Effects of processed corn silage on its digestibility and production of growing beef replacement heifers

A study was conducted to determine effects of processing whole crop chopped corn prior to ensiling on diet digestibility and growth of beef replacement heifers. Corn silage (CS) was harvested using two identical six-row self-propelled choppers, one of which was adapted with a roller-processing unit. Corn was chopped to either 13.3 mm (unprocessed; UP) or 10.6 mm (processed; PR) theoretical length of cut (TLC) and ensiled in silage bags. Over the 56-day feedlot study, 90 growing British-cross replacement heifers were randomly assigned to UP or PR CS with three pens per treatment. The diet initially consisted on a dry matter (DM) basis of 55.4% UP or PR CS, 22.3% alfalfa hay (AH), 19.6% wheat middling (WM) and 2.7% supplement (SUPP). Whole plant particle size was estimated from three sub-samples per treatment. Whole cob fraction as a percent of total dry mass was 0.0% for PR and 6.4% for UP (P<0.05). Undamaged kernels as a percent of the total dry kernel mass were 17.3 for UP and 1.8 for PR (P<0.05). There was no difference in average daily gain (ADG; 0.96 kg per day versus 1.00 kg per day), DM intake (DMI; 7.55 kg per day versus 7.59 kg per day) or feed to gain ratio (8.12 versus 7.70) between heifers fed UP or PR silages, respectively. Processing of CS did not alter ruminal pH but total VFAs and acetate concentrations were higher in heifers fed the UP treatment (P=0.04). Treatment had no affect on whole tract DM or acid detergent fiber (ADF) digestibility (P>0.05) but neutral detergent fiber (NDF) digestibility was higher in heifers fed the PR treatment (P<0.008). Processing substantially reduced the number of whole kernels in CS and increased NDF digestibility, but did not improve heifer performance on diets containing 55% of DM as CS.