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Eight female PIC Line 42 pigs (initial BW = 47.5 +/- 1.8 kg) were used in a two-period switchback design (n = 4 per treatment per period) to evaluate the nutritional difference between a genetically modified corn and a similar nontransgenic corn. The genetically altered corn (gdhA+) contained a glutamate dehydrogenase gene isolated from Escherichia coli. The non-transgenic corn was the same variety lacking the transgenic cassette, grown at the same two locations. Pigs were surgically fitted with steered ileocecal valve cannulas for collection of ileal digesta. Diets were made up of primarily one of the two corn sources. Dietary AA profiles were adjusted using crystalline AA to match Illinois Ideal Protein Ratios. Pigs were limit-fed at 8% of metabolic body weight (BW0.75) in two equal feedings at 0600 and 1800 daily throughout the experiment. The study consisted of two 15-d periods. Each period consisted of a 7-d acclimation period, a 3-d total collection of feces and urine, two 12-h ileal collections, and a 3-d adjustment period between ileal collections to ensure adequate hydration. Crude protein, leucine, methionine, alanine, aspartic acid, glutamic acid, and tyrosine concentrations were greater (P < 0.05) in the gdhA+ corn than in the nontransgenic variety. The presence of the gene did not alter (P > 0.17) BW gain. Similarly, DM digestibility, fecal N excretion (grams per day), apparent total-tract N digestibility, N balance, net protein utilization, and N retained as percentages of absorbed were not affected (P > or = 0.32) by the gene modification. Apparent ileal AA digestibility values did not differ (P > 0.31) between the two dietary treatments. Results of this study suggest corn that contains the E coli. gene for glutamate dehydrogenase was nutritionally equivalent to the unaltered variety.

A steer finishing trial was performed to determine the effect of short-term dietary regimens on conjugated linoleic acid (CLA) content of muscle tissues. The experimental design was an incomplete 3 x 2 factorial, with three levels of soybean oil (SBO; 0, 4, and 8% of diet DM) and two levels of forage (20 vs. 40% of diet DM). Forty Angus x Hereford steers averaging 504 +/- 29.0 kg were allotted randomly to one of four treatments for the last 6 wk of the finishing period. Treatments were: 80:20 concentrate:forage control diet (C); 80:20 concentrate:forage + 4% SBO (C4); 60:40 concentrate:forage + 4% SBO (F4); and 60:40 concentrate:forage + 8% SBO (F8). After 42 d on the experimental diets, steers were sacrificed and samples were collected from the chuck, loin, and round muscle groups. Fatty acid (FA; mg/100 mg of FA) composition was determined by gas-liquid chromatography. Data were statistically analyzed with mixed models procedures. The performance and carcass quality model included the effects of SBO and forage. The model for FA composition included the effects of SBO, forage, muscle group, and interactions. Orthogonal contrasts were used to determine linear effects of SBO. There were no differences in growth performance among treatments (P > 0.05). Increasing dietary SBO linearly decreased dressing percent (P = 0.04), and tended to linearly decrease marbling score (P = 0.12) and quality grade (P = 0.08). The only CLA isomer detected in tissue samples was cis-9,trans-11. Addition of SBO to diets linearly increased linoleic acid (18:2n-6; P = 0.04) and tended to linearly increase linolenic acid (18:3n-3; P = 0.10) in muscle tissues. The CLA in lean tissues was decreased (P = 0.005) with SBO-containing diets. These findings suggest that increased PUFA may limit ruminal production of CLA and trans-vaccenic acid (VA) and/or may depress stearoyl-CoA desaturase expression or activity in lean tissues, which in turn limits CLA formation and accretion in tissues. Increasing dietary forage tended to increase 18:0, 18:2n-6, CLA, and 18:3n-3 (P < 0.15), suggesting that increased forage may mitigate toxic effects of PUFA on ruminal biohydrogenation, thereby increasing the pool of CLA and VA available for CLA formation and accretion in tissues. Short-term feeding of elevated SBO and forage levels can alter FA profiles in muscle tissues.