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Influence of Thermo-Ammoniation on Quality of Warm-Season Grass Hay for Steers¹

University of Nebraska, Lincoln 68583

Abstract

Warm-season grass hay is an important source of winter feed for cattle production in the Northern Great Plains. Frequently, these forages are harvested at mature stages. Chemical treatment offers a management tool to improve the value of this resource. This study was conducted to evaluate the use of thermo-ammoniation for improving forage quality of warm-season grass hay. Immature switchgrass, Panicum virgatum L., (Swi-I); mature switchgrass, (Swi-M); and mature indiangrass, Sorghastrum nutans (L). Nash, (Ind-M) were fed without treatment (CTR) or thermo-ammoniated with 3% anhydrous ammonia for 23 h at 85 C (NH₃) to mature Angus and Hereford crossbred steers (407 kg). Two sequential 6x6 Latin-square trials, at ad libitum or equalized intakes, were used to evaluate the influence of thermo-ammoniation on voluntary intake and digestibility, as well as rates of overall disappearance, rates of passage and neutral detergent fiber (NDF) digestion and particle size distribution of ruminal digesta. Thermo-ammoniation increased digestibility, intake, rate of disappearance and rate of NDF digestion. In general, increases were greater with either of the mature hays than with Swi-I. Rate of passage of nondigested residues, as determined from the excretion of chromium-mordanted fiber, was not affected by thermo-ammoniation. A greater proportion of the ruminal digesta had smaller particle sizes with Swi-M CTR or Ind-M CTR than with the other hays, which were more rapidly digested and more rapidly passed. The results are interpreted to indicate that thermo-ammoniation markedly improves the feeding value of mature, warm-season prairie hay, primarily by increasing digestibility and allowing increased voluntary intake.

¹ Published with the approval of the Director as Paper No. 8130, Journal Ser., Nebraska Agr. Exp. Sta.

² Present address: Iberia Res. Sta., Louisiana Agr. Exp. Sta., Louisiana State Univ. Agr. Center, P. O. Box 466, Jeanerette, LA 70544.

³ Dept. of Anim. Sci.

⁴ Dept. of Agron.

⁵ Biometrics and Information Systems Center.