I. Pivato

Effects of Different Maturation Systems on Bovine Oocyte Quality, Plasma Membrane Phospholipid Composition and Resistance to Vitrification and Warming

The objective of this study was to evaluate the effects of different maturation systems on oocyte resistance after vitrification and on the phospholipid profile of the oocyte plasma membrane (PM). Four different maturation systems were tested: 1) in vitro maturation using immature oocytes aspirated from slaughterhouse ovaries (CONT; n = 136); 2) in vitro maturation using immature oocytes obtained by ovum pick-up (OPU) from unstimulated heifers (IMA; n = 433); 3) in vitro maturation using immature oocytes obtained by OPU from stimulated heifers (FSH; n = 444); and 4) in vivo maturation using oocytes obtained from heifers stimulated 24 hours prior by an injection of GnRH (MII; n = 658). A sample of matured oocytes from each fresh group was analyzed by matrix associated laser desorption-ionization (MALDI-TOF) to determine their PM composition. Then, half of the matured oocytes from each group were vitrified/warmed (CONT VIT, IMA VIT, FSH VIT and MII VIT), while the other half were used as fresh controls. Afterwards, the eight groups underwent IVF and IVC, and blastocyst development was assessed at D2, D7 and D8. A chi-square test was used to compare embryo development between the groups. Corresponding phospholipid ion intensity was expressed in arbitrary units, and following principal components analyses (PCA) the data were distributed on a 3D graph. Oocytes obtained from superstimulated animals showed a greater rate of developmental (P<0.05) at D7 (MII = 62.4±17.5% and FSH = 58.8±16.1%) compared to those obtained from unstimulated animals (CONT = 37.9±8.5% and IMA = 50.6±14.4%). However, the maturation system did not affect the resistance of oocytes to vitrification because the blastocyst rate at D7 was similar (P>0.05) for all groups (CONT VIT = 2.8±3.5%, IMA VIT = 2.9±4.0%, FSH VIT = 4.3±7.2% and MII VIT = 3.6±7.2%). MALDI-TOF revealed that oocytes from all maturation groups had similar phospholipid contents, except for 760.6 ([PC (34:1) + H]+), which was more highly expressed in MII compared to FSH (P<0.05). The results suggest that although maturation systems improve embryonic development, they do not change the PM composition nor the resistance of bovine oocytes to vitrification.

Avaliação de diferentes doses de eCG na ressincronização da ovulação em vacas nelore lactantes submetidas à IATF

The aim was to evaluate the use of eCG in resynchronization (RS) in lactating Nelore cows, understand the interaction between dose, presence or absence of estrus, presence or absence of the corpus luteum (CL) and pregnancy rate. Were used 775 cows in first TAI and that not pregnant (449) were resynchronized 30 days after. Ultrasound (US) to observe the presence or absence of CL was performed before first TAI and when the RS. On day 0 (D0) an intravaginal device (IVD) with 1 g of progesterone and intramuscular (IM) 2 mg estradiol benzoate was administered. On D8 devices were removed and applied IM 1mg estradiol cypionate; 0.53mg of sodium cloprostenol, Group - 0 (G0) didn´t received eCG, G200 received 200 IU and G300 300 IU. Estrus was observed and insemination (AI) performed 48 hours after the removal of the IVD. US was performed 30 days after AI. The treatments didn´t affect the occurrence of pregnancy in estrus. In cows that didn´t show estrus, there´s no difference in the occurrence of pregnancy between the G200 and G300 but with G0. The cumulative pregnancy rate after 40 days of the breeding season was (77.54%). The cumulative pregnancy rate in 40 days enables the RS as a way to optimize reproductive management on beef cattle farms.