Endocrine abnormalities and hormonal therapy

Routine measurement of estrogens, testosterone, T4, insulin, FSH, and LH at least four times per year (e.g., during each of the four seasons) may improve the efficiency of stallion management. Benefits may not be realized in the short term but will provide valuable historical data on individual stallions that, when added to other data, will improve ability of management personnel to initiate early treatment and delay or slow declining fertility. This ability will be greatly improved as more data and products become available. There appears to be a relationship between low total estrogen concentration/high FSH concentration and subfertility. This condition is associated with high average breedings per pregnancy. A decrease in concentration of estrogen and an increase in FSH concentration often precede a decline in fertility associated with oligospermia. Hypogonadotropic stallions have not been reported. This condition is not likely to be a cause of declining fertility in stallions and greatly limits the potential efficacy of GnRH therapy in subfertile stallions. Much research must be done to elucidate the etiology of testicular degeneration associated with increased FSH concentrations and decreased estrogen concentrations in stallions. At present, no reliable hormonal therapeutic protocols exist that will improve fertility in subfertile stallions.