Q: What are the factors that can affect semen quality in breeding stallions?
A: There are a whole host of factors which affect semen production in stallions. Two of these are fixed factors, which breeders are forced to ‘cope’ with and some are modifiable factors, which breeders can adapt for to improve semen quality and thus fertility.
Fixed factors:
- The breed of the stallion. There is scientific evidence to suggest that certain breeds of horses have poorer quality semen than others. Friesian semen, for example, is said to be of lower quality and to freeze poorly.
- Genetics. Some stallions are just less fertile than others, and as we are breeding for performance traits not fertility, poor fertility is commonly passed from generation to generation. In other species fertility is a key factor when selecting animals for breeding, but not in the horse.
Modifiable factors:
- Dietary change. Significant dietary changes can affect semen output and quality.
- Nutrition. A major issue is the large quantities of the female hormone oestrogen in some horse feeds. This negatively impacts semen production, by interfering with the stallion’s own hormone levels.
- Body condition. Horses who are too thin will have poor semen quality, because they are not receiving enough nutrition to support reproductive health. Overweight stallions, on the other hand, will carry a lot more fat in their scrotums and this insulates the testicles, making them warmer. The testicles function less well at higher temperatures, so this can impact semen quality.
- Medication. We don’t know the effects of all medications on sperm quality, but certain medications have been proven to have a negative effect.
- Trauma. Damage to the genitals can negatively impact semen quality.
- Illness. A fever can affect sperm production and viability. If a stallion spikes a fever he may be infertile until the new sperm have completed their production cycle, which takes approximately 60 days.
- Hot weather. High ambient temperatures affect fertility. The testicles hang outside the body so that they are kept at a temperature a few degrees below that of the rest of the body, and this is the optimal temperature for sperm production. If the weather is hot, meaning the testicles are hot, sperm production can be negatively impacted.
- Stress. Prolonged or acute stress from any cause affects semen quality and production.
- Management. Stallions kept in close proximity to mares, rather than just other stallions or geldings, have higher testosterone levels, better libido and better semen quality.