Progesterone and estrous behaviour in dairy cattle : associations with embryonic and endometrial gene expression

Estrous expression, particularly the intensity and duration of estrous behaviour, have been associated with progesterone (P4) concentrations and fertility outcomes in dairy cattle. However, the mechanisms underlying this relationship remains unclear. The main objective of this dissertation was to evaluate whether different P4 concentrations before estrus and different intensities of estrous behaviour were associated with differences in gene expression in early embryos and the uterine endometrium of lactating dairy cows and heifers. Post-pubertal Holstein heifers and lactating cows were randomly assigned into two treatment groups: High/Control P4 or Low P4. Animals received a pre-synchronization protocol followed by the P4 treatments applied during superovulation in heifers and before estrus in cows. Physical activity was monitored using a wearable sensor, and the intensity and duration of estrous behaviour were measured. Animals were subsequently classified as having high or low estrous expression using the median values for intensity and duration. In heifers, embryos and endometrial samples were collected 7 days post artificial insemination (AI). In cows, endometrial biopsies were performed at 7 and 14 days post-estrus. Embryos classified as good morphological quality were randomly allocated into three biological replicates per treatment group and subjected to transcriptomic analysis. Endometrial samples were evaluated for the expression of 91 target gene transcripts. High P4 embryos had downregulation of genes related to neurological and cell differentiation processes, as well as upregulation of trophoblast-related genes compared to Low P4. An interaction effect between the P4 treatment and estrous behaviour was observed for endometrial gene expression. Heifers treated with low P4 and displaying low estrous expression had upregulation of immune-related genes in the endometrium 7 days post-AI. Low P4 concentrations before estrus in cows displaying low intensity and duration of estrus were linked to decreased endometrial expression of growth factors, and increased expression of genes related to the immune system and PG2α synthesis 14 days post-estrus. Additional estradiol (E2) analysis indicated that E2 concentrations near estrus onset may partially explain differences in embryo and endometrial gene expression. Together, these findings support the concept that estrous behaviour may reflect underlying physiological and molecular mechanisms associated with fertility in dairy cattle.