Frequent determination of dry matter (DM) content of ensiled forages is imperative for precise mixing of TMR diets. The methods for on-farm DM determination should be fast, easy to use, and comparable with the standard oven-drying measurements. The objective of this study was to compare a novel method using a pocket-sized micro-spectrometer combined with cloud-based calibrations (Reveal, Cargill Inc.; 1,417 samples included in the calibration) with other rapid methods: 1) Koster tester run for 30 min (KT 30 min); 2) Koster tester run until constant weight or maximum time of 70 min (KT final); 3) laboratory near infrared spectroscopy (DS2500 model, Foss) calibrated using 11,728 samples oven-dried at 60°C for 16 h (Lab NIR); and 4) 60°C oven for 16 h (Oven DM). Samples of corn, alfalfa, and grass silages (10 samples per forage class) were sourced from dairy farms and selected to represent a large range of DM (ranged from 19 to 63%). Concordance correlation coefficients (CCC) between methods was calculated using epiR package of the R software. The CCC indicated that all methods were highly correlated with Oven DM (considered standard method in this study) and among each other when compared within forage class (data not shown) and when combining all samples in one set (all CCC >0.90). Results of DM content obtained with each method were compared with Oven DM using a t-test for paired means (Table). KT 30 min overpredicted DM by 8% (P < 0.05), indicating that 30 min was not sufficient time to accurately measure DM content. Compared with Oven DM, KT Final resulted in lower DM values (P < 0.05), likely associated with the fact that Oven DM was determined at 60°C for 16h and not at higher temperatures. Dry matters obtained by Lab NIR and Reveal were not different from Oven DM, indicating that Reveal is a valid alternative for fast determination of DM content in forages on farms. Table 1 (Abstr. W32).

	Mean DM, %	SD	Mean difference with oven DM,1 %	SD	P-value	95% CI for differences
Oven DM	37.7	13.2	—	—	—	—
KT 30 min	40.7	11.1	2.91	3.91	0.01	1.43 to 4.40
KT Final	36.6	12.3	−1.19	2.77	0.03	−2.25 to −0.14
Reveal	37.4	11.6	−0.36	3.23	0.55	−1.59 to 0.86
Lab NIR	38.3	13.3	0.49	3.04	0.39	−0.66 to 1.65

1t-test for paired means (oven DM vs. the rest).