Mule embryos share identical morphological features to horse embryos

Area of Science:

• Reproductive Biology
• Comparative Embryology
• Equine Science

Background:

• Understanding equine and mule embryo development is crucial for reproductive success in horses and the breeding of mules.
• Previous research has not extensively compared the nuclear morphometry of horse and mule embryos.

Purpose of the Study:

• To compare the nuclear morphometry of horse and mule embryos.
• To test the hypothesis that mule embryos have higher micronuclei and nuclear fragmentation indexes than horse embryos.

Main Methods:

• Twenty-two mares were assigned to receive semen from a horse and a donkey in a crossover design.
• Horse and mule embryos were recovered eight days post-ovulation, stained, and imaged using fluorescence microscopy.
• Nuclear morphometry, including compact, mitotic, and fragmented nuclei, was assessed using ImageJ software.

Main Results:

• No significant difference was found in embryo size or fragmented nuclei index between horse and mule embryos.
• Mule embryos showed a trend towards a higher number of mitotic nuclei compared to horse embryos (P=0.08).
• The mitotic nuclei index was significantly higher in mule embryos (3.2% ± 0.4%) than in horse embryos (2.2% ± 0.2%) (P=0.02).

Conclusions:

• Horse and mule embryos share similar nuclear ultrastructure features.
• Mule embryos possess a significantly higher mitotic index compared to horse embryos, indicating potential differences in early developmental processes.