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Effect of Ammoniation of Wheat Straw on Performance and Digestion Kinetics in Cattle¹

Oklahoma Agricultural Experiment Station, Stillwater 74078^,5

Abstract

The effects of ammoniation of wheat straw (35 g NH₃/kg of dry matter) on physical and chemical characteristics, kinetics of digestion and relationship to voluntary intake by cattle were studied. Intact or ruminal-cannulated steers were offered untreated or ammoniated wheat straw ad libitum, plus a soybean meal-mineral-vitamin supplement. Ammonia treatment increased (P<.01) the fragility of the straw: 67.8 vs 58.0. This estimate was determined from the amount of dry matter that passed through a 1-mm sieve after 20 s of grinding and 10 min of sieving. It also increased the crude protein content (CP; percentage dry matter): 9.3 vs 4.6 (P<.01); in vitro dry matter digestibility (IVDMD, percentage at 72 h): 47.6 vs 37.3 (P<.05) and extent of in situ disappearance of dry matter (DM) and cell wall constituents (CWC) after 48 h incubation: 38.96 vs 13.98 and 45.62 vs 21.18 (P<.05), respectively. Steers fed ammoniated straw tended to have higher concentrations of ruminal NH₃-N: 13.0 vs 9.1 mg/dl (P<.06), while no differences were found in ruminal pH. Ruminal liquid flow rate (%/h) increased with ammoniation: 2.97 vs 2.34 (P<.05), and solids dilution rate also tended to be faster after ammoniation (P<.10). Voluntary intake of straw DM was increased (P<.01) more than 30% by ammoniation. Observed changes in physical and chemical properties of straw brought about by ammoniation may be responsible for differences in rate of digestion, residence time within the rumen and voluntary intake.

¹ Journal Article No. 4395 of the Oklahoma Agr. Exp. Sta., Stillwater 74078.

² Visiting scientist, financially assisted by CONACYT, Mexico. Present address: Institute Nac. Invest. Pecuarias. SARH. Av. Lopez Mateos Sur No. 117. Guadalajara, Jalisco, Mexico CP44110.

³ Anim. Sci. Dept.

⁴ College of Arts and Sciences, Statist. Dept.

⁵ Acknowledgments are expressed to Ms. J. Sum- mers and D. Perry for analytical assistance, Mr. Ken Poling for care of experimental animals and Mrs. C. Gray for the word processing of the manuscript.