Generally, assuming a filly is healthy and on a good plan of nutrition, she can be bred as early as two years of age, although many breeders suggest waiting until three years of age. Mares can continue to produce foals well into their late teens or early to mid 20’s.

Stallions that are 2 or 3 years old are expected to have smaller daily sperm outputs and spermatozoa reserves. Because of this sexual immaturity, 2-year-old stallions should be limited to breeding a small number of mares, if any at all. Daily spermatozoa production is also influenced by season.

Although most stallions begin to produce sperm as early as 12 to 14 months, most are at least 15 months or older before they can successfully breed. Few stallions are used at stud before two years of age and most stallions acquire full reproductive capacity at around three years of age.

Mares can continue to produce foals well into their late teens or early to mid 20’s. However, mare owners should realize that the prognosis for fertility of an older mare decreases each year.

Well-Known Member. Colts can become fertile from 6-12 months depending on the individual, and of course there will be exceptions coming slightly earlier or later.

A mare typically shows regular estrous cycles during long days (late spring and summer months). Her ovaries will produce follicles, and she will show behavioral signs of estrus (heat) such as frequent urination, “winking” her vulva, and being receptive to the stallion.

Foal heat usually occurs between 5 and 13 days postpartum. The jenny’s cervix is usually longer than that of the mare, with a smaller diameter.

A male horse and a female donkey have a hinny. But hinnies and mules can’t have babies of their own. They are sterile because they can’t make sperm or eggs. They have trouble making sperm or eggs because their chromosomes don’t match up well.