Ge­netic ties to “roar­ing” iden­ti­fied

EQUUS - - Eq Letters - By Chris­tine Barakat and Mick McCluskey, BVSc, MACVSc

New re­search of­fers ge­netic support for the the­ory that “roar­ing” is more likely to be seen in tall horses.

Tech­ni­cally known as re­cur­rent la­ryn­geal neu­ropa­thy (RLN), roar­ing oc­curs when a por­tion of a horse’s lar­ynx is par­a­lyzed, block­ing the air­way. In ad­di­tion to cre­at­ing a dis­tinct noise when the horse works, RLN can also greatly re­strict ath­letic ef­forts.

For the study, vet­eri­nar­i­ans at

Michi­gan State and Cor­nell univer­si­ties se­lected 550 Thor­ough­bred horses. An en­do­scopic ex­am­i­na­tion of the air­ways was per­formed on each horse, his height was doc­u­mented and a blood sam­ple was taken for ge­netic anal­y­sis. Horses with RLN were graded based on how the con­di­tion would af­fect per­for­mance. Con­trol an­i­mals were older but had nor­mal la­ryn­geal func­tion.

The data pro­duced by gene map­ping showed that the re­gion of the equine genome gov­ern­ing height and that as­so­ci­ated with RLN over­lapped. “Think of it this way: You’ve got the DNA, which is like a long road, hun­dreds and hun­dreds of miles long,” ex­plains Ed Robin­son, BVetMed, PhD. “And you’ve got dis­tance mark­ers ev­ery 20 or 30 miles. Us­ing th­ese mark­ers we were able to de­ter­mine that the area of the DNA as­so­ci­ated with height is very near that in­volved in roar­ing. They are at the same dis­tance marker, so to speak. This means that the two char­ac­ter­is­tics are very likely ge­net­i­cally linked to each other in some way.”

Th­ese find­ings support anec­do­tal ob­ser­va­tions that taller horses are more likely to be roar­ers. In fact, the data sug­gests that 16.5 hands is a thresh­old of sorts: Horses of that height and larger were more likely to be roar­ers.

Robin­son says that the ap­par­ent link be­tween height and RLN may be a re­flec­tion of nerve func­tion: “Nerves have to trans­port ma­te­ri­als that are vi­tal to their sur­vival along their full length in both di­rec­tions. It’s pos­si­ble, in a longer necked an­i­mal, that some of this trans­port be­comes dis­rupted, dam­ag­ing the nerve.” He adds, how­ever, that RLN may also be con­trolled by its own genes that are near the genes for height. “This study doesn’t ex­plain ev­ery­thing, but it does send us look­ing in the right di­rec­tion.”

Re­gard­less of the spe­cific mech­a­nisms that lead to RLN, the study sug­gests that se­lec­tive breed­ing to re­duce the in­ci­dence of the con­di­tion in a pop­u­la­tion would also pro­duce a de­crease in av­er­age height. “When the two are so closely linked, you can’t in­flu­ence one with­out the other,” says Robin­son. “That said, I don’t an­tic­i­pate any­one bas­ing

Ref­er­ence: “Ge­nomic anal­y­sis es­tab­lishes cor­re­la­tion be­tween growth and la­ryn­geal neu­ropa­thy in Thor­ough­breds,” BMC Ge­nomic, April 2014

breed­ing choices on roar­ing alone. It does af­fect per­for­mance, but there is surgery to fix it, and it doesn’t seem to be a huge con­cern among breed­ers at this point.”

Although this study was limited to Thor­ough­breds, Robin­son says the find­ings may be ap­pli­ca­ble to warm­bloods, who are also prone to roar­ing. “There is quite a bit of Thor­ough­bred blood in some of the warm­blood breeds,” he says. “It would be in­ter­est­ing to see if this same cor­re­la­tion ex­ists.”

LONG SHOTS: New re­search sug­gests that Thor­ough­breds mea­sur­ing 16.5 hands or taller are more likely to be “roar­ers,” mean­ing a por­tion of the lar­ynx is par­a­lyzed and blocks the air­way.

Newspapers in English

Newspapers from USA

© PressReader. All rights reserved.