External Observation
Observe the cow's external behavior: In the early stages of estrus, cows tend to be more active, agitated, and vocal. They may show resistance to other cattle. As they enter the estrus period, they become more receptive to mounting. When mounted, they remain still with their legs not moving. Towards the end of estrus, the cow becomes calmer and gradually stops accepting mounts.
Check for changes in the vulva: During estrus, the vulva swells, becomes soft, and appears relaxed. As estrus progresses, the vulva begins to shrink, lose its fullness, and develop wrinkles.
Examine the vaginal mucosa and cervix: In the early stage of estrus, the vaginal walls appear reddened, flushed, and shiny. The cervix becomes red and opens slightly, allowing about one finger to pass through. As estrus comes to an end, the redness and swelling of the vaginal mucosa decrease, and the cervix starts to close gradually.
Observe the mucus discharge: In the initial phase of estrus, the mucus is clear and resembles egg white, with poor stretching ability. During the peak of estrus, the mucus becomes more viscous, resembling a glass rod, and stretches easily, often sticking to the tail, hips, or hindquarters. Just before ovulation, the mucus turns white, thick, and less stretchy, with a reduced volume. To check this, take a small amount of mucus between your thumb and index finger. If you can stretch it 5 to 7 times (with a distance of 5 to 7 cm), the cow is likely to ovulate within the next 3 to 4 hours, making it the ideal time for artificial insemination. If it stretches more than 8 times, it might be too early, while 3 to 5 stretches indicate it's possibly too late.
Monitor milk production: Most cows experience a slight drop in milk yield during estrus, which can also be a useful indicator when combined with other signs.
Rectal Examination
Rectal examination is a key method to identify estrus by feeling the changes in the uterus and ovaries. In the early stages of estrus, the uterus feels soft, and one ovary is enlarged with visible follicles. These follicles feel firm and lack elasticity, and this stage typically lasts around 10 hours.
During the middle of estrus, the rectal exam reveals a softer uterus, with the follicles increasing in size—usually 1 to 1.5 cm in diameter. They are prominent on the surface of the ovary and feel elastic, giving a "volatility" sensation. This stage usually lasts 8 to 12 hours.
As estrus nears its end, the cervix becomes softer, and the follicular wall thins out. The follicle becomes very noticeable, resembling a cluster of ripe grapes. It has a distinct texture and is easily palpable. This final stage typically lasts 8 to 10 hours.
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