Meta-analysis: Effect of corn silage harvest practices on intake, digestion, and milk production by dairy cows

A meta-analysis was performed to determine effects of DM content, kernel processing (PROC), and theoretical length of cut (LOC) of whole-plant corn silage (WPCS) on intake, digestion, and lactation performance by dairy cows using a data set composed of 106 treatment means from 24 peer-reviewed journal articles from 2000 to 2011. Categories for DM content at silo removal and PROC and LOC at harvest were ≤ 28% (VLDM), > 28 to 32% (LDM), > 32 to 36% (MDM), > 36 to 40% (HDM), and > 40% (VHDM) DM; 1 to 3 or 4 to 8 mm roll clearance or unprocessed; and 0.48 to 0.64 cm, 0.93 to 1.11 cm, 1.27 to 1.59 cm, 1.90 to 1.95 cm, 2.54 to 2.86 cm, and ≥ 3.20 cm LOC. Data were analyzed using Proc Mixed in SAS, with WPCS treatments as fixed effects and trial as a random effect. Milk yield was decreased by 2 kg/d per cow for VHDM. Fat-corrected milk yield decreased as DM content increased. Total-tract digestibility of dietary starch was reduced for VHDM compared with HDM and LDM. Processing (1 to 3 mm) increased total-tract digestibility of dietary starch compared with 4 to 8 mm PROC and unprocessed WPCS. Milk yield tended to be 1.8 kg/cow per day greater, on average, for PROC (1 to 3 mm) and unprocessed WPCS than for 4 to 8 mm PROC. The LOC of WPCS had minimal effect on any of the parameters evaluated. Starch digestibility and lactation performance were reduced for dairy cows fed diets containing WPCS with > 40% DM or WPCS with insufficient kernel processing.