QUESTION: When buyers purchase a weanling, how comfortable can they feel that the radiographs and upper airway scope won't change significantly over the next year?
ROLF EMBERTSON: They should not feel very comfortable. Changes can and do occur.
Radiographic abnormalities (RA) noted in weanlings at the November sale can change significantly by the time they are yearlings at the September sale. Most of the radiographic changes are improvements, but many are not. It is important to note that some radiographic abnormalities are of minor concern clinically.
There were three presentations at the 2016 AAEP convention that looked at changes in RA in Thoroughbred (TB) horses from weanling to yearling.1,2,3 One study looked at changes in carpal and fetlock RA.1 This study looked at repository radiographs of 722 TB horses at the November weanling sale and then again at the September yearling sale. The study showed that the majority of the abnormalities noted at the weanling sale improved by the time of the yearling sale.
Another study looked at changes in stifle RA in the same 722 TB horses (1444 stifles).2 In weanlings, 86% of the femoropatellar joints (femoral trochlear ridges and patella) were normal. Of these normal femoropatellar joints, 97% were still normal as yearlings. Of the horses in which femoropatellar OCD abnormalities were found on the weanling radiographs, 80% of the abnormalities resolved by the September yearling sale. In weanlings, 95% of the medial femoral condyles (MFCs) were normal. Of these normal MFCs, 98% remained normal as yearlings. Of the horses in which MFC abnormalities were found on the weanling radiographs, 64% improved to some extent by the September yearling sale.
Another study focused on radiographic abnormalities of the MFC.3 The grading system was different than the above study. There were 188 TB horses (376 stifles) that had radiographs evaluated as both a weanling and a yearling. Radiographs of the MFCs were considered normal in 68% of the weanlings. Eighty-five percent of the normal MFCs as a weanling were also normal as a yearling. Of the horses in which MFC abnormalities were found on the weanling radiographs, 63% appeared normal by the September yearling sale.
Many OCD lesions in the hocks and stifles are not very apparent radiographically in weanlings and become more apparent as a yearling. Some small fragments around the fetlock are not very apparent radiographically as a weanling. With age, part of the cartilage portion (not visible radiographically) of these fragments will ossify, making the fragment appear larger and more apparent when a yearling. Some articular fragments occur and OCD lesions develop after the November weanling sale and are found on spring survey radiographs as a yearling.
The upper airway (UA) of the young horse gradually matures with age, so there are normally subtle differences from weanling to yearling. Abnormalities of the UA can be seen at any age, but some are more common to see in the yearling than the weanling. During endoscopic examination of the UA, nasal occlusion is often used to evaluate function during stress.
Dorsal displacement of the soft palate (DDSP) is generally easier to induce with nasal occlusion the younger the horse. DDSP also occurs more easily in a horse with UA inflammation or a small, flaccid epiglottis, regardless of age. A cleft palate is present at birth and usually diagnosed well before a weanling or yearling sale.
Rostral displacement of the palatopharyngeal arch is one of the abnormalities of the congenital anomaly, laryngeal dysplasia. This should be identified as a weanling, and the horse not entered in a yearling sale. However, the abnormality may be subtle.
The epiglottis is usually more flaccid in the weanling than yearling. This normally stiffens as it matures. Epiglottic entrapment and sub-epiglottic cysts are uncommon, but generally more common in the yearling than the weanling.
Arytenoid cartilage movement during stress of the UA is usually more consistent in the yearling than the weanling. This has more to do with the horse cooperating during the exam than expression of a disease process. The actual development of arytenoid paralysis would be rare to see in a weanling. This usually does not occur until later in the yearling year or as a 2 year old.
Arytenoid chondritis, due to inflammation or infection, would be rare to see in a weanling and uncommon to find in the yearling.
Dr. Rolf Embertson graduated from Michigan State University with a Bachelor of Science in Zoology in 1976. He also attended Michigan State where he graduated from Veterinary School in 1979 followed by an internship at Illinois Equine Hospital. Dr. Embertson completed a Large Animal Surgery Residency at the University of Florida, followed by an Equine Surgery Residency at The Ohio State University. In 1986, he became a Diplomate of the American College of Veterinary Surgeons. Dr. Embertson is a Surgeon and Shareholder at Rood & Riddle.
- Atwood KE, Spike-Pierce DL, Wittum TE, Grigoleit SL. Prevalence and evolution of carpal and fetlock abnormalities in Thoroughbred weanling to yearling sales radiographs. Proceedings, AAEP (2016).
- Spike-Pierce DL, Atwood KE, Wittum TE, Grigoleit SL. Evolution of stifle abnormalities in Thoroughbred weanling to yearling sales radiographs. Proceedings, AAEP (2016).
- Santschi EM, Prichard MA, Whitman JL, Berk JT, Peterson ES, Canada NC, Morehead JP. Formation and prevalence of radiographic abnormalities of the medial femoral condyle in Thoroughbred horses from six to 20 months of age. Proceedings, AAEP (2016).
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