Effects of laser power, wavelength, coat length, and coat color on tissue penetration using photobiomodulation in healthy dogs.

Photobiomodulation is an accepted regenerative medicine treatment modality used to stimulate tissue repair, mediate inflammation, and improve mobility in humans and animals. The objective of this study was to assess the influence of laser power and wavelength, coat length and color, and shaving on photon delivery by therapeutic laser in dogs. Forty-seven dogs of various breeds and coat colors (17 black, 15 brown, and 15 white) and with varying coat lengths were assessed with 2 commercially available veterinary lasers. Photons were delivered to the lateral aspect of the inguinal fold and calcaneal tendon, with direct penetration through the dermis, as well as dermis and tendon, as measured with a thermopile laser sensor. Significant impacts on laser transmission were noted for laser power ( = 0.001), wavelength ( < 0.002), coat color ( < 0.001), and shaved coat ( < 0.001). Percent transmission was higher for a class IV 810/980 nm wavelength laser at 0.5 W than for a class IIIb 904 nm laser ( < 0.001). There was a significant difference between transmission of photons among white, brown, and black coats, with less transmission noted with increasing coat pigment ( < 0.001). Transmission was greater at higher power levels (3 W, 5 W) Results showed significant differences in laser transmission for all variables assessed, with the exception of coat length, which was not a significant predictor of laser transmission. As transmission was significantly reduced in darker and unshaved areas, higher power lasers may be necessary for darker pigmented dogs and shaving of hair is recommended before laser therapy.