Our objective was to compare dry matter degradation (DMD), volatile fatty acid (VFA) production, and gas production among dried distillers grains with solubles (DDGS) with varying fat contents. We hypothesized that DDGS with greater fat content would decrease fermentation and impact VFA and gas production. Three 24-h in vitro trials were conducted on different days with the Ankom Technology in vitro bottle system using rumen fluid pooled from 3 cannulated lactating dairy cows. Six DDGS samples (DG1 to DG6) were tested from different sources that varied in fat content. A soybean meal (SBM) sample was included as a control. Samples were incubated in duplicate F57 fiber filter bags within each bottle and bottles were run in triplicate for each feed within a trial. Gas pressure was measured every 10 min by sensors in the bottle caps. Fluid samples were collected for VFA analysis at 24 h from each bottle. Data were analyzed using MIXED procedures of SAS 9.4 and means were compared using PDIFF. Results are shown in Table 1. The 24-h DMD was least in DG2 and DG3, which had the greatest fat contents. Total VFA, acetate, and butyrate production were similar among DDGS, which were all less than SBM. Propionate production did vary among DDGS and DG3 with the highest fat had the least propionate production. All DDGS had less gas production than SBM and it varied among DDGS but did not appear to correspond with fat. Overall, the fat content in DDGS affects DMD and propionate production. Difference sources of DDGS had different gas production, but it was not attributable to fat content. Table 1. Production parameters of dried distillers grains with solubles (DDGS) with varying fat contents compared with soybean meal (SBM) as control

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	-
Ether extract, % DM	7.62	9.52	10.48	5.63	5.79	4.97	0.85	-
24-h DMD, %	50.3b	44.1d	39.9e	47.5c	47.8c	48.4bc	61.4a	0.84
Acetate, mmol/g	5.00b	4.31b	4.78b	5.83b	6.41b	6.56b	10.59a	0.82
Propionate, mmol/g	5.76ab	5.20ab	4.89b	5.90ab	6.33a	5.96ab	7.05a	0.49
Butyrate, mmol/g	1.26b	1.13b	1.06b	1.34b	1.35b	1.42b	2.31a	0.15
Total VFA, mmol/g	12.7b	11.0b	11.2b	13.8b	14.8b	14.7b	21.7a	1.58
Gas production, mL/g	64.5b	57.7b	54.5bc	45.6c	54.8bc	65.9b	83.6a	10.44

^a–eValues with unlike superscripts differ by P < 0.05 using pdiff.