The Gluck Equine Research Center in Lexington, Kentucky, held a seminar on equine Rotavirus in July 2021. A number of interesting facts were elucidated that have practical applications to equine practice. For starters, the incidence of equine Rotavirus A (RVA) tends to occur predominantly in foals 6 months of age, with fatalities occurring mostly in foals 3 months. From age 6–60 months, the incidence is 4-6%. Rotavirus is transmitted via the fecal-oral route, resulting in diarrhea with or without colic.
There is a conditionally licensed killed vaccine against the G3 genotype, but currently the G14 genotype is on the rise at an overall incidence of about 16% of cases. Even in vaccinated mares, a central Kentucky study identified that of 21% of the foals with Rotavirus, 26% were infected with the G3 strain and 74% with the G14 strain.
Watery diarrhea develops in foals 24-72 hours old. Damage to the brush border of the intestinal epithelium results in limited production of lactase to digest milk. A foal then loses nutritional energy while milk fermentation causes bloat, pain, gastric reflux and ulcers. Additional complications can develop, such as pyloric/duodenal stenosis and potential rupture.
Many practitioners rely on heavy antibiotic use to manage these cases. While antibiotics don’t necessarily change the disease trajectory, they are important to address gastrointestinal inflammation and to reduce translocation of bacteria that can result in septic arthritis and other opportunistic bacterial systemic disease that might overwhelm a compromised foal.
Another newly identified form of rotavirus is Rotavirus B (RVB), often associated with overeating disease. While RVA is the most common rotavirus affecting horses, in 2021, RVB cases started cropping up in foals two to five days old suffering from diarrhea and dehydration, especially in February and March.
At the seminar, Feng Li, DVM, PhD, William Robert Mills Chair in Equine Infectious Disease, Gluck Equine Research Center, spoke about the discovery of RVB, which might have originated from ruminants.
David Horohov, PhD, director of the Gluck Equine Research Center and chair of the Department of Veterinary Science, described work in progress at Gluck to develop a subunit vaccine for RVB since this viral strain doesn’t grow well enough in vitro, making it di cult to produce antigens.
In a 2021 foal diarrhea study conducted by Emma Adam, DVM, PhD, DACVIM, DACVS, of the Gluck Equine Research Center, RVB was detected in 19/84 study foals. Of the 19, clostridial overgrowth was identified in 16, of which 10 were sick. Of the 84 study foals, 66 foals were positive for C. perfringens.
There is a contrast in RVA signs compared to clostridial diarrhea, which has a low volume and is dark and bloody, potentially leading to circulatory shock. C. perfringens type A is ubiquitous in the soil, and in many cases foal feces are loaded with Gram positive rods. e outcome of the study noted that C. perfringens and C. difficile are found in healthy and sick foals.
Management of Sick Foals with Diarrhea
A discussion on management of sick foals on the farm is all-important to an equine practitioner. Laurie Metcalfe, DVM, of Rood & Riddle Equine Hospital in Lexington, and Scott Bailey, DVM, MS, DACT, resident veterinarian of Claiborne Farm in Lexington, both emphasized key factors in managing foal diarrhea:
• Use of hyperimmune plasma containing C. perfringens A, especially if given within the initial 12 hours. It can be given intravenously with other hyperimmune plasma, or 200-300 ml administered orally via a nasogastric tube.
• Supportive care is essential. Metcalfe stressed that without treatment, a young foal with Rotavirus isn’t likely to survive. An intravenous catheter and intravenous fluids with 2% dextrose are important for care.
• Limit nursing immediately via a muzzle to decrease milk consumption that creates osmotic diarrhea due to Rotavirus damage to small intestinal villi and absorptive capacity.
• Antibiotics are initiated, especially if a foal is less than 2 weeks old, to protect against septic arthritis: PPG (44k IU/ kg IM bid) and amikacin (25 mg/kg IV sid). Some use metronidazole to target Clostridial species, but others don’t; yet it does have some anti-inflammatory properties for the bowel.
• Use gastro-protectants such as Bio- Sponge, sucralfate, GastroGard and probiotics. It is noted that the gut takes seven to 14 days to heal, so this treatment should continue for sufficient time.
• Lactaid to address lactose intolerance and to help with milk digestion
• Pain control is also important.
A thermo-microchip (Bio-Thermo from Merck Animal Health that uses the Equitrace app) inserted into a day-old foal allows the readout of body temperature on an app without having to touch a foal.
