1 Sex-linked trait identification method
The sex-linked trait identification method uses the principle of sex-linked inheritance to cultivate natural male and female strains. Through crosses between different strains, based on the color of the feathers of newborn chicks, The speed of feather growth accurately identifies males and females.
1.1 Feather speed identification method
The speed of chicken feather growth is mainly controlled by a pair of genes on the sex chromosomes, so it is sex-linked inheritance. Use a fast-feathering rooster (kk) with a slow-feathering hen (K-). The chicks born with slow feathering are male chicks (Kk), and the fast-feathering chicks are female chicks (k-). The male and female can be identified accurately based on the feather speed. The rate is around 99, and the method is simple and quick.
When identifying, open the wings of the hybrid chicks produced by the above-mentioned hybridization, and observe the relative lengths of the main wing feathers and the covering main wing feathers: those with main wing feathers 2 mm longer than the covering main wing feathers are fast feathers and are female chicks; the rest are female chicks. The situation is slow feather and male chick [4].
1.2 How to identify feather color and feather spots
The silver-white down feathers of chickens are dominant (S), the golden down feathers are recessive (s), and the horizontal spotted feathers are Dominant (B), non-barred feathers are recessive (b), these feather colors and feather spots are also sex-linked inheritance. When a rooster (ss) with golden yellow genes is mated with a hen (S-) with silver-white genes, the chicks born will be male chicks (Ss) with silver-white feathers and female chicks (s-) with golden-yellow feathers. ). Similarly, use a non-striped rooster (bb) with a horizontal-spotted hen (B-). The chicks born will be male chicks (Bb) with horizontal spots, and the chicks born with non-striped spots will be female (b-). It is more accurate and easier to identify male and female chicks based on their feather color and feather spots [4].
2 How to identify the male and female anuses of chicks
Experience has proven that the identification should be carried out within 12 hours after the chicks emerge from the shell. Because more than 24 hours after the chicks hatch, the muscles around the anus contract tightly, making it difficult to turn the anus, and the reproductive protrusions will also change shape and even sink deep into the cloaca, making them difficult to see. ． Therefore, the cutting time shall not exceed 24 hours at the latest. Identification was performed under a 60-watt lamp. When identifying, hold the chick with your left hand, hold the chick's neck between the middle finger and the ring finger, and hold the legs between the ring finger and the little finger. Use your left thumb and index finger to squeeze toward the abdomen to expel the feces, and then place your left thumb on the left side. Next to the pubic bone, place the right index finger on the right pubic bone opposite to the right thumb. Place the right thumb on the lower part of the cloaca and the navel. Place the thumb of the left hand and the index finger of the right hand in a zigzag shape, and then push up with the right thumb to open it. cloaca. When turning the anus, the movements of the left and right hands must be coordinated; do not turn the anus completely, which will affect the identification.
When identifying, first observe whether there are reproductive protrusions. If there are no protrusions, it must be the female chick. If there are protrusions, there are two possibilities, namely male chicks or female chicks. At this time, the distinction should be made based on the tissue shape of the reproductive protrusions. The outline of the reproductive protrusion of the male chick is obvious and substantial: the foundation is solid; the surface of the reproductive protrusion is tight, shiny and elastic; it is not easily deformed by compression and stretching; the blood vessels are well developed and easy to become congested when stimulated; in addition, the front end of the reproductive protrusion of the male chick is pointed; The outline of the reproductive protrusion of the mother chick is not obvious, atrophied, and the surrounding tissue is weak, giving a sense of isolation; the surface is soft and transparent, has poor elasticity, and is easily deformed when compressed or stretched; the blood vessels are underdeveloped, and it is not easy to become congested when stimulated; in addition, the reproductive protrusion of the mother chick is not easily engorged. The front end is rounded.
This method of male and female identification of chicken chicks requires skilled personnel to operate and is suitable for small chicken farms.
3 Automatic identification of chicken embryos
Embrex Company of the United States published the company’s patent (Patent No. 6506570) on the method of measuring allantoic fluid in eggs in the National Patent and Trademark Office, including the determination of Elevated levels of sex hormones, such as estrogen in poultry eggs, indicate that a hen is about to hatch [5]. The principle of automatically identifying the gender of chicken embryos is to detect the estrogen contained in the allantoic fluid of female chicken embryos but not in the allantoic fluid of male chicken embryos. The estrogen level in the allantoic fluid of 17-day broiler chicken embryos can already be determined using an RIA kit. detection. The estrogen level in the allantoic fluid of male embryos is generally not detectable, and even if it can be detected, it is often lower than 42 pg/mL, while the level of estrogen in the allantoic fluid of female embryos is generally 11.3 to 830.0 pg/mL[6 ].
The hatching effect of unhatched fertilized eggs will not be affected after treatment. Cell sampling from eggs hatched 1, 2, or 3 days after hatching can seriously interfere with embryonic development.
4 Ultrasonic scanning method (US) to identify the gender of chicken embryos
Ultrasonic scanning is mainly used to show the position of the blastoderm in eggs, but its use is rarely used. The main reason is that its wavelength cannot pass through the complete eggshell, so most of the energy cannot enter the egg. To show the position of the blastoderm, the only way is to remove the eggshell and the outer membrane of the shell. Therefore, this method is suitable for laboratory operation, but not suitable for production.
5 Cytometer to identify the gender of chicken embryos
The Z and W sex chromosomes of chickens are significantly different, and the genomic DNA content of roosters is usually about 2 times greater than that of hens. This difference may be different for different strains or varieties. Therefore, the sample size of males and females in each breed should be expanded to quantify the range of genome size variation in this species [8]. Although the flow cytometer is fast and relatively accurate, the instrument itself is relatively expensive and requires dedicated personnel to operate it, so it is not suitable for use in particularly large chicken farms.
6 PCR technology to identify the gender of chicken embryos
PCR technology has been used to identify the gender of 5-7 day chicken embryos. The basic procedure is: ① Construct a pair of specific primers based on a specific sequence on the selected W chromosome. ②Extract DNA from chicken embryo cell samples and perform PCR reaction under appropriate conditions. ③Use agarose gel electrophoresis to detect PCR products, and set negative and positive controls at the same time. If there is a band at the predetermined position and the negative and positive controls are normal, it means that there is a W chromosome in the sample and it is judged to be female. PCR is sensitive and accurate in chicken embryo sex identification, requires less sample and does not require DNA purification, making it suitable for use in large chicken farms [9].
7 Nuclear magnetic resonance imaging to determine the gender of chicken embryos
Using two different nuclear magnetic resonance imaging (MRI) systems, four tests were conducted in total, which can Position the blastoderm of the egg in a vertical or horizontal position. There is a deviation in the blastoderm, so the operation of chicken embryos must be carried out in intact eggs. This operation is a bit difficult, but it can also be used for gender identification. At present, this chick sex identification technology is still in the experimental stage.