Get The Most Out Of Stallion Semen

Practitioners must think carefully before recommending tests and products.

It’s false economy to scrimp on pre-season tests and stallion care if you end up with a low pregnancy rate. But with everyone cutting costs, practitioners must think carefully before recommending tests and products.


Costly supplements are often the first things to go when money gets tight. But one type of supplement might be worth the cost for stallion owners. 

Texas A&M University has conducted research on omega-3 fatty acid supplements, the results of which showed improvement in sperm function, specifically that of increased sperm longevity. 

Pete Sheerin, DVM, Dipl. ACT, of Rood and Riddle Equine Hospital in Lexington, Ky., discusses with clients the use of omega-3s in stallions that have sperm longevity problems. 

“The research performed using these products showed an increase in longevity of extended semen stored at 4 degrees Celsius,” he says. “It has also been used in horses used for live cover exclusively hoping to also increase the longevity. Omega-3s are also reported to help with immune function and inflammation, so they potentially help with overall horse well-being.”

Some owners opt to keep their stallions on the supplement year-round, but there is another method. “If clients are going to use these supplements, they need to start a minimum of 60 days prior to the start of the breeding season,” Dr. Sheerin says. “The reason is the length of the spermatic cycle in the horse. The sperm that are ejaculated began the process 60 days earlier and thus need to be exposed to the omega-3s for that time period.”

Though no damaging effects have been reported after feeding omega-3s, one of the researchers, Dickson Varner, DVM, Dipl. ACT, of Texas A&M University’s Department of Large Animal Clinical Science, says the potential exists. Sperm are more susceptible to oxidative damage when more unsaturated fatty acids are incorporated in the sperm membrane, so he suggests feeding antioxidants in addition to omega-3 fatty acids. The antioxidants he recommends are vitamin C, vitamin E and alpha-lipoic acid. Supplements available on the market include antioxidants and omega-3s in one formula, such as Platinum Bar EQ by Platinum Performance.

Semen Analysis

When evaluating semen, the standard morphology/motility analysis and sperm chromatin structure assay are two choices. But which is economically feasible for the clinic and the farm? 

“Sperm chromatin structure assay [SCSA] and sperm membrane integrity assessments for many problem stallions [are good choices],” says T.L. Blanchard, DVM, Dipl. ACT, of the College of Veterinary Medicine and Biomedical Sciences at Texas A&M.

“The SCSA and membrane integrity stains can detect abnormalities in what otherwise appear to be normal sperm,” he says.

For routine semen evaluation, Sheerin uses morphology/motility/concentration for total sperm numbers and uses the SCSA on stallions with reproductive problems related to semen quality. Some farms and veterinarians perform the SCSA annually when they evaluate the stallion, but Sheerin says the use of this assay depends on the economic investment in the stallion. 

“We send our SCSA samples to a commercial laboratory for processing,” he says.  “The sample is sent on liquid nitrogen, so we need a dry shipper to send the sample. We have several of these to ship the frozen semen we have stored at Rood and Riddle.

“For the morphology evaluation, I am fortunate to have a microscope that allows differential interference contrast microscopy in addition to phase contrast microscopy. This type of microscopy allows more of a three-dimensional view of the sperm. Our motility analysis is performed using computer-assisted semen analysis.” 

Semen Extenders

The time sperm remains viable varies from horse to horse, and a semen extender can help when shipping. Sheerin says it’s important for practitioners to try different extenders to see which works best for a particular horse.

Dr. Blanchard says he prefers extenders with less sediment, such as INRA 96. Results obtained in France suggest that INRA 96 can be used to preserve semen up to 72 hours. “It usually works well for maintaining motility of sperm,” he says. 

“The extenders typically tried with problem horses include INRA 96, VMD-Z,” Sheerin says. “Many of the reproductive supply companies sell proprietary extenders reported to help motility.”

When purchasing extenders, look at the reputation of the company, the veterinarians advise. If you’ve never heard of the company, tread lightly. Referrals from fellow practitioners are important.

New Clinic Equipment

Innovative products are coming onto the market, such as sperm concentration and motility software for computer attachments to microscopes. But practitioners have to carefully consider the investment. 

“In these economic times, the big question that one would need to answer is although many of the new products are interesting and would be fun to have, does it increase your efficiency or provide enough new information to justify its purchase?” Sheerin says. “There is a new device for calculating the concentration of semen that can calculate concentration after extender has been added that would be handy to have for semen freezing. Unfortunately, I don’t do enough semen freezing to justify the $15,000 to $18,000 cost.”

This article first appeared in the January 2010 issue of Veterinary Practice News.

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