310 SEASON INFLUENCE UPON SEMINAL PLASMA PROTEINS IN BROWN SWISS BULLS

Abstract

Seminal plasma is a complex of secretions of the male accessory reproductive organs and appears to exert important effects on sperm function (Shivaji et al. 1990 Proteins of Seminal Plasma, Wiley, New York, NY, USA). The protein quality of the seminal plasma may affect positively the bulls’fertility (Killiam et al. 1993 Biol. Reprod. 49, 1202-1207). Peptides of 55 and 66 kDa were present in bulls with excellent spermatic conditions for example motility and vigor. On the other hand, 16- and 36-kDa peptides were observed with unfavorable spermatic conditions (Chacur et al. 2009 Anim. Reprod. 6, 339). The objective was to determine the influence of season on seminal plasma proteins in Brown Swiss bulls. Semen from 33 Brown Swiss bulls 24 months of age was collected by electroejaculation during winter (from June to August) and summer (from December to February) in the southern hemisphere in 2008. Semen samples were collected with 14-day intervals totalizing 196 ejaculates. Samples of semen were centrifuged (1500g/15 min) and the seminal plasma was conditioned in cryotubes and stored at -20°C until further processing. Proteins were extracted from 200 μL of each sample in 2 mL of extraction buffer composed of 0.625 M Tris-HCl, at pH 6.8, in 2% SDS, 5% fi-mercaptoethanol, and 20% of glycerol. Percentages of different plasma proteins by season were statistically compared by the chi-square test with significance level at P < 0.05). Proteins were quantified according to Bradford (1976 Anal. Biochem. 72, 248-254) and electrophoresis was performed according to Laemmili (1970 Nature 227, 680-685). Gels were fixed with isopropanol: acetic acid: water (4:1:5 v/v) for 30 minutes and stained in the same solution with 2% of Coomassie Blue R250. In 26 bulls, the absence of high molecular weight (HMW; 55 kDa, 66 kDa, and 80 kDa) proteins was found in the summer. There was a significant increase (P < 0.05) in total spermatic defects, acrosome defects, and distal cytoplasmatic droplets in these bulls. The 40-kDa protein that reflected low fertility was observed in 10 bulls in the summer with semen quality decreases. The 11 bulls showed presence of HMW (55 kDa) in the winter. In 11 bulls, HMW (55 kDa, 66 kDa, or 80 kDa) proteins were present with a satisfactory semen condition according to Killiam et al. (1993 Biol. Reprod. 49, 1202-1207). In conclusion, the seasons of the year may influence the presence of proteins in seminal plasma. There was a direct relationship of the season with seminal plasma proteins. The presence of the proteins of 20 kDa, 55 kDa, 66 kDa, and 80 kDa suggested an increase of the semen quality during the winter.

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