184 Follicular characteristics and pregnancy rates in suckling Bos indicus cows synchronised with oestradiol-based or gonadotrophin-releasing-hormone-based protocols with a lengthened proestrus
G. A. Bó B C , L. Pinargote A , B. Bernal A , B. Mendoza A , V. Ocampo A and A. V. Cedeño A BA Instituto de Reproducción Animal Ecuador, Guayaquil, Ecuador
B Instituto A.P. de Ciencias Básicas y Aplicadas, Universidad Nacional de Villa María, Villa María, Córdoba, Argentina
C Instituto de Reproducción Animal Córdoba, Paraje Pozo del Tigre, Gral. Paz, Córdoba, Argentina
Reproduction, Fertility and Development 35(2) 220-220 https://doi.org/10.1071/RDv35n2Ab184
Published: 5 December 2022
© 2023 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of the IETS
Oestradiol/progesterone-based fixed-time AI protocols are extensively used in Bos indicus cattle in Latin America. However, recent restrictions on the use of oestradiol in animals producing beef destined for the EU requires the evaluation of alternative protocols. Two experiments were designed to evaluate ovulatory follicle size, time of ovulation, and pregnancy rates to AI (P/AI) in Bos indicus beef cows who were synchronised using an oestradiol-based (J-Synch) and two gonadotrophin-releasing-hormone-based (Co-Synch) protocols, all with lengthened proestrus. Cross-bred Bos indicus suckled cows (n = 60 in Experiment 1 and 1,161 in Experiment 2), who were 60 to 90 days postpartum, with a CL or at least one follicle ≥ 8 mm in diameter (detected by ultrasonography) and a body condition score between 2 and 4 (scale of 1–5) were randomly allocated into one of three groups. On Day 0, cows in the J-Synch 7-day group received 2 mg of oestradiol benzoate and an intravaginal device with 0.5 g of progesterone (P4). Cows in the two Co-Synch groups received 100 µg of gonadorelin (GnRH) on Day 1 (Co-Synch 6 day) or on Day 2 (Co-Synch 5 day), respectively. On Day 7, all cows received 500 µg of cloprostenol (PGF2α), 300 IU of equine chorionic gonadotrophin (ECG); cows in the two Co-Synch groups also received a second dose of PGF2α 8 h later. In addition, all the cows were tail painted for oestrus determination at the time of AI. Cows who had tail paint loss ≥ 50% by 70 h after P4 device removal were inseminated at that time and cows without tail paint rubbed off received GnRH at that time, then were inseminated 6 to 8 h later. In Experiment 1, cows were examined by ultrasonography twice daily from P4 device removal to ovulation and serum P4 concentrations were determined on Day 7 after AI. In Experiment 2, cows were examined for pregnancy diagnosis 30 days after AI. Data were analysed using the GLM mixed procedure for continuous data in Experiment 1 and for binary data with a logit link in Experiment 2. In Experiment 1, the mean (± s.e.m.) time of ovulation did not differ (P = 0.33) among groups (J-Synch 7 day: 104.3 ± 4.7 h; Co-Synch 6 day: 102.6 ± 4.5 h and Co-Synch 5 day: 100.0 ± 3.5 h). Likewise, the diameter of the preovulatory follicle and plasma P4 concentrations 7 days after AI did not differ among groups (J-Synch 7 day: 14.3 ± 1.3 mm and 5.5 ± 0.5 ng/mL; Co-Synch 6 day: 13.3 ± 1.1 and 5.2 ± 0.6 ng/mL; Co-Synch 5 day: 14.5 ± 1.2 mm and 5.6 ± 0.9 ng/mL, respectively). In Experiment 2, the percentage of cows in oestrus at AI was 68.1% (791/1161) and did not differ among groups (J-Synch 7 day: 70.1% 291/415; Co-Synch 6 day: 68.0% 252/370; Co-Synch 5 day: 66.0% 248/376). However, P/AI was greater (P = 0.01) in cows in the J-Synch 7-day group (55.0% 228/415) than those in the Co-Synch 6-day (45.0% 167/370) and Co-Synch 5-day (38.5% 145/376) groups. In conclusion, the greater P/AI obtained with the oestradiol-based protocol suggest that further improvements are required for the GnRH-based protocols to improve P/AI in suckling Bos indicus beef cows.
