Observations on the development of bovine morulae on various cellular and noncellular substrata.

The objective was to determine the effect of various cell types on the development of bovine embryos in vitro. Morulae were collected from beef and dairy cows 4 to 5 d after the onset of estrus (d 0). Embryos were randomly allocated to nine treatments: (1) microdrops of Ham's F-10 medium (HF-10) under paraffin oil (HF-10); (2) HF-10 over a substratum of collagen without paraffin oil (HF-10/clg); (3) HF-10 with bovine uterine fibroblasts grown on a collagen substratum (HF-10/clg-fib); (4) Minimal Essential Medium (MEM) without paraffin oil (MEM); (5) microdrops of MEM under paraffin oil (MEM/oil); (6) MEM with bovine uterine fibroblasts (MEM/Buf; (7) MEM with bovine testicular fibroblasts (MEM/Btes); (8) MEM exposed to uterine fibroblasts for 24 h to condition the medium (MEM/Con), and (9) MEM with 1 mm cubes of bovine endometrial tissue (MEM/End). In all cases, media were supplemented with 10% (v/v) heat-treated fetal calf serum. Observations were made at 24 h intervals, with the stage of embryo development recorded. Morulae developed into expanded blastocysts more frequently (P less than .05) in HF-10, MEM, MEM/oil, MEM/Buf, MEM/Btes and MEM/Con than in HF-10/clg, HF-10/clg-fib and MEM/End. More (P less than .01) blastocysts hatched in MEM/Buf and MEM/Btes than in the other media. In addition, nine of 12 (MEM/Buf), eight of 11 (MEM/Btes) and two of two (HF-10/clg-fib) hatched blastocysts attached to the fibroblast monolayers, an observation that was uncommon in treatments without cells. These data suggest that the co-culture of bovine embryos with bovine fibroblasts in a superior system for promoting embryo hatching and attachment in vitro.