The current in vitro experiment was performed to test the effects of supplementing lipid extract algae (LEA) in lactation dairy diets on ruminal fermentation in a 2 (level of forage in diets) × 2 (without vs. with LEA) factorial design with 4 independent runs of continuous cultures (n = 4). Diets with LEA completely replaced mixture of soybean meal and canola meal (50:50 in a DM basis). The data in this experiment were analyzed using the Proc Mixed procedure of SAS using a model that included fixed effects of level of forage, LEA supplementation, and their interaction and a random effect of fermentor within independent run. Feeding LEA decreased culture pH, regardless of level of forage, but the decrease of culture pH was greater under high-forage diet compared with low-forage diet, resulting in an interaction between level of forage and LEA. Under high-forage diet, total VFA concentration increased with feeding LEA, but it was not affected in low-forage diet, leading to a tendency (P = 0.08) of level of forage and LEA interaction. Adding LEA decreased ammonia-N concentration both in high- and low-forage diet. Overall results in this experiment indicate that feeding LEA in lactation dairy diets did not interfere with in vitro ruminal fermentation. The decreased ammonia-N concentration due to feeding LEA may have resulted from less degradation of N fraction in LEA compared with mixture of soybean meal and canola meal. Table 1. In vitro effects of lipid extract algae supplemented in dairy diets

Item	Diet1					SEM	P2
HF			LF
–LEA	+LEA	–LEA	+LEA	FC	LEA	INT
Mean culture pH	6.25a	6.04b		6.07	6.00	0.047	<0.01	0.05	0.05
Total VFA, mM	29.1b	34.0a		34.4	32.5	2.77	0.30	0.60	0.08
Individual VFA3
Acetate (A)	46.1	47.3		47.3	47.7	3.92	0.21	0.33	0.53
Propionate (P)	36.5	36.8		40.6	38.7	2.64	0.01	0.45	0.30
A:P	1.26	1.29		1.19	1.24	0.168	0.06	0.54	0.47
Ammonia-N, mg/dL	8.04	5.36		6.54	3.10	0.403	<0.01	<0.01	0.31

^a–bMeans within a row with different superscripts differ (P < 0.05). ¹HF–LEA = high-forage diet (HF; 60% forage:40% concentrate) without lipid extract algae (LEA); HF+LEA = HF with LEA; LF–LEA = low-forage diet (LF; 40% forage:60% concentrate) without LEA; and LF+LEA = LF with LEA. ²FC = forage-to-concentrate ratio in the diet; LEA = supplementation of LEA; and INT = interaction between FC and LEA. ³Expressed as mol/100 mol.