THE INFLUENCE OF INDEX SELECTION FOR IMPROVED GROWTH AND CARCASS CHARACTERISTICS ON APPETITE IN A POPULATION OF LARGE WHITE-PIGS

Correlated genetic changes in the level and pattern of average daily food intake (ADFI) were evaluated in a population of pigs under index selection over an 11-year period. Performance testing was carried out in single sex groups of two or three full-sibs over the live-weight range 27 to 87 kg on an ad libitum feeding regime. The selection index incorporated liver-weight gains, ultrasonic backfat thickness and a group food conversion ratio. Samples of boars from a contemporary control line were used to measure genetic change over time. Cumulated correlated responses in ADFI for boars and gilts showed considerable variation between years but the values were always negative and tended to increase up to year 7 but increased no further from then on. Thus, in year 11 the cumulated responses for ADFI in boars and gilts were -0.25 (s.e. 0.06) kg (P < 0.001) and -0.19 (s.e. 0.05) kg (P < 0.001) respectively, the corresponding regressions of cumulated response on year number being -0.012 and -0.017 kg. The relationship between food intake and live weight was compared in samples of boars and gilts from the selection line (S) and boars from the control line (C) during the final year of the study. The regression of ADFI on live weight for the two boar lines differed in intercept but not in slope with S line boars consuming, on average, 0.23 kg/day less meal than the C line boars over the test period. The regression equations for S line boars and gilts differed in slope and elevation with gilts consuming relatively more food daily up to around 60 kg live weight and less subsequently.