Trimming a horse's ears is somewhat controversial. Some people believe the ears should never be trimmed. Others will remove the hair from both the outside and inside of the ear. The traditional method, however, is to hold the horse's ear together and trim off only the untidy, excess hair. Trimming inside the ear removes the horse's protection from flies and can increase the risk of ear mites. A horse with trimmed ears should wear a fly hood when turned out. It's much easier not to trim inside the ear in the first place. Trimming only the excess looks just as neat.
1 Professional organizations and the U.S. Government Printing Office can also be indicators that a book is scholarly.  Book reviews can provide clues as to if a source is scholarly and highlight the intended audience.
Primary sources are written by the scientists that performed the experiment and are writing about it. They are normally found in peer-reviewed journals. Your example is of a primary source. Primary sources can cite other articles, but must be based on novel research. Secondary sources are commonly found in general magazines and newspapers in the science sections. They cite original research, and contribute nothing new or original to the report.