Histological observation of the endometrium in repeat breeder cows

The endometrium plays an important role during attachment and implantation of embryos. Using histological techniques, we evaluated the morphological changes of the endometrium in repeat breeder cows. Endometrial biopsy specimens were obtained from 5 Holstein repeat breeder cows, 5 normally cyclic Holstein cows and 5 normally cyclic Holstein heifers on Days 1 and 8 after estrus. On Day 1, in the repeat breeder cows, the glandular secretions and supranuclear vacuolation were observed, but glandular mitoses were not observed, whereas these secretory characteristics were not observed in the normal cows. However, the appearance of stromal mitoses, stromal edema and pseudodecidual reaction was observed as in the normal cyclic cows. On Day 8, in the repeat breeder cows, the characteristics on the glandular indices were not different from those on Day 1, and were similar to those of the normal cows on Day 8. But, the characteristics on the stromal indices, the stromal mitoses and pseudodecidual reaction, were not observed, although these characteristics were observed in the normally cyclic cows. The presence of advanced morphology in the gland on Day 1 and the stroma on Day 8 indicates that these two events are controlled independently. These endometrial asynchrony might result in cows repeat breeding.