Effect of GnRH immunisation on hormonal levels, sexual behaviour, semen quality and testicular morphology in mature stallions.

This research article explores the effects of gonadotrophin-releasing hormone (GnRH) immunisation on sexual behaviour, hormone levels, semen quality, and testicular morphology in breeding stallions.

Research Methodology and Data Collection

• The study involved four Standardbred stallions, which served as the sample size. Three of these were used as the experimental group and one as the control group.
• Semen from the stallions was collected twice a week for four months before the start of the experiment. The collection was carried out to establish a baseline understanding of the horses’ seminal qualities.
• The experimental stallions received regular doses of a GnRH-BSA conjugate which induced an immune response against GnRH. The schedule of immunisation was five times with the first four taking place at 2-week intervals and the fifth taking place 4 weeks after the fourth.
• Observations were made concerning the behaviour of the stallions and especially their libido, and semen was collected once a week for post-immunisation examination.
• The researchers took blood samples weekly for the purpose of analysing the GnRH antibody titre. They also took blood every third week for testosterone and estrone sulphate analysis.
• They also carried out measurements of the testicular size, seminal quality including sperm concentration and morphology, ejaculate volume, and sperm motility. The stallions were castrated at the end of the study and the researchers performed a histological examination on their testes.

Research Findings

• After the GnRH immunisation, all experimental stallions produced antibodies against GnRH. Their plasma testosterone concentration dropped, but the level of the decrease was not uniform across all stallions.
• Two of the stallions had high levels of antibodies while the third one had a moderate level. Four weeks after the first immunisation, the researchers observed a reduction in libido in the stallions.
• They also found marked changes in semen quality in the two stallions with high antibody titres, two months after the initial immunisation. This was reflected in reduced sperm motility, ejaculate volume, and total number of sperm. There was also a decrease in the number of normal sperm and an increase in abnormalities such as unusual head shapes, proximal cytoplasmic droplets, and detached heads.
• The third stallion, which had a moderate level of antibodies, only showed slight changes in semen quality. The control stallion showed no changes at all.
• Another notable finding was that the experimental stallions all experienced a decrease in the size of their testes. Furthermore, the testes of two of the stallions had substantial histological changes.

Conclusion

• From the experiment, researchers concluded that GnRH immunisation effectively induced the production of GnRH antibodies, which suppressed the function of the stallions’ testes and androgen secretion. However, there was substantial variation in the responses among the stallions.
• The study also revealed that the immunisation did not completely suppress libido, indicating that additional research is necessary to fully understand the impacts and potential therapeutic applications of GnRH immunisation.