hormones, deep fertilization and embryo transfer, and achieved the goal of high quality and efficient production.

(A) to strengthen seed selection and matching

1. Select breeding sheep and eliminate sterile rams in time.

Choose a ram from the offspring of a ewe with high fertility. Pay attention to choose anti-sterility under unfavorable environmental conditions, because it is easier to show and find breeding sheep with poor fertility under unfavorable environmental conditions.

According to the research, the content of luteinizing hormone (LH) in the peripheral blood of male lambs with multiple births is high, and the growth of testis mainly depends on LH. The first estrus of the daughter of a big testicle ram is earlier than that of a small testicle ram. Therefore, the size of testis can be used as an early important index for selecting prolific rams. According to Zhang Zhongcheng et al. (1995), there is a strong correlation between the scrotum circumference of ram and the concentration of serum testis and the amount of ejaculation, that is, the ram growing around the scrotum has strong reproductive ability. Check the quality of semen regularly, and find and eliminate rams with poor mating ability and low pregnancy rate in time.

2. Strengthen ewe selection

Choose a ewe with strong reproductive ability. The lambing rate of ewes changes with age. Generally, the twin rate is the highest at 4-5 years old, lower at 2-3 years old, and the lowest at the first birth. 1 The baby is a ewe with twin lambs, which is very fertile. Choosing ewes with twin lambs at the first birth and multiple births at the first three births can improve the twin lamb rate and fertility of ewes. Selecting multiple ewes according to their families is also a selection method. For example, the Brula strain bred in Australia has an average lambing rate of 265,438+00%. First, choose 65,438+0 ram and 65,438+03 ewe with 3-4 lambs, and then add 65,438+0 ram with 5 lambs and L ewe with 6 lambs.

The lambing rate of smooth ewe (with naked face and no fine hair under eyes) is higher than that of wool ewe (with fine hair on face) 1 1%. Twin lambs born by young, big and naked ewes should be given priority.

3. Reasonable collocation

Reasonable selection is an effective measure to improve fertility. Single and twin ewes, different breeding combinations, the rate of twin lambs is different. For example, single x double is 5 1.85%, double x single is 38.27%, and double x double is 52.43%. Using double rams with double ewes can significantly improve the rate of double lambs.

(b) the use of multiple birth genes

The practice of raising sheep at home and abroad has fully proved that it is a quick, effective and simple method to improve fertility by crossing multiple breeds with local breeds. For example, Landers sheep, Bulula sheep and romanov sheep are used as male parents abroad, and small-tailed Han sheep and Hu sheep are used as male parents at home, which obviously increases the number of lambs. France crossed its own French island ewe with Landers ram. The lambing rate of the second generation ewes is 65,438+0,865,438+0.4%, and there are three ewes every two years, each with 2.53 ewes. In the United States, Landris sheep and Bulula sheep are used as male parents to cross with local Lan Breeze ewes. As a result, the number of lambs per ewe increased by 0.9 on average.

Shandong Dongying Shengli Oilfield Management Bureau obtained an ideal new group of mutton sheep (including 62.5% blood of poll Dorset sheep and 37.5% blood of small tail Han sheep) by crossing poll Dorset sheep with small tail Han sheep, and crossing the first generation with poll Dorset sheep with the second generation. The lambing rate reached 202.29%, and the weight of 8-month-old ewes increased by 22. 1kg and 0kg respectively. In Ziniquan Sheep Breeding Farm in Xinjiang, the blood of Hu sheep was introduced into Xinjiang military reclamation fine-wool sheep, and several fine-wool sheep were cultivated. The reproductive rate reached 182%, which was 60% ~ 70% higher than that of fine-wool sheep under the same conditions. Xinjiang Academy of Animal Husbandry and other units introduced Hu sheep to cross with local Karakul sheep on 1975 to breed multi-embryo Karakul sheep, and the lambing rate increased from 108% to 167%.

