Upgrading of sorghum stover with anhydrous ammonia or urea treatments

Abstract

The effects of anhydrous ammonia and urea treatments of sorghum stover on intake, in vivo digestibility, in situ dry matter degradation and nitrogen balance on sheep were compared. Untreated, ammonia-treated (3% dry matter (DM) basis) and urea-treated (5.3% and 25% water, DM basis) stovers were fed ad libitum to four sheep, supplemented with 300 g of barley and 30 g of a mineral/vitamin mix for 25 days. Both treatments resulted in a smaller decrease in the fibre content of stover, but total nitrogen contents were markedly increased with urea (18.9% of DM) and ammonia (17.0% of DM) treatments compared with untreated stover (9.3% of DM). The free ammonia nitrogen and the fibre-bound nitrogen (N-NDF) contents were increased by the ammonia (+2.4 g kg −1 and +0.6 g kg −1 DM, respectively) and the urea (+4.4 g kg −1 and +0.4 g kg −1 DM) treatments. Ammonia treatment resulted in an increase in the DM intake from 31.4 g DM kg −1 W 0.75 for untreated stover to 47.2 g DM kg −1 W 0.75; urea treatment increased DM intake to 46.8 g DM kg −1 W 0.75. Organic matter, fibre and crude protein digestibilities were increased when stover was treated. The highest crude protein digestibility and nitrogen retention values were obtained with the urea treatment (66.6% and 6.2 g day −1 respectively), while the highest fibre digestibility (NDF) value was recorded with the ammonia treatment (65.1%). Rumen cellulolytic activity measured as in situ dry matter degradation showed the same pattern of variation as in in vivo fibre digestibility. Ammonia and urea treatments increased the potentially degradable fraction from 61.4% for untreated stover to 80.1% and 68.4% respectively. The rate of degradation also increased from 2.88% h −1 for untreated stover to 2.92% h −1 and 3.67% h −1, respectively, with ammonia and urea treatments. Both anhydrous ammonia and urea treatments increased the intake and digestion of sorghum stover by sheep. Urea is as effective as anhydrous ammonia in improving the nutritive value of sorghum stover.