io8 THEORY OF FEEDING. 



and climate. We cannot therefore express the nutritive value 

 of a food by a formula ; but must be content to estimate it by 

 general considerations. 



CAUSES AFFECTING THE NUTRITIVE VALUE OF VEGETABLE 



FOOD. 



1. Age. With age, the percentage of nitrogenous matter in 

 plants decreases, and that of woody fibre increases. We can- 

 not, however, assume that the nitrogenous matter in young 

 plants is always as valuable as that in older ones. Dr. 

 Voelcker points out that unripe roots are poorer in sugar than 

 mature roots, and that they contain hurtful organic acids 

 (notably oxalic acid), and imperfectly elaborated nitrogenous 

 matter, which are the cause of their being unwholesome. 

 Therefore, in choosing the period of growth for economically 

 utilising those plants which our horses consume as a whole 

 (e.g., grass and clover), we should try to select the happy 

 medium between a maximum of nutriment and a minimum of 

 woody fibre, which as a rule will be obtained in the making of 

 hay from the plants in question, by cutting them during the 

 period of flowering and not later than t:he first appearance of 

 seed. Further maturity will undoubtedly entail loss in the 

 nutritive constituents of the stalk and leaves, and an excess 

 of woody fibre in them. When plants, like oats, in the 

 ordinary way, are grown for their grain, the nutritive value 

 of their other parts is not considered. 



2. Conditions of Growth (climate, soil, manure, moisture, 

 etc.). The respective percentages of the constituents of 

 plants vary greatly according to their conditions of growth. 

 For instance, hay made from grass grown on rich land, highly 

 manured, and well supplied with moisture, will contain a larger 

 percentage of nitrogenous matter than that made from similar 

 grass produced under less stimulating influences. The nitro- 

 genous matter of the former will, however, be less nutritive as 



