Reproduction (AAEP 2003)
Feeding for Stallion Fertility
Research has shown that boars can be fed a specific diet to increase fertility, and the same might be true of stallions. Steven Brinsko, DVM, PhD, Dipl. ACT, from Texas A&M University, discussed the potential of feeding a nutraceutical to stallions to enhance their fertility.
He said the nutraceutical, originally developed for boars, was enriched with a specific omega-3 fatty acid to improve semen quality, pregnancy rate, and litter size. Brinsko said research showed that feeding the nutraceutical achieved this by changing the lipid content of semen--in particular by increasing the ratio of docosahexaenoic acid (DHA) to docosapentaenoic acid (DPA). DHA is an omega-3 fatty acid, whereas DPA is an omega-6 fatty acid.
Sperm lipids are high in polyunsaturated fatty acids (PUFAs), in particular, DHA and DPA. These fatty acids are obtained primarily from dietary precursors; in other words, the body converts them from PUFAs in feed. However, they have competitive enzymatic pathways in their conversion, meaning you can't just increase DHA precursors alone to increase levels of DHA because linoleic acid (the precursor to DPA) can inhibit the conversion of precursors in feed to DHA. Unfortunately, the fat source of most equine rations is corn and soybean oil, both of which are very high in linoleic acid, the parent compound of DPA. A diet of this nature would favor the conversion to DPA over DHA and could have a negative impact on the quality of stallion semen, including tolerance of sperm to cooling and freezing. It is known that preformed dietary DHA readily transfers to sperm in other species.
Therefore, Brinsko did a study to determine if feeding a DHA-rich nutraceutical would increase the ratio of DHA to DPA in equine semen and whether that would enhance semen quality and improve the response of sperm to cooling and freezing. He concluded that feeding the nutraceutical increased the ratio of DHA to DPA in stallion semen. The quality of fresh semen was unaffected, but the supplement improved the motion characteristics in cooled and frozen-thawed semen.
The ratio of DHA to DPA was increased, but was not optimized by the supplement alone. Brinsko said stallion managers might see more improvement in semen quality by also changing the source of fat in the diet rather than just top-dressing a supplement.
Brinsko said that care needs to be taken when feeding polyunsaturated fatty acids because unless they are processed and stored properly, they can spoil and can lose potency. He said stallion selection for use of this supplement is also important. This supplement is something that might be cost-effective for those stallions that have poor to marginal semen quality when it is cooled or frozen, said Brinsko. (See article #4971 online.)
Particles Enhance Semen Quality
The technique of using saline-coated silica particles in solution to filter and therefore enhance semen quality in humans has been around for years. Now, it is being tried to improve semen of stallions. Information about this procedure was presented at the AAEP Convention by Margo MacPherson, DVM, MS, of the University of Florida, from a study done in collaboration by the University of Florida and Texas A&M University.
MacPherson said a company called NidaCon International recently investigated the use of saline-coated particles for animal sperm. MacPherson was part of the team that studied their product, EquiPure, for separating and selecting stallion sperm.
Basically, EquiPure coated particles are in a test-tube type container. When semen is added, the particles act as a filter to help trap sperm with defects. MacPherson said many sperm with abnormal midpieces, bent tails, and coiled tails were trapped using EquiPure.
Therefore, the researchers concluded that EquiPure was effective for selecting morphologically normal sperm, and this method could be useful in preparing sperm of subfertile stallions for low-dose insemination programs. (See article #4970 online.)
AI Made Simple
Ed Squires, PhD, an honorary Diplomate in the American College of Theriogenologists (reproduction), of Colorado State University, discussed a simplified strategy for insemination of mares with frozen semen. In the past, a veterinarian might check a mare every four to six hours once she was in heat and had been given hCG (human chorionic gonadotropin) or Ovuplant (deslorelin), then inseminate her as close to ovulation as possible. The new protocol centers around breeding a mare twice each cycle after administration of hCG or Ovuplant. If the mare ovulates within 18 and 52 hours of treatment, then viable sperm should be available within the window of 12 hours prior to or six hours after ovulation.
Squires said daily exams were sufficient when mares were inseminated at fixed times after administration, multiple inseminations did not adversely affect fertility, and there were no detrimental effects to the mares bred more than once in the cycle with frozen semen.
Therefore, timed insemination with frozen semen at 24 and 40 hours after giving hCG or Ovuplant resulted in pregnancy rates comparable to those obtained with single post-ovulatory administration with the mare inspected via ultrasound every four to six hours. (See article #4978 online.)
Squires also discussed recent studies of a new commercially available product called equine follicle-stimulating hormone (eFSH, from Bioniche Animal Health).
Squires says uses of eFSH include increasing ovulation, embryo recovery, and pregnancy rates; enhancing mare fertility; stimulating multiple pre-ovulatory follicles for oocyte collection; and improving the time of first ovulation of the year.
He recommended that mares undergoing a superovulatory procedure have their ovaries scanned with ultrasound to select mares with follicles 20 mm or smaller, or perhaps suppress their follicular development with progestins and estradiol prior to eFSH treatment.
Protocol for eFSH is to begin treatment five to seven days after ovulation, with eFSH injected twice per day. On the second day give prostaglandin. Continue treatment until several 35 mm follicles develop, stop treatment, give hCG, and collect. Studies have shown it takes about seven days for the twice-a-day treatment regimen to produce several follicles 35 mm or larger.
