Abstract

Background:
Artificial insemination (AI) is widely used to improve genetic progress and reproductive efficiency in sheep production systems, including Dorper sheep. The success of AI programs for liquid semen depends on the ability to maintain semen quality during storage. Although milk–egg yolk extenders are commonly used for ram semen preservation, the optimal egg yolk concentration for maintaining sperm quality under different storage conditions remains unclear.

Aim:
This study evaluated the effects of 5% and 10% egg yolk extenders on the quality of Dorper ram semen stored at room temperature (≈25°C) and 5°C.

Methods:
Semen was collected from healthy Dorper rams using an artificial vagina and divided into four treatment groups based on the extender concentration and storage temperature. Semen stored at room temperature was evaluated at 0, 2, 4, 6, and 8 hours, whereas semen stored at 5°C was evaluated daily for 5 days. Sperm quality was assessed based on progressive motility, sperm vitality, and plasma membrane integrity. Oxidative stress was evaluated by measuring malondialdehyde concentration and catalase activity. Data were analyzed using one-way analysis of variance followed by Tukey’s test (p < 0.05).

Results:
Within each storage condition, semen diluted with the 5% milk–egg yolk extender consistently maintained higher sperm motility, vitality, membrane integrity, and oxidative stability compared with the 10% extender.

Conclusion:
These findings indicate that a 5% milk–egg yolk extender is a practical and effective option for the shortterm preservation of Dorper ram semen for AI.

Key words: Dorper sheep; Liquid semen preservation; Milk–egg yolk extender; Sperm quality; Artificial insemination.