Detailed Explanation of Key Points of Artificial Insemination Technology for Small-Tailed Han Sheep
????I. Estrus Detection of Ewes to Be Mated Is the Key
The estrus behavior of Small-Tailed Han sheep differs from that of goats; the signs of estrus are not obvious, and only a few sheep can be identified by this method. The main methods are the teaser method and the vaginal examination method.
1. Teaser Method
The teaser method uses a ram to search for ewes in estrus, correctly identifying those in estrus. However, when using this method in rural areas, rams and ewes must be raised separately to ensure the ram's libido for seeking ewes in estrus. When the teaser ram is placed into the ewe flock, if the ram sniffs the ewe with its nose or teases her with its hooves and the ewe stands still, or if the ewe actively approaches the ram, she is a ewe in estrus, then the vaginal examination method is used for further confirmation.
2. Vaginal Examination Method
In ewes in estrus, the vaginal mucosa is congested and red, the surface is smooth and moist, with transparent mucus exuding; the cervix is congested, relaxed, and open, with mucus flowing out. When these signs are present, the ewe can be confirmed to be in estrus.
????II. Semen Collection and Semen Processing Technology for Sheep
Artificial insemination technology for sheep can be divided into fresh semen artificial insemination and frozen semen artificial insemination. It is best to use fresh semen artificial insemination for sheep, as the conception rate is higher.
1. Semen Collection
Before semen collection, first install and disinfect the sheep artificial vagina, and apply a small amount of disinfected petroleum jelly to the front 1/3-2/3 of the inner liner to achieve lubrication. Pour 40-42°C warm water (150-180ml) slowly from the filling hole into the space between the outer shell and the inner liner of the artificial vagina, so that the water temperature between the outer shell and inner liner reaches 38-40°C. The water temperature can vary with the season, slightly higher in winter than in summer. Blow an appropriate amount of air into the artificial vagina to adjust the pressure, with the opening of the artificial vagina forming a "Y" or "X" shape as appropriate. Then use a ewe as a mount animal, preferably a ewe in estrus. The Small-Tailed Han sheep has a greater body height than the Dorper sheep. When the Dorper sheep cannot easily mount the ewe, the ewe should be placed in a slightly lower position. When the ram mounts the ewe's back, quickly guide the ram's penis into the artificial vagina. After the ram ejaculates, hold the artificial vagina upright with the end containing the semen collection cup facing down, and remove the semen collection cup for semen examination. If the ram mounts several times without ejaculating, at the beginning of semen collection the ram should be pushed down several times before collecting semen, or the ram's exercise is insufficient and should be increased.
The normal ejaculate volume of Dorper sheep is 1-1.5ml, milky white with a cloudy appearance. Observe the density and abnormality rate under a microscope. Only when sperm motility reaches above 0.6 and semen density is at "medium" or above can it be used, that is, each milliliter of semen reaching 2-4 billion sperm can be used for production. The sperm abnormality rate must be ≤15% to be qualified.
Semen that has passed examination can be used directly for insemination, but it is best to dilute it according to the dilution ratio requirements. If insemination is not for preservation at the time, it can be diluted with VB12 or milk (used after boiling and filtering through 8 layers of gauze).
????III. Insemination Technology
1. Insemination
Timely and accurately depositing a certain amount of high-quality semen into the cervix of a ewe in estrus is the key to ensuring conception. During the insemination procedure, first wipe and disinfect the vulva of the ewe to be inseminated with benzalkonium bromide, then wipe clean with water or physiological saline cotton balls. Place the ewe's hind ribs on a horizontal bar about 70-80cm above the ground, or have two people lift the sheep's hind legs. The inseminator inserts a vaginal speculum or endoscope into the ewe's vagina, finds the cervix by adjusting the depth and angle, slowly inserts the insemination instrument 1.0-2.0cm into the cervix, slowly injects the required amount of semen (0.05-0.1ml of raw semen), then moves the insemination instrument back and forth for massage for about 1 minute. After withdrawing the vaginal speculum or endoscope from the vagina, slap the ewe's thigh once to make the cervix contract, which helps prevent semen from flowing out.
2. Insemination Time and Frequency
When the ewe begins to show signs of estrus, the first insemination should be controlled to begin after 8-12 hours (for frozen semen, appropriately delayed by several hours). The characteristics of cervical mucus can also serve as an indicator for timely insemination. The indicator is when transparent mucus becomes cloudy and finally becomes cheese-like; at this time, the insemination effect is best. Generally, 1 teaser detection and 2 inseminations are adopted, that is, after teasing in the morning of the same day, the first insemination is performed in the afternoon, and another insemination is performed the next morning; if teased in the afternoon, inseminate once in the morning and once in the afternoon of the next day.
①Accurate judgment of ewe estrus is the key to ensuring the conception rate. It is recommended to use the teaser ram method for estrus detection.
②Deep insemination of 1.5-2.5cm can effectively improve the conception rate, and it should be as deep as possible so that the conception rate can be high.
③In winter when the temperature is low, the insemination instrument should be warmed to body temperature before placing semen in it to prevent sperm from cold shock.
④After use, the insemination instrument should be rinsed with water promptly and flushed 1-2 times with distilled water. After inseminating each sheep, it should be disinfected with alcohol cotton balls and then rinsed twice with physiological saline before use.
⑤Avoid all equipment that contacts sperm from carrying water, as water can cause sperm death. Therefore, it can be rinsed with physiological saline more than twice before use.
⑥After insemination, the ewe should remain in the original restraint position for a while before being released for activity, to prevent semen from flowing back.
⑦For insemination of virgin ewes, due to their narrow vagina, the insemination instrument cannot reach the cervix, and insemination can only be performed at the bottom of the vagina. Therefore, during insemination, the amount should be at least doubled.