Corn silage is a staple feed for many commercial dairies. Variation in corn silage kernel processing and ensiling extent may impact rumen and total-tract starch digestibility (TTSD, % of starch), however there is question about the variation in starch digestibility for fermented silage. The objective of this study was to survey Midwestern US dairy farms and evaluate if corn silage kernel processing score (KPS), corn silage rumen starch digestibility and fecal starch content (and TTSD) varied for herds feeding fermented corn silage. Fecal and corn silage samples were collected from 59 commercial dairy farms in Wisconsin during summer 2018. TTSD was calculated using the Fredin et al. (2014) equation. Silages were assumed to have fermented at least 6 mo, sampling from farms feeding 2017 crop. Fecal starch content, corn silage starch, KPS (% starch < 4.75mm) and in situ rumen starch digestibility (% starch; 6mm grind) at 0h (isSD0; washout fraction) and 7h (isSD7) were determined by a commercial laboratory (Rock River Laboratory, Watertown, WI). Corn silage samples were analyzed for nutritive parameters by NIR. Dairies were surveyed for TMR nutrient composition, dry matter intake (DMI, kg) from farm records, milk production (kg), milk fat (MF, %) and protein (MP, %) per cow. Energy corrected milk (ECM, kg) was calculated as (12.95 × milk kg × BF) + (7.65 × milk kg × MP) + (0.327 × milk kg) and feed efficiency (FE) as ECM/DMI. KPS, isSD0 and isSD7 correlations with TTSD, ECM and FE were explored by multivariate methods with JMP Pro v14.0. Independent pairwise correlations were significant (P < 0.05) for TTSD and KPS (r = 0.26), KPS and isSD0 (r = 0.33), isSD0 and TTSD (r = 0.52), isSD0 and isSD7 (r = 0.60). Trends were evident (P < 0.10) for isSD0 and DMI (r = 0.26), isSD7 and TTSD (r = 0.24), ECM and isSD0 (r = 0.24) and ECM and isSD7 (r = 0.24). Survey population statistics are presented here. The coefficients of variation suggest variation exists in kernel processing and starch digestibility for fermented silages. Table 1 (Abstr. W144).

Parameter	Mean	SD	CV
Corn silage
DM	33.0	4.4	13.3
Starch	33.3	4.7	14.2
KPS	65.5	7.0	10.7
isSD0	80.9	9.1	11.3
isSD7	88.7	3.7	4.1
Dairy measures
Fecal Starch	2.1	1.7	78.0
TTSD	97.3	2.1	2.1