Page 57 - November 2015

“Mule foals also seem to have a higher inci- dence, due to what we call ‘donkey factor’ (a difference in the blood types between horses and donkeys). NI foals can occasionally be seen in Quarter Horses,” he says. NI can happen
in any breed, but it occurs more commonly in some than in others.
It’s important to keep an eye on every foal after it is born and have a veterinarian examine each foal within the first 12 to 24 hours after birth. “The veterinarian will take a blood sample and assess the foal. Not only do we measure antibody levels (to see if the foal got adequate passive transfer disease protection from the dam), but at the same time we can do a red blood cell count. This could give a clue if the foal will have a problem with NI and you can catch it early,” says Slovis.
DeaDly antiboDies
During the final phase of pregnancy, the mare creates colostrum rich in antibodies to be absorbed by the foal when he first nurses. This gives him instant protection against dis- eases he might encounter. All the antibodies the mare has developed via natural exposure to diseases or from vaccination against influ- enza, herpes virus, etc., will be represented in the colostrum, including antibodies against the foal’s blood cells if he inherited a blood type from his sire that is not compatible with that of the dam and to which she has been previously exposed.
Since the foal’s ability to absorb antibod- ies through the gut wall directly into his bloodstream and lymph system is greatest during the first few hours of life, and then gradually diminishes as the intestinal lining closes, the foal is most at risk from his dam’s deadly colostrum during the first day. After his intestine can no longer absorb antibodies at approximately 24 hours of age, and after the mare’s regular milk comes in, it is safe for him to drink her milk.
“To check for possibility of risk, we draw blood from the mare during the last 2 to 4 weeks of gestation,” Slovis says. “We try to time it appropriately because mare’s gestational range is so wide; they may foal as much as 3 weeks early or 3 weeks late. We usually watch for mammary development, and then draw blood to test for antibodies. We generally don’t know the blood type of the stallion, but the blood types commonly involved (for which
the mare would develop antibodies) are Aa
and Qa. There are many more that have been implicated, but these are most common. There are more than 10, and the screening test only checks for 4 types. So, if you get a negative test, this doesn’t mean you are safe. It just means there’s low risk,” he explains.
The foal must be muzzled to prevent it from nursing its mother when there is no one around to supervise. A nylon muzzle is preferred over a leather muzzle, as it is lighter weight, easier for the foal to breath, easier to clean, and do not encourage mold and bacterial growth.
The mare must be stripped of colostrum by frequent milking to make sure it is safe for the foal to nurse after approximately 24 hours of age when her regular milk comes in and when the foal’s intestines can no longer absorb antibodies. The best way to do this is with a mare milker, as it fills the bottle more quickly than milking by hand. It is more comfortable to the mare and will not make her sore, and is safer since you don’t have to bend down under the mare.
signs of ni
“There are various degrees of NI,” says Slovis. “Depending on severity, you may see signs in a young foal as early as 12 hours of age or as much as 4 or 5 days later. It all depends on the type of antibody and how much the foal ingested. He may just seem a little lethargic, but some of these foals may suddenly collapse when they’re only 12 hours old if they are short on oxygen. When this happens, they may have kidney failure or liver disease because there’s not enough oxygen getting to these vital organs.” The foal may have been lively and vigorous at birth, nursing a lot and often. But, the antibodies he’s ingesting start attacking his red blood cells, which can no longer carry oxygen.
Some of these foals will have a fever, which can confuse the diagnosis. The red blood cell breakdown can trigger a fever response. This is why you need a veterinarian to help with diagnosis. Another sign is jaundice. “When red blood cells are destroyed, this produces bili- rubin,” says Slovis. This pigment is carried around the body by the bloodstream. The gums, whites of the eyes, and other mucous membranes look yellow. “It can also make the brain yellow and disrupt the normal nerve conduction in the brain. The foal may go into seizures and die because the brain is not functioning properly. This condition is called kernicterus, causing some of the neurons in the brain to die.”
“We can save some of these foals. It all depends on how bad they are. If they are down on the ground with seizures, the prognosis is poor. But if they are just lethargic, we can save them. The main thing is to stop the destruction of red blood cells,” Slovis says.
“How soon the foal shows signs depends on how much antibody the mare put into her colostrum,” says Lu. “If she was exposed recently via placental hemorrhage about the time she was making antibodies, she might have fewer antibodies in the colostrum and it might take longer for the foal to show signs, and the signs may be mild,” she says.
It is important to have an accurate diagnosis because signs of NI can be similar to those of several other problems. “Other conditions that cause weakness and lethargy include sepsis from bacterial infection and depression associated with ‘dummy foal syndrome’,” she says.
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equine health