THE FATTENING OF MATURE ANIMALS 351 



the fat contained in the animal body is that of a reserve of 

 energy for the vital activities, which may be drawn upon when 

 the feed supply is insufficient and replaced when feed is abun- 

 dant, while the protein of the mature animal is subject to much 

 smaller fluctuations. It would be expected, therefore, that the 

 gain made by a mature animal on a liberal ration would consist 

 largely of fat. That such is indeed the case has been shown 

 in two ways, viz., by means of comparative analyses of the car- 

 casses of lean and fattened animals, i.e., comparative slaughter 

 tests (284), and by means of balance experiments (285) from 

 which the composition of the organic matter gained may be 

 computed. 



442. Comparative slaughter tests. The classic example of 

 this method is Lawes and Gilbert's well-known investigation l 

 into the composition of animals slaughtered for human food, 

 the results of which are recorded in Chapter II (97). 



The two pigs analyzed were from the same litter, and were believed 

 to be very closely comparable at the beginning, so that it was possible 

 to compute directly the composition of the increase during fattening. 

 The other animals analyzed were not regarded as comparable. In 

 order to estimate the composition of the increase in cattle and sheep, 

 Lawes and Gilbert compute the weights of protein, fat, ash and total 

 dry matter contained in the bodies of a large number of animals 

 before and after fattening, using in the former case the analytical 

 results obtained on the half-fat ox and the store sheep and in the 

 latter those on the fat ox and fat sheep. The differences, of course, 

 show the gain of each ingredient. In the case of sheep and swine, 

 they utilize the results of their own fattening experiments. In the 

 case of cattle, the computations are based upon the results of experi- 

 ments by others. The oxen whose composition was compared were 

 mature animals. The sheep, on the other hand, were yearlings. 

 Neither the age nor the weight of the pigs is stated, but their pig 

 feeding experiments in general were made with animals ranging from 

 somewhat over 100 Ib. to 160 Ib. in weight. The results as to this 

 species, therefore, presumably relate to only partially mature animals. 



In 1876-1877, Henneberg, Kern and Wattenberg 2 investigated 

 the composition of the increase in weight of mature sheep in 

 fattening. Their analyses were of the carcasses only but the 



1 Phil. Trans., II, 1859, p. 493. 2 Jour. Landw., 26 (1878), 545. 



