EFFECT OF LETROZOLE: A NON-STEROIDAL AROMATASE INHIBITOR ON OVARIAN FUNCTION AND ESTRUS SYNCHRONIZATION IN DAIRY CATTLE
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Date
2023
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ICAR-NDRI, BENGALURU
Abstract
Estrus synchronization is becoming a necessity in the period of contemporary reproductive biotechnology for the augmentation of bovine fertility. There is demand for the development of short-term, cost-effective estrus synchronization protocols for adaptation at the field level. Letrozole, a non-steroidal aromatase inhibitor, can be an alternative approach for estrus synchronization in cattle. Letrozole reversibly inactivates the aromatase enzyme responsible for the synthesis of estrogen, delays the preovulatory LH surge, and prolongs the life span or induces growth of the dominant follicle by increasing LH pulse frequency. To date, most of the studies on the use of Letrozole for estrus synchronization have been conducted in beef cattle, and a perusal of the literature revealed a lack of studies on dairy cattle and also in indigenous cattle. With this background, the objectives of the present study were to determine the effect of Letrozole on ovarian function in dairy cattle and to evaluate the efficiency of Letrozole on estrus synchronicity and ovulation rate. In the present study, a total of 18 Deoni cows were selected and grouped as a blank vaginal sponge group (n = 6), a blank vaginal sponge plus PGF2α plus GnRH group (n = 6), and a Letrozole vaginal sponge plus PGF2α plus GnRH group (n = 6). The ovaries of all the animals were observed ultrasonographically before and after treatment to monitor follicular growth, ovulation, and corpus luteum development. Animals that came to heat in each group were inseminated with Deoni bull semen. Results of the present study revealed that treatment with Letrozole intravaginal sponges for four days at random stages of the estrous cycle resulted in synchronization of the estrus. The diameter of the dominant and pre-ovulatory follicles significantly (p < 0.05) increased in the Letrozole treatment group as compared to the control group. The diameter of the resultant corpus luteum (CL) formed after ovulation was significantly larger (p < 0.05) in the Letrozole treatment group. Similarly, the CL volume and area were significantly larger (p < 0.05) in the Letrozole treatment group, indicating the luteotropic property of Letrozole. There was no significant difference in CL blood flow area between the Letrozole treatment and control groups. Ovulation was more synchronous in the Letrozole treatment group. The present study demonstrates that the Letrozole+PGF2α+GnRH protocol improved the ovulation rate, increased the growth of the dominant follicle, the size of the preovulatory follicle, and the resultant CL. It is suggested that the Letrozole-based protocol can effectively be used for estrus synchronization programmes in Bos indicus cattle.