This study examined the effects of three diluents--skim milk (M), TesT (TE) and Tris-trehalose (TR)--on quality of ram semen stored at 5 degrees C over a long term. Percentage of motile spermatozoa (PM), motility score (MS), percentage of intact acrosomes (PIA), and percentage of swollen spermatozoa under hypoosmotic conditions (PS) were assessed after cooling and every 24 h up to day 16. There was a significant effect (p < .01) of diluent type in the conservation rates after cooling for PM. The TR diluent achieved greater values (94.7 +/- 1.36%) than TE (82.4 +/- 3.08%), while M showed an intermediate value (89.3 +/- 2.17%). In relation to time of storage, TR diluent showed the highest PM values up to day 12, but differed (p < .05) from TE medium only until day 4. The TR extender maintained a PM > 50% up to day 8, while TE and M were greater than 50% up to day 5. Skim milk maintained progressive movement of sperm cells for longer (MS = 3 until day 5) than the other diluents. There were no significant differences in PIA among the 3 media during the first 6 days of storage (except in day 2), and M showed the lowest value afterward. There was no significant extender effect on PS for the first 3 days, but after day 6 diluent M also showed the lowest values of this variable.