I. Identifying Estrus in Ewes is Critical
Accurately identifying estrus in ewes is essential for successful breeding, especially in breeds like the Small Tail Han sheep, where estrus signs are often subtle and not easily noticeable. Unlike goats, these sheep may show only minimal behavioral or physical cues. As a result, only a small number of ewes can be identified through visual observation alone. The primary methods used are the teaser ram method and vaginal examination.
1. Teaser Ram Method
The teaser ram method involves using a male ram to detect estrus in ewes. In rural settings, it's important to keep the ram separate from the ewes until the time of testing. The ram’s libido must be strong enough to effectively identify estrus. When introduced to the group, the ram will sniff or nudge the ewes. If the ewe stands still or actively approaches the ram, this indicates estrus. A follow-up vaginal exam is then conducted to confirm the stage of estrus.
2. Vaginal Examination
During estrus, the vaginal mucosa becomes swollen, moist, and shiny, with a clear mucus discharge. The cervix appears red, relaxed, and slightly open. The presence of mucus flow is a key indicator that the ewe is in heat. This method is commonly used alongside the teaser ram technique to ensure accurate identification of estrus.
II. Sperm Collection and Semen Processing
Sheep artificial insemination can be performed using either fresh or frozen semen. Fresh semen is generally preferred due to its higher viability and effectiveness. Proper collection and handling of semen are crucial for successful breeding outcomes.
1. Semen Collection
Before collecting, a sterile artificial vagina is prepared and lubricated with a small amount of sterilized vaseline. Warm water (40–42°C) is poured into the device to maintain an optimal temperature. The pressure inside the artificial vagina should be adjusted to mimic natural conditions. The ewe should be placed in a slightly awkward position to encourage the ram to mount. Once the ram ejaculates, the semen is collected and examined under a microscope for quality parameters such as density and motility.
2. Semen Processing
A typical ejaculation volume from a Dorper ram is 1–1.5 ml, with a milky appearance and some cloudiness. Under a microscope, the sperm concentration should be above 0.6, with at least 200–400 million sperm per milliliter. The abnormality rate should not exceed 15%. If the semen is not used immediately, it can be diluted with VB12 or filtered milk for storage.
III. Insemination Techniques
1. Insemination Procedure
Timely and accurate delivery of high-quality semen into the ewe’s cervix is vital for successful conception. Before insemination, the ewe’s genital area is cleaned with benzalkonium chloride solution and wiped with saline-soaked cotton balls. The ewe is positioned on a raised platform or with her hind legs elevated. Using an insemination gun or endoscope, the operator gently inserts the device into the vagina, guiding it toward the cervix. The semen is slowly injected, followed by gentle massage to help retain the semen within the reproductive tract.
2. Timing and Frequency of Insemination
Estrus typically lasts 12–24 hours, with the best time for insemination occurring when cervical mucus changes from transparent to cloudy and eventually to a thick, cheese-like consistency. It is common practice to perform one trial and two inseminations: the first in the afternoon after checking, and the second the next morning. For ewes showing signs in the evening, the second insemination is done the following afternoon.
3. Important Precautions
- Accurate estrus detection is critical for high conception rates; using a teaser ram is recommended.
- Deep insemination (1.5–2.5 cm) increases pregnancy rates, so the insemination depth should be maximized.
- During cold weather, semen should be warmed to body temperature before use to avoid shock to the sperm.
- All equipment should be rinsed with water and washed with distilled water after each use. Disinfect with alcohol swabs between animals.
- Avoid contact with water during handling, as it can damage the sperm. Use saline instead.
- After insemination, allow the ewe to rest in a stationary position for a short time to prevent semen backflow.
- Virgin ewes may have a narrow vagina, making deep insemination difficult. In such cases, increase the dose to ensure better success.
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