Effect of semen extenders on sperm parameters of ram semen during liquid storage at 4 °C

Abstract

The objectives of this study were to compare the DNA fragmentation index (DFI), mitochondrial membrane potential (MMP) and objective sperm motility during liquid storage of ram sperm stored in egg yolk, skim milk or soy bean extract based extenders. Five adult rams (2 Dorset Horn and 3 Dorset Horn crossbred) ranging from 24 to 36 months of age, were used in the study. Semen from each ram was divided into 3 aliquots. Aliquots were diluted with either egg yolk, skimmed milk or soybean extract based extenders (10×107spermperml), and stored at 4°C. The DFI and MMP were assessed with the aid of flow cytometry and sperm motility parameters evaluated using the computer assisted sperm analyzer (CASA) system on days 0, 2, 4, 6 and 8 of storage. The MIXED procedure of SAS was used to perform a repeated measures analysis of covariance, to test for the effects of days of storage (0, 2, 4, 6, and 8), extenders (egg yolk, milk or soy based), and the interactions on the DFI, MMP and the sperm motility parameters. The DFI and MMP performed significantly different between extenders (P<0.01), and DFI and MMP were significantly different between days of the storage (P<0.0001). A significant extender×day of storage interaction was recorded for DFI and MMP (P<0.05). The computer assisted sperm motility parameters were significantly (P<0.05) different between the extenders, except for amplitude of lateral head displacement (ALH) and beat cross frequency (BCF). The sperm motility parameters were also significantly different regarding the days of storage (P<0.05). A significant extender×day of storage interaction was also recorded for all sperm motility parameters (P<0.05). Generally, the egg yolk and soy based extenders gave better protection to the sperm, compared to the milk based extender during liquid storage. The soy based extender appeared to be an appropriate substitute for semen extenders prepared from animal sources, especially as there exists a concern regarding microbial contamination of products (milk and egg yolk), from animal origin.