322 



THE ROTHAMSTED EXPERIMENTS. 



Variations 

 in quanti- 

 ties of dif- 

 ferent con- 

 stituents 

 per Head 

 per day. 



Yield of 

 milk in 

 summer 

 greater in 

 quantity 

 but poorer 

 in quality 

 than in 

 winter. 



Further in- 

 vestigation 

 required. 



being the lowest during the best grazing months, but con- 

 siderably higher than the average during the last four or five 

 months of the year, when more dry food was given. The 

 percentage of solids not fat was considerably the lowest 

 during the later months of the grazing period, but average, or 

 higher than average, during the earlier and later months of 

 the year. 



It may be observed that, according to the average percent- 

 ages given in the table, a gallon of milk will contain more of 

 both total solids and of butter-fat in the later months of the 

 year; that is, when there is less grass and more dry food 

 given. 



Turning now to the last three columns of the table, it is 

 seen that although, as has been shown, the percentage of the 

 several constituents in the milk is lower during the grazing 

 months, the actual amounts contained in the quantity of milk 

 yielded per head, are distinctly greater during those months. 

 Thus, the amount of butter-fat yielded per head per day is 

 above the average of the year from April to September inclu- 

 sive ; the amounts of solids not fat are over average from 

 April to August inclusive ; and the amounts of total solids 

 yielded are average or over average from April to August 

 inclusive. 



From the foregoing results, it cannot be doubted that the 

 quantity of milk yielded per head is very much the greater 

 during the grazing months of the year ; but that the percent- 

 age composition of the milk is lower during that period of 

 higher yield, and considerably higher during the months of 

 more exclusively dry-food feeding. Nevertheless, owing to 

 the much greater quantity of milk yielded during the grazing 

 months, the actual quantity of constituents yielded per cow 

 is greater during those months than during the months of 

 higher percentage composition, but lower yield of milk per 

 head. It may be added, that a careful consideration of the 

 number of newly calved cows brought into the herd each 

 month shows that the results as above stated were perfectly 

 distinct, independently of any influence of the period of 

 lactation of the different individuals of the herd. 



The few results which have been brought forward in rela- 

 tion to Milk-production are admittedly quite insufficient ade- 

 quately to illustrate the influence of variation in the quantity 

 and composition of the food, on the quantity and composition 

 of the milk yielded. Indeed, owing to the intrinsic difficulties 

 of experimenting on such a subject, involving, as has been 

 pointed out, so many elements of variation beside those which 

 it is sought to investigate, any results obtained have to be 

 interpreted with much care and reservation. Nevertheless, 



