Increase in post-thaw viability by adding seminal plasma proteins to Sanmartinero and Zebu sperm ¤ Incremento en la viabilidad espermática post-descongelación por la adición de proteínas del plasma seminal a semen de toros Sanmartinero y Cebú Aumento da viabilidade espermática pós-descongelamento, com a adição de proteínas do plasma seminal de sêmen de touros das raças Sanmartinero e Zebu

Summary Background: cryopreservationdecreasesspermviabilitybyapproximately50%. Objective: the objective of this study was to determine the effect of the addition of seminal plasma proteins on post-thawing sperm viability in Sanmartinero and Zebu semen. Methods: semen samples from 10 bulls of each breed were used, and seminal plasma was subjected to two-dimensional electrophoresis to establish the relationship between the relative amount of each protein spot and sperm viability. Then, seminal plasma was subjected to exclusion chromatography to separate the fraction containing these proteins.This fraction was added in doses of 0.5, 1.0, 1.5 and 2.0 mg, to 1 x 10 6 . Sperm was thawed and incubated at 37 °C for 1 h to determine its effect on postthaw viability. Sperm were frozen using two media (citrate-fructose-yolk and Bioxcell ® ). Results: we found one protein spot (16.20 kDa, PI 5.5) in Sanmartinero seminal plasma that correlated (r = 0.64 p<0.001) with viability. This spot was found in 21-25 chromatography fractions. The percentage of post-thaw viable sperm increased 20% (p<0.05) at 1.0 and 1.5 mg of the fraction when sperm was frozen using citrate-fructose-yolk; it increased 25% (p<0.01) with 0.5 mg when it was frozen with Bioxcell ® media. Addition of 0.5 mg of the fraction to semen cryopreserved with Bioxcell ® resulted in a greater (p<0.05) percentage increase of viable sperm in Sanmartinero semen (23 ± 8.3%) compared with Zebu semen (6.0 ± 2.0%). Conclusions: these