Kara A. Kolster DVM DACT
Theriogenologist, Springfield Veterinary Center, Glen Allen, Virginia, USA
The results of a thorough semen analysis as well as breeding history may help determine the cause of subfertility in a stud dog. However, in over 50% of cases the underlying cause may not be known. In these cases, management of living conditions, overall health, and diet should be optimized in attempt to improve semen quality.
Heat stress
Normal spermatogenesis occurs at temperatures three to five degrees lower than body temperature. Infection, skin irritation on the scrotum, high environmental temperatures, excessive hot air blow drying, and obesity are all things that can increase scrotal temperature above the ideal range for sperm production. The effects of increased temperature may be temporary, however any prolonged or repeated insult to the testes increases the risk of permanent damage. Management of living conditions and general husbandry to reduce the risk of heat stress may be beneficial to some dogs. This can include limiting breedings, or planning frozen semen collections, if appropriate, to the cooler months of the year.
Infection
A multitude of bacteria can cause infections in the reproductive tract. Many of these are opportunistic infections by normal flora, such as mycoplasma and ureaplasma, which makes causation difficult to prove. Brucella is never normal flora and should be tested for in all cases of unexplained subfertility or pregnancy loss. B. canis and B. suis have both been found in the dog. B. suis requires additional testing as it will not be detected by the routine canine brucellosis tests. There is no evidence that viruses act directly on male fertility, but they can be passed through seminal plasma and cause pregnancy loss in the female.
Medications
All medications and supplements should be discussed as part of a breeding soundness evaluation. Many medications, including steroids, anti-fungals, and some antacids and behavioral medications may affect semen quality.
Breeding management
The chances of achieving pregnancies with subfertile stud dogs can be improved by breeding management strategies. Accurate determination of ovulation in the bitch allows for optimum timing of insemination, giving subfertile sperm the best chance to fertilize her eggs. Limiting the number of bitches bred at one time will provide each bitch with the highest number of sperm possible. Transcervical (intrauterine) insemination may improve pregnancy rates by initially transporting the subfertile sperm closer to the site of fertilization. Collecting semen no more than once every 2 to 3.5 days produces the highest number of sperm per collection from most dogs. “Clean out collections” do not substantially affect sperm quality in normal dogs, but regular collections (e.g. every 1-2 weeks) may affect epididymal function and thereby improve sperm quality in subfertile dogs. Success rates are generally higher with natural breeding or fresh semen insemination than with chilled shipped or frozen semen, so consider limiting the types of insemination offered for these dogs.
Dietary supplements
Veterinarians and breeders have used numerous dietary supplements in attempts to improve semen quality in stud dogs. There is limited data to show benefits in dogs, however based on information in humans and other animals, and knowledge of how the testes function, there is enough evidence to suggest some supplements can be helpful. All dietary supplements should be used cautiously and as directed by your veterinarian. Harmful side effects can occur with excessive supplementation.
Beneficial supplements
The supplements most likely to improve semen quality are n-3 polyunsaturated fatty acids (PUFA) and antioxidants, including vitamin E, selenium, zinc. They have been shown to potentially improve motility, membrane integrity, and total sperm number. Folic acid may also be beneficial, although there are no studies looking at its use alone, only in combination with other supplements.
Some supplements do have the potential to cause harm if used excessively or in high doses. Excessive selenium supplementation can actually increase sperm damage. Supplementing PUFA without other antioxidants may also increase sperm damage. Lower quality PUFA products may contribute to heavy metal (e.g. mercury) toxicity. Toxic doses of zinc cause hemolytic anemia in dogs. Excessive levels of vitamin E, folic acid, and selenium may decrease sperm motility in humans and poultry.
Glucosamine and glycosaminoglycans, most commonly chondroitin sulfate, have been anecdotally reported to improve semen quality in multiple species. It is a component of several nutritional supplements marketed for male dogs. However, there are no documented beneficial or harmful effects of supplementation.
Non-beneficial, non-harmful supplements
There is no evidence that saw palmetto is helpful to sperm quality or prostate health in dogs. Limited data in humans only shows possible effects on clinical signs that dogs with prostate disease do not exhibit.
Potentially harmful supplements
Cottonseed meal is used as a protein source in livestock feed and is an ingredient in some supplements marketed for reproductive health in dogs. However, cottonseed meal commonly contains a toxin called gossypol that is known to cause sperm damage and infertility in livestock. There are also multiple reports of death in dogs that were fed or accidentally ingested toxic doses of cottonseed meal.
Phytoestrogens are plant compounds that have estrogen-like activity in animal. Flaxseed, soybeans, and legumes are common ingredients in dog foods and supplements that contain phytoestrogens. Some phytoestrogens have actually been used to intentionally cause infertility in dogs as an alternative to spaying or neutering in developing countries. Reproductive effects of phytoestrogens may vary with individual phytoestrogens, sex, dose and duration of exposure, and timing of exposure during reproductive development. The safest approach is to avoid significant amounts of phytogestrogens in dog food or supplements, especially in cases of subfertility.
Conclusion
The cause of subfertility in the dog is identified in 50% of cases or fewer. In cases where the cause is known, the chance of restoring fertility may be as low as ten percent. In cases where the cause is not known or not treatable, management through dietary supplements and individually tailored breeding management strategies may help improve chances of fertility. Owners should be cautioned that these dogs will likely never be reliable producers. The physical, financial, and emotional costs of pursuing breeding attempts should be weighed against the stud dog’s potential genetic contribution to his breed.