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Effect of Supplemental Sodium Bicarbonate on Nutrient Digestibilities and Ruminal pH Measured Continuously¹

The Ohio State University^,5, Wooster 44691

Abstract

A technique was used to monitor continuously ruminal pH using a strip-chart recording pH meter. Ruminal pH measurements were made in four ruminal-cannulated crossbred wether lambs (avg initial weight, 42.5 kg). For 1.5 h daily, lambs were given ad libitum access to 50% concentrate-50% chopped orchardgrass hay diets supplemented with 0, 1.5, 3.0 and 4.5% sodium bicarbonate (NaHCO³). A split-plot Latin-square design was used to evaluate NaHCO³ level and day of adaptation on the percentage of time (%T) that ruminal pH was 6.6, 6.2, 5.8, 5.4 and 5.0. No effect due to day of adaptation existed for ruminal pH measurements (P>.10), while the effect of dietary NaHCO³ level was quadratic (P>.01) for the %T that ruminal pH was 6.2 and 5.8, and linear (P>.01) for the %T that ruminal pH was 5.4. To evaluate the effects of NaHCO³ on nutrient digestion, the same diets were fed to eight wether lambs (avg initial weight, 38 kg) at 85% of their ad libitum intake in a replicated 4 x 4 Latin-square digestion trial. Digestibilities of dry matter (DM) , organic matter, N and fiber fractions were not different due to level of NaHCO³ (P>.10). Ash digestibility increased with increasing levels of dietary NaHCO³ (P<.01). Four ruminal-cannulated mature Hereford steers were also given ad libitum access to the diets in a split-plot Latin-square trial to evaluate effects of dietary NaHCO³ level on ruminal pH and in situ digestion of soybean meal N and orchardgrass DM. During incubation of the dacron bags for 3, 6, 9, 12, 24 and 36 h, ruminal pH increased linearly (P<.05) with increasing level of NaHCO³. Soybean meal N disappearance at 3, 6, 9, 12 and 24 h of incubation and orchardgrass DM disappearance at 24 and 36 h also increased linearly with increasing level of NaHCO³. Ruminal solid and liquid dilution rates were not affected by level of supplemental NaHCO³ (P>. 10). The results of these trials suggest that increasing level of dietary NaHCO³ greatly increases the proportion of time ruminal pH is above critical levels for ruminal protein and dry matter digestion, but does not affect total tract nutrient digestion when 50% concentrate diets are fed.

¹ Salaries and research support provided by State and Federal Funds appropriated to the Ohio Agr. Res. and Devel. Center, The Ohio State Univ. Journal Article No. 89-85.

² Present address: Dept. of Anim. Sci., Univ. of Illinois, Urbana 61801.

³ Dept. of Anim. Sci.

⁴ Reprint requests: Dept. of Anim. Sci., Ohio Agr. Res. and Devel. Center, Wooster 44691.

⁵ The Ohio Agr. Res. and Devel. Center.

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