1918] EXPERIMENT STATION RECORD. 73 



DAIRY FARMING— DAIRYING. 



Some nitrogen studies with dairy cows in milk, F. S. Ptttney and C. W. 



Larson {Pennsylvania Sta. Rpt. 1915, pp. 250-293, pis. 4). — The studies here 



reported were undertaken for the purpose of giving a thorough experimental 



trial of the method of computing dairy rations according to the Armsby net 



energy standard (E. S. R., 27, p. 176). 



The digestion trials, which were conducted during the winters of 1914 and 

 1915, were made with three groups of 3 cows each. During the tests each 

 group was fed (1) timothy hay, silage, and grain mixture No. 286 (corn meal, 

 distillers' grains, cottonseed meal, gluten feed, and wheat bran 4: 1.25: 1 : 1 :1) ; 

 (2) alfalfa hay, silage, and grain mixture No. 286; and (3) alfalfa hay, silage, 

 and grain mixture No. 287 (the above concentrates mixed in the proportion of 

 2:1.25:1.5:1:1). 



The energj- requirements for maintenance and the energy supplied in the feed 

 were calculated according to the method already noted (E. S. R., 19, p. 65). 

 The energy requirements in the milk were calculated at the beginning of each 

 test from the average milk production according to formulas which are set 

 forth. Enough roughage, in the proportion of 5 lbs. of silage to 1 lb. of hay, 

 was fed to maintain properly the energy requirements of the animal and to pro- 

 duce 5 lbs. of milk. In addition to the roughage, enough of each grain mixture 

 was fed to balance the energy requirements as found by using the above-men- 

 tioned formulas. No attention was paid to the amount of protein fed. 



The 9 cows used in the experiments represented several breeds and showed a 

 wide range in age, average milk yield, fat content of milk, and stage of lacta- 

 tion. Each winter the visible excreta was collected from one cow from each 

 group for three periods of from 5 to 10 days each. The nitrogen in composite 

 samples of feces, urine, and milk, and the fat and specific gravity of milk were 

 determined. Analyses were also made of the feeds used. Tabulated dato show 

 for each cow and period the amount of feed offered and refused, the average 

 live weight, the yield and analyses of milk, the water consumed and urine and 

 dung excreted, the calculated nitrogen balance, the percentage distribution of 

 nitrogen in outgo, the difference between total digestible protein fed and pro- 

 tein requirements according to Eckles (E. S. R., 30, p. 773), and the percentage 

 of nitrogen utilized. 



It is noted that little difference existed in the daily amount of water drunk 

 on the different rations. However, the average daily urine excreted was 

 noticeably less when timothy hay was fed. The average daily milk yield was 

 also slightly less when timothy hay was fed. The average live weight of the 

 cows was maintained. There was practically no difference in the average daily 

 excretion of dung on the different rations. 



The calculated nitrogen distribution in the 1914 tests showed that there was 

 a noticeable increase in the percentage of nitrogen in the urine on the rations 

 when more nitrogen was fed. The largest percentage of nitrogen was secured 

 in the milk when the ration contained a small amount of nitrogen. During the 

 feeding of alfalfa and grain mixture No. 287, 7 cows showed a gain of nitrogen. 

 When the cows under three months of lactation period are compared with those 

 over five months the results possibly indicate that the former group were still 

 drawing nitrogen from their bodies to furnish milk. These results were for the 

 most part confirmed in the 1915 tests. Most of the cows used in 1915 were 

 early in their period of lactation, but the average of those under three months 

 on lactation period showed an increase of nitrogen in percentage of milk. The 

 average percentage utilization of nitrogen for all the cows and periods in 1914 

 was 62 and in 1915, 50. The authors believe that this difference may be due to 



