Effects of post-ethanol extraction sorghum silage as an alternative forage in growing and finishing diets on steer performance, carcass characteristic and nutrient digestibility

Abstract Text: Two experiments evaluated use of post-ethanol extraction sorghum silage as an alternative forage to hay in feedlot diets. In experiment one (Exp1), 72 crossbred steers (397 ± 23, SD) were used to evaluate growth and carcass characteristics. Steers were blocked by BW into pens of 6 steers and randomly assigned to growing diets containing 40% (DM basis) of sorghum silage (SS; 57.6% NDF) or grass hay (CON; 63.3% NDF) for 56d (n = 6 pens per treatment). Within each treatment steers transitioned to dry-rolled corn-based finishing diets (fed for 56d) containing 6% effective NDF contributed by the forage source, resulting in forage inclusions of 16% for SS and 13.1% for CON. Experiment two (Exp2), utilized a sub-sample of steers (n =12 per treatment) housed in pens equipped with Growsafe bunks for determination of growing phase diet total tract digestibility. From d28 - 42, steers received titanium dioxide at approximately 10 g^-1·steer^-1·day^-1. Fecal samples were collected on d 41 and 42. Fecal and total mixed ration samples were dried, and ground for analysis of DM, OM, NDF, ADF, CP, ether extract (EE), and starch. Data were analyzed using PROC MIXED of SAS with the fixed effects of treatment and block (Exp1) or treatment (Exp2); significance was determined at P ≤ 0.05 and tendencies at P ≤ 0.10. Growing phase DMI and ADG did not differ due to treatment (P ≥ 0.19); however, SS-fed steers had improved G:F compared to CON (P = 0.04). Finishing period ADG or G:F did not differ (P ≥ 0.15), despite SS-fed steers having lesser (P = 0.008) DMI than CON-fed steers. No differences in DMI, ADG, or G:F over the whole trial were noted between treatments (P ≥ 0.12), nor were any carcass traits affected (P ≥ 0.23). Growing phase total tract apparent digestibility of DM and starch did not differ (P ≥ 0.19), due to treatment; however, OM digestibility tended to be greater (P = 0.09) in SS-fed steers. During the digestibility assessment period DMI was lesser (P = 0.003) in SS-fed steers. Steers fed the SS diet had greater (P ≤ 0.03) digestibility of EE, CP, NDF, hemicellulose, and cellulose than CON-fed steers. Interestingly, CON-fed steers had greater (P < 0.0001) ADF digestibility than SS-fed steers.  These data suggest that post-extraction sorghum silage can be effectively utilized in feedlot diets as an alternative forage.

Keywords: sorghum silage, cattle performance, digestibility