The objective of this study was estimate the apparent total-tract starch digestibility (ATTSD) in dairy herds, as well as its correlation with corn ensiling time. There were 20 commercial herds in the Paraná State, South Brazil, TMR-fed with predominantly Holstein cows. In all herds, only the high-producing groups were included in the study, with an average milk yield of 41 ± 6 L/cow/d, representing 33 ± 13% of lactating cows, and a total of 1655 cows. To check the influence of silage fermentation time on the starch digestibility, each farm was sampled in 2 distinct periods; fall season when most producers were using corn silage (CS) with short ensiling time (132 ± 132 d), and spring season with CS of longer ensiling time (260 ± 46 d). In each period 3 samples were collected per herd; TMR, CS and feces. Starch contents were determined in quadruplicate by enzymatic colorimetric method. To estimate ATTSD 2 equations were used: only with fecal starch as input (Eq1 = 100 × (1–0.0125 × %fecal starch)); and using lignin as marker (Eq2 = 1 − ((%TMR lignin/%fecal lignin) × (%fecal starch/%TMR starch))) × 100). The average values of 40 samples of corn silage and TMR were 31.15 ± 3.44% DM, 42.36 ± 3.86% NDF, 21.19 ± 2.11% ADF, 2.49 ± 0.68% lignin, 30.45 ± 4.29% starch, and 45.38 ± 3.75% DM, 34.99 ± 3.21% NDF, 16.72 ± 2.16% ADF, 1.92 ± 0.66% lignin, 27.02 ± 4.37% starch, respectively. The average fecal starch content was 3.40 ± 3.1% and 3.93 ± 2.50% for spring and fall samples, respectively. Apparent TTSD estimates were 95.42 ± 2.38% and 95.43 ± 5.15% to Eq1 and Eq2, respectively, with a high correlation between them (r = 0.83; P < 0.01). Positive correlation between ensiling time and ATTSD calculated by Eq2 was also detected (r = 0.31; P < 0.05), showing that CS with longer fermentation contributes positively to the increased starch utilization. We also observed moderate negative correlation between CS dry matter and ATTSD (r = −0.28; P < 0.05), indicating that dried CS reduces TTSD. In general, dietary starch was efficiently utilized, but some factors such as ensiling time and plant maturity influence starch digestibility of the dairy cow diets.