Changes in Ram Semen Quality between Subsequent Ejaculates.

The objective of this study was to compare ram semen quality characteristics from a first to a second semen collection on the same day. Six 5-mo old Hampshire rams at the SDSU sheep unit had a semen evaluation performed at six week intervals between October and April. Semen was collected by electro-ejaculation and evaluated both by a veterinarian trained in visual semen quality scoring and with a computer assisted sperm analysis system (CASA). Data were analyzed using the MIXED and CORR procedures of SAS. There were significant positive correlations (P < 0.01) in the visual score for both motility and morphology scores between the first and second collections. When semen was analyzed by CASA there was a positive correlation (P < 0.01) between the first and second collection for distal droplets, percent normal, percent motile, percent progressive, curvilinear velocity, and straight line velocity. Although, there was no significant difference in the actual visual score between the first and second ejaculate for morphology (P = 0.85) or motility (P = 0.49). Furthermore, when evaluated with the CASA there was no significant difference in the value between the first and second ejaculate for morphology (P = 0.99), motility (P = 0.12), or proximal droplets (P = 0.74). However, the percentage of progressively motile sperm tended to increase from the first to the second ejaculate (P = 0.07; 23% to 33%). Curvilinear velocity also tended to increase from the first to the second ejaculate (P = 0.06; 132 ± 11.9 um/sec to 164 ± 11.9 um/sec), and straight line velocity did increase (P = 0.05) from the first collection to the second (73.8 ± 8.1 um/sec to 96.6 ± 8.1 um/sec). In conclusion, a comparison of duplicate semen samples, sperm morphology and motility measurements were similar using subjective or objective analytics. However improvements were detected in percentage of progressive sperm and velocity of sperm (both curvilinear and straight line) with a second sampling. Although the objective analytics at least tend to show sampling differences for several sperm motion traits the results from this study support industry practices for a single semen sample to subjectively assess semen quality characteristics in a ram.