Influence of Post-Pubertal Ram Semen Quality on Ewe Conception Rates.

The objective of this study was to evaluate changes in semen quality for up to 6 months after puberty in young rams. Six 5 mo-old Hampshire rams at the SDSU sheep unit had a breeding soundness examination (BSE) performed every six weeks from October to April (5 collections). Semen was collected by electro-ejaculation and evaluated subjectively by a trained veterinarian and with a computer assisted sperm analysis system (CASA). At the initial BSE exam four of the six rams had already reached puberty (> 50% motile and > 70% normal), one additional ram reached puberty by the second collection period, and the last ram reached puberty by the fourth collection period. Data were analyzed with the first or pubertal collection as time 1 using the MIXED procedure of SAS. By visual evaluation there was no effect of collection period on sperm morphology (P = 0.41); however, motility score did increase (P = 0.05) as interval post puberty increased. Based on CASA analysis, there was no effect of collection period on morphology (P = 0.13), percent motile (P = 0.51), percent progressive (P = 0.25), curvilinear velocity (P = 0.74), or straight line velocity (P = 0.53). Based on BSE scores three rams were selected (highest, lowest and intermediate) for exposure to 10 synchronized ewes per ram. Conception rates of ewes mated were 60%, 100% and 25%, respectively; however these conception rates were not correlated with visual motility or morphology scores at the first (P = 0.36 and 0.53) or last BSE (P = 0.98 and 0.47). Nor were they correlated with CASA morphology (P = 0.57 and 0.63), percent motile (P = 0.64 and 0.90), percent progressive (P = 0.68 and 0.89), curvilinear velocity (P = 0.99 and 0.84), or straight line velocity (P = 0.81 and 0.99). In conclusion, motility score improved as post puberty interval increased, but morphology score was unchanged. CASA data supports the observed lack of change in morphology scores over time when related to puberty status. In addition, there was no correlation between subjective scores or objective measures and synchronized conception rates. Finally, a ram BSE evaluation is an important fertility index however is not predictive of overall fertility.