Post-thawing quality of ram spermatozoa is impaired by inclusion of boar seminal plasma in the freezing extender

•Boar and ram seminal plasma (SP) were added to the freezing extender for ram sperm.•Protein content was quantified in pooled SP samples.•Membrane integrity was reduced for ram sperm with intact acrosome in contact with boar SP.•There were fewer intact ram spermatozoa extended with boar SP.•Total and progressive ram sperm motility were lower with both SP.

Addition of seminal plasma (SP) to freezing extenders may help reducing post-thawing sperm cryoinjuries. This study evaluated the effects of adding heterologous (boar) SP to the freezing extender on ram sperm quality after thawing. Protein content was quantified in pooled SP samples from rams and boars. Five ejaculates from four rams were frozen in a Tris-egg yolk-glycerol extender including: no (control), ram and boar SP (both at 20% of the volume, with 48 μg protein/mL). After thawing, total and progressive motility for sperm treated with SP were lower than that of the control (P < 0.05). For spermatozoa with intact acrosome, those in contact with boar SP had the lowest membrane integrity (P < 0.05), but for spermatozoa with damaged acrosome, the lowest membrane integrity occurred for those in contact with ram SP (P < 0.05). Greater percent of high post-thawing mitochondrial membrane potential occurred in the control than in contact with both SP (P > 0.05). Apoptotic-like changes were similar among treatments (P > 0.05), but there were fewer intact spermatozoa extended with boar SP than in the control (P < 0.01). Contact with extenders including boar SP harmed ram sperm quality after thawing. Post-thawing motility was decreased for ram sperm extended in contact with both homologous and heterologous SP.