title: Selected times of insemination with microencapsulated bovine spermatozoa affect pregnancy rates of synchronized heifers.
abstract: This experiment was designed to test whether spermatozoa encapsulated in an alginate poly-L-lysine matrix had an extended fertile life in vivo after insemination. Estrus was synchronized in 417 primiparous Friesian and Jersey heifers with a system based on a CIDR-B intravaginal 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 and 48 h inseminations (61 vs 60.6%) with liquid semen diluted in Caprogen (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 reproductive tract following insemination at the 24-h insemination time was estimated to be 50 +/- 7.5 h. The increased pregnancy rate with insemination of encapsulated spermatozoa at 48 h could have been due to this process predisposing spermatozoa to capacitate soon after insemination.
authors.affiliation: Livestock Improvement Corporation, Private Bag 3016, Hamilton, New Zealand.
authors.forename: R
authors.initials: R
authors.lastname: Vishwanath
authors.forename: R L
authors.initials: RL
authors.lastname: Nebel
authors.forename: W H
authors.initials: WH
authors.lastname: McMillan
authors.forename: C J
authors.initials: CJ
authors.lastname: Pitt
authors.forename: K L
authors.initials: KL
authors.lastname: Macmillan