Improved in vitro bovine embryo development and increased efficiency in producing viable calves using defined media

Area of Science:

• Veterinary Science
• Reproductive Biology
• Biotechnology

Background:

• In vitro embryo production (IVEP) in cattle relies on culture media, often containing undefined components like BSA or FBS.
• Optimizing IVEP media is crucial for improving developmental competence and pregnancy rates.
• Korean native cattle (HanWoo) present unique reproductive physiology that may benefit from tailored IVEP protocols.

Purpose of the Study:

• To develop and optimize a chemically defined, two-step culture medium for in vitro maturation, fertilization, and embryo development in Korean native cattle.
• To evaluate the impact of specific components like polyvinyl alcohol (PVA), myo-inositol, phosphate, and epidermal growth factor (EGF) on bovine embryo development.
• To compare the developmental competence, blastocyst cell number, calving rate, and gene expression profiles of embryos cultured in the defined medium versus a conventional undefined medium.

Main Methods:

• Oocytes from HanWoo cattle ovaries were matured in vitro, fertilized, and cultured in a two-step system.
• Media formulations were systematically varied, testing different protein supplements (BSA vs. PVA), myo-inositol, energy substrates (glucose vs. phosphate), and EGF concentrations.
• Blastocyst development rates, total cell numbers, calving rates after embryo transfer, and mRNA transcript abundance (interferon-tau, glucose transporter-1, IGF2 receptor) were analyzed.

Main Results:

• Defined media with PVA and myo-inositol improved blastocyst formation rates compared to BSA-only media.
• The addition of phosphate and 10 ng/mL EGF to the PVA-myo-inositol medium further enhanced blastocyst development (up to 52%).
• The optimized defined medium resulted in significantly higher calving rates and increased expression of interferon-tau and glucose transporter-1 mRNA in blastocysts compared to undefined media.

Conclusions:

• A chemically defined culture medium, supplemented with PVA, myo-inositol, phosphate, and EGF, significantly improves in vitro bovine embryo development and subsequent calving rates.
• This defined medium supports enhanced embryo competence and viable offspring production without negatively impacting blastocyst cell numbers.
• The improved outcomes are associated with altered gene expression, suggesting a more favorable developmental environment provided by the defined medium.