(3) aquaculture control technology

Adopt new breeding technology, control breeding cycle and shorten lambing interval. Improve the frequency of lambing and pregnancy effect, increase the number of lambing per fetus, and fully tap the reproductive potential.

(1) Estrus induction: During estrus of ewes, normal estrus, mating and intensive lambing are induced by means of early weaning of lambs, hormone treatment and biological stimulation, so as to improve the reproductive capacity of ewes.

① Early weaning: control the lactation period of ewes, so that ewes can resume their sexual cycle activities as soon as possible and shorten the lambing interval. The time of early weaning can be determined according to the different production needs, feeding conditions and management level of weaned lambs. Early weaning time should not be too early, because the preparation cost of artificial milk is high, so it is generally weaned at the age of 2.5-3 months after delivery. Wang Liming et al. (1990) experiment showed that the average weight of the fine-wool sheep fed in the house and weaned early at the age of 4 months was 3.04kg higher than that of the control group (4 months). By the time of breeding, the weight of ewes in early weaning group was 53.2 kg, which was 2.65438 0.5 kg higher than that in control group. The reproductive rate and twin rate of early weaning group were 8.65438 0.9% and 7.64% higher than those of control group, respectively. It can be seen that early weaning of lambs is not only beneficial to the development of lambs and the improvement of weaning weight, but also beneficial to fattening and mating of ewes and improving their fertility.

② Hormone treatment: that is, inducing ewes to mate in estrus in non-mating season, so as to increase the frequency of lambing. The specific method is that lambs are weaned early, then ewes are treated with progesterone for more than 10d days, and injected with pregnant horse serum gonadotropin (PMSG) after stopping the drug, which can cause estrus and ovulation. Generally speaking, ovulation rate, conception rate and lambing effect are not as good as normal breeding season.

(3) Biological stimulation: mating before the normal breeding season through the change of environmental conditions and sexual stimulation. Before the breeding season 1 month, some measures should be taken to breed early. First, adjust the light cycle, shorten the day, and achieve the purpose of estrus and ovulation; The second is sexual stimulation. By using the ram effect, before the normal breeding season, the experimental ram with insemination or penis transposition can be released to the ewe, which can promote the ewe to estrus in advance. Sexual stimulation of ram can not only advance estrus season, but also make ewe estrus tend to be synchronous. Most ewes are in estrus within 24 days (sheep) and 30 days (goats) after being put into rams.

The key to ensure the ram effect is that the ewe must be strictly isolated from the ram for more than 1 month, so that it can't hear, see or smell. A ewe that has been mixed with a ram for a long time will not have a ram effect. Ram effect method is simple to operate and is an applicable technology to improve the effect of artificial insemination.

(2) Estrus synchronization: According to the changes of ovarian function and morphology, the estrous cycle of ewes can be divided into follicular phase and luteal phase. Estrus synchronization technology is to manually intervene the estrous cycles of ewes in different States (early, middle and late follicular phase or luteal phase) and adjust them to the same benchmark, so as to achieve the purpose of estrus synchronization (focusing on estrus within 2-3 days).

Drugs can induce estrus synchronization. According to the nature and physiological regulation of the drugs used, they are divided into two categories: one is progesterone substances that strengthen luteal phase to inhibit follicular growth and development, delay estrus and prolong estrus cycle. Secondly, prostaglandin and its analogues, which can promote luteal degeneration, are used to inhibit luteal phase, accelerate luteal degeneration and reduce progesterone level, thus promoting the release of pituitary gonadotropins, advancing estrus and shortening estrus cycle. The former can be used all the year round, and the latter is only suitable for luteal phase, that is, in the normal breeding season.

