(Author's note: Sera, Inc., who markets oral and IV equine IgG products approved by the USDA, sponsored a roundtable discussion on Biological Solutions for Biological Problems in Lexington, Ky. Participating in the roundtable were: Michelle LeBlanc, DVM, of the University of Florida, who acted as moderator; William V. Bernard, DVM, Diplomate American College of Veterinary Internal Medicine, a partner in the Rood and Riddle Equine Hospital near Lexington; Jonathan Davis, DVM, resident veterinarian at Milfer Farm, Unadilla, NY; Dan Watkins, DVM, a general equine practitioner from Weatherford, Texas; and Oscar Swanson, DVM, a racetrack practitioner from Louisville, Ky. Following are excerpts and discussions from the roundtable.)
The topics covered in the roundtable on Biological Solutions for Biological Problems included failure of passive transfer (also see The Horse of February 1996, page 37), treatment of Rhodococcus equi in foals; exercise-induced pulmonary hemorrhage, and general use of oral IgG.
Dan Watkins, DVM, said at his clients' farms, tests are run on foals for IgG, and immunotherapy is utilized for that and to try and prevent Rhodococcus equi. He said in years past, plasma was given to foals which were at risk of failure of passive transfer (FPT). Recently, however, he had been using oral IgG (Seramune) on the foals prophylactically before they first nurse. He said the product is given orally, and the first dose is the easiest to administer because the foals will suckle it out of the syringe. He said the next two doses are more difficult to administer because the foals have had a taste of milk and don't like the product as well.
Watkins said his initial dose was 150 cc, followed by two doses of 150 cc each two hours apart.
"The farms I deal with have mares sent off the farm to be bred," Watkins said. "We find it a benefit to check the foals, and if they are less than 400 (on their IgG check), then they need some kind of supplementation."
Johnathan Davis, DVM, noted that the post-partum blood checks for IgG at the Thoroughbred farm where he is the resident veterinarian are done when the foals are 30-36 hours of age. He said anything over 800 is good, and that he watches any of the foals that are between 400-800. If they seem to be at risk, they are supplemented with oral IgG.
He conducted a study on his farm in 1994 where he gave foals oral IgG (two doses of 150 cc each) via a nasogastric tube in the first 12 hours of life to see if there was a significant response of protection against R. equi and what effect it had on IgG levels. He noted that he was pleased with the results. In 1995, he tried the same regimen, but utilizing a syringe. He said he had questions whether foals got full doses of the treatment when administered by farm personnel.
William V. Bernard, DVM, Diplomate ACVIM, said that in the ambulatory/hospital practice, they consider a level of 600 the cutoff for considering foals for FPT. He said most people in the Central Kentucky area draw blood at 12-24 hours to check IgG levels and either use IgG products or plasma. Most in that area consider levels less than 400 failure of passive transfer and will give some type of supplementation, usually intravenously. In the clinic, he said he uses plasma on very sick or septic foals because besides the IgG components, the plasma has other beneficial products.
Bernard noted that a healthy foal on a well-managed farm is at less risk of disease than a foal in more challenging conditions. Therefore, foals with the same IgG levels might or might not need supplementation depending on their surroundings and general health.
"It's important to put everything together--the mare, her colostrum, the birth process, and even other sick foals on the farm," he said.
Davis countered that he is cautious saying that foals with an IgG level of less than 800 is okay, even if other parameters are fine and the foal shows no clinical problems at the time. He said he has seen these "healthy" foals have a severe onset of respiratory distress and succumb quickly. Davis said he wants to give foals oral IgG in order to get them "as immunocompetent" as possible before they are stressed.
"I embrace the product with the cofactors that might be in it to help cellular immunity," he added.
Michelle LeBlanc, DVM, added that in the last 15 years, she also has seen that IgG levels don't always match with potential illness.
"I've seen foals that look normal, but their CBC (complete blood count) shows a slight problem," she said. "The foal might have adequate IgG at 24 hours, but they don't do as well at seven to 10 days of age because of subclinical disease."
