During the B-ultrasound examination of cattle, the image shows that after giving birth, the corpus luteum on the ovary of young cows is small, most of which are white strong echo reflections. There are a large number of small white spots on the B-ultrasound image of cattle, and the shape is irregular. It is estimated that it is a degenerated corpus luteum (corpus albicans) or a scar left after the corpus luteum degenerates. The functional corpus luteum is small, with a diameter of 10mm.

In the first estrus cycle after giving birth, the growth of follicles in young cows shows a dynamic development pattern. The B-ultrasound image of cattle shows that after the dominant follicle appears, the dominant period of the follicle is longer, the number of dominant follicles is larger (follicles larger than 8mm), and the mature follicles maintain the mature period too long. Is this the reason for the long estrus cycle? The estrogen level in the body has not reached the threshold, and the concentration and secretion of LH have not reached the peak, so it causes the appearance of ovulatory follicles with a diameter of 15mm-20mm, but the maintenance stage of no ovulation.

In the recovery stage after delivery, the cows were observed by B-ultrasound. In the first estrus cycle, the ovarian follicle development wave was mainly 3 or 4 follicle development waves. The long estrus cycle was 4 follicle development waves. The short estrus cycle was 3 follicle development waves.

The cows were observed by B-ultrasound. The duration of the follicle development wave of the first-born cows after delivery was longer than that of the follicle wave of the empty-stomach young cows.

In short, the long pregnancy interval of cattle limits the speed of offspring production and genetic improvement. Cows have a long period of non-estrus after delivery, so shortening the interval from delivery to estrus and conception again is an important link to improve the reproductive efficiency of cows. According to the reproduction law of the first-born cows after delivery, the cows were observed by B-ultrasound. They seized the effective opportunity, adopted scientific management methods and measures, and achieved timely breeding, so as to further improve the reproductive capacity of the first-born cows after delivery.

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