I. Identifying Estrus in Ewes
Accurately identifying estrus in ewes is crucial for successful breeding, especially in breeds like the Small Tail Han sheep, where estrus signs are often subtle and not easily detectable. Unlike goats, these sheep do not show obvious behavioral changes, making it difficult to identify them through observation alone. Therefore, more reliable methods such as the teaser ram test and vaginal examination are commonly used.
1. Teaser Ram Test
The teaser ram method involves using a mature ram to detect estrus in ewes. In rural settings, it's important to keep the ram separate from the ewes and ensure its libido is high. When the ram approaches the ewes, it may sniff or nudge them. If the ewe stands still or actively approaches the ram, it is likely in estrus. This behavior should be confirmed with a vaginal examination to ensure accuracy.
2. Vaginal Examination
During estrus, the vaginal mucosa becomes swollen, moist, and slightly red. There is also a clear mucus discharge, and the cervix appears relaxed and open. The presence of this mucus is a strong indicator that the ewe is in heat and ready for breeding.
II. Sperm Collection and Semen Processing
Artificial insemination in sheep can be done using either fresh or frozen semen. Fresh semen is generally preferred because it maintains higher viability. Proper collection and processing techniques are essential to ensure the quality of the semen used for insemination.
1. Semen Collection
Before collecting semen, the artificial vagina must be properly prepared. It should be cleaned and disinfected, with a small amount of sterile vaseline applied to the inner tube for lubrication. Warm water (40-42°C) is then poured into the artificial vagina to maintain an optimal temperature. The pressure inside the device should be adjusted, and the opening should be shaped like a "Y" or "X" for easier insertion. A ewe in estrus is placed in a slightly awkward position to prevent the ram from climbing on her. Once the ram mounts, the penis is introduced into the artificial vagina, and semen is collected after ejaculation. The collected sample is then examined for quality.
2. Semen Processing
A typical ejaculate from a Dorper ram ranges between 1-1.5 ml and appears milky with a cloudy texture. Under a microscope, the sperm density should be above 0.6, with at least 200-400 million sperm per milliliter. The abnormality rate should not exceed 15%. Qualified semen can be used directly or diluted with solutions like VB12 or milk (after filtration). If not used immediately, it should be stored properly to maintain viability.
III. Artificial Insemination Techniques
1. Insemination Procedure
Proper timing and technique are key to successful insemination. Before inserting the catheter, the ewe’s genital area should be cleaned with benzalkonium chloride and wiped with a saline-soaked cotton ball. The ewe is positioned so that her hind legs are raised, allowing easy access to the vagina. Using a speculum or endoscope, the cervix is located and the insemination catheter is gently inserted 1.0-2.0 cm into the cervical canal. The semen is slowly injected, followed by gentle massage to help retain the sperm. After removal, the ewe’s thigh is lightly tapped to encourage the cervix to close.
2. Timing and Frequency
Insemination should be performed when the ewe shows clear signs of estrus. Typically, the first insemination is done 8-12 hours after the onset of estrus, with a second dose 12-24 hours later. Signs such as changes in cervical mucus—becoming cloudy and eventually cheese-like—indicate the best time for insemination. A common protocol is one trial followed by two inseminations: the first in the afternoon, the second the next morning, and another in the afternoon if the ewe is still showing interest.
3. Important Precautions
- Accurate estrus detection is critical for a high conception rate. Using rams for assessment is recommended.
- Deep insemination (1.5-2.5 cm) increases fertility, so the catheter should be inserted as far as possible.
- During cold weather, warmed semen should be used to avoid shock to the sperm.
- All equipment should be thoroughly cleaned and disinfected after each use.
- Avoid contact with water; use saline instead to prevent damage to sperm.
- After insemination, the ewe should remain in place for a short period to reduce the risk of semen backflow.
- Virgin ewes may require deeper insertion or double the dose due to vaginal stenosis.
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