Evaluation of in vitro embryo production according to the cyclicity of Nellore (Bos indicus) cows submitted to opu in different postpartum moments

The aim of the present study was to evaluate the effect of postpartum days and cyclicity at 45 days postpartum on in vitro embryo production. A total of 17 Nellore cows, presenting eutocic labor and physiological postpartum, were used and were maintained with calves along all experimental period. Females were submitted to ovum pickup (OPU; 20G; 90 mmHg; ALOKA SSDV 500), in the following postpartum moments: T1- 11.5 days; T2- 25.5 days; T3- 39.5 days; T4- 53.5 days; T5- 66,8 days and T6- 81.4 days. The means (±SEM) of body condition score (1-5) during the postpartum moments were: T1: 2.72±0.04; T2: 2.82±0.04; T3: 2.82±0.04; T4: 2.83±0.05; T5: 2.84±0.04 and T6: 2.88±0.06. Immediately before the OPU, all visible follicles (≥2mm) were quantified and classified according to the diameter [small follicles (SF = <6mm), medium follicles (MF = 6 to 10 mm) and large follicles (LF ≥ 10mm)]. The variables were analyzed using PROC GLIMMIX (SAS 9.2®). Cyclicity effects [presence (C) or absence (NC) of corpus luteum] at 45 days, days postpartum and the interaction of these factors were evaluated. There was no interaction in any variables analyzed. Ciclicity did not influence the number of aspirated follicles (NC:38.3±3.2; C:44.5±2.9; P=0.35), cleavage rate (NC=56.7% e C=60.0%; P=0.30) and blastocyst rate (NC=30.2% e C=34.3%; P=0.37). Concerning postpartum period, there was a higher number of aspirated follicles when the animals were aspirated 81.4 days postpartum compared to previous moments (T1:36.8±4,8c; T2:35.8±4,9c; T3:37.8±4, 4cb; T4:38.6±4,7cb; T5: 43.4±5,6b; T6: 54.2±6,9a; P<0.001). There were also differences between the periods in oocyte recovery rate (T1:88.6%a; T2:73.3%b; T3:73.3%b; T4:81.4%ab; T5:87.1%a; T6:79.4%ab; P=0.03). Regarding the blastocyst rate, animals aspirated 11.5 days after calving showed lower values compared to other periods (T1:23.3%b; T2:34.9%a; T3:38.9%a; T4:33.7%a; T5:32.5%a; T6:31.6%a, P=0.01). However, the number of blastocysts (T1:7.6±1.5; T2:9.2±2.2 ; T3:10.8±2.2; T4:10.6±2.1; T5:12.3±2.2; T6:13.6±2.7; P=0.06), cleavage rate (T1:60.4%; T2:49.0%; T3:61.7%; T4:64.7%; T5:59.8%; T6:54.1%; P=0.08) and the number of cleaved embryos (T1:19.7±3.2; T2:12.9±2.8; T3:17.1±3.0; T4:20.4±3.3; T5:22.6±4.2; T6:23.3±4.6; P=0.10) per OPU session did not differ between different postpartum periods. Thus, although the effect of cyclicity at 45 days postpartum had no effect on in vitro production of Nellore embryos, the postpartum period significantly affected the number of follicles aspirated, the oocyte recovery rate and the blastocyst rate.