The role of clover as a factor affecting the summer decline in the vitamin A potency of New Zealand butterfat : being a thesis submitted in partial fulfilment of the requirements for the degree of Master of Agricultural Science of the University of New Zealand, Massey Agricultural College, March 1955
Prior to 1913 it was generally assumed that all fats had similar nutritive values and that their only function in the diet was to supply energy. In that year, however, McCollum and Davis (1) of Wisconsin, found in agreement with the earlier observations of Hopkins (2), that rats failed to grow on purified diets in which olive oil, almond oil and lard provided the sole source of fat, whereas normal growth resulted in the presence of milk fat, egg-yolk fat, or cod-liver oil. Almost simultaneously Osborne and Mendel (3), working independently at Yale, observed the growth response or rats on a purified diet of "protein-free milk", protein, and starch was greatly enhanced when fat was supplied as butter-fat (or as whole milk powder) but not as lard. In a subsequent communication (4), Osborne and Mendel confirmed these results and called attention to the prevalence of an inflammation of the eyes of their rats restricted to the lard diet, a condition which they noted to be speedily alleviated by the introduction of butterfat into the diet. Shortly afterwards a similar eye condition, to which they gave the name xerophthalmia, was described by McCollum and Simmonds (5) and likewise shown to be relieved by a supplement of butter or cod-liver oil.