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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34 TheHorse.com THE HORSE February 2016 O'Grady then touched on the venogram, a procedure veterinarians use to visualize blood flow within the foot. He cautioned that venograms might not be beneficial in the acute stage, as the lamellae is edematous (fluid-filled) and the veterinarian won't be able to see how to alter treatment plans. He also does not like to administer nerve blocks, which are required to perform a venogram, in laminitic horses. On the farriery side, O'Grady said each horse should be treated individually using biomechanical principles to change the forces on the laminitic foot. These involve redistributing the load on the foot, ad- dressing breakover, and applying heel elevation if necessary, he said. If a horse in the acute stage is wear- ing shoes, he recommends removing them early. This, he said, will transfer the horse's weight from the hoof wall and lamellae (as the shod horse's sole and frog do not touch the ground) to the hoof's entire solar surface. Next, O'Grady suggested trimming the affected toe(s) in moderation from the outer surface to remove excessive length. Don't take anything off the sole, he said. Rather, square and bevel the toe to im- prove breakover. O'Grady also noted that deformable bedding, such as sand, can help acutely laminitic horses, as it allows the horse to position his feet as desired. He mentioned the use of cushioned hoof boots for pain relief and noted that while they're conve- nient, there are mixed reviews regarding their usefulness. As the horse moves from the acute to the chronic stage, the farrier can choose from several footwear options. Wooden shoes, he said, are useful for chronic cases, but they can even be used in some acute cases. O'Grady recommended using casting material around the perimeter of the hoof for extra support. Farriers also have many hoof pads and packings at their disposal for manag- ing laminitic horses. While anecdotal evidence might support some of their uses, O'Grady stressed that there is no scientific proof that any pad or packing effectively supports horses with laminitis. "Unfortunately, many of the treatment regimens, both medical and farriery tech- niques, used to treat acute laminitis are based on tradition, theoretical assump- tions that a given treatment should work, and anecdotal evidence that a certain type of treatment has worked on previous cases," O'Grady said. What is well-documented, however, are the forces and mechanics of the horse's foot, such as what structures are involved in weight-bearing and which ones deal with tension when the coffin bone rotates or sinks, he said. But even with such knowledge, not every case can be saved. "With severe cases, we are often unable to rehabilitate the horse to where it has an acceptable quality of life," he said, due to insufficient laminar structures remain- ing within the hoof to achieve realign- ment and accept weight." O'Grady emphasized the importance of knowing when to stop treatment and opt for euthanasia. "It is unlikely that this disease can ever be fully eliminated, nor is it likely that there will ever be a single drug or other line of therapy to consistently treat acute of chronic laminitis," he said. "So, our clinical and research efforts should be di- vided between prevention and treatment." Breeding the Problem Mare In theory, breeding is simple: Mare plus stallion equals foal. But it's not always that straightforward. From sterile stal- lions to noncycling mares, veterinarians are often faced with challenging cases that require problem-solving. Reproduction specialist Patrick McCue, DVM, PhD, Dipl. ACT, described manag- ing the problem mare. He is a professor of equine theriogenology at Colorado State University's Equine Reproduction Laboratory. Several scenarios can lead to a patient being labeled a "problem mare," he said, including: ■ Not becoming pregnant after being bred to a fertile stallion over the course of three estrous cycles; ■ Being unable to successfully carry a foal to term; ■ Having known reproductive pathology (disease or damage); or ■ Having reproduction-related behavior issues. McCue reviewed conditions that can contribute to these clinical pictures. What Impacts Sperm Output? Stallion semen quantity and quality can vary among individuals. Ed Squires, MS, PhD, Dipl. ACT (hon.), professor at the University of Kentucky's Gluck Equine Research Center, in Lexington, reviewed some of the factors affecting sperm production: Age "The timing for testicular degeneration varies in stallions and may occur as early as 12 to 15 years or, in some stallions, after 20 years of age," Squires said. In general, semen output decreases with age. Thus, it's important to re-evaluate a stud's book each year to ensure he's not being stretched too thin. Season "Output in the winter is about half of what it is in late spring and summer," Squires said. "This seasonality is controlled by the length of daylight." Breeders can increase sperm counts in February and March by keeping stallions under artificial light starting in mid-December. Managers generally do not do this because even though the sperm output will increase earlier in the year, numbers will also decline earlier. This could pose a problem for late-season breeding. Testis size "Testicular volume can be used to determine whether the stallion has normal size testicles for his age and whether he is providing the expected number of sperm in the ejaculate based on his testicular volume," Squires said. Ejaculation frequency A stallion can only produce so much sperm, so it stands to reason that breeding him too frequently could reduce his counts. For best results, Squires said, researchers have determined that breeders should collect stallions in artificial insemi- nation programs every other day during the breeding season. "For natural mating, the pri- mary factor determining how many times a stallion can be bred per day is the stallion's sex drive," he said. This generally amounts to one to three covers spread throughout the day. Sex drive So, what controls a stallion's sex drive? Unfortunately, Squires said, researchers and veterinarians aren't sure. "We do know that factors such as using (breeding) a stallion heavily as a 2-year-old, being kicked during mating, pain during mounting, an inappropriate artificial vagina, or the height of the phantom can all negatively affect sex drive," he said. Understanding all these factors can help managers and veterinarians take steps to help improve a stallion's fertility.—Erica Larson