The radiation wavelengths to which pigs are maximally sensitive are slightly lower than those for humans. Within the range of 465 to 680 nm, pigs can distinguish wavelength differences as small as 20 nm (Signoret et al., 1975). Pigs have good color vision and may respond to the novelty of a change in the color of the handlers' uniform (Hemsworth, 2007). The retina contains a substantial population of two types of cones with sensitivity peaks at about 439mm (indigo) and 556mm (green-yellow) in the spectrum of visible light (Neitz and Jacobs, 1989).