Microencapsulation of bovine spermatozoa: effect of capsule membrane thickness on spermatozoal viability and fertility

This study was undertaken to investigate the relationship between the cationic polymer (poly-L-lysine) concentration and microcapsule membrane thickness, maintenance of spermatozoal motility in vitro, and pregnancy rate in 335 oestrous synchronized Friesian heifers. Semen was extended in CAPROGEN™ containing 5% egg yolk and a final encapsulated spermatozoal concentration of 20 × 106 spermatozoa ml−1. Four concentrations of poly-L-lysine were studied (0.025, 0.05, 0.075, and 0. 1%, w/v). Microcapsule membrane thickness resulting from these concentrations was 3.22 ± 0.54 μm (mean ± SD), 5.30 ± 0.31 μm, 7.12 ± 0.41 μm, and 7.44 ± 0.85 μm, respectively (P < 0.05). Spermatozoal viability, as assessed by motility estimates at 24 h intervals during 120 h of incubation at 37°C, was not influenced by polymer concentration or different than unencapsulated controls. For fertility evaluation approximately 65 Friesian heifers were inseminated with spermatozoa either unencapsulated or encapsulated with one of the four polymer concentrations. Oestrous synchronization was accomplished with the combination of a progesterone-impregnated CIDR-B® device containing a 10 mg oestradiol benzoate capsule inserted for 10 days with administration of 12.5 mg of prostaglandin F2α on Day 6 of CIDR-B® insertion. Heifers were inseminated in the uterine corpus at 24 h after CIDR-B® removal which constituted the pro-oestrous stage of the cycle for 95.5% of the heifers. Inseminate dose rate was 5 × 106 spermatozoa in 0.25 ml. Pregnancy rates were similar for heifers inseminated with encapsulated and unencapsulated spermatozoa (49.4 vs. 48.6%). hese studies we conclude that poly-L-lysine concentration does influence the microcapsule membrane thickness without affecting maintenance of spermatozoal motility in vitro or fertility of oestrous synchronised Friesian heifers.