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Effects of Diet Concentrate Level and Sodium Bicarbonate on Site and Extent of Forage Fiber Digestion in the Gastrointestinal Tract of Wethers¹

University of Kentucky², Lexington 40546-0215

Abstract

Four adult wethers (45 kg) with permanent ruminal and abomasal cannulae were used in a repeated measures Latin-square arrangement of treatments to quantitate the effects of diet concentrate level and sodium bicarbonate (NaHCO₃) on site and extent of forage fiber digestion in the gastrointestinal tract. Experimental diets consisted of Kentucky-31 tall fescue hay, soybean meal and a semi-purified concentrate mixture in ratios of 95:5:0, 76:4:20, 57:3:40 and 38:2:60; NaHCO₃ represented 0 or 7.5% of the concentrate mixture. Ruminal digestion (% of intake) of neutral detergent fiber (NDF) and hemicellulose decreased linearly (P<.05), whereas acid detergent fiber (ADF) digestion responded in a cubic (P<.05) fashion to increasing concentrate level; NaHCO₃ improved ruminal digestion of NDF (P<.10) and ADF (P<.05), but not hemicellulose. Post-ruminal digestion (% of rumen non-degraded) of NDF and ADF tended to increase, whereas hemicellulose digestion responded in a cubic (P<.05) fashion to increasing concentrate level; NaHCO₃ decreased (P<.05) post-ruminal digestion of all fiber fractions. Total tract digestion of NDF and ADF showed a cubic (P<.05) response, whereas hemicellulose digestion responded in a quadratic (P<.05) fashion to increasing concentrate level; NaHCO₃ had no effect on total tract digestion of any fiber fraction. Correlations of ruminal hemicellulose digestion with mean pH (r= .33; P= .07) and minimum pH (r= .30; P= .09) were attained in a 24-h feeding cycle. Path coefficient analysis revealed forage hemicellulose degradability to be more pH-sensitive and less responsive to NaHCO₃ than ADF degradability when concentrate was fed. Concentrate feeding and NaHCO₃ altered the primary sites of forage fiber digestion in the gastrointestinal tract, but did not systematically influence the extent of total tract utilization.

¹ This paper (No. 85-5-149) is published with the approval of the Director of the Kentucky Agr. Exp. Sta.

² Dept. of Anim. Sci.