Fertility Assessment in Sorraia Stallions by Sperm-Fish and Fkbp6 Genotyping.

The research article examines the fertility in Sorraia stallions, an endangered horse breed, by analyzing their sperm quality and genetic factors. The research reveals that while the stallions’ sperm concentration is normal, the quality of motile and morphologically-norm sperm is consistently low. Despite the lack of genetic susceptibility for impaired acrosome reaction, the relatively higher rate of sex chromosome aneuploidies contributes to their subfertility.

Research Context and Purpose

• The Sorraia horse breed, native to the Iberian region, is endangered and known for low genetic variability, high levels of inbreeding, and subfertility. The subfertility is characterized by poor sperm quality.
• The researchers studied 11 Sorraia stallions, all of which were physically normal but subfertile.
• The study aims to investigate the cause of the low fertility rate in Sorraia stallions, specifically looking into possible chromosomal abnormalities or genetic predisposition for impaired acrosome reaction (a sperm dysfunction).

Research Methodology

• The stallion’s sperm was analyzed through karyotyping and sex chromosome sperm-FISH (a technique to study genetic material).
• Additionally, the research looked into the FKBP6 gene, which is a susceptibility location for impaired acrosome reaction.
• The sperm concentration was found to be normal (>300 million cells/ml). However, the proportion of progressively motile sperm (21%) and morphologically normal sperm (28%) was low in all stallions.
• Furthermore, most of the sperm (89%) had normal haploid sex chromosome content, but 11% carried different variances of sex chromosome aneuploidies, a genetic irregularity where an organism has an abnormal number of chromosomes.

Research Findings

• Despite the presence of aneuploidies, no connection could be established between the percentage of these irregularities and inbreeding level, sperm shape, or stallion age.
• The researchers sequenced the FKBP6 gene exon 4 for SNPs g.11040315G>A and g.11040379C>A, revealing that none of the stallions carried the susceptible genotype (A/A-A/A) for impaired acrosome reaction.
• All stallions exhibited a G/G-A/A genotype, confirming the low genetic variability.
• The research concludes that chromosomal abnormalities and genetic predisposition for impaired acrosome reaction could not be seen as contributing factors for the subfertility among the Sorraia stallions.
• Nevertheless, the relatively higher rate of sex chromosome aneuploidies within the stallion’s sperm could partly explain the subfertility within the breed.