Effects of calcium-ammonium nitrate on in vitro fermentation of bahiagrass hay with supplemental molasses

Abstract Text: A randomized complete block design was used to determine the effects of increasing amounts of calcium-ammonium nitrate (CAN) on in vitro fermentation of bahiagrass hay (Paspalum notatum). In vitro fermentation consisted of 100 mL of a 4:1 buffer:ruminal fluid inoculum and 0.7 g of a substrate composed of 80:20 bahiagrass hay:molasses (DM basis) incubated for 48 h in 125-mL serum bottles. Three d (block) of incubation were performed. Duplicate bottles in each d were randomly inoculated and received 1 of 4 treatments: 1) negative control (no added NPN; NEG); 2) control (0.75% urea in the substrate DM; CTL); 3) 1.2% CAN (0.38% urea and 1.2% CAN in the substrate DM; 1.2CAN); and 4) 2.4% CAN (2.4% CAN in the diet DM; 2.4CAN). Treatments CTL, 1.2CAN and 2.4CAN were iso-nitrogenous. Two ruminally cannulated Angus crossbred steers (348 ± 29 kg BW) fed bahiagrass hay ad libitum and 2.27 kg (as is) of a 50:50 molasses:crude glycerol mixture, daily, were used as ruminal fluid donors. In vitro organic matter digestibility (IVOMD) was determined using the same amounts of substrate and inoculum from the in vitro batch culture. Data were analyzed using the mixed procedure of SAS with the fixed effect of treatment and the random effect of d. Means of duplicate bottles within d were considered the experimental unit. Contrasts were used to determine the effect of NPN (NEG vs. others), linear effects of CAN and quadratic effects of CAN. Gas production increased (P = 0.023) when adding NPN (295 vs. 301 ± 2.0 mL/g of OM incubated for NEG vs. NPN, respectively) and linearly decreased (P < 0.001) as nitrate amounts increased. Adding NPN increased (P = 0.015) IVOMD, while a linear (P = 0.001) decrease occurred as nitrate increased; however, no difference (P = 0.351) was observed between CTL and 1.2CAN. Methane production decreased linearly (P = 0.001) with the addition of nitrate (4.81 vs. 0.65 ± 0.325 mmol/g substrate fermented for CTL vs. 2.4CAN, respectively). There was no effect (P > 0.05) of NPN or nitrate on total VFA (mM), acetate:propionate, or molar proportions of any VFA analyzed. Added NPN improved the IVOMD of bahiagrass hay as expected in a CP deficient forage. Inclusion of 2.4CAN reduces IVOMD and methane production, while 1.2CAN also reduces methane production without affecting IVOMD, implying a potential intervention to decrease methane emissions. 

Keywords: fermentation, nitrate, non-protein nitrogen