PERFORMANCE AND CARCASS RESPONSES TO DIETARY INCLUSION OF RAW SOYBEANS (CV. MAPLE AMBER) BY BOARS FED AD LIBITUM FROM 30 TO 95 KILOGRAMS LIVEWEIGHT

Abstract

Cull raw soybeans (SB), cv. Maple Amber, containing 17% oil and 36% crude protein (CP), were included as 0, 4.5, 9, 13.5, 18 and 22.5% of barley-based diets formulated to contain 16% CP. The mash diets were fed ad libitum to a total of 53 Landrace boars over the period from 30 to 95 kg average liveweight using a randomized block design with three replicates. Live performance responses to the increase in dietary SB content included a decline in overall growth rate (from 830 to 639 g d−1, P < 0.01) and efficiency of feed conversion (from 333 to 269 g gain per kg feed, P < 0.01). Post-kill measurements indicated an effect of dietary SB level on side weight (from 46 to 43% of carcass, P < 0.01), liver weight (from 24.8 to 28.2 g kg−1 warm carcass, P < 0.01) and areas of lean in the loin cross-section (from 31 to 26 cm2, P < 0.01) and ham face (from 137 to 121 cm2, P < 0.01) for pigs fed 0 and 22.5% SB diets, respectively. Analyses of samples of longissimus dorsi revealed a reduction in CP content (from 22.9 to 21.5%, P < 0.01) and increase in moisture content (from 74.4 to 75.4%, P < 0.05) for pigs fed the highest SB level compared to the control pigs. Iodine absorption numbers of the outer backfat layer increased, from 58 to 70 (P < 0.01), with the SB level fed. Sensory evaluation revealed a significant (P < 0.05) increase in incidence of off-flavor in loin roasts from boars fed diets containing more than 9% SB. The overall results suggested that a diet containing up to 5% SB would be unlikely to adversely affect performance or carcass merit of growing-finishing pigs. Key words: Pig, soybeans, live performance, carcass criteria, meat quality