12 Bulletin 81 



forage plants. Maximum amounts of digestible nutrients are generally 

 obtained when plants are cut in full bloom ' or shortly after. Earlier cut- 

 ting gives less yield, while a later cutting results in a lowering in quality 

 greater than the increase in quantity. 



Weather. — Wet or dry weather influences different crops on different 

 soils variously, and affects digestibility in sundry ways. 



Long keeping. — Many experiments show lessened digestibility as a re- 

 sult of long keeping, due in some measure to loss of leaves and, also, to 

 actual loss of dry matter. 



Concentrated food added to coarse fodders — Protein. — A feed rich in easily 

 digestible protein does not affect the digestibility of the coarse fodder. 



Concentrated food added to coarse fodders — Fat. — Small quantities of fat 

 seem to increase digestibility. More than ten ounces a day depresses diges- 

 tibility. If not fed by itself but as oil cake or meal, more than this may be 

 fed without causing such depression. 



Concentrated food added to coarse fodders — Carbohydrates. — Additions of 

 starch, sugars, etc., until they amount to 10 percent or more of the dry 

 substance of a ration depress the digestibility, particularly of the protein 

 and fiber. If nutritive ratios exceed 1:8 some of the carbohydrates are sim- 

 ilarly affected. 



Roots and potatoes. — If the dry substance of these make up more than 

 15 per cent of that of the entire ration, digestibility is decreased ; other- 

 wise it is not affected. If fed with a nitrogenous concentrate, more than 

 15 per cent of dry matter can be fed without lessening digestibility. 



Grains and byproducts are more digestible than roughages ; immature 

 crops than those which are mature; and ground feeds than those which are 

 unground. 



DIGESTION COEFFICIENTS 



Inasmuch as the rates of digestibility are unequal for the same nutrient 

 in different feeds, and under different conditions and eaten by various^ 

 kinds of animals, the determination of these rates for each fodder in 

 each condition and for each class of animal is needed. This knowledge 

 is gained by digestion experiments, wherein rations of definite composition 

 are fed in known quantities. After prolonged feeding with the experimental 

 ration has cleared the stomach and intestines of the residues of other rations 

 previously fed, the solid excreta as well as the food are weighed and analyzed 

 for several days. Income and outgo are thus measured. The amount of 

 the undigested crude nutrients passed in the dung subtracted from the 

 total amounts fed gives the amounts digested with a fair degree of accuracy. 



Repetition with many animals and under diverse conditions serves to 

 lessen the disturbing effect of individuality and to favor an approximation. 



i Corn is an exception. 



