Effect of breed and sperm concentration on the changes in structural, functional and motility parameters of ram-lamb spermatozoa during storage at 4 °C

The objectives of this study were (1) to determine the changes in structural, functional and motility parameters of ram-lamb semen stored at two different concentrations at 4 °C for 8 days in egg-yolk based extender and (2) to determine the effect of breed of ram-lambs on the changes in structural, functional and motility parameters of ram-lamb semen from different breeds stored at two different concentrations at 4 °C for 8 days in egg-yolk based extender. Two different concentrations suitable for laparoscopic and cervical insemination were employed in this experiment. A total of 14 ram-lambs (Polled Dorset-5, Suffolk-5, Katahdin-4) with satisfactory breeding potential were selected. Semen samples were collected by electro-ejaculation. Semen samples were extended to 50 and 200 million sperm per ml with a commercial egg yolk based extender (Triladyl^®, Minitube of America, Verona, WI, USA) at room temperature and were stored at 4 °C. The sperm DNA fragmentation index (DFI), percentages of high mitochondrial membrane potential (hMMP) and plasma membrane integrity (PMI) were assessed using flow cytometry as part of structural and functional parameters on Days 0, 1, 4, 6, and 8. A computer assisted sperm analyser (HTM-IVOS, Version 10.8, Hamilton Thorne Research, Beverly, MA, USA) was used to assess the sperm motility parameters on Days 0, 1, 4, 6, and 8. PROC MIXED procedure was used to determine the effect of days of storage, concentration and breed. The concentration and days of storage significantly affected the sperm structural, functional and motility parameters (P < 0.0001). Significant concentration × days of storage interaction was found for all structural and functional parameters. There was a significant concentration × days of storage interaction for average path velocity, curvilinear velocity, straightness and linearity. Overall changes in the sperm structural, functional and sperm motility parameters over the storage period were less dramatic in the 200 × 10⁶ ml^-1 concentration when compared to 50 × 10⁶ ml^-1 concentration. The hMMP and total progressive motility were influenced by breed. In conclusion, the quality of structural, functional and motility parameters declined as days of storage were increased and the magnitude of changes in the parameters was less dramatic at the higher concentration.