Study on comparative efficacy of different protocols in synchronization of estrus in goats

Introduction

In goats achieving consistent productivity is often challenged by seasonal breeding, which is regulated by photoperiod-mediated changes in melatonin and dopamine that suppress gonadotropin-releasing hormone (GnRH) during longer daylight periods (Wakabayashi et al., 2010; Fatet et al., 2011) [9,3] . Indigenous solutions like Avikesil-S®, a 350mg natural progesterone sponge developed by ICAR-CSWRI, have shown promising results in goats, alongside emerging non-hormonal alternatives like the "buck effect" and nutritional flushing which address consumer concerns regarding chemical residues (Babu et al., 2020; Mishra et al., 2023) [2,7] . Recent pharmacological advances have further highlighted Selective Estrogen Receptor Modulators (SERMs) like clomiphene citrate and third-generation aromatase inhibitors like letrozole. These agents modulate hypothalamic-pituitary signaling and suppress estrogen synthesis to promote a controlled follicular rebound, thereby improving corpus luteum function and reducing embryonic loss (Gupta et al., 2021; Yapura et al., 2015) [5, 10] . This transition toward precision reproductive management not only enhances conception rates but also enables advanced techniques like embryo transfer and synchronized kidding. The present study aimed to record and compare the efficacy of these diverse synchronization protocols on the reproductive parameters and hormonal profiles of indigenous goats to optimize performance in low-input production systems.

Materials and Methods

The study was conducted at the Department of Livestock Farm Complex, Veterinary College, Hebbal, Bengaluru, from May to August 2025. Eighteen healthy, non-pregnant does (1-4 years old) with at least two prior natural estrus cycles were selected following clinical and gynecological examinations. Animals were maintained under a semi-intensive system, grazing during the day and housed indoors at night, with ragi straw supplemented with vitamins and minerals and water provided ad libitum. All goats were dewormed with Fenbendazole (7 mg/kg BW) and confirmed non-pregnant via ultrasonography (Honda HS/2000, Japan). Does were randomly allocated into three groups (n = 6 each). Group I received 350 mg natural progesteroneimpregnated intravaginal sponges (Avikesil-S®) for seven days, followed by 125 µg Cloprostenol sodium (PGF 2α ).

Group II was treated with polyurethane sponges impregnated with 7.5 mg Letrozole for seven days, also followed by PGF 2α . Group III received oral drenching of 750 mg Copper Sulphate (CuSO 4 ) and 150 mg Clomiphene citrate daily for five days, with PGF 2α on Day 5.

Estrus detection was performed twice daily using teaser bucks, with "stand-to-be-mounted" behavior as the primary indicator. Synchronized does were naturally serviced by fertile bucks. Blood samples (2 mL) were collected via jugular venipuncture on the day of 0, 3, 5, 7 th day of treatment and on the day of estrus and serum estrogen (E 2 ) and progesterone (P 4 ) were analyzed using ELISA (Calbiotech, Inc. [1,2,4] , while shorter exposure likely minimized displacement compared with longer protocols (Jangir et al., 2023) [6] . Estrus induction was 83.33% (5/6) across groups, indicating that progesterone, letrozole and clomiphene effectively induced behavioral heat under semi-intensive management (Shakya, 2017) [8] . Time to onset of estrus differed by treatment-33.6±4.48 h (Group I), 56.0±4.38 h (Group II) and 86.4±5.87 h (Group III)-reflecting the distinct pharmacokinetics of progesterone withdrawal, aromatase inhibition and clomiphene action (Yapura et al., 2015) [10] . Estrus duration was comparable (28.8±2.40 h for Groups I and II; 31.2±2.40 h for Group III), providing an adequate mating window across protocols (Gavimath et al., 2023) [4] . Conception rates were 80% (4/5 mated) in Group I and 100% (5/5 mated) in Groups II and III, demonstrating that non-steroidal letrozole and clomiphene supported high fertility comparable to progesterone sponges (Gupta et al., 2021) [5] . Hormonal profiles showed pronounced P4 and E2 peaks with progesterone sponges (P4 up to 11.76 ng/ml, E2 51.31 pg/ml), a steady P4 rise and estrogen rebound with letrozole (P4 to 9.60 ng/ml, E2 38.03 pg/ml), and moderate P4 fluctuations with clomiphene (peak 8.66 ng/ml, E2 31.98 pg/ml), consistent with their mechanisms and supportive of luteal function and conception (Yapura et al., 2015) [10] .

