In vitro evaluation of cryopreserved bovine sperm and its relation to field fertility in fixed-time artificial insemination.

This study aimed to assess characteristics of bovine cryopreserved sperm and evaluate its relation to field fertility in fixed-time artificial insemination (FTAI). Semen samples of 16 bulls were used to inseminate 811 Nellore cows, and four of these bulls were also used to inseminate 101 Nellore heifers. Samples of the same ejaculate used for FTAI from each bull were analysed in the laboratory after thawing. Sperm motility and vigour were subjectively assessed by light microscope, and integrity of the plasma and acrosome membranes, and H2 O2 production were evaluated by flow cytometer. Relation among sperm characteristics and pregnancy rate of cows and heifers were evaluated by univariate and multivariate logistic regression. Subjective sperm motility and vigour did not affect the probability of pregnancy in cows or heifers. In univariate analysis for pregnancy in cows, sperm traits related to acrosome injury positively affected probability of pregnancy mainly when associated with plasma membrane integrity; H2 O2 production seems to be less important than plasma membrane integrity in affecting probability of pregnancy. In multivariate analysis, sperm traits related to injured acrosome positively affected probability of cow and heifer pregnancies while intact acrosome was negatively related to cow pregnancy. Intact plasma membrane and high H2 O2 production were positively related to cow pregnancy but negatively related to heifer pregnancy. Results suggest that a capacitation-like status of the acrosome may benefit probability of pregnancy in cows.

Vitrification of bovine preantral follicles with dimethylsulfoxide and sucrose plus alfa-tocopherol / Vitrificação de folículos pré-antrais bovinos com dimetilxulfoxido e sacarose adicionado de alfa-tocopherol

The objective of this study was to evaluate the vitrification of bovine preantral follicles with dimethylsulfoxide (D) and sucrose (S) plus α-tocopherol 5mmol/L (T5) or 10mmol/L (T10) and, evaluate the thawed with minimal essential medium (m) with or without sucrose (s). Ovaries of cows were collected from slaughterhouse for the experiment I (n=66) and II (n=51). In the laboratory ovarian fragments were randomly assigned either to fresh control and 8 vitrification treatments (Controle and Dm; Dms, DSm; DSms; DST5m; DST5ms; DST10m; DST10ms). Ovarian fragments were placed in vitrification solution (5 min) and immersed in liquid nitrogen (-196°C), after a week, the fragments were thawed and analyzed. In the experiments I, preantral follicles were morphologically observed for histological evaluation, (normal; degenerated and developing of stage). In the experiment II, preantral follicles were mechanically isolated from ovarian tissue and examined with trypan blue, where dead and live corresponded to stained or non-stained. The treatments DSm, DSms and DST10m were effective in preserving the morphology in situ. However, the viability of isolated preantral follicles after vitrification remained high only in treatment DST10m. Thus, DST10m preserves survival rates and morphological integrity during vitrification of bovine preantral follicles.

Os objetivos deste estudo foram avaliar a vitrificação de folículos pré-antrais bovinos com dimetilsulfóxido (D) e sacarose (S) adicionando α-tocoferol 5mmol/L (T5) ou 10mmol/L (T10) e, avaliar o aquecimento com meio essencial mínimo (m) com ou sem sacarose (s). Ovários de fêmeas bovinas foram coletados de abatedouro, para o experimento I (n= 66) e II (n= 51). No laboratório fragmentos ovarianos foram distribuídos aleatoriamente para o controle fresco e 8 tratamentos de vitrificação (Controle e Dm; Dms, a DSm; DSms; DST5m; DST5ms; DST10m; DST10ms). Os fragmentos ovarianos foram colocados na solução de vitrificação (5 min) e imersos em nitrogênio líquido (-196°C). Após uma semana os fragmentos foram aquecidos e analisados. No experimento I, folículos pré-antrais foram observados morfologicamente para avaliação histológica (normal, degenerados e estádio de desenvolvimento). No experimento II, folículos pré-antrais foram mecanicamente isolados do tecido ovariano e examinados com o azul de trypan, observando mortos e vivos corados e não corados respetivamente. Os tratamentos a DSm, DSms e DST10m foram eficazes na preservação da morfologia in situ. No entanto, a viabilidade de folículos pré-antrais isolados após a vitrificação manteve-se elevada apenas no tratamento DST10m. Assim, DST10m preservou as taxas de sobrevivência e integridade morfológica durante a vitrificação de folículos pré-antrais bovinos.