The breeding task of small-tailed Han sheep should focus on consolidating and further improving the two major performances of reproduction and meat production, at the same time, improving the body structure and fur quality, enhancing physical fitness and improving lactation performance.

(1) thoroughbred breeding (breeding of this breed)

refers to mating, breeding, purification, selection and directional breeding of small-tailed Han sheep.

① strain breeding: refers to mating breeding between different strains of the same breed of small-tailed Han sheep. Includes three stages: establishment of basic population, establishment of strains by closed breeding, and hybridization among strains.

② blood renewal: refers to the method of improving the quality of sheep by citing rams of the same breed and different blood ties of small-tailed Han sheep. Under the following circumstances, the same breed of ram with high production performance in other sheep farms can be introduced for blood renewal. First, due to the small flock and long-term closed breeding, all the individuals in the flock are related to a ram, and the phenomenon of inbreeding has appeared. Secondly, a flock of sheep are introduced to a new environment, and show some degradation in reproduction, meat production and lactation. Third, a flock of sheep, after its production performance reaches a certain level, is in a stagnant state and cannot be improved any more. (2) hybrid breeding (hybrid improvement)

refers to the method of mating between two or more different breeds of rams and ewes, and producing new breeds through seed selection, matching and cultivation.

① Step-by-step hybridization: it refers to the method of crossing the ram of superior breed with the ewe of improved breed, and then mating the hybrid ewe of the offspring with the ram of improved breed in each generation until the ideal flock is obtained, and then self-propagating, fixing the excellent traits and cultivating new breeds. Progressive hybridization is often used to change varieties with poor production performance or production types that cannot meet the needs of the national economy. For example, crossbreeding with small-tailed Han sheep to improve Tong sheep, Hotan sheep and Hu sheep, or crossbreeding with Dorset sheep, Suffolk sheep, Charolais sheep, Romney sheep and Boerwas sheep to improve small-tailed Han sheep. The blood volume of the filial generations R, F2, F3 and F4 (the first generation, the second generation, the third generation and the fourth generation) containing paternal sheep is 5%, 75%, 87.5% and 93.8% in turn. Generally, 3 ~ 5 generations are suitable for progressive hybridization.

If Dorset ram (also frozen semen or fresh semen) is used to breed small-tailed Han sheep, the first-generation hybrid ewe (Saihan R) born five months later will be bred with different Dorset rams, and the second-generation hybrid ewe (Saihan F2) born one year and four months later will be bred with another different Dorset ram, and the third-generation hybrid ewe (Saihan R) born two years and three months later will be bred.

"Step-by-step hybridization in Figure 1

② Introduction hybridization: refers to a hybrid breeding method in which external blood is properly introduced to overcome some shortcomings of the original variety on the premise of retaining the main characteristics and excellent quality of the original variety. That is to say, the ram of the imported variety crosses the ewe of the original variety once, and then the ideal male and female sheep are selected from the hybrid offspring, and then backcrossed with the ewe and ram of the original variety for 1-3 generations, and the ideal hybrids containing 1/4, 1/8 and 1/16 of external blood are selected for self-breeding

The advantages of small-tailed Han sheep are the main ones, but there are still some shortcomings. Another breed of ram which has the same production direction and can improve small-tailed Han sheep can be used for introduction hybridization (introduction hybridization). Paternal breeds should be selected for induced hybridization. At present, all foreign mutton sheep breeds are selected, such as Dorset, Suffolk, Charolais, Merino, Romney and Boerwas (Figure 2).

"Introduction hybridization in Figure 2

③ Breeding hybridization: refers to the method of crossing two or more varieties to cultivate new varieties when the original varieties can't meet the needs and there are no other varieties to replace them. The process of breeding hybridization includes three stages: hybridization innovation, cross fixation and population expansion and improvement.

simple breeding hybridization: a method of breeding new varieties by crossing two varieties. For example, "Hantong Sheep" was bred in Weibei area of Shaanxi Province through simple breeding hybridization between small-tailed Han Sheep and Tongyang Sheep.

complex breeding hybridization: a method of breeding new varieties by crossing three or more varieties. If the ram of small-tailed Han sheep is first bred with the ewe of the same sheep, and then the ewe of the hybrid offspring is bred with the ram of Dorset sheep, the blood of the three-way hybrid offspring (including the same sheep, the small-tailed Han sheep and the Dorset sheep) is cross-fixed, and a new breed of mutton sheep integrating the excellent characteristics of Dorset sheep, small-tailed Han sheep and the same sheep can be bred.