Eficiência Reprodutiva de vacas Nelore em programas de Inseminação Artificial em Tempo Fixo (IATF) com Ressincronização Precoce

Abstract

The aim of this study was to assess the parameters related to the reproductive efficiency of Nelore cattle submitted to an FITI protocol with early resynchronisation. To this end, 468 animals were used, divided into two experimental groups: R30 - control group: Traditional Resynchronisation or Resynchronisation at 30 days (n = 234); R22 - test group: Early Resynchronisation or Resynchronisation at 22 days (n = 234). The two groups underwent 3 IATFs, according to the following protocol: On D0, an intravaginal device impregnated with 0.5 mg of progesterone (DIB®, Zoetis, São Paulo, Brazil) was inserted and 2 mg of oestradiol benzoate (BE) (Bioestrogen®, Biogénesis Bagó, Curitiba, Brazil) was applied intramuscularly (IM). On D8, the implant was removed and 0.4 mg of oestradiol cypionate (E.C.P.®, Zoetis, São Paulo, Brazil), 2.5 mg of Dinosprost tromethamine (Lutalyse®, Zoetis, São Paulo, Brazil) and 300 IU of eCG (Novormon®, Zoetis, São Paulo, Brazil) were administered IM. On D10, the females were inseminated at 2pm, 48 to 54 hours after the intravaginal device was removed (D8). In animals that did not show signs of oestrus, 2.5 ml of GnRH (Gonaxal®, Biogénesis Bagó, Curitiba, Brazil) was applied at the time of IATF. In the R30 cows, pregnancy diagnosis (GD) was carried out by transrectal ultrasound 30 days after the first IATF. At this point, the females diagnosed as empty underwent resynchronisation. A second resynchronisation was carried out, so that in an interval of 80 days, three IATFs were carried out. In the R22 cows, resynchronisation took place 22 days after the first IATF, with no previous diagnosis of pregnancy, by inserting an intravaginal P4 device associated with the administration of BE (1mg). GD was normally carried out 30 days after insemination, accompanied by removal of the P4 device. The females diagnosed as empty continued with the hormonal treatment, and the second AI was carried out two days later, the same procedure being repeated once more. Around 49 females underwent ultrasound examinations to observe follicular dynamics. The ultrasound examinations began on Day 8 of each protocol, i.e. when the P4 intravaginal devices were removed, and were repeated on D10. From D10 onwards, US was carried out every 12 hours until ovulation was confirmed. Statistical analysis was carried out using the Statistical Analysis System for Windows® software (SAS, 2000). Binary logistic regression was used to measure the association between pregnancy (dependent variable), ECC, groups and reproductive category. To assess follicular dynamics, the ovulation rate was estimated, the time of ovulation and the average follicle diameter (DFOL) was measured for the different measurement times. The boxplot graph was plotted using R Studio software to assess the dispersion of follicle diameter growth. When comparing the cumulative pregnancy rates between groups R30 (80.77%) and R22 (82.91%), no differences were found using the SNK test (P<0.01). With regard to ECC, well-nourished cows lactated more often. When looking at the reproductive category, it was found that multiparous cows had a better pregnancy rate (60.31%) with early resynchronisation, while with traditional resynchronisation the primiparous and multiparous categories had 46.56% and 43.92%, respectively. With regard to observing the follicular dynamics of the females submitted to early resynchronisation, the total number of ovulated females was 85.71%, around 69.05% of the females ovulated 72 hours after the progesterone implant was removed and the overall average follicle diameter (DFOL) was 13.64mm±3.48mm.