Abstract
Background:
Intracytoplasmic sperm injection (ICSI) technique has low efficiency in cattle. This has mainly been attributed to the oocyte activation failure due to oocyte and/or sperm factors.
Aim:
Our aim was to evaluate the effect of conventional ICSI and Piezo-ICSI with bull or human sperm on bovine oocyte activation and embryo development and to assess its relationship with PLCɀ activity of both species.
Methods:
In vitro matured bovine oocytes were randomly divided into five groups and were fertilized as follows: conventional ICSI using bovine sperm with chemical activation (control), conventional ICSI using bovine sperm, Piezo-ICSI using bovine sperm, conventional ICSI using human sperm, and Piezo-ICSI using human sperm. PLCɀ activity was determined in bull and human sperm samples.
Results:
Within the groups using bull sperm, the oocytes fertilized by conventional ICSI had the lowest values of 2 pronuclei (PN) formation and cleavage, Piezo-ICSI increased both percentages, and ICSI + chemical activation presented the highest 2 PN, cleavage and blastocyst rates (P<0.05). Within the groups using human sperm, the oocytes fertilized by Piezo-ICSI presented higher 2 PN and cleavage rates than those activated by conventional ICSI (P<0.05). Piezo-ICSI with human sperm increased bovine oocyte activation as much as conventional ICSI + chemical activation with bovine sperm (P<0.05). Higher values of PLCɀ activity were found in human sperm compared with bovine sperm (P<0.05).
Conclusion:
Our results suggest that the higher stability of the bovine sperm in combination with its relative low content of PLCɀ impair bovine oocyte activation after ICSI.

Key words: Bovine, ICSI, Piezo-ICSI, PLCɀ, Oocyte activation