① Progesterone method: Put the foam plastic vaginal suppository impregnated with progestogen into the cervix of ewe. Sheep treatment 12- 14d, goat treatment 16- 18d. On the day of taking out the suppository, pregnant mare serum gonadotropin (PMSG) was injected into muscle for 400-500 IU, and ewe was treated for 2 days. Fertilization on the day of estrus and the next day 1 time. Synchronous estrus can also be combined with regular insemination, that is, the treated ewes are inseminated 1 time at a specified time (48 and 60 hours after the suppository is taken out), and the rate of lambing ewes can reach about 70% without checking estrus.

Vaginal embolization is the main method of administration, and other methods such as intramuscular injection, oral administration and subcutaneous implantation are rarely used now. The types and dosages of commonly used drugs are: megestrol acetate 40-60mg, megestrol acetate 40-50mg, fluoprogesterone 30-60mg, progesterone150-30-60mg, etc. You can choose any one.

Vaginal suppository can be made by yourself. Take a piece of foam plastic, process it into small pieces with a diameter of 2 ~ 3 cm and a thickness of 2 ~ 3 cm respectively, and tie nylon thread with a length of 35 ~ 45 cm for taking bolts. Each piece of foam plastic is soaked in appropriate progesterone preparation solution (mixed with vegetable oil).

Using vaginal embolization to treat ewes has the advantages of high estrus synchronization rate, simple method and stable and reliable effect. For example, the experiment of Zeng Peijian et al. (1997) showed that there were 256 ewes in estrus from 24 to 48 hours after treatment, accounting for 93.8% of the total number of treatments, of which 75. 1% were in estrus before 36 hours. Wang Liming et al. (200 1) treated 172 ewes with small tail Han sheep, and 36 hours after treatment, 164 ewes were in estrus, and the estrus rate was 95.4%.

② Prostaglandin method

Prostaglandins used for estrus synchronization are type F and its analogues. There are synthetic prostaglandin F2a preparations abroad and cloprostenol produced in Shanghai at home. Intramuscular injection of prostaglandin F2a or its analogues can make ewes at 5 ~ 14d (sheep) and 6 ~ 17d (goat) estrus at the same time, which can generally make ewes estrus within 2 ~ 3d.

Prostaglandin method is also effective in estrus synchronization, but it is not as economical as vaginal embolization because of the high cost of drugs.

2. Superovulation is called superovulation when the ewe is in estrus cycle and gonadotropin is injected to make the follicular development and ovulation more than normal. Generally, a ewe treated by superovulation can ovulate 1 time, and even more than 10 mature eggs for many times. Superovulation has important uses. First, superovulation technology is used to treat ewes for mating and conception, which significantly improves the lambing rate of ewes. Second, superovulation breeding, embryo transfer, MOET breeding and speeding up the cultivation of new varieties with excellent ewes as donors. There are two ways to deal with superovulation; Follicle-stimulating hormone (FSH) reduction therapy, the donor sheep started intramuscular injection on 12 ~ 13d after estrus, once every morning and evening, with an interval of 1 2h, and the total dose was 200 ~ 300 U (sheep) and150. Treatment of serum gonadotropin (PMSG) in pregnant horses: on the first 12- 13 day of estrus cycle, PMSG, sheep1500-2,500 iu, goat1000-2,000 iu were injected intramuscularly for 24 hours after estrus.

3. Twins induction technology

(1) supplementary feeding aphrodisiac method: improving the nutritional level of ewes 1 month before breeding, especially supplementing protein feed, can not only promote ewes to estrus, but also increase the number of ovulation once, and induce ewes to have more twins.

(2) Hormone treatment: The experiment showed that subcutaneous injection of PMSG 600 ~ 12 or 13 on the day of estrus cycle could promote ovulation. Due to different breeds and individuals, the response to hormones is very different, so it is difficult to find a uniform dose suitable for each sheep. Therefore, the appropriate dosage should be determined after the preliminary test of specific varieties in the local area. This method is most suitable for varieties that produce single lamb, but not for varieties that produce more than two lambs, which is easy to cause multiple births and high mortality.

