The objective of this study was to determine the effects of 2 Saccharomyces cerevisiae fermentation products—Diamond V Original XPC (XPC) and NutriTek (NutriTek)—on in vitro VFA production on TMR from various US regions. Six TMR representing the Midwest (2), South Central (1), Southwest (1), Northeast (1), and Southeast (1) were evaluated. Serum bottles (100 mL) containing 0.3 g TMR and treatment (Control, XPC, or NutriTek) were inoculated with buffered rumen fluid and incubated for 12 and 24 h. Three replicate experiments were performed to generate 9 replicates per treatment, diet, and time point. Data were analyzed using the GLM model of JMP. Significance was defined as P ≤ 0.05. Averaged across diets, XPC resulted in higher (P < 0.001) VFA concentrations than Control, while NutriTek further increased (P < 0.001) VFA concentrations over XPC (Table 1). Within individual TMR diets, XPC increased acetate (4.0 to 7.6%), propionate (4.8 to 16.9%), butyrate (4.6 to 6.7%) or total VFA (2.9 to 11.0%) over Control (P ≤ 0.01) on all TMR diets at 12 h or 24 h. NutriTek increased acetate (4.1 to 12.6%), propionate (9.5 to 24.9%), butyrate (7.9 to 18.5%) or total VFA (6.8 to 16.6%) over Control (P ≤ 0.03) for all TMR diets at 12 and 24 h. There were no diet by treatment interactions (P ≥ 0.17). In conclusion, XPC and NutriTek were able to enhance VFA production on a range of TMR diets in vitro. NutriTek further enhanced ruminal VFA production over XPC on multiple diets tested. Table 1. In vitro VFA production by rumen microbiota incubated with two Saccharomyces cerevisiae fermentation products averaged across six TMR diets

Time/Treatment	VFA (mM)
	Acetate	Propionate	Butyrate	Total
12 h
Control	16.8a	11.3a	2.6a	31.2a
XPC	17.8b	12.4b	2.7ab	33.5b
NutriTek	18.5c	13.2c	2.9b	35.2c
SEM	0.2	0.2	0.1	0.3
24 h
Control	24.7a	15.9a	3.9a	45.4a
XPC	25.6b	16.5b	4.1a	47.2b
NutriTek	26.7c	17.0c	4.3a	49.9c
SEM	0.2	0.2	0.1	0.3

^a–cMeans without a common superscript differ by P ≤ 0.05.