Our objective was to determine the effect of fat content in dried distillers grains with solubles (DDGS) on the rumen degradability of dry matter (DM) and neutral detergent fiber (NDF). A secondary objective was to evaluate the effect of types of bags used for ruminal incubation on DM digestibility. Three ruminally cannulated primiparous Holstein cows (33.2 ± 3.41 milk kg/d; 19.5 ± 1.40 dry matter intake kg/d; 601 ± 17.2 kg body weight) were used to determine the rumen degradable dry matter (RDDM) and rumen degradable neutral detergent fiber (RDNDF) from 6 different distiller’s grains (DG1 to DG6) samples from different sources that varied in fat content. A soybean meal (SBM) sample was included as a control. The feeds were incubated in the rumen for 0, 2, 4, 8, 16, 24, 48, 72, and 120 h using F57 fiber filter bags with 25 µm porosity and Dacron bags with 50 ± 10 µm porosity from Ankom Technology. Ruminal rate of passage (Kp) of concentrates averaged 6.38 ± 0.21%/h among the 3 cows. Rumen degradation constants for DM and NDF were estimated using the NLIN procedures in SAS 9.4 and means were compared using PDIFF. The RDDM differed among the DDGS with DG1, DG4 and DG5 having greater RDDM and lower fat contents. The Dacron bags had more RDDM than the F57 filter bags. The RDNDF and NDF rate of digestibility (NDF K_d) were similar among the DDGS and all were less than SBM. Therefore, differences in RDDM in DDGS that vary in fat content are thought to be more related to rumen degradability of other nutrients such as protein rather than NDF. Table 1

Item	DG1	DG2	DG3	DG4	DG5	DG6	SBM	SEM
DM, %	92.1	93.2	92.9	91.9	91.5	92.0	90.4	—
CP, % DM	30.9	30.0	28.7	31.2	29.9	32.0	22.2	—
RUP,1 % CP	58.1	71.5	71.6	63.8	65.9	65.2	36.6	—
NDF, % DM	29.3	34.6	34.5	31.7	28.7	29.2	9.4	—
Ether extract, % DM	7.62	9.52	10.48	5.63	5.79	4.97	0.85	—
Dacron RDDM, % DM	58.4b	49.7d	46.4e	59.1b	59.9b	55.1c	66.0a	1.90
F57 RDDM,% DM	45.1ab	39.0bc	34.1c	47.8a	44.5ab	41.3b	49.3a	1.69
F57 RDNDF, % NDF	20.5b	20.9b	20.4b	19.5b	19.4b	18.4b	32.9a	2.27
NDF Kd, %/h	1.81b	1.97b	1.86b	1.72b	1.66b	1.49b	4.14a	0.22

^a–eValues with unlike superscripts differ by P < 0.05 using PDIFF. ¹Ross method used for RUP estimation.