This is critical to biosecurity as well as reducing stress on a foal due to restraint for rectal temperature readings. It also reduces the manpower necessary to hold the foal, acquire a temperature reading, record and report the data.
Many of these Rotavirus cases are difficult to manage on the farm due to ileus that results in intestinal cramps and colic that is poorly responsive to analgesic medications. Complete nursing restriction and NPO might necessitate intravenous nutrition and continuous rate infusion (CRI) of fluids. Round-the-clock monitoring and treatment are best accomplished in a hospital setting.
Metcalfe also pointed out some potential problems related to a Rotavirus outbreak:
• Isolation units at the hospital filled to capacity
• Gastric or duodenal ulcer rupture due to outflow obstruction, a classic sequela to Rotavirus
• Morale of staff and veterinarians suffers from intensive treatment, especially of many foals.
• There is a need for consistent and aggressive biosecurity.
• Negative impact on ability of sick foals to thrive due to being underweight and difficulty in catching up with healthy foals
With good supportive care, most foals can survive. The protocol for RVB is comparable to RVA treatment.
Treatment Costs of Rotavirus
Gerry Duffy, manager of Stonerside Farm for Godolphin, emphasized that costs associated with foal sickness from Rotavirus can mount up in dollars as well as other direct and indirect costs. As an example, management of 14 sick foals treated for four to seven days amounts to nearly $50,000 when factoring in hospitalization, PPE equipment and disinfection, and staff salaries.
Yet he warned that indirect costs might be even greater due to the virus’ negative impact on a foal’s ability to thrive. A normal foal needs to add three to four pounds a day, but if sick, this growth is stunted, and it can be difficult for a foal to catch up enough in developmental stages to be successful at racing.
Sick foals tend to be 5-12% underweight, and if weakened or compromised, many tend to develop secondary cases of other diarrhea and have the potential for joint infection or laminitis. In addition, there is indirect cost on staff at a veterinary hospital or on the farm due to exhaustion and diminished morale from treating these very sick foals.
Novel Biosecurity Practices to Prevent Disease Transmission
Rotavirus can persist in the environment up to nine months, especially on wood or porous walls. Because bedding and manure are contaminated with the virus, these materials should not be spread on pastures. Overcrowding is also known to increase risk of outbreaks.
Bailey presented a novel idea of how to manage and prevent Rotavirus infections on the farm. Claiborne Farm has robust biosecurity protocols, but despite that, foals were getting infected and no therapeutic regimen prevented occurrence of Rotavirus. So, they stopped prophylactic antibiotics and instead revamped biosecurity with a changed policy of foaling in a single barn on concrete and rubber flooring. Additional disinfection was implemented using quaternary ammonium compounds (or peroxygen compounds) sprayed twice daily on high-touch surfaces—bleach is not effective. Warm room surfaces are also cleaned and disinfected daily. Foot mats were used for each foaling stall with Virkon solution. Each stall had its own set of PPEs (boots, gloves and gowns) for stall entry.
Then, within three to four hours, or at least by 24 hours of age, the mare and foal were moved to a nursery barn. They were turned out for 10 days in a half-acre area, then grouped in 40-acre pastures a er that. After the mare and foal leave the foaling barn, all foaling stalls are power washed and disinfected with Virkon and allowed to dry for three to 12 hours. Rotavirus can persist in the environment for up to nine days, so extra care is taken to eliminate it from the environment.
The results observed by Bailey were that after implementation of changed biosecurity protocols, only 9/96 (9%) of foals developed diarrhea. Six of these resolved within 72 hours without treatment, and only three foals needed hospital care due to sepsis (n=1), Salmonella (n=1) or Tyzzer’s disease (n=1); the latter two illnesses were independent of Rotavirus infection.
Duffy also implemented foaling changes by foaling only outside in a small paddock. Foals weren’t touched for seven days, not even to help with nursing; this seemed to break the cycle. Reducing human intervention with outside foaling leaves things up to Mother Nature. Not only did most of the foals never spend a night in a stall, but with outside living, there is less work for the help, less use of shavings and it was better for the horses. Another important point he suggested was that mares not be bred until at least March so they will foal when weather conditions are better.
The conclusion from these changes in foaling protocol was that aggressive biosecurity management of the environment and eliminating indoor stabling for newborn foals prevent disease transmission.