The Horse

OCT 2017

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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TheHorse.com THE HORSE October 2017 18 use companion animals because we have quite a few mares and foals, but for someone with one mare and foal, I believe it's a good idea for the foal to have a gentle, preferably older companion." The most stressful form of weaning, she says, is putting two foals together in a stall and leaving the mares out in the pasture. "They can hear their dams, and studies have shown that when two foals are in the same stall, their cortisol levels are higher than when they're by themselves in a stall. I've also found that the foal will bond with you when you enter the stall instead of bonding with the other foal." As far as your mares go, Mixer says she removes all grain from their diets for one week post-weaning and keeps them turned out for exercise, which helps reduce mammary swelling. "I monitor them closely and have had very few mares develop mastitis (mammary gland infection) over the years with this method," she says. Studying Immune Response On the research side of weaning, Adams studies ways to support horses' immune systems and thereby minimize their susceptibility to weaning-related health problems. Here are two recent investigations she conducted. Study 1: PPVO Adams examined the ef- fects of the immunomodulator Parapox- virus ovis (PPVO, a large double-stranded DNA virus that's a commercially available intramuscular product) on cell-mediated immunity in abruptly weaned foals. Researchers have previously shown PPVO to enhance cell-mediated immune responses and dial down the severity of infectious disease outbreaks among horses and other species. Adams and her colleagues admin- istered PPVO (or a sterile diluent as a control) to—and took blood samples from—pony foals ages 3 to 4 months at set time points prior to weaning, at wean- ing, and post-weaning. The team weaned the foals abruptly and placed them out of their dams' sight in a neighboring pasture. "We were measuring cell-mediated immune responses, which are really important for combating viral infections and intracellular bacterial infections that often are causative agents to the respiratory and GI problems that foals can succumb to during weaning," Adams says. Regardless of treatment, the foals' immune responses declined significantly post-weaning and took up to 21 days to rebound to normal. "We were hoping that the cell- mediated immune response in the foals that received PPVO would not be suppressed or that it would actually be enhanced a bit or supported through the time of weaning, but there was no treat- ment effect, in particular on the produc- tion of the lymphocyte (small white blood cell) interferon-gamma (IFN-γ), a key player in cell-mediated immune respons- es," Adams says. However, what the 21-day window of vulnerability revealed is that it's par- ticularly important to practice optimum biosecurity during this time. A bit of extra diligence could help prevent exposure to pathogens that might be introduced from outside your facility, so be sure to keep foals away from ingress and egress areas and new horses and to enforce good handler hygiene. Also, monitor your weaned foals closely during this time frame. "We all hear about newly weaned foals with snotty noses," Adams says. And be on the lookout for foals that are "off their feed" or develop diarrhea. These signs warrant a call to your veterinarian. Study 2: P. acnes Adams also studied pony foals ages 6 to 7 months under stress from abrupt weaning to determine the effects of Propionibacterium acnes on cell-mediated immunity and nasal shed- ding of respiratory pathogens. P. acnes bacteria exist naturally in skin flora and are commercially available as an intrave- nous immunostimulant. Foals received P. acnes injections or saline (control group) at set time points before, during, and after weaning, at which time researchers also checked vital signs, plasma cortisol concentrations, im- mune function, and pathogen presence. They also watched for outward signs of disease, such as coughing and nasal discharge. Adams and her colleagues hoped that P. acnes would boost cytokine (immune- cell-produced proteins that facilitate cell communication and orchestrate immune response) production in the foals, which in turn would activate T-cells (lympho- cytes responsible for cell-mediated im- mune response) to amp up their defense during weaning. What's New With WEANING? Many farm managers place weanlings with a calm, gentle, preferably older companion horse. PAM MACKENZIE In one study, foal immune responses took 21 days to return to normal post-weaning

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