158 PREGNANCY RATES IN RECIPIENT COWS TREATED WITH PROGESTERONE VAGINAL DEVICES AND INDUCED TO OVULATE WITH ESTRADIOL BENZOATE GIVEN AT THE TIME OF DEVICE REMOVAL OR 24 h LATER

Abstract

Although treatments with progesterone (P4) releasing devices, estradiol benzoate (EB) and eCG have been shown to result in acceptable pregnancy rates after embryo transfer, the treatment requires that the cows be run through the chute at least four times for treatments. An experiment was designed to compare pregnancy rates in cows treated with P4 releasing devices plus EB and eCG, and induced to ovulate with EB given at device removal or 24 h later. Non-lactating Bos taurus × Bos indicus crossbred beef cows (n = 165), with a body condition score between 2.5 to 3.5 (1 to 5 scale), were treated with a P4-device (DIB, Syntex, Argentina) and 2 mg EB i.m. (Syntex), on Day 0 and 400 IU of eCG i.m. (Novormon, Syntex) plus 150 μg D(+)cloprostenol i.m. (Ciclase, Syntex) on Day 5. On Day 8, DIB devices were removed and cows were randomly divided into two groups to receive either 1 mg EB i.m. at the time of DIB removal (EB0) or 24 h later (Day 9; EB24). Recipients were observed for signs of estrus for 48 h after DIB removal. On Day 16, all recipients observed in estrus and with >1 CL or a single CL with an area >256 mm² were selected to receive fresh embryos on Day 16 (EB0) or Day 17 (EB24). Furthermore, 20 recipients not observed in estrus but with a CL >256 mm² were randomly selected and transferred. The embryos used were 28 Grade 1, 40 Grade 2, and 24 Grade 3. Ovarian ultrasonography was performed on Day 0, to determine ovarian status (only cows with a CL or a follicle >10 mm and uterine tone were used), on Day 16 to measure CL area, and 60 days after embryo transfer to determine pregnancy status. Quantitative data were analyzed by Student's t-test and qualitative data were analyzed by logistic regression. There were no differences between groups in the mean (± SEM) CL area on Day 16 (EB0: 300.3 ± 12.0 mm² and EB24: 324.9 ± 11.7 mm²; P = 0.14), the proportion of recipients in estrus (EB0: 38/82, 46.3%, and EB24: 34/83, 41.0%; P = 0.49), the number of recipients with >1 CL or a CL >256 mm² (EB0: 68/82, 82.9%, and EB24: 72/83, 86.7%; P = 0.49) and the number of recipients pregnant/transferred (EB0: 31/49, 63.4%, and 20/43, 46.5%; P = 0.23). Furthermore, there were no significant effects of embryo quality (P = 0.31) or technician (P = 0.12) on pregnancy rates. The mean interval from DIB removal to estrus was shorter (P = 0.001) for recipients in the EB0 group (22.7 ± 1.0 h) than for those in the EB24 group (37.4 ± 1.2 h). Nevertheless, pregnancy rates did not differ (P = 0.14) between recipients seen in estrus (EB0: 21/38, 55.3%, and EB 24: 16/34, 47.1%) and those not seen in estrus but with a CL >256 mm² on Day 16 (EB0: 10/11, 90.9%, and EB24 4/9, 44.4%). It was concluded that the two treatments evaluated are equally efficacious for synchronizing Bos taurus × Bos indicus recipients. Furthermore, the use of EB at device removal could reduce the number of trips through the chute without affecting pregnancy rates.

Research was supported by Syntex S.A., Estancia El Mangrullo S.A., and Agencia Cordoba Ciencia S.E.