The addition of buffers such as K₂CO₃ have been investigated in how they alter ruminal fermentation and reduce accumulation of milk fat inhibitors (MFI). Thus, we hypothesized that prilled saturated free fatty acids (FFA; C16:0 and C18:0) combined with K₂CO₃ would provide a slower, more prolonged release of K₂CO₃ than feeding it alone in reducing production of MFI. Four treatments were randomly assigned to 8 continuous culture fermenters for 2 periods of 10 d. Treatments included 4 combinations of FFA (Supplement A) and K₂CO₃ coated with prilled fatty acids (1:1; Supplement B) representing 1.25:0 (1), 0.83:0.83 (2), 0.42:1.66 (3), and 0:2.5% DM (4) of supplement A to B ratios. All treatments provided 1.25% DM of FA with K₂CO₃ increasing gradually from 0 to 1.25% DM. Data were analyzed using the MIXED procedure of SAS as a randomized complete block design with blocks of period and fermenters; where linear, quadratic and preplanned polynomial contrasts where evaluated. Addition of K₂CO₃ altered pH and biohydrogenation (Table 1). There was a quadratic increase in total VFA (P < 0.01) but butyrate was reduced linearly (P < 0.05), while valerate and isoacids increased quadratically with increasing K₂CO₃. Adding K₂CO₃ tended to increase the outflow of C18:1 (P = 0.09), C18:2 (P = 0.06) and reduce C18:3 (P = 0.06) linearly. Biohydrogenation intermediates, trans-10 and trans-12 18:1, were quadratically reduced with K₂CO₃. These results indicate that combinations of prilled fatty acids and K carbonate increase pH and reduce production of biohydrogenation intermediates linked to milk fat depression exhibiting a quadratic response. Table 1. Biohydrogenation and pH profile of fermenters fed 4 combinations of supplements A and B

Item	TRT				SE	Contrasts, P-value
	1	2	3	4		L	Q
pH	6.06	6.26	6.32	6.22	0.06	0.07	0.03
pH, h to 6.0	2.00	2.75	3.75	2.25	0.29	0.21	<0.01
pH, h < 6.0	7.00	4.50	3.00	5.50	0.68	0.08	<0.01
min pH	5.57	5.63	5.69	5.59	0.10	0.69	0.19
max pH	6.83	6.84	6.95	6.85	0.17	0.65	0.49
Biohydrogenation
18:2	58.00	55.47	43.91	52.45	7.77	0.06	0.09
18:3	68.77	66.14	56.65	64.20	6.30	0.05	0.06