8 
DEPARTMENT BULLETIN 1492, U. S. DEPT. OF AGRICULTURE 
grades has been made for all the hogs within each of the main experi- 
mental feeding plans included in the study. In the case of the iodine 
number complete records were not available, but recent determina- 
tions on additional samples have furnished sufficient data to establish 
grade limits in a large number of cases. The marking off of grade 
limits is often difficult, owing to the low correlation of gradings and 
fat constants. The limits as here given do indicate the maximum 
number of hogs possible to include within the indicated limits for 
the data at hand. Those groups showing similar limits are classed 
together. 
Reference to the lists of feeds and feed combinations given in 
Table 1 shows that a large number of these (ration Group A) were 
grouped together for the general refractive-index grade limits, as 
previously stated (4)- Fats which have been formed on rations 
containing the basal feeds, corn, brewers' rice, peanuts, soy beans, 
peanut meal with corn, and also corn following soy beans alone or 
supplemented with a medium ration of corn, show similar correlation 
of refractive-index and iodine values to committee grades. This list 
covers a range from the hardest to the softest fats which have been 
observed in soft-pork experiments. Studies on the fatty-acid com- 
position of fats produced on the feeds just mentioned have shown (3) 
a pronounced rise in linolic acid and a drop in saturated acids, with 
increasing softness. In fact, the change in iodine number and refrac- 
tive index is reflected very closely in the change in the linolic acid. 
Soy-bean feeding has caused a more abrupt rise in linolic acid, accom- 
panied by a drop in oleic acid, than with peanut feeding, although 
the degree of softness was similar. An approximate ratio of one part 
stearic to two parts palmitic acid was found in fats from hogs fed 
corn, brewer's rice, peanuts, and soy beans. The total amount of sat- 
urated acids, however, appears to be an excellent criterion of firmness 
and to explain numerous cases in which the fat constants and the 
percentage of linolic acid are at variance with the grading on the 
carcass. Certain examples of this will be mentioned later. 
Table 1. — Refractive index and iodine number limits for grades of carcasses 
Ration Group A 
Ration Group B 
Ration Group C 
Ration Group D 
1. Corn and supple- 
1. Rice polish and 
1. Corn following 
1. Pigs of slaughter 
ments. 
tankage. 
peanuts to pigs 
weight under 
2. Brewers' rice and 
2. Rice bran and 
of initial 
125 pounds. 
supplements. 
tankage. 
weight of 85 
3. Peanuts. 
3. Corn or brewers' 
pounds or over. 
4. Soy beans. 
rice following 
5. Corn following (4). 
both (1) and 
6. Soy beans and 
(2). 
medium ration 
of corn. 
7. Corn following (6). 
8. Peanut meal with 
corn. 
REFRACTIVE INDEX 
Number of hogs 
Carcass grade: 
Hard 
1,025 
299 
139 
1.4596 and below... 
1.4597 to 1.4598 
1.4599 to 1.4600 
1.4601 to 1.4614 
400. 
1.4597 and below 
1.4598 to 1.4601 
1.45602 to 1.4605 
1.4606 to 1.4618 
1.4619 and above 
1.4592 and below. .. 
1.4593 to 1.4596 
1.4597 to 1.4600 
1.4601 and above. .. 
Occasional oily 
1 .4594 and below. 
Medium hard.. 
Medium soft... 
Soft 
1.4595 to 1.4598. 
1.4599 to 1.4601. 
1.4602 to 1.4619. 
Oily 
1 .4620 and above. 
