Equine Science Update
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Should owners expect any adverse effects from having their horse implanted with a microchip?

Microchips are becoming widely used as a means of identification of horses. They are being evaluated as a permanent means of identification for the National Animal Identification System (NAIS) in the USA. They are now required for issue of  equine passports in UK.

Generally, the recommended site of injection is in the nuchal ligament, just below the mane, midway between the poll and the withers, on the left side of the neck.  Some breed societies may have slightly different recommendations.

Megan Gerber and colleagues at the Pennsylvania State University Department of Dairy and Agricultural Science, conducted a study to assess the inflammatory response to microchip insertion - and to see if the chips migrated after being inserted.

Eighteen Quarter horses were divided at random into three groups. Seven horses had a microchip implanted. Seven horses were injected with an empty needle. Four horses were left as controls and were not injected at all.

To measure the response to injection, the researchers assessed skin temperature, area of swelling and the pressure needed to evoke a pain response.

The inflammatory reaction that occurred after microchip insertion was similar to that produced by injection with the empty needle.

Individual horses showed an localised increase in temperature after injection. But when the groups were compared statistically there was no increase in temperature in either the horses implanted with the microchip or those injected only with the empty needle.

The micro chipped horses were more sensitive to skin pressure 2 hours and 1 and 3 days after implantation than were the horses injected with the dry needle only.

Swelling was first noticed two hours after injection and had disappeared after three days.

There was no difference in the extent of swelling between the two injected groups.

“Inflammation was more pronounced in horses that were tense during insertion of microchips or needles”  Gerber explains. “Those animals that were more tense or jumped during insertion had the largest swelling areas, increased sensitivity and heat around the insertion area.”

The researchers also took radiographs after implantation and 1,2 4 and 6 months later to monitor the position of the chip in relation to fourth vertebra. No movement of the chip was detected.

“ Horse owners can expect slight swelling to occur and localised heat at the injection site to increase several degrees between 6 hours and three days post injection” they conclude. “There may be increased sensitivity to that area up to three days after insertion.”

“When performed according to standard protocol, microchip insertion is not detrimental to the health of the horse in terms of inflammation or migration.”

For more details:

Health Factors associated with microchip insertion in horses.
MI Gerber, AM Swinker, WB Staniar, JR Werner, EA Jedrzjewski, AL Macrina.
J Eq Vet Sci. (2009) 29, 414.

For more on the National Animal Identification System see:
http://animalid.aphis.usda.gov/nais
Written by Mark Andrews. Published online 24.07.09. Updated 27.07.09
© Copyright Equine Science Update  2009
Microchipping horses.
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