Performance of steers on soybean supplemented corn diets with and without peanut skins and the characteristics of the beef produced on those diets

The objectives of this investigation were (1) to determine the growth and carcass traits of steers fed full fat soybean supplemented diets with and without peanut skins and (2) to evaluate sensory characteristics and chemical composition of beef produced on those diets. Steers (n=35) grazed pasture during the 1987 summer and were fed a maintenance diet (DM) during the fall. After removal from DM, they were divided into 7 groups of 5 steers per group. One group of steers was killed directly off DM (0 DOF). Two groups were fed a control corn diet (D1); two groups, a corn + full fat soybeans diet (D2) and two, a corn + full fat soybeans:peanut skins diet (D3). From each diet, one group was killed after 56 days of feeding (56 DOF) and the other at 112 DOF. Steers were weighed at 0, 56 and 12 DOF, and average daily gain (ADG) at 56 DOF calculated. For each steer, selected carcass traits were determined and samples of subcutaneous fat (SF) and the longissimus muscle (LM) were obtained. Total lipids (%) and the fatty acid (FA) composition of lipids in the SF and LM were determined. FA were grouped into types: SAT 10-15C(10:0, 11:0, 12:0, 13:0, 14:0 & 15:0); SAT 16-24C (16:0, 17:0, 18:0, 20:0, 22:0 & 24:0), MONO (14:1, 15:1, 16:1, 17:1. 18:1 & 20:1). PUFA6 (18:2ω6, 18:3ω6, 20:4ω6, 20:5ω6 & 22:5ω6), PUFA3 (18.3ω3, 20:5ω3, 22:5ω3 & 22:6ω3) and UNKNOWNS (81 FA). Other FA (11) were also measured, and sensory scores and shear values (WB) of LM were determined. All dependent variables were statistically analyzed as a function of DOF and diet. ADG56 and ADG112 were analyzed as a function of diet and ADG period. The FA were also analyzed as a function of sampling site, and the FA of LM were correlated with sensory scores.

The following variables Increased in value (P<.05) with increasing DOF from 0 to 112: steer wt, 372 to 538 kg; hot carcass wt (HCW), 185 to 316 kg; rib eye area, 56.1 to 79.2 cm²; fat thickness. .22 to 1.25 cm; kidney, pelvic and heart fat, 1.0 to 2.1; yield grade 1.7 to 2.9; quality grade, standard to low choice; lipid in 5F, 60.4 to 83.1%, and in LM, 2.6 to 8.0%; MONO in SF, 36.5 to 44.1%; PUFA6 in SF, 1.5 to 2.6%; MONO in LM, 38.4 to 47.4%; taste score, 4.2 to 5.8 and acceptability score, 4.4 to 5.7. Other variables decreased in value (P<.05) during the same 112 DOF period: % SAT 16-24C in SF, 48.1 to 42.8%; PUFA in SF, .7 to .3%; SAT 16-24C in LM, 43.1 to 38.7%; PUFA3 in LM, 1.8 to .5%; UNKNOWNS in LM, 4.3 to 2.2%., and WB, 4597 to 2960 g.

All steers fed D1 had a higher ADG56 (1.70 kg/day) than those fed D2 or D3 (1.23 and 1.22). Steers fed D1 through 56 DOF had a significantly heavier HCW (301 kg) than those fed D2 (279 kg) or D3 (272 kg) and a higher AOG, (1.7 versus 1.2 kg/day). Steers fed D2 contained higher levels of MONO and lower levels of 14:0, 16:0 and 18;3(ω)6 in LM than those fed D3 (P<.05), and steers fed D1 had lower levels of 18:3ω3 in the LM than those fed D2 or D3 (P<.05). Compared with the LM, the SF had higher levels of saturated FA and lower % of polyunsaturated and unknown FA (P<.05). The highest correlation coefficients between sensory scores and % FA were taste with A15:0, 15:1 top and 18:3ω3 (-.71, -.70 and -.64, respectively, P<.001).