174 Pregnancy per AI in grazing suckled beef cows subjected to estradiol salts- or GnRH-based fixed-time AI protocols

L. Ferré; J. Jaeschke; N. Cerviño; B. Salom; N. Formia; R. Rearte; M. Kjelland; M. Colazo; J. Thomas; L. de la Sota

doi:10.1071/RDv37n1Ab174

RESEARCH ARTICLE

174 Pregnancy per AI in grazing suckled beef cows subjected to estradiol salts- or GnRH-based fixed-time AI protocols

L. Ferré ^A , J. Jaeschke ^B , N. Cerviño ^C , B. Salom ^D , N. Formia ^E , R. Rearte ^E , M. Kjelland ^F , M. Colazo ^G , J. Thomas ^H and L. de la Sota ^E

+ Author Affiliations

- Author Affiliations

^A INTA-CEI Barrow, Tres Arroyos, Buenos Aires, Argentina

^B Biogénesis Bagó SA, Garín, Buenos Aires, Argentina

^C CONICET, CABA, Buenos Aires, Argentina

^D Private Veterinarian Practice, Urdampilleta, Buenos Aires, Argentina

^E INIRA, FCV-UNLP, La Plata, Buenos Aires, Argentina

^F Mayville State University, Mayville, North Dakota, USA

^G Leduc Farm Animal Hospital, Leduc, Alberta, Canada

^H University of Missouri, Columbia, Missouri, USA

Reproduction, Fertility and Development 37, RDv37n1Ab174 https://doi.org/10.1071/RDv37n1Ab174

Estrogen-based protocols are commonly combined with a progestin-releasing intravaginal device (P4RID) and prostaglandin (PG) to synchronize follicle wave emergence before AI in Bos taurus cattle, with pregnancies per AI (P/AI) ranging from 40% to 55%. Gonadotrophin-releasing hormone (GnRH)-based protocols + P4RID + PG rely on the presence of a physiologically mature dominant follicle at initial GnRH. Failure to induce ovulation represents a major obstacle to improve P/AI. Pre-synchronization by PG + P4RID 7 days in advance of GnRH increases the likelihood of ovulation following GnRH. The aim of this trial was to evaluate fertility in suckled beef cows using standard (i.e. no pre-synchronization) estradiol versus GnRH FTAI protocols with or without pre-synchronization. Cyclicity status was determined in multiparous Angus suckled cows by ultrasound (US). Animals were randomly assigned based on cyclicity status, body condition, days postpartum, and weight. All reagents were supplied by Biogégesis-Bagó. Group 7-Day Estradiol (n = 350) received 2 mg of estradiol benzoate-EB on Day 0 and 1 mg of estradiol cypionate-EC on Day7. Group 7-Day GnRH (n = 349) received 10.5 µg of GnRH on Day 0 and at the time of FTAI. Group 7 and 7 GnRH (n = 343) received 150 µg of PG on Day 0 and 10.5 µg of GnRH on Day 7 and at the time of FTAI. All animals received 1.0 g of P4 (P4RID) for 7 days and 150 µg of PG and 300 IU of eCG at the time of P4RID withdrawal. A single technician performed AI at 52 ± 2 h after device removal for the estradiol group and 66 ± 2 h for the GnRH groups, using semen from a proven sire. Pregnancy diagnoses were performed 35 days after FTAI by US. Data were analyzed using the GLIMMIX procedure (SAS, 9.4). Results are presented in Table 1. The 7 and 7 GnRH protocol, which involved the PG administration and P4RID insert 7 days before GnRH, resulted in enhanced P/AI. Estrus expression before FTAI also increased P/AI, which indicates the correlation between the estrus expression and fertility.

Table 1.Least squares means of beef postpartum suckled cow pregnancy estimated according to fixed time AI (FTAI) protocols and effect of estrus expression on pregnancy rate on beef postpartum suckled cows (n = 1042).

Treatments	Estrus	Pregnant/total	Estimated P/AI	95% CI
7-Day Estradiol		203/350	51%^a	45%−57%
7-Day GnRH		210/349	52%^a	45%−58%
7 and 7 GnRH		246/343	64%^b	57%−70%
7-Day Estradiol	+	176/280	62%^a	56%−68%
7-Day GnRH	+	193/305	63%ª	57%−68%
7 and 7 GnRH	+	235/312	75%^c	70%−79%
7-Day Estradiol	−	27/70	38%^b	28%−50%
7-Day GnRH	−	17/44	38%^b	25%−54%
7 and 7 GnRH	−	11/31	36%^b	21%−54%

^a–cValues with different superscripts differ by a Fisher’s protected t-test (P < 0.05).

This study was funded by PICT-2021-I-A-00312 and by IPCVA-2023–29389 to LBF.