INHERITANCE AND PLANE OF NUTRITION IN SWINE: I. EFFECTS OF SEASON, PLANE OF NUTRITION, SEX AND SIRE ON FEEDLOT PERFORMANCE AND CARCASS CHARACTERISTICS

Abstract

Four trials, involving 124 pigs, were conducted to study the effects of differing planes of nutrition on swine characteristics and to study the relative response of specific genetic groups of pigs to these differing planes. Seasonal and sex effects were also evaluated. Equalized limited feeding to a scale of 75 per cent of the U.S. N.R.C. recommended levels for bacon hogs was compared to liberal feeding wherein pigs were fed to appetite three times daily and to ad libitum feeding.Winter-fed pigs grew slower, were less efficient, had a higher dressing percentage and shorter carcasses than summer-fed pigs.As the plane of nutrition increased, average daily gains increased, feed conversion ratios were correspondingly inferior, dressing percentage rose, backfat thickness increased and area of loin and total Record of Performance score decreased.Females outgained barrows under equalized limited feeding, whereas barrows outgained females at a similar feed requirement by eating more feed under liberal feeding. Female carcasses were superior to those of barrows with a tendency for the differences to be greater under the equalized limited feeding system.Genotype × plane of nutrition interactions were significant for average daily feed consumed (P <.05), average daily gain (P <.01), length (P <.05), and total R.O.P. score (P <.01). Under equalized limited feeding pigs with the ability to gain both rapidly and efficiently tended to produce superior carcasses while under liberal feeding rapid gains seemed to reflect mainly increased feed consumption and a trend toward inferior feed conversion and fatter carcasses.