A "cresty" neck refers to excessive fat deposits along the top of a horse's neck. This is not to be confused with a fit horse that has developed the muscles of the top-line of the neck and back, a desirable trait.

A thick and heavy crest is considered abnormal and usually occurs in conjunction with obesity, Equine Metabolic Syndrome (EMS), and sometimes PPID (Cushing's Disease), or a combination of these conditions. All of these are associated with laminitis (founder). For this reason, this observation should be taken seriously.

A reasonable amount of fat along your horse's neck and back, with no other sign of any problems or abnormalities may not be cause for concern. A modest amount of crest is within normal limits for many horses. But it can be difficult to discern what is normal for a particular horse, given that some breeds normally carry more weight in the neck area, such as Morgan horses, and certainly some donkeys. Likewise, there is a fine line between an "Easy Keeper" and an overweight horse. That said, huge, floppy crests and excessive top-line fat can be a sign of impending problems for donkeys too.

In many cases, horses that are fat over the neck will also have accumulation of fat on either side of the tail head and along the back.