External Observation
Observe the cow's external behavior: In the early stages of estrus, cows tend to be more active, agitated, and may vocalize frequently. They often show resistance to other cattle. As estrus progresses, they become more receptive to mounting. When mounted, they stand still with their legs stiff and do not move. Towards the end of estrus, the cow becomes calmer and gradually stops accepting mounts. Check the vulva for changes: During estrus, the vulva becomes swollen, soft, and relaxed. Over time, it begins to shrink, develop wrinkles, and return to its normal size. Examine the vaginal mucosa and cervix: In the initial phase of estrus, the vaginal walls appear reddened, flushed, and shiny. The cervix becomes pink and open, allowing about one finger to pass through. As estrus ends, the redness and swelling of the vaginal mucosa decrease, and the cervix slowly closes. Observe the mucus discharge: In the early stage of estrus, the mucus is clear, thin, and resembles egg white. It tends to be sticky and less stringy. During peak estrus, the mucus becomes more viscous, resembling a glass rod. It stretches easily and adheres to the tail, hips, or hindquarters. Just before ovulation, the mucus becomes thick, white, and less abundant, with reduced stretchability. To assess this, take a small amount between your thumb and index finger. If you can stretch it 5–7 times (distance of 5–7 cm), the cow is approaching ovulation and should be bred within the next 3–4 hours. If it stretches more than 8 times, it’s too early; if only 3–5 times, it’s too late. Monitor milk production: Most cows experience a slight drop in milk yield during estrus, which can be an additional indicator of heat.
Rectal Examination
Rectal palpation is a key method for identifying estrus in cows. During the early stage of estrus, the uterus feels soft, and one ovary is enlarged. You may feel follicles on the ovary, which are firm and lack elasticity. This phase typically lasts around 10 hours. During the middle stage of estrus, the uterus remains soft, and the follicle increases in size, reaching a diameter of 1–1.5 cm. It becomes prominent on the surface of the ovary and feels elastic, almost "bouncy." This stage usually lasts 8–12 hours. In the final stage of estrus, the cervix becomes softer, and the follicular wall thins out. A distinct fluctuation can be felt, resembling a ripe grape. This is a strong sign that ovulation is imminent, and the cow is ready for breeding. This stage typically lasts 8–10 hours.
By combining external observations with rectal examination, farmers can accurately determine the best time for artificial insemination, increasing the chances of successful pregnancy in dairy cows.
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