2.3. In vitro fertilization (IVF)
IVF took place in droplets (90L) containing tyrode albumin lactate pyruvate (TALP) supplemented
with 6mg/mL fatty acid free BSA (Sigma–Aldrich), 100mMsodium pyruvate (Sigma–Aldrich),
75g/mL gentamicin (Sigma–Aldrich), 11g/mL heparin and 44g/mL PHE (2mM penicillamine,
1mM hypotaurine, 250mM epinephrine; Sigma–Aldrich).
All experiments were carried out using frozen semen from Nelore or Angus bulls. A different bull
(from a total of two Nelore and two Angus) was used for each replicate to diminish bull effect. Semen
was thawed in a 37◦C for 20 s and spermatozoa were washed in a discontinuous Percoll gradient
(Pharmacia, Uppsala, Sweden) prepared by adding 2mL of 45% Percoll to 2mL of 90% Percoll in a
15mL centrifuge tube (Cornning®). The semen samples were added on the top of Percoll gradient and
centrifuged at 900×g for 25min. After removal of the supernatant, spermatozoa were re-suspended
in IVF medium, counted in a Neubauer chamber and sperm suspension (10l of a final concentration
= 1×106 cells/mL) was added into each droplet. Incubation was carried out at 39 ◦C in a saturated
humidity atmosphere containing 5% CO2 and 95% air for 10–14 h.