Colostral growth factors. Possible role in bovine udder epithelial cell regeneration.

Growth of the secretory epithelium during prepartum time, and for a short period after calving, is under hormonal control by estrogen, progesterone and prolactin. The mechanism(s) by which these hormones act is not known but colostrum and milk have been shown to contain different growth promoting substances. In an attempt to unravel these relationships the effect of bovine colostrum on cellular proliferation in vitro have been characterized. Colostral thermostable factors not present in milk nor associated with fat, potently induce the proliferation associated enzyme, ornithine decarboxylase, in fibroblast cell lines. However, mammary epithelial cells appear to proliferate in response to different colostral heat sensitive factor(s) that await further characterization.