The Board shall cause an examination and inspection of all cattle, bison, sheep, swine, goats, horses, mules, and other equines, and the food products thereof, slaughtered and prepared in the establishments hereinbefore described for the purposes of intrastate commerce to be made during the nighttime as well as during the daytime when the slaughtering of said cattle, bison, sheep, swine, goats, horses, mules, and other equines, or the preparation of said food products, is conducted during the nighttime.