(3) Immunization: using synthetic exogenous steroid hormones as antigens to immunize ewes, so that the body produces reproductive hormone antibodies, which combine with the corresponding endogenous hormones in the blood, inactivate some or all steroid hormones, weaken or eliminate the negative feedback of hypothalamus-pituitary, enhance the secretion of FSH and LH, and lead to more mature ovulation of follicles.

At present, there are two kinds of immune preparations used in China. One is Australian Science and Technology Organization (CSLRO), and domestic similar products include Lanbin (Lanshuang) developed by Lanzhou Animal Husbandry Research Institute and Lamb Seedling (Shangshuang) developed by Shanghai Institute of Biochemistry. Their chemical components are androstenedione -7a- carboxyethyl sulfide, human serum albumin, testosterone -3- carboxymethyl bovine serum albumin and testosterone. Australia and Shangshuang were immunized 1 time 7 and 4 weeks before mating, and lml was injected into each animal every time. Before breeding, blue cream (oil) 1 5 days was injected, each animal was 2m 1. In 1987, the reproductive rate of Australian double-exempted fine-wool ewes used by Wang Liming and others was136.1%(1083/8145), which was 20. 5% higher than that of non-immunized ewes. Xinjiang Production and Construction Corps autograph 1-4 Relationship between pituitary hormones and ovarian hormones

Since 1990, the application of double lamb skin in fine-wool sheep production has been widely promoted and achieved remarkable results. For example, 199 1 year immunized 49,800 ewes with lanshuang * * *, the average lambing rate was 23.5% higher than that without immunization, and the average reproduction rate was 137.4%. One group of ewes ***2 10 were all immunized, and the twin birth rate reached 7 1.4% (150). From 65438 to 0990, the Institute of Animal Husbandry and Veterinary Medicine of Shandong Academy of Agricultural Sciences, combined with the cold matching test of sheep, immunized more than 200 ewes with "Australian double". As a result, the rate of twin lambs has increased by about 20%.

Precautions for immunization methods: First, the injection time and dosage stipulated by various immunization preparations must be strictly observed, otherwise the effect will be poor; Second, we should pay attention to the nutrition of ewes, and the fattening conditions of immunized ewes should be kept above the medium level in order to obtain satisfactory results. For example, the lambing rate of ewes with large weight and high angularity is 65,438+058.8%, while the lambing rate of ewes with poor fat thickness is only increased by 6% ~ 10%. Third, choose healthy ewes, preferably not primiparous or aged ewes, so as not to affect the immune effect. Fourthly, in order to ensure the normal development and survival of twin lambs, the nutritional level of twin lambs during lactation should be appropriately improved, and they should be fed and managed in groups.

Step 4: Birth control

Applying some hormones to pregnant sheep before the expected date of delivery can promote early delivery. Progesterone can also be used to prevent the initiation of delivery mechanism and delay delivery. Usually, exogenous sex hormones, such as dexamethasone 1 0-15 mg or 2mg of flumethasone, are injected within the expected date of delivery1week, and the labor process starts about 36 hours after injection and ends at 72 hours. Premature delivery is prone to miscarriage. Estrogen can also cause childbirth. Such as intramuscular injection of estradiol benzoate 15 ~ 20 mg, all of which were administered in about 48 hours. This method can also promote mammary gland secretion, which is beneficial to the development of lambs, but it is prone to dystocia.

For some special-purpose sheep and goat breeds, such as lambskin sheep, induced labor can improve the quality of lambskin. Chu Yanpu et al. (198 1) injected diethylstilbestrol into the muscles of Hu sheep about 140d pregnant, with a dose of 4mg each time and an interval of 9-1 0h. Each sheep was injected with oxytocin for 20IU, and lambing began after 3-4 hours. The results show that. This method has practical value for Shandong Qingshan sheep. While strengthening the breeding of this breed, the quality of green goat skin can be improved quickly and effectively with proper artificial induction of labor.