Lewis & Short

lactesco, ĕre, v. inch. n. [lacteo].

  1. * I. To turn to milk: omnis fere cibus matrum lactescere incipit, Cic. N. D. 2, 51, 128; Plin. 20, 21, 84, § 230 al.
  2. II. To have milk for suckling, to become capable of giving suck: asinae praegnantes continuo lactescunt, Plin. 11, 41, 96, § 237: pectore, Aug. Ep. 150: segetes facit lactescere, to become milky, Serv. Verg. G. 1, 315; v. 2. Lactans.