Detailed Explanation of Key Points on Small-tailed Han Sheep Breeding Techniques
The Small-tailed Han sheep has the characteristics of 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 and improved livestock breed, and is praised by people as China's “national treasure,” the world's “super sheep,” and “long-legged sheep.”
Estrus Season
The Small-tailed Han sheep belongs to the category of animals that experience estrus multiple times throughout the year. However, since sheep are short-day breeding livestock, most begin estrus in mid-August each year when daylight changes from long to short and temperatures begin to drop, so estrus occurs mostly in autumn. Therefore, artificial light control can be used to determine the mating time. In summer, shading the sheep for a period each day to shorten the photoperiod can make the mating season appear earlier; in autumn, using lights in the sheep shed to extend the lighting time can make the mating season end earlier.
Temperature has an important influence on estrus in ewes. Every autumn, if the weather clears after rain and turns cool, a batch of ewes in the flock will come into estrus.
Sexual stimulation has a certain effect on estrus in ewes. Placing a ram into the flock can induce ewes to begin estrus or come into estrus earlier.
Nutritional status also has a clear effect on estrus in ewes. With good nutrition and good body condition, estrus begins earlier. Otherwise, estrus begins later, the duration of estrus is shorter, and the number of estrous cycles is fewer.
Rams can mate throughout the year, but libido is highest in autumn with good semen quality, lowest in winter, and semen quality is poorest in summer. Shearing rams before hot weather arrives is beneficial for cooling and preventing summer infertility.
Signs of Estrus
Normally, ewes in estrus are spiritually excited, emotionally restless, bleat loudly, climb walls, butt doors, and wag their tails; their appetite decreases and feed intake is reduced; the vulva becomes red and swollen, with secretions adhering to the vulva and tail base. They like to approach rams and accept mounting by rams. Rams often sniff and lick the vulva of estrous ewes and the urine the ewes have scattered on the ground. The estrus symptoms of Small-tailed Han sheep are not very obvious, especially in virgin ewes. Therefore, careful observation must be paid, and it is best to use a ram for teasing to detect estrous ewes in a timely manner.
When using a ram for teasing, to prevent unwanted mating, the ram should be handled as follows:
1. Attach a teasing apron. Use one piece of white cloth measuring 40 cm * 35 cm, with ties at the four corners, and fasten it under the belly of the teaser ram.
2. Penile deviation. This makes it possible only to mount, not to copulate.
Duration of Estrus
The time from the beginning of estrus symptoms to the end of estrus symptoms is the duration of estrus. The duration of estrus in Small-tailed Han sheep is 1.5-2 days, with an average of 44 hours.
Estrous Cycle
From the previous estrus to the next estrus in a ewe, a series of cyclical changes occur in the reproductive organs and the entire organism. This repeated sexual activity is called the estrous cycle. According to the changes occurring in the ovary, reproductive tract, and vulva, an estrous cycle can be divided into 4 stages: proestrus, estrus, metestrus, and diestrus. The estrous cycle of Small-tailed Han sheep is 15-21 days, with an average of 18 days.
If a ewe can still come into estrus after lambing within the breeding season, it is called postpartum estrus. The time of postpartum estrus is 20-60 days after lambing. The average is 35 days.
Mating Season
The determination of the mating season should be based on the estrus season, the planned number of lambings, and the lambing time. If lambing is desired in January-February, mating should be in August-September; if lambing is desired in March-April, mating should be in October-November.
Lambs born from mating in August-September each year and lambing in January-February of the following year are winter lambs. Winter lambs have the advantages of high birth weight, fast growth and development, high survival rate, and good uniformity. Therefore, where conditions permit, winter lambing should be arranged as much as possible.
Mating Time
Sheep ovulate 8-24 hours after the onset of estrus. The fertile lifespan of the released eggs is about 12 hours, and the suitable fertilization time is 8-20 hours after estrus. Therefore, the appropriate mating time is 8-20 hours after estrus, when the introduced sperm and the released eggs can meet synchronously at the upper 1/3 of the fallopian tube. To ensure the conception rate, repeat mating is often carried out in practice, that is, a ewe detected in estrus in the morning is mated once in the morning and once again in the afternoon; a ewe detected in estrus in the afternoon is mated once in the evening and once again the next morning. The interval between the two matings is 8-16 hours. Generally, mating 2 times per estrus is sufficient.
Mating Methods
1. Free mating: that is, rams and ewes are normally kept mixed in the flock, and after ewes come into estrus, rams mate freely. The advantages are saving labor and feed; as long as the ratio of rams to ewes is appropriate, the rams are energetic, and semen quality is good, the conception rate is also quite high. The disadvantages are that rams chase estrous ewes, affecting fattening; lambing periods are not uniform, making management inconvenient; inbreeding is unavoidable, causing inbreeding depression; the expected lambing date cannot be known; and reproductive tract diseases are easily transmitted. The way to overcome the above disadvantages is to keep rams separately during the non-mating period and, during the mating period, arrange and rotate rams among the ewe flocks in a planned manner.
2. Hand mating: this enables estrous ewes to mate with rams in a planned way. This method helps improve the utilization rate of rams, allows reasonable selection of breeding stock and mating combinations, and can determine the expected lambing date. The practice is to keep rams and ewes separately. When a ewe is in estrus, select a suitable ram for the ewe to mate with. With this method, the estrus period of ewes must be grasped promptly and accurately, and teaser rams should be used for teasing as much as possible to ensure that the mating opportunity is not missed.
3. Artificial insemination: this is an advanced breeding technique that uses artificial insemination equipment to collect ram semen, subject it to quality inspection, motility determination, dilution, and other processing, and then introduce it into the reproductive organs of estrous ewes to make them conceive. Artificial insemination can increase the utilization rate of excellent breeding rams. One semen collection from a ram can inseminate 10-15 ewes, and in one breeding season can inseminate 300-500 ewes. In contrast, with natural mating, one ram can mate with only a few ewes per day and can mate with only about 100 ewes in one breeding season. Since the mating ram and ewes do not come into direct contact, the transmission of certain diseases can be avoided.