Relationship between bull field fertility and in vitro embryo production using sperm preparation methods with and without somatic cell co-culture

Abstract

Experiments were designed to compare rates of embryonic development following oocyte exposure to cyropreserved spermatozoa from bulls of varying proven fertility, utilizing 3 different sperm preparation methods prior to oocyte introduction. These included 1) sperm co-culture with bovine oviductal epithelial cells (BOEC); 2) sperm co-culture with buffalo rat liver cells (BRLC); or 3) control culture in a routine, cell-free culture system. Semen from 9 bulls was classified by lifetime 60- to 90-d nonreturn rates as having either (mean ± SEM) high (n=3) 73.2 ± 3 a , medium (n=3) 70.3 ± 2 b or low (n=3) 65.8 ± 3 c field fertility ( ac P< 0.01; bc P< 0.05). There was no difference in embryo cleavage rates for spermatozoa from the high (58 ± 18%), medium (57 ± 23%) or low (57 ± 18%) fertility groups. Development to morula or beyond of oocytes fertilized with high (53 ± 30%) or low (58 ± 27%) fertility semen tended (P<0.10) to be higher than of those fertilized with medium fertility (33 ± 28%) semen. This lack of relationship between in vivo fertility and in vitro embryo outcome was consistent across all sperm preparation methods. Therefore, pooled data were used to evaluate the effect of sperm preparation on embryo outcome. There was no difference in embryo cleavage rates between BOEC monolayers (51 ± 22%), BRLC monolayers (60 ± 20%) and the cell-free controls (60 ± 17%). Subsequent embryonic development to compact morula and beyond was higher (P<0.01) with the BRLC monolayer treatment (61 ± 28%) than with the BOEC monolayers (42 ± 33%) or control culture (39 ± 24%). In conclusion, these studies suggest that there is no predictive relationship between bull field fertility (in the ranges evaluated here) and in vitro embryo cleavage or development rates. However, oocytes inseminated with sperm cells co-cultured on BRLC monolayers develop to the morula stage or beyond at a higher rate than oocytes inseminated with spermatozoa from the BOEC or cell-free system.