Age
Sperm production by a stallion is dependent on age. A breeding manager must have an understanding of how often a stallion might be used. Over-use in a young stallion and under-use in an older stallion are both potential problems. The testis of a stallion inceases in size with age. The scrotal width was found to increase from 96 mm in 2 to 3 year olds to 100 mm in 4 to 6 year olds and 109 mm in stallions older than 7 years. Since sperm production is dependent on the amount of testicular tissue, the larger the testes, the more sperm can be produced. In addition, the epididymis also increases with age. The tail of the epididymis is where sperm are stored between ejaculates. The larger this structure, the more sperm can be released in a single ejaculate from a sexually rested stallion. For example, twice the number of sperm are in the body of the epididymis in a 10 to 16 year old stallion as compared to a 2 to 4 year old. A comparison of seminal characteristics is shown for three age groups of stallions in the following table:
| Effect of Age
on Seminal Characteristics of Stallions |
|||
| Age (Year) |
|||
| Characteristics* | 2 to 3 |
4 to 6 |
9 to 12 |
| Seminal Volume | |||
|
2 |
5 |
13 |
|
14 |
26 |
29 |
|
16 |
31 |
43 |
| Spermatozoa | |||
|
120 |
161 |
161 |
|
1.8 |
3.6 |
4.5 |
| Motility (%) | 55 |
63 |
60 |
| # of Stallions Tested | 7 |
16 |
21 |
*Mean of five successive ejaculates.
The table above demonstrates that a stallion is not mature in terms of seminal characteristics until 4 to 6 years of age. Once a stallion reaches 4 to 6 years of age there was minimal changes in seminal volume or sperm numbers. Even though a 2 year old has enough semen to breed some mares, it not recommended to use these males for breeding due to the possibility of acquiring abnormal sexual behavior. Even a 3 year old should only be used on limited mares. Evaluating the number of sperm produced each year before the breeding season is a good idea to determine how many mares or collections a stallion may be used for each week. Keep in mind that after 12 years of age you are monitoring a stallion to determine when sperm numbers begin to decrease due to increasing age.
Effects of