No abstract

Romosinuano (Romo) and Costeño con cuernos (CCC) are Bos taurus criollo breeds (adapted to the conditions of the tropics) that presented higher plasmatic Progesterone (P4) concentration during the luteal phase compared to non-adapted genotypes. The central hypothesis was that these P4 concentrations could modulate the uterine receptivity. Blood and endometrial biopsy samples were obtained on days 0, 5, 10, 15, and 20 of the estrous cycle (day 0 = estrus) of animals of different genotypes [Romo (n = 14), CCC (n = 14), and Crossbreed Brahman × Holstein (Cross, n = 13)]. Tissuesamples were used for morphometry and immunohistochemistry analyses. Data analyses were performed with Proc Mixed of SAS. The criollo breeds have higher P4 concentrations on days 5 and 15, higher values of superficial glandular area (all days) and density (days 0, 5, 10, and 15) than Cross cows (P < 0.05). ESR1 and PGR immunostaining were higher on days 0, 5, and 15 and on days 0 and 15, respectively for CCC and Romo when compared to Cross (P < 0.05). In conclusion, tropical adapted bovine breeds possess more receptive to embryo uterine environment than non-adapted breeds. This is mediated by a higher serum progesterone concentration, a strong P4 signaling, and greater developed uterine-gland morphology.