In Vitro and in Situ Digestion Characteristics and Feedlot Performance of Cattle Fed Steam-Flaked Enogen (high-amylase) Feed Corn

Enogen Feed Corn (EFC; Syngenta Seeds, LLC) is genetically modified to express high amylase content in grain. In vitro and in situ studies evaluated impact of moisture addition before steam conditioning (0, 3, and 6%), steam conditioning time (15, 30, and 45 min), and percentage of EFC (0, 25, 50, 75, or 100) mixed with Mill-run corn using a 3 x 3 x 5 factorial arrangement in a randomized complete block. Particle size distribution; in situ dry matter disappearance (ISDMD); starch availability; and in vitro fermentation (gas production and VFA) were measured. Grain mixtures were tempered with water 1 h, steam conditioned, and flaked to 360 g/L. Data were analyzed as mixed models (SAS, ver 9.4), with moisture, conditioning time, percent EFC, and 2- and 3-way interactions as fixed effects, block as random effect. Gas production analyses included time as a repeated measure. Linear and quadratic contrasts were examined. No 2- or 3-way interactions were observed (P > 0.10). Mean geometric particle size of flaked grains decreased linearly in response to EFC content (P < 0.01). Particle size was unaffected by moisture addition (P > 0.10), but responded quadratically to conditioning time (P < 0.01), with 30 min yielding the smallest particle size. Starch availability increased with greater levels of EFC and added moisture (P<0.01), and was optimal for 30-min steam conditioning (quadratic effect, P<0.01). ISDMD and in vitro production of gas, acetate, propionate, valerate, and total VFA increased with increasing proportion of EFC (P<0.01). VFA was greatest with 30 min steaming (P < 0.05); but moisture addition was without impact (P > 0.10). In a follow-up study with feedlot heifers (n=700; 314 ± 8.5 kg initial BW), cattle were blocked by origin and initial BW, allocated to 28 pens, and fed diets containing Mill-run or EFC. Grains were flaked to achieve similar starch availabilities, targeting densities of 360 and 390 g/h and mill throughputs of approximately 5445 and 8165 kg/h for Mill-run and EFC, respectively. Cattle transitioned to finishing diets (7% alfalfa, 93% concentrate; 300 mg/d monensin; 0.4 mg/d melengestrol acetate; no tylosin) over 21 d and harvested after 136 d on feed. Compared to Mill-run corn, Enogen Feed Corn improved feedlot performance and decreased energy inputs for grain processing.

Item	Mill-run	Enogen	SEM	P-value
ADG, kg	1.60	1.69	0.028	<0.01
Gain:feed	0.1602	0.1681	0.0022	<0.01
Liver abscess, %	34.4	26.6	2.47	0.03
HCW, kg	366.2	372.1	6.41	<0.01