The ultimate design of a microencapsulated AI dose is to continuously release sperm over a period of time in the female reproductive tract, thus alleviating the need for estrus detection. The objective of Trial 1 was to determine in vitro sperm release times for three microcapsule membranes. Semen was collected from four bulls, pooled, extended in 20% egg yolk TEST to a concentration of 80 = 10⁶ cells/ml, and encapsulated. Microcapsule membranes were constructed from isomers of polylysine: .1% poly-L-lysine (PLL), .1% poly-D-lysine (PDL), and a 50:50 mixture of the isomers (PLPD). Microcapsules were incubated at 37°C in a buffer containing .5% heparin or .5% trypsin and evaluated at 0.5, 1, 2, 4, 8, and 16 h post-encapsulation. For sperm encapsulated there were no significant differences in sperm motility. However, peak time of maximum sperm release differed between PLL and PDL membranes at 2 and 4 h of incubation. In Trial 2, sperm viability and microcapsule membrane stability were assessed post-thaw using PLL or PDL, two encapsulating temperatures (5°C or 23°C) and two times of glycerol addition (prior or post encapsulation at 5°C). Semen was extended to 80 = 10⁶ cells/ml and encapsulated. Capsules from all treatment combinations were incubated in .5% trypsin and evaluated as in Trial 1. In addition, motility was estimated at 1, 3, 6, and 9 h post-thaw. Motility from the unencapsulated control and capsules with glycerol addition prior to encapsulation, was superior (P < .05). Additionally, sperm release from capsules prepared at 5°C with glycerol addition post encapsulation was greater than all other treatments (P < .05). Time of peak sperm release for capsules was similar to the previous trial. There was a positive correlation between average capsule diameter and sperm release for both trials (P < .05). These data suggest that a combination of PLL and PDL capsules may complement each other in timing of sperm release and may be utilized in an inseminate mixture for extending the effective release in the female / Master of Science