Specificities of boar semen spermatozoa make them sensitive to temperature variation

03.04.2019

As you can observe in this drawing, the plasma membrane is a network of lipids and proteins and is composed of:

• Phospholipid bilayer (with satured and unsatured fatty acid)
• Proteins
• Cholesterol
• Glycoprotein
• Glycolipid

Membrane fluidity refers to the viscosity of the lipid bilayer. When the temperature decreases, interactions between phospholipids appear and the membrane becomes more rigid and can be described as a “glass state”. Some components, such as the cholesterol rate, could help the membrane to better stand the temperature drop.

Contrary to other mammalian spermatozoa, swine spermatozoa are characterized by a high content of polyunsaturated fatty acids and a low concentration of cholesterol. Due to this particular composition, the cold shock point is quite high, thus making boar spermatozoa more sensitive to temperature drops. 

During semen processing, the temperature goes down from 37°C just after collection to 17°C for the storage. 

• During the first phase (38°C to 25°C), only the spermatozoa metabolism is affected. This transition period is reversible. The motility of the sperm decreases, which helps prolong the survival of the sperm. But temperature fluctuations between 38 and 25°C both speed up and slow down the activity of the spermatozoa, which reduces the viability of the sperm.
• Below 25°C, the plasma membrane starts to be affected and become more rigid. 
• Below 15°C, the boar spermatozoa membrane could have an irreversible cold shock. The membrane becomes more porous and the spermatozoa lose their internal components. The sperm viability and fertility decreases.

Bailey et al., 2008; Martín Hidalgo et al., 2011; López Rodriguez et al., 2012; Schulze et al., 2013