immune response | Horse Racing Free Tips

Too Much Of A Good Thing: Can A Horse Be Vaccinated Too Often?

When preparing for vaccinations, it's helpful to know what a horse has been vaccinated for in the past. If a horse's vaccination history is unknown, it's best to assume that he has not received any vaccinations at all and use the protocols designed for unvaccinated horses, which might include boosters of some vaccinations. Additional doses of most vaccinations will not harm a horse, reports EQUUS magazine.

The strangles vaccine is the one exception: it should not be given if a horse's vaccination history is unknown. In rare cases, horses that have had strangles before and those that have been repeatedly vaccinated for the disease may have a serious complication called purpura hemorrhagica if they are vaccinated again, according to Dr. David Horohov of the Maxwell H. Gluck Equine Research Center in Lexington, Ky.

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Purpura hemorrhagica is an immune reaction that causes the blood vessels in the head, legs, and abdomen to swell. This condition is painful for the horse as circulation is impaired. Horses with purpura hemorrhagica can be very depressed and it can take a long time for the swelling to abate. Purpura hemorrhagica can be fatal if it isn't treated effectively or in a timely manner.

Though the risk of purpura hemorrhagica is small, it's best to pull a strangles titer on a horse with an unknown history. The titer will show if a horse carries antibodies to Streptococcus equi. If he does show titers, he doesn't need to be vaccinated again.

Read more at EQUUS magazine.

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Is Blood Type Important In Equine Blood Transfusions?

If you've never been to a large equine clinic, it might be difficult to imagine that there are such things as blood transfusions or blood donors for horses, but a viable blood supply is crucial for horses who are critically injured.

Horses have eight blood “types,” and nearly 30 equine antibody factors, which means there are nearly 400,000 different combinations of blood characteristics in the horse. In contrast, humans have eight blood types and antigens.

Humans receiving blood transfusions must be given blood with compatible antigens; if the antigens don't match, the body's immune response can be deadly. Prior to a transfusion, both donor and recipient blood are cross-matched to be sure the types are compatible.

In horses, mismatched blood won't lead to death and severe adverse reactions are rare, but researchers wanted to learn more about how important it was to match equine blood donors and recipients.

Dr. Rose Nolen-Walston created a study to investigate the long-term impact of matching blood transfusions on horses. She used 20 healthy horses for blood samples and then typed each of them. The samples were cross-matched to see if any adverse reactions occurred; any incompatibility was scored on a 0 to 4 scale. The horses were then paired as donors and recipients for two compatible and eight incompatible transfusions.

The transfusions were completed and the horses monitored for five days. Seven of the eight horses that had received the incompatible transfusions developed minor reactions including an increased heart rate, hives and a low-grade fever.

The horses also had blood drawn one hour after the transfusion and randomly over the next 35 days. This told the research team how quickly the recipient's body destroyed the donor blood and replaced it with its own type.

Horses given incompatible blood destroyed it seven times faster than they destroyed the compatible blood. Horses given compatible blood had a more gradual decline, lasting about 70 days. Nolen-Walston concluded that giving a horse a transfusion with matched blood results in longer benefits.

Read more at EQUUS.

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