ABSTRACT
Semen cryopreservation is widely used in assisted reproductive technologies, but it reduces sperm quality dramatically. The aim of this study was to develop a model using basal semen quality to predict the outcome of postthaw semen parameters and improve the efficiency of cryopreservation in a human sperm bank. Basal semen parameters of 180 samples were evaluated in the first stage, and a multiple logistic regression analysis involving a backward elimination selection procedure was applied to select independent predictors. After a comprehensive analysis of all results, we developed a new model to assess the freezability of sperm. Progressive motility (PR), straight-line velocity (VSL) and average path velocity (VAP) were included in our model. A greater area under the receiver operating characteristic curve was obtained in our model when compared with other indicators. In the second stage of our study, samples that satisfied the new model were selected to undergo freeze-thawing. Compared with the first stage, the rate of good freezability was increased significantly (94% vs 67%, P = 0.003). By determining basal semen quality, we have developed a new model to improve the efficiency of cryopreservation in a human sperm bank.
ABSTRACT
Procedeu-se à criopreservação do sêmen de oito tourinhos Gir Leiteiro, com idade média de 25 meses, pré-selecionados para elevada pontuação (média 84,4±5,6) na classificação andrológica por pontos (CAP), em dois diferentes diluidores: um à base de lactose-gema-glicerol e outro à base de lecitina de soja. As curvas de resfriamento e congelação foram padronizadas com o auxílio da máquina CRYOGEN®. Os parâmetros pós-congelação avaliados no sêmen submetido aos dois diluidores - motilidade, vigor, defeitos maiores, menores e totais, defeitos de acrossoma, cauda dobrada, reação ao teste hiposmótico (Thos) e células normais - foram comparados aos do sêmen fresco, exceto para Thos e entre eles. O sêmen de todos os animais foi congelado com êxito no diluidor lactose-gema-glicerol. Houve diferença (P<0,05) em todas as variáveis analisadas no sêmen fresco e pós-congelado, exceto para defeitos maiores. Entre diluidores, houve diferença (P<0,05) para motilidade, vigor, cauda dobrada e Thos. Estes resultados indicam que a seleção pelo CAP médio >80 é um bom índice para selecionar touros com maior taxa de espermatozoides viáveis pós-congelação.
Semen cryopreservation from eight young dairy Gyr bulls was performed using two different semen extenders. Bulls aging 25 months old and pre-selected for a high average score (84.4±5.6 in a 0-100 scale) in Zebu breeding soundness evaluation (BSE) composed the experimental group. Extenders were based on lactosis-egg yolk-glycerol and soya lecithin. Chilling and freezing curves were standardized by CRYOGEN® machine. Post-thaw features evaluated in semen frost in both extenders - motility, vigor, major, minor and total deffects, morphological alteration in acrossome, bent tail, reative cells to hyposmotic sweeling test (Thos), and normal cells - were compared to the ones in the fresh ejaculate (except Thos) and among them. It was possible to freeze semen from all animals in the lactosis-egg yolk-glycerol extender. There were difference (P<0.05) in all analyzed features between fresh and cryopreserved semen, except for major deffects. Between extenders, there were differences (P<0.05) in motility, vigor, bent tail, and Thos. All bulls had successfull semen freezability. These results sustain that pre-selection for high BSE values (average >80 points) is a good index to identify bulls with good post semen - thaw features. However, the choice of the extender is critical for obtaining acceptable results.