MICROENCAPSULATION OF BOVINE SPERMATOZOA - EFFECT OF CAPSULE MEMBRANETHICKNESS ON SPERMATOZOAL VIABILITY AND FERTILITY

This study was undertaken to investigate the relationship between the cationic polymer (poly-L-lysine) concentration and microcapsule membra ne thickness, maintenance of spermatozoal motility in vitro, and pregn ancy rate in 335 oestrous synchronized Friesian heifers. Semen was ext ended in CAPROGEN(TM) containing 5% egg yolk and a final encapsulated spermatozoal concentration of 20 X 10(6) spermatozoa ml(-1). Four conc entrations of poly-L-lysine were studied (0.025, 0.05, 0.075, and 0.1% , w/v). Microcapsule membrane thickness resulting from these concentra tions was 3.22 +/- 0.54 mu m (mean +/- SD), 5.30 +/- 0.31 mu m, 7.12 /- 0.41 mu m, and 7.44 +/- 0.85 mu m, respectively (P < 0.05). Spermat ozoal viability, as assessed by motility estimates at 24 h intervals d uring 120 h of incubation at 37 degrees C, was not influenced by polym er concentration or different than unencapsulated controls. For fertil ity evaluation approximately 65 Friesian heifers were inseminated with spermatozoa either unencapsulated or encapsulated with one of the fou r polymer concentrations. Oestrous synchronization was accomplished wi th the combination of a progesterone-impregnated CIDR-B(R) device cont aining a 10 mg oestradiol benzoate capsule inserted for 10 days with a dministration of 12.5 mg of prostaglandin F-2 alpha on Day 6 of CIDR-B (R) insertion. Heifers were inseminated in the uterine corpus at 24 h after CIDR-B(R) removal which constituted the pro-oestrous stage of th e cycle for 95.5% of the heifers. Inseminate dose rate was 5 X 10(6) s permatozoa in 0.25 ml. Pregnancy rates were similar for heifers insemi nated with encapsulated and unencapsulated spermatozoa (49.4 vs. 48.6% ). From these studies we conclude that poly-L-lysine concentration doe s influence the microcapsule membrane thickness without affecting main tenance of spermatozoal motility in vitro or fertility of oestrous syn chronised Friesian heifers.