Evaluation of kernel processing and processor type in whole-plant sorghum silage: effects on nutrient digestibility and animal performance in backgrounding beef heifers

Abstract

Two experiments were conducted to assess the effects of feeding whole-plant sorghum silage (WPSS) with different kernel processing techniques (KP). Experiment 1 contrasted KP for WPSS on intake and apparent total tract digestibility (ATTD) in beef heifers (n = 24, 13 ± 1 mo, 267 ± 10.9 kg of initial body weight [BW]) housed in individual pens (36 m2). Grain sorghum was harvested at hard dough, switching the kernel processor to obtain the WPSS treatments: A) unprocessed (UNP), B) conventionally processed (CONV), and C) shredlage processed (SHRD). Heifers (8/treatment) received ad libitum WPSS from their respective treatment, plus soybean meal top-dressed at 0.5% BW/d (DM basis). Feed, and feces were collected for 5 d; feed was offered once daily, and orts were collected the following day. Fecal samples were collected twice daily, and ATTD was determined using indigestible neutral detergent fiber (NDF) as a marker. Data were analyzed as a completely randomized design, with heifer as the experimental unit, and the following contrasts were performed 1) Processing: UNP vs. (CONV + SHRD) and 2) Processor: CONV vs. SHRD. Processing WPSS increased the ATTD of starch by 4.5% (P = 0.01), reduced fecal starch by 27.5% (P = 0.01), and reduced the change of NDF from feed to orts by 39% (P < 0.01). Heifers fed SHRD had 6.6% greater ATTD of NDF than CONV-fed heifers (P = 0.04). Experiment 2 evaluated the effects of feeding either SHRD or CONV-processed WPSS on growth performance of beef heifers. Whole-plant grain sorghum was harvested at the hard-dough stage, switching the KP as in experiment 1. Angus heifers (n = 96, 15 ± 1 mo, 249.6 ± 28.6 kg of BW) were blocked by initial BW, and randomly assigned to pens (8 heifers/pen, 6 pens/treatment). Diets consisted, all on a DM basis, of WPSS, either SHRD or CONV, at 90.5%, expeller soybean meal at 7.0%, and a vitamin–mineral–protein concentrate at 2.5%. After 14-d of adaptation, growth was measured for 56 d, and feed was offered once daily. Data were analyzed using a randomized complete block design with the pen as the experimental unit. Heifers fed CONV had a 9.6% greater gain-to-feed ratio (P = 0.05) and a 7.4% greater Kleiber ratio (P = 0.05) than SHRD-fed heifers. Apparent net energy of gain tended to be 7.1% greater in CONV-fed heifers (P = 0.06). In conclusion, kernel processing WPSS increased starch digestibility and reduced fecal starch concentration. Using SHRD increased NDF digestibility and feeding CONV-processed WPSS resulted in enhanced growth performance.