FEEDING UREA TO DAIRY COWS 3 



PLAN OF THE EXPERIMENT 



When the project was organized in the autumn of 1939, because of priority of 

 other investigations, there were no cattle available for the feeding trials in the 

 herd at Massachusetts State College. An arrangement was made therefore with 

 the State Department of Mental Health to utilize the milking herd at the Med- 

 field State Hospital. This herd consists of approximately sixty Holstein cows, 

 rather uniform in size, above average in production, and of the same general 

 breeding. 



Twenty-four cows were chosen for the work and were divided into two groups 

 of eight and sixteen individuals respectively (see Table 1).. The group of eight 

 cows was designated as the "double reversal" group, and was further divided into 

 two groups of four cows each, referred to in Table 1 as Groups A and B. These 

 cows were alternated between the "urea" ration so-called, and the "regular" 

 ration so-called at eight-week^ intervals, with one week allowed in between for 

 change-over. A period of thirty-two weeks (two eight-week periods for each 

 group on each ration) in each of two successive lactation periods, was originally 

 planned for, but this was shortened later to twenty-eight weeks because some 

 individuals dried off sooner than anticipated. 



The group of sixteen cows was designated as the "continuous" group, and 

 was subdivided into two groups of eight cows each, referred to in Table 1 as 

 Groups C and D. These sub-groups were kept continuously on the same ration 

 for two complete, successive lactation periods. Group C on urea. Group D on 

 the regular ration. 



'Seven-week intervals in the second lactation. 



Table 1. — Comparative Data on the Groups of Cows at the Start 

 OF the Feeding Trials in January, 1940 



'Double Reversal" Groups 



Gro«p A 



Group B 



Range Average Range Average 



Age... years and months. . 2-10 to 5-11 4-8 2-11 to 5-9 4-3 



Stage in lactation day.. 5lh to 21st 18th 2d to 21st 10th 



Average daily milk yield in 



last lactation pounds. . 40 to 54 45 36 to 55 47 



Average fat test of milk in 



last lactation percent.. 3.01 to 3.33 3.25 3.25 to 3.61 3.43 



Live weight pounds*.. 1,070 to 1,355 1,238 1,090 to 1.340 1,178 



General condition Good Good 



"Continuous" Groups 



Group C Group D 



Age years and months 2-4 to 6-4 4-4 2-7 to 7-5 4-7 



Due date** Jan. 13 to Mar. 22 Feb. 10 Feb. 2 to Apr. 32 Mar. 7 



Average daily milk yield in 



last lactation pounds . 35 to 45 40 37 to 44 40 



Average fat test of milk in 



last lactation percent.. 3.13 to 3.62 3.36 3.04 to 3.60 3.38 



Live weight .pounds*.. 1,155 to 1,450 1,330 1,210 to 1,440 1,341 



General condition G^od Good 



♦Average of two weighings on consecutive days. 

 **At the start of the experiment in January, 1940, the cows in Group C and D were either dry 

 or within a few weeks of drying off. As they freshened they were assigned to their respective 

 groups and were started on the experimental rations. 



