The objective of this study was to evaluate the effects of glycerin in replacing corn grain on ruminal fermentation of lactating dairy cows. Eight rumen cannulated Holstein cows (184 ± 50 DIM; 29.38 ± 0.89 kg/d milk yield; 594 ± 39 kg BW) were assigned in a replicated 4 × 4 Latin square design, with 21 d of experimental periods. Cows were assigned within each square to receive one following diets: Control or 0% glycerin; 7% of glycerin; 14% of glycerin; and 21% glycerin added to diets in replacing corn ground. On 20 d of experimental period, ruminal fluid samples were collected before (0), 2, 4, 6, 8, 10 e 12 h after morning feeding for analysis of the ruminal pH, NH₃ and volatile fatty acids (VFA). Data were analyzed as repeated measures in PROC MIXED (SAS for Windows 9.0), in the statistical model the effects of animal, period, square, treatment, beyond the effects of time with their interactions with treatment were considered. There was no effect of glycerin on total VFA (P > 0.05); but glycerin inclusion in the diet increased propionate and butyrate, and decreased acetate concentrations, resulting in lower acetate: propionate ratio (P < 0.05). Cows fed glycerin had lower ruminal pH in the first time of collect (P < 0.05). Ruminal NH₃ was linearly decreased as glycerin levels increased (P < 0.05). Glycerin inclusion in the diets of lactating dairy cows changed ruminal fermentation, with increase in propionate concentration, that indicate better efficiency the use of the energy diet. Table 1.

Item	Inclusion of glycerin, % of DM				SEM	P-value
0	7	14	21	Diet	Time	Diet × Time	Lin	Quad
pH	6.31	6.38	6.38	6.32	0.03	0.65	<0.01	<0.01	0.89	0.22
NH3, mg/dL	23.74	21.52	18.05	17.54	0.49	<0.01	<0.01	0.19	<0.01	0.39
Total VFA, mM	119.11	111.40	108.16	113.87	2.26	0.41	<0.01	0.85	0.37	0.16
Acetate, mM	74.37	58.82	55.37	53.12	1.42	<0.01	0.04	0.44	<0.01	0.05
Propionate, mM	24.76	25.11	27.06	33,68	0.74	<0.01	<0.01	0.06	<0.01	0.05
Butyrate, mM	14.27	21.16	20.21	19.46	0.44	<0.01	<0.01	<0.01	<0.01	<0.01
C2:C31	3.05	2.39	2.21	1.73	0.05	<0.01	<0.01	<0.01	<0.01	0.20

¹Acetate:propionate ratio.