. 2021 Nov 25;3(1):19–25. doi: 10.3168/jdsc.2021-0156

Table 2.

Near-infrared spectroscopy parameters and levels of in vitro rumen fermentation products from calibration, cross-validation, and prediction¹

Fermentation product	Nc	Np	Spectral preprocessing	LV	Calibration					Cross-validation					Prediction
Fermentation product	Nc	Np	Spectral preprocessing	LV	R²	RMSE	SEC	Slope	Offset	R²	RMSE	SECV	Slope	Offset	R²	RMSE	RPD	SEP	Slope	Offset	Bias
Acetic acid, mmol/L	151	67	SG	4	0.95	2.71	2.71	0.95	2.40	0.94	2.87	2.88	0.94	2.52	0.94	2.91	4.20	2.84	0.93	3.76	0.70
Propionic acid, mmol/L	154	56	—	8	0.80	1.80	1.80	0.80	2.62	0.78	1.91	1.92	0.80	2.62	0.81	1.76	3.69	1.78	0.88	1.62	0.08
Butyric acid, mmol/L	132	54	SNV	7	0.87	1.09	1.10	0.87	1.03	0.84	1.24	1.24	0.86	1.15	0.85	1.15	3.27	1.16	0.94	0.54	0.10
Valeric acid, mmol/L	140	61	SNV	8	0.74	0.17	1.17	0.74	0.22	0.66	0.20	0.20	0.69	0.26	0.69	0.22	3.28	0.21	0.63	0.36	0.07
Isobutyric acid, mmol/L	148	57	—	8	0.81	0.12	0.12	0.81	0.11	0.76	0.13	0.13	0.78	0.12	0.82	0.11	3.94	0.11	0.87	0.07	0.00
Isovaleric acid, mmol/L	145	43	SG	9	0.84	0.23	0.23	0.84	0.14	0.77	0.28	0.28	0.80	0.17	0.73	0.25	1.95	0.25	0.96	0.08	0.04
Methane, mmol/L	260	112	—	9	0.86	3.45	3.45	0.86	1.31	0.85	3.66	3.66	0.86	1.39	0.89	3.05	3.05	3.06	0.89	1.02	−0.14
Total gas, mL/g of OM	877	441	—	11	0.92	23.29	23.30	0.92	10.60	0.91	24.07	24.09	0.91	11.21	0.91	24.97	3.30	24.99	0.09	10.09	0.66

Nc = number of samples of calibration set; Np = number of samples of prediction set; LV = latent variables; SG = Savitzky-Golay polynomial derivative; SNV = standard normal variate; RMSE = root mean square error; SEC = standard error of calibration; SECV = standard error of cross-validation; SEP = standard error of prediction; RPD = ratio of prediction to deviation.