137 Kinetics of In Vitro Embryonic Development According to the Follicular Population in Bos Indicus

The present study aimed to evaluate the effect of the follicular population from cull Nelore (Bos indicus) on the kinetics of in vitro embryonic development. At random stages of the oestrous cycle (Day –5), a total of 28 cull Nelore cows were synchronized with an intravaginal progesterone device associated with oestradiol benzoate (2.0 mg IM). At the same moment, a dose of prostaglandin F2α (2.0 mg im) was also administered to promote luteolysis and absence of corpus luteum (CL) at the time of ovum pick-up (OPU). Five days later (Day 0), all cows underwent an OPU session and the recovered oocytes were submitted to in vitro embryo production (IVEP). The same procedures were repeated 2 times at 30-day intervals (Day 25 and Day 55). Semen from a single batch of a previously tested bull was used for all IVEP. Blastocyst production and hatching were verified on Days 7, 8, and 9 of the IVEP. Data were analysed by the GLIMMIX procedure of SAS 9.3® (SAS Institute Inc., Cary, NC, USA). Data of the 3 OPU sessions were grouped and the cows were classified into 3 categories according to the follicular population: Low (19.7 ± 0.9 follicles, n = 27), Medium (33.5 ± 0.8 follicles, n = 29), and High (58.7 ± 3.2 follicles, n = 28). The Low category had a lower rate of viable oocytes [(number of viable oocytes/total number of oocytes) × 100; 62.0 v. 69.5%; P = 0.02] and cleavage rate [(number of cleaved/total number of oocytes) × 100; 55.9 v. 66.8%; P = 0.001] than the High category. The blastocyst formation rate [number of blastocysts/total number of oocytes) × 100] on Day 7 and Day 8 was lower for Low and Medium compared with the High category (Day 7: 26.1b v. 29.0b v. 35.1a %; P = 0.001; and Day 8: 29.2b v. 30.2b v. 34.7a %; P = 0.05). No differences were found in blastocysts rate on Day 9 among Low, Medium, and High categories (14.1 v. 15.9 v. 16.2%; P = 0.61). However, Low category had a lower percentage of hatched blastocysts [(number of hatched blastocysts/number of blastocysts) × 100] on Day 7 compared with High category (2.9 v. 12.0%; P = 0.01). These results reported that cull Nelore with High follicular population showed higher rates of embryo production and hatched blastocysts compared with cows with Low follicular population. We concluded that the kinetics of in vitro embryonic development was compromised in cull Nelore (Bos indicus) with low follicular population submitted to OPU-IVEP. This research was supported by Fapesp 2012/50533–2 (GIFT).