FAfTORS ALTERTXO XITRITIONAL VALI'E 013 



in butter is most marked dm'ing the early days of growth following wean- 

 ing. The specific growth-promoting properties of butter as compared with 

 coi-n oil could no longer be demonstrated Avhen the rats were maintained 

 on a stock diet until they were thirty daj^s of age, instead of being weaned 

 and placed on the test diets at the usual period of twenty-one days. It was 

 also indicated that the need for butter was accentuated when the animals 

 were placed on test diets at fourteen days of age rather than at the usual 

 period of twenty-one days. However, these results have not been sup- 

 ported by tests carried out in other laboratories. For example, Deuel and 

 Movitt^'^ reported that rats weaned at fourteen days of age grew as rapidly 

 on a diet containing corn, cottonseed, olive, peanut, or soybean oil, or a 

 vegetable margarine fat, as they did on one containing butterfat. More- 

 over, Zialcita and MitchelP^^ demonstrated that rats weaned at the early 

 age of seven days could be raised as satisfactorily on a special liquid diet 

 containing corn oil as was possible on one in which butterfat was employed. 

 These negative findings would seem to discount the age factor as related 

 to a specific requirement for butterfat. 



c' . Experiments on Rats Subjected to Undernutrition: Another pro- 

 cedure which has been employed to compare the nutritional value of fats 

 is to study their effect upon growth when added to diets which yield insuffi- 

 cient calories to meet the normal need. Under such conditions, if a fat 

 possesses a special merit in times of stress, its superiority should he evident. 

 When this procedure was tested and the caloric levels were such that 

 growth progressed at a subnormal rate, no differences were noted by the 

 Deuel group, irrespective of whether butterfat, corn, cottonseed, olive, 

 peanut, or soybean oil, or a vegetable margarine fat, was the fat employed.*" 

 When the animals were given the same diets ad libitum, the growth response 

 to the vegetable fat diets and to the butterfat regimen remained similar.*-^ 



d'. Experiments on Rats Receiving Growth Hormone: A somewhat 

 different method for comparing nutritional value which has been employed 

 in the study of the comparative nutritional value of fats consists in using 

 the growth hormone as a stress factor. By means of this method one can 

 gain information as to whether or not deficiencies may develop in associ- 

 ation with the greater growth rate which occurs. If fats have different 

 nutritional values one fat should presumably be able to supply this need to 

 a greater extent than another fat is capable of doing. It has been reported 

 that, when growth hormone is given to rats on a vitamin A-deficient diet, 



326 H. J. Deuel, Jr., and E. Movitt, J. Nutrition, 29, 237-244 (1945). 



327 H. J. Deuel, Jr., C. Hendrick, and M. Crockett, /. Nutrition, SI, 737-746 (1946). 