Conclusion

The study demonstrated that all three protocols effectively induced a preovulatory E₂ peak sufficient to initiate estrus and support high conception rates. Avikesil-S® yielded the earliest onset of estrus, while letrozole and clomiphene achieved higher conception rates; despite significant variation in estrus onset, other reproductive parameterssponge retention, estrus duration, and overall pregnancy outcomes-remained largely consistent across treatments. These findings confirm that non-steroidal protocols such as letrozole and clomiphene can match conventional progesterone preparations in efficacy, offering practical, cost-effective alternatives for precision reproductive management in indigenous goats. Ultimately, protocol selection should consider drug availability, ease of administration, and farm management practices, and further multi-breed, multi-season studies are recommended to optimize timing and dosing for broader field application.

References

1. Babu M, Murthy VC, Sahadev A, Narayana Swamy M, Ravindranath BM, Naveen Kumar S. Efficacy of short term Avikesil-S® with cloprostenol for estrus synchronization in Jamnapari goats. Front J Vet Anim Sci. 2019;8(1):6-10.
2. Babu M, Murthy VC, Sahadev A, Sudha G, Narayana Swamy M, Ravindranath BM, Naveen Kumar S. Estrus synchronisation in Sirohi goats using short term Avikesil-S® with prostaglandin. Int J Curr Microbiol Appl Sci. 2020;9(6):1090-1095.
3. Fatet A, Pellicer-Rubio MT, Leboeuf B. Reproductive cycle of goats. Anim Reprod Sci. 2011;124(3-4):211219.
4. Gavimath S, Murthy N, Sahadev A, Raju SB, Gavisiddappa K, Bajanthri S, Rajashekar R. Intravaginal non-steroidal drug, an alternative to steroidal drug in estrus synchronization of does. Pharm Innov J. 2023;12(2):3167-3170.
5. Gupta C, Murugan M, Ramprabhu R, Sathesh Kumar S, Saravana Pandian AS. Efficacy of clomiphene citrate in augmenting fertility of anoestrous goats. Indian J Small Rumin. 2021;27(1):47-49.
6. Jangir TC, Kumar S, Pandey AK, Luthra RA. Effect of self-made intravaginal progesterone sponge on fertility in goat. Indian J Anim Reprod. 2023;44(2):55-63.
7. Mishra SK, Pandey S, Meena R, Yadav A, Narayan P, Sahu A. Effect of different estrus synchronization protocols on reproductive performance of Barbari goats. J Anim Res. 2023;13(5):877-882.
8. Shakya NK, Shukla SN, Shrivastava OP, Inwati P, Bisen A. Effects of eCG administration along with progesterone-based vaginal sponge on fertility response in Sirohi goats. Pharm Innov J. 2022;11(5):1615-1618.
9. Wakabayashi Y, Nakada T, Murata K, Ohkura S, Mogi K, Navarro VM, Clifton DK, Mori Y, Tsukamura H, Maeda KI, Steiner RA, Okamura H. Neurokinin B and dynorphin A in kisspeptin neurons of the arcuate nucleus participate in generation of periodic oscillation of neural activity driving pulsatile gonadotropinreleasing hormone secretion in the goat. J Neurosci. 2010;30(8):3124-3132.
10. Yapura D, Bell AC, Wilson DL, Miller E. Timingdependent effects of letrozole on follicular waves and estradiol profiles in heifers. Reprod Domest Anim. 2015;50(3):434-440.