83 Effect of Synchronization Treatment and Estrus Expression on Conception Rates and Pregnancy Losses in Recipients Receiving In Vitro-Produced Embryos

Abstract

The objective of this study was to evaluate the effect of synchronization treatment and oestrus expression on conception rates and pregnancy losses in recipients receiving in vitro-produced (IVP) embryos. Crossbred beef cows (n = 407) with a corpus luteum (CL) determined by ultrasonography and body condition between 2.5 and 4.5 (1 to 5 scale) received a progesterone-releasing device (DIB 0.5 g, Zoetis, Argentina) and 2 mg of oestradiol benzoate (EB, Gonadiol, Zoetis) on Day 0 and were randomly allocated to 1 of 2 treatments. Recipients in the Conventional group (n = 201) had their devices removed and received 500 µg of cloprostenol (PGF, Ciclase, Zoetis), 0.5 mg of oestradiol cypionate (ECP, Cipiosyn, Zoetis), and 400 IU of eCG (Novormón, Zoetis) on Day 8. Recipients in the J-Synch group (n = 206) had their devices removed and received PGF and eCG on Day 6. All recipients were tail-painted at device removal to determine the presence of oestrus on Day 10 (a.m.) in the Conventional group and on Day 9 (a.m.) in the J-Synch group. All recipients not in oestrus in both groups received 100 µg of gonadorelin (GnRH, Ovurelin, Bayer, New Zealand) at that time. In addition, the paint was observed again in the p.m. and it was recorded. Recipients were examined by ultrasonography 7 days after oestrus or GnRH treatment (Day 16 in the J-Synch group and Day 17 in the Conventional group) and those with a CL = 16 mm in diameter received an IVP fresh embryo non-surgically. Pregnancy was determined by ultrasonography 23 and 53 days after embryo transfer and calving rates were recorded. Data were analysed using generalized linear models for binary data and a logit link (InfoStat, https://www.infostat.com.ar/). The proportion of recipients transferred was higher (P < 0.05) in the Conventional group (90.0%, 180/201) than in the J-Synch group (83.5%, 172/206). However, conception rates and the percentage of recipients pregnant/treated did not differ between groups (Conventional: 36.6%; 66/180 and 32.8%; 66/201 v. J-Synch: 39.0%; 67/172 and 32.5%; 67/206). Although no interaction was detected between treatments and oestrus expression, the conception rate was higher (P < 0.05) in recipients showing oestrus (39.1%, 124/317) than in those not showing oestrus (25.7%, 9/35). Furthermore, embryo/fetal losses between 30 and 60 days were not affected by the synchronization treatment (P > 0.11), but they were lower (P < 0.01) in recipients showing oestrus (5.6%, 7/124) than in those not showing oestrus (66.7%, 6/9). Similarly, fetal losses between 60 days and calving tended to be lower (P < 0.06) in recipients showing oestrus (20.5%, 24/117) than in those not showing oestrus (66.7%; 2/3). Calving rates were higher in recipients showing oestrus (29.3%, 93/317) than in those not showing oestrus (2.9%, 1/35; P < 0.01). In conclusion, although both synchronization treatments performed similarly, recipients not showing oestrus after progesterone device removal had lower conception rates and higher pregnancy losses than those showing oestrus at the expected time after treatment.