62 EXPERIMENT STATION BULLETIN 354 



4 





energy than in protein. If large energy deficits are to be avoided, mid- 

 summer pasturage of relatively mature growth must be supplemented with 

 a liberal allowance of grain when production exceeds 40 pounds of milk. 



The results of this series of studies on protein, and requirements of 

 lactating cows are now being prepared for publication. This will report the 

 physiological results of 25 digestion and metabolism balance experiments 

 carried out with seven cows at different stages of lactation, and 46 such ex- 

 periments with dry cows to determine the requirements of protein and ener- 

 gy for maintenance. 



This completes the work concerned with "nutrition studies on the pro- 

 tein and energy requirements of lactating cows." The project is now re- 

 vised to provide for a study of the "physiological utilization of immature 

 pasture grass by lactating cows." The Department of Agricultural and 

 Biological Chemistry, co-operating, will make the necessary chemical 

 analyses of feed and excreta. 



E. G. RiTZMAN, N. F. CoLovos, A. D. Littlehale 



Effect of Vitamin A on the Utilization of 

 Energy and Protein by Calves 



The work, this year, was carried out with six purebred bull calves 

 which were about four days old when the experimental feeding began. The 

 method of procedure was about the same as during the previous year, two 

 calves being given a deficient Vitamin A intake, two a normal intake, and 

 two an excess intake. The chief difference consisted in supplying the vita- 

 min in the form of carotene instead of cod liver oil concentrate as before, 

 and of supplying the D requirements in form of irradiated yeast. Three 

 digestion balanced were carried out on each calf (with the exception of one 

 of the normals) at about 12, 20, and 28 weeks of age. Thirty respiration 

 experiments to determine the total heat production and the basal metabo- 

 lism also were conducted during this time. Again blood samples were ob- 

 tained periodically and analyzed for carotene, Vitamin A, ascorl)ic acid, 

 calcium, and phosphorus. 



No final statement on the results obtained can be made at this time as 

 some of the chemical analyses involved have not been completed. How- 

 ever, it may be stated that the calves on the deficient ration (one-twentieth 

 of normal requirement) developed spasms after a relatively short period 

 of deficient Vitamin A intake, but showed no apparent irreparable eye dam- 

 age as was the case previously when Vitamin A was supplied in the form 

 of cod liver oil. 



Intestinal disturbance, poor growth, and defective vision which often 

 result during the early growth stage*, when calves are raised on skim milk 

 and cereal products, can be avoided by feeding even moderate dosages of 

 Vitamin A, either in the form of carotene supplemented with irradiated 

 yeast or with cod liver oil. 



This completes the work on Vitamin A, the results of which are now 

 being prepared for publication. A study of Vitamin D will follow 

 immediately. 



N. F. CoLovos. E. G. Ritzman, H. A. Keener, A. D. Littlehale 



*Bcforc calves can properly digest good roughage. 



