Effects of replacing corn in beef feedlot diets with chemically or thermochemically treated corn stover and distillers grains on growth performance, carcass characteristics, and ruminal metabolism

Ethanol expansion in the U. S. has increased the competition for corn grain to be used as food, fuel, and feed. Although this has increased availability of ethanol co-products, such as modified wet distillers grains with solubles (MWDGS), finding reduced-cost alternative feeds when corn grain and ethanol co-product price are expensive, due to season and demand, is still a challenge for producers. One alternative feedstuff that is inexpensive and easily accessible is corn stover (CS); however; CS is poorly digested due to its advanced physiological maturity. Therefore, the objectives of this research were to evaluate the effects of replacing corn in feedlot finishing diets with CS treated by various methods, chemically (with calcium oxide (CaO), sodium hydroxide (NaOH), or both CaO and NaOH) and physically (anaerobic or extrusion), and included in diets containing MWDGS on: (1) growth performance, carcass characteristics, and feedlot economics; and (2) diet digestibility and ruminal metabolism of beef cattle. These objectives were evaluated in a series of 3 experiments. In the first experiment, Angus × Simmental steers were allotted in a completely randomized design to 1 of 3 dietary treatments: (1) 55% corn, 35% MWDGS, 5% vitamin/mineral supplement, and 5% untreated, ground CS on a DM basis (CON), (2) CS treated with 5% CaO (DM basis) and stored in an Ag Bag (BGCS), or (3) CS treated with 5% CaO (DM basis) and extruded (EXCS). Both treated CS diets contained 20% CS, 40% MWDGS, 35% corn, and 5% vitamin/mineral supplement (DM basis). There were no differences (P ≥ 0.11) in feedlot performance or carcass traits between BGCS and EXCS throughout the study; therefore, only the contrast of CON versus BGCS and EXCS (combined) are discussed for these parameters. Feeding CaO-treated CS reduced (P ≤ 0.03) average daily gain (ADG), dry matter intake (DMI), gain:feed ratio (G:F), and final body weight (BW) when compared to steers fed CON. Carcasses from steers fed either BGCS or EXCS diets had decreased (P ≤ 0.03) backfat (BF), yield grade (YG), and hot carcass weight (HCW) and tended (P = 0.07) to have a decreased percentage of kidney, pelvic, and heart fat (KPH) when compared to carcasses from steers fed CON. There were no differences (P ≥ 0.16) among dietary treatments for longissimus muscle (LM) area or marbling score (MS), regardless of dietary treatment. Cattle fed BGCS had a less expensive (P < 0.01) cost of gain when compared to cattle fed EXCS. There were no differences (P = 0.11) in cost of gain for cattle fed the treated CS diets compared to steers fed the corn-based ration, CON. Total feed costs per head were less (P < 0.01) for cattle fed treated CS diets, and BGCS in particular. In Chapter 3, 2 experiments were conducted to evaluate the effects of chemical and thermochemical treatment of CS, treated with CaO or a combination of CaO and NaOH, on feedlot growth performance, carcass traits, and ruminal metabolism. In Experiment 1, cattle were allotted in a completely randomized design to 1 of 5 dietary treatments: (1) CON, (2) BGCS, (3) CS treated with 5% CaO (DM basis) and extruded (5 EXCS), (4) CS treated with 4% CaO and 1% NaOH (DM Basis) and extruded (4,1 EXCS), or (5) CS treated with 3% CaO and 2% NaOH (DM Basis) and extruded (3,2 EXCS). All treated CS diets contained 20% CS, 40% MWDGS, 35% corn, and 5% vitamin/mineral supplement (DM basis). There were no differences (P ≥ 0.20) in ADG, G:F, BF, MS, LM, or YG among dietary treatments. However, cattle fed CON had increased (P = 0.02) DMI compared to cattle fed the treated CS diets. A second experiment was conducted to evaluate the effects of the aforementioned diets on apparent digestibility and ruminal metabolism. Apparent total tract digestibility of NDF and ADF increased (P < 0.01) for cattle fed treated CS diets compared to cattle fed the control diet, regardless of the treatment applied. There was a time × treatment interaction (P < 0.01) for ruminal pH. Ruminal pH was lowest in cattle fed BGCS from 0 to 6 hours post-feeding compared to cattle fed all other diets. Cattle fed the BGCS and EXCS diets had the greatest (P < 0.01) mean acetate concentrations, resulting in increased (P = 0.01) total VFA concentrations. Furthermore, there was a time × treatment interaction (P < 0.01) for acetate: propionate (A:P) ratio. At 0 h, A:P ratio for cattle fed all treated CS diets was greater (P = 0.01) when compared to cattle fed CON. After 3 and 6 h post-feeding, A:P ratio for treated CS diets decreased, and did not differ (P = 0.47 and P = 0.16, respectively) from the CON diet. This effect in A:P ratio was primarily driven by the shift in acetate, as there was no effect (P = 0.31) of treatment on propionate concentrations. These data indicate that replacement of corn in beef feedlot diets with bagged, CaO-treated CS, when fed in combination with MWDGS, may offer lower feed costs. However, these reductions in total feed costs were caused from the reductions in feedlot gain. Although growth performance was inconsistent in our feedlot experiments, it appears that LM area and MS are unaffected by feeding treated CS in beef feedlot diets during the finishing phase. Additionally, treating CS with either CaO or NaOH improved apparent total tract fiber digestibility, regardless of chemical or physical processing method. This improvement in digestibility also increased acetate concentrations. Therefore, treated CS, fed in combination with MWDGS, may be an alternative feed for cattle when corn grain is expensive or unavailable. Further validation of the input costs of this feed associated with feeding treated CS in feedlot rations appears warranted