The percentage of ejaculated sperm that survived cold shock was increased by adding egg yolk, amaranth, or DNA to the saline or citrate diluents in which the sperm were suspended. The beneficial effect of egg yolk was blocked in a concentration dependent manner by the addition of seminal plasma. Heating the seminal plasma did not reduce this blocking ability, unless the seminal plasma and egg yolk were heated together. The percentage of washed sperm surviving cold shock was reduced by adding seminal plasma or the retentate of dialysed seminal plasma to the saline or citrate storage diluents. The addition of diffusate of dialysed seminal plasma increased the percentage of sperm surviving cold shock. The size of the detrimental factor(s) in seminal plasma indicated that it acts by destabilising the sperm cell membrane. Adding egg yolk, but not amaranth, to the storage diluents increased the percentage of washed sperm surviving cold shock. The addition of seminal plasma, or the retentate of dialysed seminal plasma, decreased the percentage of sperm surviving cold shock in citrate and egg yolk diluents, but not in an amaranth diluent. It was concluded that egg yolk competes with the destabilising factor(s) in seminal plasma for sites on the cell membrane whereas amaranth binds these destabilising factor(s).
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