Efeito da lipoproteína de baixa densidade sobre a qualidade do sêmen canino submetido à criopreservação

Abstract

Egg yolk is one the most used external cryoprotectors for semen preservation. Its composition includes low-density lipoprotein (LDL). The LDL cryoprotecting action is attributed do the incorporation of phospolipids and cholesterol to the cell membrane, as well as to its association with proteins present in seminal plasma, preventing that they could take such substances from the cell membrane, making such membrane more stable and decreasing sperm sensitivity to cold shock. However, egg yolk also contains other substances detrimental to the sperm, which can lead to reduction in motility and in the phospolipids and cholesterol content. The objective of this study was to evaluate the effect of the replacement of egg yolk by LDL in extenders for canine semen frozen and cooled at 5 ºC considering parameters of semen quality. In Experiment 1 (EXP1) 5 ejaculates were collected from 4 Cocker Spanil dogs and, after centrifugation, extended according to 4 treatments: Tris-Glucose plus 20% egg yolk (T1), Tris-Glucose plus 6% LDL (T2), TrisGlucose plus 8% LDL, Tris-Glucose plus 10% LDL. After semen incubation at 20°C during 1 h, the temperature was gradually reduced during 2 h up to 5°C. Sperm motility (MOT), membrane integrity (MI) and morphology (MOR) were evaluated were evaluated at 24, 48, 72 and 96 h, along with the maximum survival time (MST). In Experiment 2 (EXP2), semen samples were collected from 4 Cocker Spanil (3 repetitions) and 2 German shepherd (4 repetitions), following the same procedures of EXP1. Subsequently, the same treatments of EXP1 were applied at 5°C, with the inclusion of glycerol at 10% (final concentration equal to 5%) for freezing. Straws were thawed in liquid Nitrogen at 5 cm. After thawing, the same semen quality parameters were evaluated. In EXP1, MST was lower for T1 than for the other treatments (P < 0,01), but T2, T3 and T4 did not differ (P > 0,05). MOT and MI did not differ among T2, T3 and T4 at 24, 48, 72, and 96 h in EXP1 and after thawing in EXP2 (P > 0,05), but all those 3 treatments present superior results in comparison with T1 (P < 0,01), in both experiments. MORF did not differ among treatments in both EXP1 and EXP2 (P > 0,05). In conclusion, purified LDL can replace egg yolk in extenders for canine semen cooled at 5ºC or frozen.