Seasonal variation in the total volume of Leydig cells in stallions is explained by variation in cell number rather than cell size.

The research investigates the seasonal variation in the volume of Leydig cells (responsible for testosterone production) in stallions. The findings suggest that this variation is due to the number of these cells rather than their individual size, with cell numbers rising during the breeding season.

Research Methods

Two studies were carried out using stereological methods to determine whether the seasonal variation in Leydig cells volume was due to a change in:

• Number of Leydig cells,
• Size of individual Leydig cells.

First Study

• Number of Leydig cells were calculated in 28 adult stallions, from the breeding and nonbreeding seasons.
• The calculation considered several variables such as nuclear volume density, parenchymal volume, and the volume of individual Leydig cell nuclei.
• The average volume of individual Leydig cells was calculated.
• The result showed the average volume of Leydig cells was almost the same across seasons, but their numbers were 57% higher in the breeding season.
• This resulted in a 58% higher total volume of Leydig cells in the breeding season due to the increase in cell numbers.

Second Study

• The numbers of Leydig cells were determined in 43-48 adult horses for each 3-month period over a year.
• The results showed the number of Leydig cells in May-July (breeding season) was significantly higher than in August-October or February-April, and significantly higher than in November-January.

Conclusion

• The research concluded that seasonal variation in the total volume of Leydig cells in adult stallions is due to the fluctuation in the number of Leydig cells and not their individual sizes, suggesting an annual cycle of these cells.