An excellent video tutorial on using a Rake Brush by Lisa Lachri.
The late Cinnamon Cooney, AKA the Art Sherpa, has done a series of YouTube video on how to paint fur. This Painting Curly Fur video is one of them, and this video links to others. A video that shows how to paint fur on a White Tiger.
More from the Art Sherpa Cinnamon Cooney who shows how to use a Rake or Comber Brush, and compares a Fan Brush with a Comber Brush whilst painting grass.
Maron Dutton has done a small booklet on Pet Portrait Painting. Although her book is oil-paint based, it shows some useful techniques. Here is a link to her Pet Portrait book.
Maron Dutton has done numerous videos on YouTube. Although her style is oil-paint based, her videos show some useful techniques. Here is a link to one of her videos regarding animal underpainting.