2i8 Bulletin 397 



Hansen (igo6, a and b, 1908, 191 1, 1914) has used the alternation 

 system in experiments extending over ten years. His method differs 

 somewhat from Hills' in that no ration was used twice except the basal 

 ration, which was fed during the first and the last period in order to show 

 the decrease in production due to the advancing lactation period. Hansen 

 used feeding periods of fourteen days in most of his work. 



Morgen and his coworkers (1905, 1906, 1907) have conducted extensive 

 experiments with sheep and goats relative to milk production, using the 

 alternation system. The feeding periods varied from three to four weeks, 

 about half this time being preliminary. These investigators did not use 

 any ration more than once in a given experiment, except the basal ration. 

 In some experiments the latter was fed during the first and the last period, 

 in others it was alternated with the different trial rations. 



A considerable number of other investigators have used the alternation 

 system rather extensively. The work of the men referred to in the pre- 

 ceding paragraphs is cited as typical of experiments conducted under 

 this system and as illustrating certain common variations in procedure. 

 Further examples appear unnecessary. 



The continuous system 



In the continuous system competitive rations are fed to two groups 

 of cows continuously — Ration A to Group I and Ration B to Group II. 

 An essential feature of this system is that the groups shall be so made 

 up as to be of equal productive capacity. Therefore the question of the 

 selection of animals is of prime importance. Feeding periods have varied 

 from two months to an entire lactation period or longer, according to 

 the investigator. 



Haecker (19 14) has used the continuous system in experiments relative 

 to milk production extending over the years 1902 to 1909. He used from 

 eight to ten cows in a group, and the feeding trials extended over two or 

 three months. Among other investigators who have made considerable 

 use of the continuous system may be mentioned Williams (1904), Fraser 

 and Hay den (191 2), Caldwell (19 13), Davis (19 15), and WoU, Humphrey, 

 and Oosterhuis (1914). 



The combined continuous and alternation system 



Hills has tested a system which he calls the combined continuous and 

 alternation system. In this scheme three groups of animals, equal as 

 regards probable productive capacity, are made up. To one group the 

 basal ration is fed continuously, to the second group the trial rat-ion is 

 fed continuously, while the third group is alternated on the two rations. 



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