Proestrus, Follicle Dynamics, and Hormone Profiles in Jersey Cows during Synchronization and Re-synchronization after Preovulatory Follicle Aspiration

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Reports of length of proestrus, follicle dynamics, circulating hormones, and intrafollicular hormones of estrual animals are scarce. Furthermore, no studies have investigated alterations in cow response to re-synchronization following preovulatory follicle aspiration. Therefore, objectives of this study were to determine length of proestrus, follicle dynamics, and circulating estradiol (E2) and progesterone (P4) concentrations in estrual animals; determine factors influential of proestrus; compare intrafollicular E2 and P4 at estrous onset, 11 h, and 18 h post first standing mount; and determine if re-synchronization beginning 9-10 days after preovulatory follicle aspiration was related to changes in preovulatory follicle dynamics, steroid hormone profiles, and estrual response. Non-lactating, Jersey cows (n=40) underwent pre-synchronization, synchronization, preovulatory follicle aspiration, and re-synchronization. Blood collection and ovarian mapping were performed during each synchronization. Analysis of variance was used to determine differences in intrafollicular hormones at estrous onset and 11 or 18 h post estrous onset, as well as differences in proestrus, follicle dynamics, and circulating hormones between synchronization and re-synchronization. Development of a preovulatory follicle and estrous expression were similar between synchronizations. Length of proestrus was 43.1 ± 1.35 h and 44.6 ± 1.37 h during synchronization and re-synchronization. Serum E2 at prostaglandin F2⍺ (PGF) was negatively associated with length of proestrus. Serum E2 concentration at estrus, and P4 at and prior to PGF were higher in re-synchronization. Follicle diameter at PGF was smaller in re-synchronization. Follicular fluid E2:P4 ratio was 30.03 ± 3.92, 6.35 ± 4.68, and 2.65 ± 5.06, at estrous onset, 11 h, and 18 h after estrous onset, respectively. This study sheds light on preovulatory follicle development and hormone profiles during synchronization and re-synchronization in Jersey cows. Detailed account of length of proestrus, hormone profiles in estrual animals, and intrafollicular hormone profiles add to scarce, but essential, data surrounding the bovine follicular phase.