Avaliação in vitro e in vivo da adição de diluentes na refrigeração do sêmen de carneiros da Raça Dorper

Abstract

The aim of the present study was to assess the in vitro and in vivo viability of sperm cells following the addition of diluent in the refrigeration process of sheep semen and the fertilization of oocytes following the insemination of superovulated ewes. In Experiment I, three ejaculates from each of three Dorper breeders were used, collected with an artificial vagina during three repetitions with three-day intervals. The macroscopic and microscopic characteristics of the semen were analyzed before and after the pooling, analyzing sperm concentration, DNA integrity and acrosome integrity as well. The pooled semen was divided into five equal parts. Dilution was performed (1:3, semen:diluent) to establish the diluent groups: Equimix (DI), Laiciphos Green Ovine (DII), FR 4 (DIII), Equimix-Yolk [Equimix with 20% egg yolk (DIV)] and Tris-Yolk (DV; control). Each group was subdivided in quadruplicate, refrigerated and kept at 4 °C until the evaluations (MIP, vigor, DNA integrity and acrosome integrity), corresponding to 0, 12, 24, 36 and 48 hours. In the in vitro assessments, DI exhibited the greatest drop in MIP at 12 h in comparison to the other groups (p<0.05). At 24 h, DII, DIV and DV exhibited the highest MIP (p<0.05), with no significant differences between one another (p>0.05). At 48 h, DII and DV were superior to the other groups (p<0.05). Regarding vigor, DII and DV had higher values (p<0.05) than DI and DIII at 12 hours and DIV had the highest values at 24 hours (p<0.05). In all groups, there was total preservation of DNA integrity and a high number of spermatozoids with intact acrosomes for all the intervals studied. In Experiment II, the same collection method and processing of the ejaculates from the three Dorper breeders were performed. A pool was formed of the threeejaculates of each animal, divided into two equal parts at a 1:3 proportion in order to establish the experimental groups: Equimix-Yolk (DI) and Tris-Yolk (DII; control). Each group was subdivided into two aliquots: fresh – F (F-DI and F-DII), which was used immediately; and refrigerated – R (R-DI and R-DII), which was kept at 4 °C for a storage time of 24 hours. Laparoscopic inseminations were preformed with an inseminate volume of 0.25 mL per uterine horn, which was when the ovary evaluations were performed. Thirty-nine embryo harvesting procedures were performed, 19 using refrigerated semen and (R-DI and R-DII) and 20 using fresh semen (F-DI and F-DII). In the in vivo test, a general rate of 71.0% (237/334) of fertilized structures was obtained, 59.3% (198/334) of which were viable embryos. There was no significant variation (p>0.05) between the types of semen and diluents. Among the total number of embryos, 86.4% exhibited quality Grades I and II, with the refrigerated semen of R-DI obtaining the best percentage (100%)(p<0.05). The ovarian status at the time of insemination affected fertilization, as better results were obtained for the fresh semen of F-DI when the ovary was ovulating. For F-DII, this status exhibited a smaller number of fertilized structures (p<0.05). At the end of the experiments, it was concluded that both the Laiciphos Green Ovine and Tris-Yolk can be used in the conservation of semen at 4 °C for 48 hours, whereas Equimix added with 20% egg yolk is recommended for use in semen storage (4 °C) of up to 24 hours. The refrigeration of ovine semen at 4 °C for 24 hours is viable for use inembryo transference programs. Equimix added with 20% egg yolk resulted in a fertilization rate and embryo quality similar to the traditional Tris-Yolk.