IMPACT OF DIFFERENT BUFFERS ON MEASURES OF POST-RUMINAL FERMENTATION

Tanya Gressley, Ph.D.With an emphasis on increased production, dairy cow rations have shifted to higher energy feeds with higher concentrations of starch. High starch rations are rapidly digested within the rumen, causing pH levels to decline and ruminal acidosis. However, there is also increased passage of fermentable carbohydrates to the intestines which can lead to intestinal acidosis. The purpose of this study was to evaluate the effects of different buffers on the severity of hindgut acidosis. In a 5 x 5 Latin square design, ten multiparous cows were randomly assigned to treatments of a high starch diet as the control (CON), the control diet supplemented with sodium bicarbonate (FSB), calcium carbonate (FCC), or calcium carbonate and magnesium oxide (FCCM), or the control diet with abomasally infused encapsulated sodium bicarbonate (ISB). It was hypothesized that the ISB, FCC, and FCCM treatments would be effective in ameliorating hindgut acidosis. Cows were housed in a tie-stall barn and were fed twice a day for ad libitum intake. Cows were infused twice daily with corn starch suspended in 1.5 L of tap water. Rumen fluid and fecal samples were collected on day 7 of each period at 4-hr intervals beginning at 6:30 am and ending at 2:30 am on the following day for measurement of pH, volatile fatty acids (VFA), and lipopolysaccharide (LPS). Feed samples were collected on day 7 of each period after the 6:30 am sampling. Milk samples were collected on day 7 during the morning and afternoon. Treatment did not affect rumen pH, but fecal pH was higher in the FCCM group (pH 6.64; P < 0.001) than in the CON group (pH 6.47; P<0.001). Time affected total rumen VFA, but not rumen lactate, acetate, propionate, isobutyrate, valerate, isovalerate, or total VFA (P > 0.10). There were no effects of treatment on fecal lactate, butyrate, isobutyrate, valerate, or isovalerate (P > 0.10); however treatment affected acetate (P = 0.04) and propionate (P= 0.03) and tended to affect total VFA (P = 0.07). Total VFA were greater for FCC and FCCM compared to CON (P = 0.03 and 0.007, respectively). Similarly, acetate was greater for FCC and FCCM compared to CON (P = 0.02 and 0.003, respectively), and propionate was greater for FCC and FCCM compared to CON (P = 0.01 and 0.005, respectively). In addition, fecal acetate was lower in FSB compared to FCCM (P = 0.05). The contrast of CON vs. (ISB + FCC + FCCM) was also significant for total VFA, acetate, and propionate, due to lower VFA for CON vs. the proposed post-ruminal buffers. Fecal dry matter was affected by time (P < 0.001), due to the lowest dry matter at 0 h (13.0%), intermediate dry matter at 4, 12, and 16 h (13.4 to 13.8%), and greatest dry matter at 8 and 20 h (14.4 and 14.5%, respectively, however treatment did not affect fecal dry matter. The data suggest that FCC and FCCM have postruminal buffering capability, but data on LPS levels and digestibility (pairing of feed and fecal composition data) will be needed to support this conclusion.Pre-veterinary Medicine and Animal Bioscience