What are the methods to improve the reproductive rate of Small-tailed Han sheep?
The Small-tailed Han sheep is an animal species under the Bovidae family and Caprinae subfamily. It is a dual-purpose (meat and fur) sheep breed in our country, characterized by fast growth and development, early maturity, strong reproductive capacity, stable genetic performance, and strong adaptability. It has been designated by the state as a famous fine livestock breed, and is praised by people as China's “national treasure”, the world's “super sheep” and “long-legged sheep”. It has also been included in the National Catalogue of Livestock and Poultry Genetic Resources for Protection. It is not only one of the best projects for farmers to escape poverty and achieve prosperity, but also the most reliable project for government poverty alleviation work, and an important measure for the state to close hillsides for reforestation, grow grass to raise sheep, and build ecological agriculture. Precisely because of the special characteristics of the Small-tailed Han sheep, raising them is highly profitable, and more and more people are doing so. Therefore, breeding technology is the key. So how can the reproductive rate of Small-tailed Han sheep be improved?
Selecting rams and ewes from multiple-lamb litters as breeding stock
Twin or multiple lambs have a hereditary nature. When selecting and retaining breeding rams and ewes, their parent generation rams and ewes should preferably be selected from reserve flocks that have produced litters of twin lambs or more. These rams and ewes with a good genetic foundation, kept for breeding purposes, can fully realize their genetic potential during rearing, increasing the probability of the ewe producing multiple lambs per litter.
Strengthening nutrition for breeding sheep
Strengthening nutrition for breeding sheep is an important measure to improve the reproductive rate. Adequate nutrition gives breeding sheep a healthy body condition and moderate fatness. Rams maintain vigorous libido, and at mating the semen contains a large number of sperm with strong vitality and high fertilization capacity; ewes can come into estrus year-round, and after mating and conception have a strong physique with good fetal development, sufficient milk after lambing, high lamb birth weight and a high survival rate, while at the same time the probability of the ewe producing multiple lambs increases. Therefore, when raising Small-tailed Han sheep, whether grazing or housed, sufficient mixed concentrate must be fed. During the non-mating period, each breeding ram should be fed 0.5-0.6 kg of mixed roughage per day; during the mating period, each should be fed 0.8-1.0 kg of mixed concentrate and 1.7-1.8 kg of roughage per day; each ewe should be fed 0.3-0.4 kg of mixed concentrate per day, and pregnant ewes should have their concentrate ration gradually increased as the number of days of pregnancy increases (especially in the later stage). The concentrate must contain sufficient protein, energy, vitamins, trace elements and other minerals, and adequate drinking water must be ensured. Green fodder is especially important for breeding sheep. This is because green fodder can make up for the deficiencies of nutrients in concentrate and roughage. It plays an important role in increasing the sperm density and vitality of rams, promoting the development and maturation of ova and multiple ovulation in ewes, increasing the probability of producing multiple lambs, promoting the development and growth of fetuses in pregnant ewes, and ensuring high lamb birth weight and a high survival rate.
Increasing the proportion of young and prime-age ewes in the flock
In a flock, young ewes bred for the first time and old or weak ewes are less fertile than prime-age ewes. According to statistics, the Small-tailed Han sheep produces fewer single lambs, generally seen only in first-time lambing ewes, while the proportion of twin lambs is relatively high. Throughout a ewe's life, reproductive rate is strongest at 3-4 years of age, and the reproductive lifespan is generally 8 years. Therefore, to improve the overall level of the flock, rationally adjust the flock structure, supplement young ewes in a planned way, appropriately increase the proportion of 3-4 year old ewes in the flock, and promptly identify and cull old, weak or low-fertility ewes. This becomes a problem that livestock technicians must face and must solve. On this basis, the goal of improving the overall reproductive rate of the flock can be achieved.
Implementing double mating
When a ewe is in estrus, implementing double mating or two rounds of mating and insemination can improve the ewe's conception rate and increase the probability of producing twin lambs. Because the estrus period of ewes is short (generally about 30 hours), the survival time of released ova is also relatively short, and the maturation time of ova in some ewes is not synchronized. Therefore, the conception rate from a single mating or insemination of a ewe is relatively low, and it is difficult to have more ova participate in fertilization. Using the double mating method can keep sperm capable of fertilization constantly present in the ewe's reproductive tract, increasing the chance of fertilization. The method commonly used in production is: for ewes confirmed to be in estrus, perform mating and insemination once each at 12 and 24 hours, with a general interval of 10-12 hours between the two inseminations, which can effectively improve the ewe's conception rate.
Early weaning of lambs
Weaning lambs early at the appropriate time and shortening the ewe's nursing period can prompt the ewe to come into estrus earlier and achieve multiple births per year. Early-weaned lambs need to be trained by humans to eat. At 10-15 days of age, feed lambs some fresh tender green grass, vegetable leaves, or fine, soft, easily digestible hay and leaves, to stimulate the early formation of the lamb's digestive function and the transition toward independent feeding by the lamb. To make lambs eat feed as early as possible, at the beginning corn and soybean flour can be mixed and cooked into porridge to feed them, or mixed into water for the lambs to drink, and roasted concentrate can also be placed in a basin for the lambs to lick on their own. Generally, lambs can feed normally by 20-30 days.
Injecting drugs or hormones to induce ewes to produce multiple lambs
A substance that promotes ovarian follicle maturation and multiple ovulation is injected into the ewe's body at a certain dose. Through hormone regulation, the ewe's sexual function activity is strengthened, promoting the development and maturation of ova, thereby releasing more ova to participate in fertilization and achieving multiple lambs per litter. According to experiments, injecting pregnant mare serum or injecting multiple-lamb hormone or twin-fetus hormone has a certain effect on inducing ewes to produce multiple lambs.
Inducing estrus and superovulation
Inducing estrus can use the “ram effect” or increase light duration to achieve the goal of bringing ewes into estrus earlier. Reproductive hormones can also be applied to induce estrus and superovulation in ewes, to achieve the goal of inducing multiple lambs. For anestrous ewes or newly weaned ewes, progesterone (such as 150-300 mg of progesterone) can be placed at the cervical opening (or 10-12 mg/day of progesterone injected), and after 10-14 days, 500-1000 international units of pregnant mare serum and 300-500 international units of chorionic gonadotropin are injected, prompting the ewe to come into estrus and ovulate multiple ova, thereby achieving the goal of inducing multiple lambs. For ewes in normal estrus, 300-700 international units of pregnant mare serum can be injected intramuscularly 4 days before the expected onset of estrus (i.e., the 12th-13th day of the estrous cycle). After estrus begins, injecting 200-300 international units of chorionic gonadotropin can prompt the ewe to come into estrus and ovulate multiple ova, thereby achieving the goal of producing multiple lambs.