Season and social environment influence the membrane integrity of ejaculated boar spermatozoa as assessed by ouabain sensitivity

Eight adult Landrace boars were housed for 12 months in one of two social environments. Socially nonrestricted boars were penned near estrual females and socially restricted boars were penned behind solid walls to eliminate visual and physical contact with other pigs. All animals were subjected to natural changes in day length. The sensitivity of ejaculated spermatozoa to ouabain (in inhibitor of Na+-K+ ATPase) was determined on 4 consecutive weeks in November, March-April, and July-August. Semen was diluted in Tyrode's solution (pH 7.4) with and without 10(-3) M ouabain. Duplicate samples of control and ouabain-treated spermatozoa were incubated at 37 degrees C for 4 h, and percent motile sperm, motility type, and motility index (combination of percent and type) were determined at hourly intervals. Ouabain-induced decreases in most motility parameters varied with season (season X treatment, P less than 0.05). At hour 4, induced decreases in percent motile sperm were more pronounced in November and July-August than in March-April for socially nonrestricted boars. Decreases in motility type were greater (P less than 0.05) in November and July-August than in March-April for socially nonrestricted boars and were greater (P less than 0.01) in November than in July-August for restricted boars. In March-April motility type decreased (P less than 0.01) to a greater extent for socially restricted vs. nonrestricted boars. Similar season and social environment differences were observed for motility index values. Given the interrelationships between ouabain sensitivity, the functional integrity of sperm cells, and fertilizing capacity, season and social environment differences in ouabain-induced motility depression probably reflect qualitative changes in boar spermatozoa.