238 THE EFFECT OF TRANSVAGINAL FOLLICULAR ASPIRATION AND THE ROLE OF PROGESTERONE IN FOLLICULAR CYSTS OF DAIRY CATTLE

Ovarian follicular cyst (CYS) is a common condition affecting 5-25% of postpartum dairy cows, increasing the number of days open, calving intervals, cow costs, and culling rates, and with an effect on fertility rates. Current hormonal treatment has variable responses. Debate exists regarding progesterone (P4) influence on CYS formation and the effect of the aspirated CYS in resumption of cyclicity. The objectives of this descriptive study were to investigate the effect of ultrasound-guided transvaginal follicular aspiration on the resumption of follicular dynamics, to determine the fate of the aspirated CYS, and to find the P4 relationship. Resumption of ovarian cyclicity was determined by ovulation, formation of a corpus luteum (CL), and a P4 rise over 3.2 nmol/L. Ten (10) postpartum (35-60 days in milk (DIM)) lactating Holstein cows with CYS were selected. They were monitored every other day by rectal palpation, ultrasonography, and P4 concentration for 30 days post-aspiration. Change in size of the aspirated CYS and emergence of a new follicular wave were recorded and images were saved electronically. Results were analyzed using Pearson correlations, linear regression, and one-way ANOVA. Of these cows, 5/10, 3/10, and 1/10 resumed cyclicity after the 1st, 2nd, and 3rd aspirations, respectively. Two (2/10) cows did not resume cyclicity during the observation period. Size of aspirated CYS was 34.6 ± 0.2 mm (mean ± SEM). Seven (7/10) cows had intermediate (0.98 ± 0.3 nmol/L) and 3/10 cows had high (8.6 ± 3.6 nmol/L) P4 concentration at aspiration. Mean times from aspiration to emergence of a new follicle, to ovulation, and to detection of a new CL were 3.6 ± 1.4, 10.5 ± 2.0, and 15.2 ± 3.0 days, respectively. New cysts grew in 4/10 cows after the first aspiration and one aspirated CYS refilled twice. Dominant follicles present at first aspiration (DFPF) had the tendency to undergo cyst turnover (4/9) or to ovulate (2/9) at a larger size (25.7 ± 3.2 mm). The CYS size was correlated (r = 0.58; P = 0.05) with circulating P4 concentration. These data, together with a significant (P = 0.05) drop in P4 concentration following aspiration (from 3.26 ± 1.5 to 2.16 ± 0.1 nmol/L), suggest that the CYS may be the source of P4. Persistence of the aspirated cyst was associated (r = 0.87) with increased days to ovulation. The significant association (r = 0.96; P = 0.01) between P4 at ovulation (2.29 ± 0.6 nmol/L) and the size of the ovulatory follicle (18.5 ± 2.0 mm) may explain the tendency of existing follicles to persist (cyst turnover) or to ovulate at a larger size. In summary, follicular aspiration was successful in inducing resumption of cyclicity and shortening days to ovulation in half of the cases with one aspiration. Persistence of the aspirated CYS increased days to ovulation. P4 may have a follicular origin and an influence on the size of the cyst and the ovulatory follicle. DFPF tend to undergo cyst turnover or to ovulate at a larger size. However, resumption of normal cyclicity may also be influenced by other factors, such as stress, disease, and energy balance.