The Collaborative International Dictionary of English v.0.48:

Low \Low\ (l[=o]), v. i. [imp. & p. p. Lowed (l[=o]d); p. pr.
   & vb. n. Lowing.] [OE. lowen, AS. hl[=o]wan; akin to D.
   loeijen, OHG. hl[=o]jan, hluojan.]
   To make the calling sound of cows and other bovine animals;
   to moo.
   [1913 Webster]

         The lowing herd wind slowly o'er the lea. --Gray.
   [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Lowing \Low"ing\, n.
   The calling sound made by cows and other bovine animals.
   [1913 Webster]