Transitional mares tend to have long, erratic cycles from February to April, depending if they have been placed under lights, said Squires. When using eFSH therapy on anestrus mares, he only had two ovulate. "If you wait until the mares are at least transitional, we got eight out of nine to ovulate within two weeks," he reported.
Squires designed a study to evaluate the efficacy of eFSH in stimulating ovulation in transitional mares. When study mares showed follicles in the 20-25 mm range and were in mid- to late transition, they were given eFSH. On average, in 7.6 days they ovulated. If mares in that same situation were given nothing, it took about 40 days for them to ovulate.
He said if a mare ovulates too early in the season, she will ovulate once and return to anestrus/transition, but will cycle later in the season. (See article #4969 online.)
WNV Vaccine and Pregnant Mares
Veterinarians crowded into the Reproduction/Perinatology (study of the near term and newborn foal) Forum to discuss various topics, including vaccination of broodmares with West Nile virus vaccine. The Forum was facilitated by Stuart Brown, DVM, a practitioner at Hagyard-Davidson-McGee Veterinary Hospital in Kentucky, and Steven Brinsko, DVM, MS, PhD, Dipl. ACT, of Texas A&M University.
Due to a 2003 article in The Denver Post saying mares were aborting their foals and foals were being born with congenital defects due to the West Nile virus vaccine (see article #4440 online), a discussion ensued about experiences of attendees with the vaccine and broodmares.
One Colorado veterinarian commented that, unfortunately, the article in The Denver Post came out at the same time that the virus hit the state. He said it took diligence to educate clients about the vaccine.
Brown pointed out that the vaccine is very efficacious, while another veterinarian pointed out that very few vaccines are actually labeled for use in pregnant mares. Despite this, veterinarians have been vaccinating pregnant mares for years without major adverse side effects. (See article #4968 online.)
The High-Risk Mare
A table topic moderated by Tom Riddle, DVM, of Rood and Riddle Equine Hospital in Kentucky, and Wendy Vaala, VMD, Dipl. ACVIM, of B.W. Furlong and Associates in New Jersey, discussed high-risk mares and other high-profile reproductive topics in the industry.
Riddle started with a discussion of non-reproductive problems in the mare that could affect her pregnancy, such as laminitis, an old performance injury, or hypothyroidism. For the laminitic mare or for one which has an old injury, pain management must be considered. Pain could affect her ability to conceive and maintain a pregnancy, said Riddle.
The discussion turned to vulvar conformation. Riddle considers it a given that a proper Caslick's (a procedure to improve the vulva seal) should be done, especially if there are signs of infertility.
Riddle said he considers an ultrasound examination of the uterus necessary for problem mares. If excess fluid is found on ultrasound, then Riddle prescribes oxytocin, cloprostenol, and uterine lavage to help the mare clear the fluid.
Vaala will use transabdominal scans on mares at 140 days of gestation. At that point in the pregnancy, the umbilical cord is more prominent, and it is easier to see more placental folding. She cautioned that sometimes placental folding can look like early placental separation when it is not.
Riddle said that he has never been too concerned over the discovery of endometrial cysts. He cited one study that found no relationship between endometrial cysts and fertility. It is typical for older mares to have cysts, he said. Riddle will let the horse "live with the cysts," although he will identify cysts on a "map" to help differentiate between a vesicle and a cyst. Riddle recommended removal of large cysts that could interfere with the movement of the vesicle or the ability of the cervix to close.
The next topic of discussion was endophyte-infected fescue and its effects on relaxin values. The hormone relaxin is produced by the fetoplacental unit to help prime and relax the mare's cervix in preparation for delivery. Endophyte-infected fescue can lower relaxin levels. Vaala said it is recommended to remove broodmares from infected fescue pastures. In addition, domperidone can be given to affected mares to reverse many of the signs of fescue toxicity.
In instances where mares have problems bonding with their foals and are not producing enough milk, Vaala likes to administer a combination of estrogen, Regumate, and domperidone. She has found that within three to four days, a mare will bond with her foal and begin producing more milk. She said that this treatment might be useful to help a nurse mare bond to a new foal.
The At-Risk Pregnancy
Riddle said progestins can be measured several times and values compared to help monitor pregnancy. If progestin levels are going down or if the values are greater than 50% of the previous value, then normal, acute, or chronic stress is indicated. Riddle said measuring levels past 310 days of gestation is not helpful because progestins will normally rise at that time.
Clinical signs of a pregnancy in jeopardy include vulvar discharge or premature udder development. Mares which have undergone a severe problem or surgery are at increased risk for pregnancy loss.
If treatment of an at-risk pregnancy is needed, Riddle will prescribe a double dose of Regumate, antibiotics, and pentoxifylline to increase circulation to the placenta. Vaala has had success with clenbuterol for cases of fetal compromise. She said it keeps mares from foaling early. She will use this off-label treatment within the last four to six weeks of the pregnancy, evaluating the mare daily with transabdominal ultrasound. (See article #4967 online.)
By Sarah L. Evers and Kimberly S. Herbert
About the Author
POLL: Visits from the Vet