Kohler G, Elvehjem C, Hart E. Science. 1936. 445
Growth of rats increases on a diet of milk produced on summer pasture compared with milk produced from winter feeding conditions. i.e. fodder. When grass juice was added to the winter milk diet, growth doubled from 2 to 4 grams a day. (See Fig. 1) It was evident there were important water-soluble substances in the juice that directly stimulate growth when added to winter milk.
Dr. Chris Reynolds' comment:
This is one of the earliest studies by Kohler demonstrating the presence of the "Grass Juice Factor" (in cereal grasses, and the profound effect it can have on accelerating animal growth. This is possibly due to bioactives in wheatgrass (and similar cereal grasses) influencing the animals' levels of growth hormone.