SELECTED TIMES OF INSEMINATION WITH MICROENCAPSULATED BOVINE SPERMATOZOA AFFECT PREGNANCY RATES OF SYNCHRONIZED HEIFERS

This experiment was designed to test whether spermatozoa encapsulated in an alginate poly-l-lysine matrix had an extended fertile life in vi vo after insemination. Estrus was synchronized in 417 primiparous Frie sian and Jersey heifers with a system based on a CIDR-B-(R) intravagin al device before the heifers were inseminated either during proestrus (24 h after device removal) or at estrus (48 h after device removal). Pregnancy rates to first inseminations did not differ between the 24 a nd 48 h inseminations (61 vs 60.6%) with liquid semen diluted in Capro gen((R)) (control) but differed with encapsulated semen (45.1 vs 68.6% ). The difference in pregnancy rates between the 2 types of semen was more pronounced (P < 0.08) in the animals that were visually detected in estrus. The mean survival time of spermatozoa in the female reprodu ctive tract following insemination at the 24-h insemination time was e stimated to be 50 +/- 7.5 h. The increased pregnancy rate with insemin ation of encapsulated spermatozoa at 48 h could have been due to this process predisposing spermatozoa to capacitate soon after insemination . (C) 1997 by Elsevier Science Inc.