Conception rates in ewes after AI with ram semen preserved in milk-egg yolk extenders supplemented with glycerol.

This study aimed at comparing the effect of ram semen preserved at 5 °C on two milk-based extenders (UHT skim milk or INRA-96(®) , 5% egg yolk) supplemented with 2% glycerol, and the preservation time (24 and 48 h) on conception rates after cervical AI of ewes. In two field trials, 1198 Merino ewes were cervical AI in spontaneous oestrus. In Experiment 1, pooled semen (6 rams) was extended in UHT-base (fresh, control) or chilled for 24 h in UHT5Y (UHT-base 5% egg yolk), INRA5Y (INRA-96(®) 5% egg yolk), UHT5Y2G (UHT5Y 2% glycerol) or INRA5Y2G (INRA5Y 2% glycerol). In Experiment 2, AI was performed with pooled semen (7 rams) used fresh (extended in UHT-base or UHT5Y2G, control groups) or chilled (extended in UHT5Y2G) for 24 or 48 h. Conception rate was determined by ultrasound 40 days after AI. INRA-96(®) - had similar conception as UHT-preserved semen (56.7 vs 55.4%, p>0.05). Addition of 2% glycerol did not modify the results (56.8 vs 55.2%, p>0.05). Fresh semen extended in UHT-base, and UHT5Y2G yielded similar conception rates (60 vs 64%, p>0.05). Preservation for 24 or 48 h in UHT5Y2G gave similar results (49 vs 47%; p>0.05). In conclusion, ram semen chilled for 24 h in UHT- or INRA-96(®) -based extenders yielded similar results, and glycerol addition did not have a detrimental effect. UHT5Y2G might be used to extend ram semen for fresh AI, or to preserve it for 24 or 48 h with acceptable results.