The Horse

MAR 2018

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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YOUR GUIDE TO THE 2017 AAEP CONVENTION SPONSORED BY A36 TheHorse.com/AAEP2017 AAEP Wrap-Up THE HORSE March 2018 minute). Anesthetized late-term pregnant women, on the other hand, have a de- creased residual respiratory volume—the amount of air remaining in the lungs at the end of respiration. "Similar changes would be expected in anesthetized pregnant mares in late gestation, particularly when they are positioned in dorsal recumbency (lying on their back)," he said. What scientists do know more about is how sedation and anesthesia impact pregnancy in horses. In one study researchers administered the sedative detomidine to 10 pregnant mares weekly from Day 14 to 60 of gesta- tion and then monthly until foaling. One mare aborted on Day 167 of gestation and another was euthanized after devel- oping a large colon torsion (twist). Six of the eight live foals born were normal, while the other two suffered from torti- collis (abnormal neck twisting) and bilat- eral upward fixation of the patella (a stifle condition). Still, he said, "the authors concluded that there were no specific adverse effects of the detomidine." However, he acknowledged that all known anesthetic techniques have the potential to decrease cardiac output, depress arterial pressures, and cause respiratory depression (slow and ineffec- tive breathing), which could lead to fetal acidosis (abnormally high blood acidity), hypoxia (inadequate oxygen supply), and hypercarbia (abnormally high blood carbon dioxide levels). Researchers haven't performed ex- tensive studies evaluating the effects of anesthesia on pregnant mares undergoing elective surgeries, Hubbell said, so veteri- narians must use findings from studies on mares anesthetized on an emergency basis. Some examples of results include: ■ "The largest retrospective study of anesthetic morbidity and mortality in horses shows that mares in the third trimester were at increased risk, with two of 16 mares dying of anesthetic complications," he said; ■ Based on results from a series of stud- ies, researchers concluded that intrave- nous agents resulted in fewer cases of fetal acidosis and hypoxia than inhaled anesthetics; ■ In four studies in which researchers evaluated colic surgery's effects on foaling rates, Hubbell said foaling rates for surviving mares were 80%, 79.4%, 66.7%, and 53.8%; and ■ "One study examined the relationship between the timing of colic surgery and gestational age, finding that mares pregnant 16 to 39 days at the time of surgery had a lower foaling rate than mares pregnant for greater than 40 days at surgery," he said. Based on this research, Hubbell sug- gested that if pregnant mares must under- go general anesthesia, the safest window is from Days 40 to 220 of gestation. "The decision to anesthetize a pregnant mare is made on a case-by-case basis," Hubbell said. "Factors to consider include the general health of the mare, her age (an increased anesthetic risk on its own), the anticipated duration of the procedure, and any previous history of foal loss. In most cases the risk of anesthetizing the mare for surgery must be weighed against the risk of leaving a condition untreated." h e Visit TheHorse.com/AAEP2017 ■ Common and Uncommon Ovarian Abnormali- ties, TheHorse.com/40224 ■ Managing Umbilical Remnant Complications in Foals, TheHorse.com/40225 Urine Trouble: Freezing Contaminated Semen Urospermia, or urine in semen, is one of the most frequent ejaculate dysfunctions in stallions. Because urine can have toxic effects on sperm and cause inflammation in the mare's uterus, it can diminish semen quality and conception rates. Sometimes, however, all veterinarians have to work with are contaminated semen samples. So, when is it okay to freeze that ejaculate for future use? Robyn Ellerbrock, DVM, Dipl. ACT, a PhD candidate at the University of Illinois at Urbana- Champaign's Department of Veterinary Clinical Medicine, in Urbana, sought to find out how urospermia affects semen's freezability for artificial insemination use. In her study, she took 64 semen samples from eight light-breed stallions and subjected each to varying levels of urine contamination. Group 1 was the control, with no contami- nation. Group 2 was 20% urine (considered low), and Group 3 was 50% urine (high). Pre-freezing, Ellerbrock confirmed that the contaminated semen had significantly higher pH, urea, and creatinine levels (which all affect semen quality) and significantly lower sperm motility, or movement. After centrifugation (to separate the sperm from the seminal plasma before freezing), however, she said the urea and creatine values had lowered and motility had increased. She then performed gradient centrifugation, a technique often used with poor-quality semen, and found that it increased sperm viability. There were no motility differences at this point between Groups 1 and 2, while Group 3's motility remained lower than Groups 1 and 2. Post-freezing and thawing, sperm viability was significantly lower in Group 3 than the other two groups, Ellerbrock said. "Ejaculate with less than 20% contamination might be suitable for cryopreservation," she said. "Highly contaminated samples may benefit from gradient centrifugation after traditional centrifugation. It's worth your while to take the extra step if faced with an ejaculate that absolutely needs to be cryopreserved."—Alexandra Beckstett MATHEA KELLEY The safest window for pregnant mares to under- go anesthesia is Days 40 to 220 of gestation.

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