Casein (milk) can be used in animal repellents. These repellents are sprayed on bushes to prevent wildlife, like deer from eating carefully landscaped bushes. Animal repalants can also be sprayed on people who may want to avoid dangerous animals.
From this article "Hydrolyzed casein (a milk product) was demonstrated to be an effective repellent for minimizing deer browse damage to plants of economic and ornamental value. Pen studies conducted with both white- and black-tailed deer confirmed that plants treated with hydrolyzed casein were strongly avoided by deer. Furthermore, baby formulas containing hydrolyzed casein were also shown to provide protection against deer browse. In a field study, hydrolyzed casein reduced deer browse damage to conifer seedlings at reforested sites across the Pacific Northwest and Vancouver Island, BC."
From this article "Recently, casein (an animal protein precipitated from milk) has been evaluated as a repellent to minimize deer damage to trees and shrubs. Retail sources of hydrolyzed casein (HC) (concentrated baby milk powders) are not as effective as pure hydrolyzed casein but do offer some protection. The product can be used in nurseries, orchards, and in reforestation projects. For the homeowner, a simple repellent formulated with glue and an HC-containing baby formula may be effective when alternative forage is available (Kimball et al. 2005)"