Corn silage analysis as influenced by sample size collected

Impact of sample size of chopped corn on nutritive quality following ensiling was evaluated. Seven corn hybrids were sampled at four locations in New York State, each with four field replicates. Material from each chopped plot was mixed and approximately 10 kg of material was collected. Samples were thoroughly mixed and 50, 100, 150, 200, 400 g, and two 600 g subsamples were removed for further processing. One 600 g sample was immediately dried, while the remaining samples were vacuum-sealed into polyethylene bags for 30 days. Samples were then evaluated for pH, dried, and ground to pass a 1-mm screen. Samples were analyzed for crude protein (CP) and starch, and analyzed in duplicate for neutral detergent fiber (aNDF) and acid detergent fiber (ADF), and digestions for 30 h in duplicate were used to determine in vitro true digestibility (IVTD) and neutral detergent fiber digestibility (NDFD). Experimental design was a randomized complete block, with a split–split plot feature, with locations as the main plot and corn hybrids as the subplot, and sample size as the sub-subplot. The pH of ensiled samples indicated that the ensiling process was adequate. Ensiled samples differed (P < 0.001) from fresh corn forage for all parameters, with a 90 g/kg difference for NDFD. Hybrid × location interactions (P < 0.05) for all parameters except NDFD were due to hybrid germplasm sources responding differently to different environments. All parameters displayed small but significant (P < 0.01) linear trends due to sample size. Neutral detergent fiber, ADF, CP, and NDFD all increased with decreasing sample size, while IVTD and starch decreased with decreasing sample size. Analysis of coefficients of variation and a power analysis indicated that variability was relatively consistent down to a 100 g sample size for all parameters except starch. Only the 50 g sample size appeared different from other sample sizes in minimum detectable contrast at a power value of 0.8. The size of a collected corn forage sample can be as low as 100 g without greatly increasing sample variability, but the smaller sample sizes influenced the absolute value of parameters. Sample size could be as small as 400 g with a negligible change in sample variability, and without a biologically significant change in nutritive value concentrations.