FEEDING STANDARDS CALCULATING RATIONS 117 



simple method of determining which feeds are most economical to use 

 in making up balanced rations for the various classes of stock is described 

 in the following chapter. (191-195) 



165. Feeding standards only approximate guides. In a previous chap- 

 ter it has been shown that the composition of a given feeding stuff is not 

 fixed, but may be materially influenced by such factors as climate, stage 

 of maturity when harvested, etc. (81) Individual animals also differ 

 from one another in their ability to digest and utilize their feed. (85-6) 

 It should, therefore, be borne in mind that tables of digestible nutrients 

 and likewise feeding standards are but averages and approximations 

 something far different from the multiplication table or a table of loga- 

 rithms. They should be regarded as reasonable approximations to great 

 vital facts and principles in the feeding of farm animals. 



The allowance of protein set forth in the standards is the minimum 

 amount recommended by the scientists for the best results. Where pro- 

 tein-rich feeds are lower in price than those carbonaceous in character 

 (197), it is often economical to furnish more protein than is called 

 for by the standards. Except in the case of very young animals, it is, 

 however, probably not advisable to feed rations having a nutritive ratio 

 narrower than 1 :4 or 1 :4.5. Where protein-rich feeds are high in price, 

 it may be economical to feed a wider ration than advised by the stand- 

 ards, tho it is rarely wise to depart far from them. 



166. limitations of balanced rations. In the preceding chapters it 

 has been shown that other factors, including vitamines (104, 120), 

 mineral matter (95-101, 119), and the right quality of proteins (93, 

 118, 148) , may be just as important in determining the value of rations as 

 the amount of protein, carbohydrates, fat, or net energy. However, 

 owing to the complexity of these new problems in animal feeding and 

 our fragmentary knowledge concerning them as yet, it is impossible to 

 take them into consideration, even in the most modern feeding standards. 



That rations balanced mathematically according to the feeding stand- 

 ards may nevertheless be unsatisfactory is shown in a striking manner 

 in experiments which have been carried on by Hart, McCollum, Steen- 

 bock, and Humphrey at the Wisconsin Station* for the past 15 years. 

 Where the entire roughage fed cows has consisted of straw from the 

 cereals, even tho the ration has been balanced according to the feeding 

 standards by the addition of grains and protein-rich grain by-products, 

 dead or weak, under-sized offspring have resulted. It has been found 

 that these results were chiefly due to the fact that the straws are very 

 low in lime. Where the roughage was legume hay, corn stover, or even 

 timothy hay or marsh hay rich in lime, normal calves resulted. When 

 lime (calcium) was supplied in such forms as wood ashes, ground rock 

 phosphate, or ground limestone, the bad results of the straws were 

 largely corrected. Where wheat grain and wheat by-products formed 

 the concentrates, poor results were secured even with good roughage. 



*Wis. Res. Buls. 17, 49; Buls. 287, 302. 



