J. Hammond and J. C. Hawk 



145 



gland which causes the changes in yield and composition assigned to 

 the period of lactation. The curves showing differences in yield and 

 composition due to the period of lactation in Fig. 2 below are taken 

 from a paper by Crowther and Ruston^ and should be compared with 

 the curves given in Fig. 1. A comparison of these two curves shows 

 that the changes in yield and composition due to "nutrition" and 

 "lactation" are essentially similar, except in the initial period due 

 possibly to the "condition" of the cows at calving. Possibly those 

 changes due to "lactation" are really due to nutrition controlled 



Fiff. 2. 



internally by the corpus luteum. If such is the case one would expect 

 the food supply to play a much more important part in influencing the 

 yield during the height of the lactation period, since the other limiting 

 factor ("internal nutrition") will be at its maximum. As an example 

 of this in actual practice Bryner-Jones"^ found that a ration containing 

 brewer's grains had a relatively greater efiect on the milk yield of cows 

 earlier in the lactation period than it did later on. 



1 Trans. High, and Agric. Soc. of Scotland, Vol. xxin, 1911. 



2 Durham C.C., Offerton Bid., No. 2, 1907. 



