Age related and seasonal changes of plasma concentrations of insulin-like peptide 3 and testosterone from birth to early-puberty in Thoroughbred male horses.

The research focuses on identifying the age-related and seasonal changes in the blood concentrations of the insulin-like peptide 3 (INSL3) and testosterone hormones in pre-puberty teenage male horses. This was achieved through the development of a new assay technology, investigating the variations in the plasma concentrations of these hormones from birth to early puberty.

Developing a New Measurement Technology

• The primary goal of the researchers was to establish a new Time-Resolved Fluorescence Immunoassay (TRFIA), alongside Enzyme Immunoassay (EIA), selectively for detecting INSL3 and testosterone concentrations from horse blood. The selection of Thoroughbred male horses was done as subjects (numbering 11).

Observations on Physical Growth

• The researchers monitored physical growth markers such as body weight, height, chest, and cannon bone size of the horses from their birth till 16 months, and a noticeable increase in these aspects was observed.

Changes in Hormone Concentrations

• The monthly blood-sampling process showed an initial increase in the mean plasma concentrations of INSL3 until two months after birth. This subsequently followed a pattern of decrease and increase until the study ended at 16 months.
• For testosterone levels, a high concentration was found at birth, which decreased sharply to a basal level within one month. The level remained low until 10 months, after which it gradually increased until the 16-month mark.

Seasonal Hormonal Fluctuations

• The study also looked into the seasonal changes in hormone concentrations. It was found that the mean plasma concentrations of INSL3 didn’t significantly differ between the breeding (March to September) and non-breeding (October to February) seasons. But testosterone levels were higher during the second breeding season when compared to the non-breeding season.

Age-related Hormonal Fluctuations

• The research also shed light on the age-related changes in hormone concentrations. An increase in INSL3 concentrations was observed during pre-puberty (1-12 months) and early-puberty (13-16 months). However, lower testosterone concentrations were noticed at pre-puberty when compared to birth and early-puberty stages.

To summarize, the researchers successfully developed a TRFIA to measure INSL3 levels in horses. The study concluded that INSL3 and testosterone concentrations have an inverse relationship in Thoroughbred male horses, as INSL3 levels increase with age while testosterone concentrations become lower during the non-breeding season. Moreover, the study proposed that INSL3 secretions are independent of the seasonal cycle, at least before puberty.