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Variations in the softness of lard produced in the record of performance testing

Iowa Agricultural Experiment Station

Abstract

The data studied are the iodine numbers* (Hanus) of back fat from 157 pigs belonging to 54 litters. Four groups of these litters were fed in the course of three summers and one small group was fed during a winter season. All pigs were self-fed free choice with corn and supplemental mixture and a mineral mixture before them at all times. In one experiment six of the lots were given some supplemental cod liver oil but otherwise the ration and pens and management were the same. The cod liver oil showed a marked softening effect, raising the iodine number an average of 6.1. The amount of cod liver oil fed was such that each pig consumed about 2.5 to 3 pounds during the feeding period of about 120 days. There was also a distinct sex difference, the lard from the females having an iodine number 1.7 higher than that from their brothers. After correcting the data for the effect of sex and the cod liver oil, there remained a correlation of + .4 between litter mates. Are variations in hardness of fat highly enough hereditary that litter mates would resemble each other closely for this reason? Could the treatment of the various litters before the experimental feeding began have made the litters so different in the hardness or softness of their fat that the long period on feed under standard conditions did not equalize those initial differences?

It seems unlikely that so complex a physiological characteristic as this can be highly enough hereditary to give a correlation as high as .4 between litter mates for that reason alone. Moreover the variance between litters sired by the same boar is actually a little larger (although the difference does not approach statistical significance) than the variance between the progenies of different boars in the same year, whereas a difference in the other direction would be expected if softness of fat were hereditary in the sense that each gene affecting it had a general tendency to make the fat harder (or to make it softer) without its own effects being much dependent upon the nature of its interactions with the other genes present. Marked differences in quality of fat at the beginning of the feeding seem unlikely since many of the litters up to weaning time were managed under as uniform conditions as was practicable while letting each sow suckle her own litter. This marked resemblance between litter mates under standardized conditions seems to need an explanation and needs to be taken into account in nutrition experiments concerning the hardness of lard and in attempts to breed pigs which differ in the hardness or softness of their lard.