In an experiment with goats and from foal studies, LeBlanc said she feels that colostrum is the best for newborns and that serum IgG levels never reached the same level as colostral immunity. However, she found benefits from giving purified IgG, especially in concert with colostrum.
"That probably helps in absorption," she said. "It's synergistic to get the product in with the colostrum."
She also agreed that there are many other components in the supplements that might help decrease disease. She noted that at a meeting in Europe, these products were found to stimulate T cell responses. (Thymus cell or T cell is a type of lymphocyte from cell-mediated immunity that attacks "foreign" invaders.)
"Maybe IgG is a marker of what's been absorbed, and we don't measure the other products," she theorized. "We give equine IgG products, but we don't know how they work."
Bernard agreed, noting: "We don't always know why something works, and sometimes there's no good reason it should."
These statements led into a discussion about why immunotherapies would benefit horses which suffer from EIPH.
Oscar Swanson, DVM, noted that with some horses which suffer from EIPH, no matter how good they are managed, they still bleed.
"You try to keep the air clean--use shavings and dust-free feeds and hay--but some racehorses can't be stopped from bleeding," he said. "Then I started treating them intertracheally with IgG, and it stopped their bleeding. I started using it when horses got down to their last straw. I use a 20-gauge needle and give them 20 cc every other day five times (a 10-day period) and on the day of the race."
He said either purified or concentrated IgG works, but, "I don't know why. I've seen it work; it's one of the tools I use. It's not the only one, and it's not the first one, but it is valuable in certain, difficult cases."
LeBlanc said there was a possible effect on neutrophil and macrophage action in immunotherapies that could have later responses.
"We don't really know what causes EIPH, so it's hard to determine why a product works," said Bernard. "There are one-layer cells between the pulmonary artery and the cell. The performance horse is bred to do what he does. Pulmonary hemorrhage is a result."
"Maybe the IgG product helps protect the airway (against irritants that contribute to EIPH)," theorized Swanson.
LeBlanc reminded that the Sera product was only licensed for use in failure of passive transfer.
Several of the veterinarians present said they felt the oral IgG products might help foals fight off or prevent illness due to Rhodococcus equi. LeBlanc said once the R. equi enters the macrophages in a foal's body, it is difficult to protect against disease. She noted that purified or concentrated IgG or plasma that provides antibodies to R. equi are given to young foals, and that it seems to confer some degree of protection.
"We use it (oral IgG) on all the babies, and we aren't eliminating R. equi, but the ones that get sick respond to treatment better," said Watkins. "We might need to come back at 60 days (when maternal antibodies are waning) and give IV plasma or IV Seramune because that's when the foals are most susceptible."
Davis said using a plasma or oral IgG product at 30-60 days that either has antibodies against R. equi (such as plasma) or somehow offers protection against the disease seems like it would have merit. He was concerned with the route of administration in that he didn't like "jugging them through their veins."
Timing of administration was deemed important to all of the participants. Bernard said he suspects that foals born in January are less susceptible to R. equi than foals born in dryer times. (R. equi is a bacteria that lives in the environment and can cause severe pneumonia, as well as being implicated in occasional diarrhea and abortion cases.) Watkins agreed, noting that his January and February babies don't tend to have the same respiratory problems in the summer that March babies have. The practitioners agreed that preventing the disease is not only better for the foals, but is more cost-effective for the farms. Foals can die from R. equi pneumonia, noted LeBlanc, so it is a serious concern to breeders.
When the practitioners had a chance to comment on the Sera products, they noted several points of interest. Decreasing cost of the product and improving administration were mentioned. Bernard said veterinarians need to be able to administer the IV product faster, like plasma. The viscosity was too great, which made it slow to administer. A company veterinary representative said viscosity depended on the raw material, so it varied slightly from lot to lot in manufacturing.
The palatability of the oral product also was discussed. The first dose was considered easy to administer prior to the foal nursing the mare, but the second two doses were much harder because the foal did not like the product after having nursed.
LeBlanc and others mentioned that it would be good to conduct research on why the product seems to work on problems besides failure of passive transfer. What are the co-factors and can they affect T cell immunity?
About the Author
Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.
POLL: University Equine Hospitals