Effects of calcium-ammonium nitrate on performance and greenhouse gas production of beef steers grazing a mixed winter forage



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Two experiments were performed to evaluate the effects of calcium-ammonium nitrate (CAN) on in vitro fermentation, in vivo CH4 production, and performance of beef steers. For experiment 1, in vitro batch cultures were conducted as a randomized complete block design using 1 of the following basal substrates: wheat (Triticum aestivum; 100% substrate DM; W); and wheat + finely ground corn (wheat:corn = 88:12, DM basis; WC; Table 3.1). Treatments included: W; WC; WC + 2% CAN in the substrate DM (WCN); and WC + 0.67% urea in the substrate DM (WCU). Treatments WCN and WCU were isonitrogenous. Two ruminally-cannulated steers were used as ruminal fluid donors. Serum bottles (125-mL) containing 50 mL of a 4:1 buffer:ruminal fluid inoculum and 0.7 g of substrate were incubated for 48 h at 39 °C under constant agitation (60 rpm). In vitro organic matter digestibility (IVOMD) was determined simultaneously in separate 100mL centrifuge tubes, the procedure consisted of 48 h of ruminal fermentation at 39 °C under constant agitation (60 rpm) followed by 48 h of post-ruminal digestion with 6 mL of 20% HCl and 2 mL of a 5% pepsin solution were added. Data were analyzed using the MIXED procedure of SAS using a randomized complete block design with 4 replicated days (block). For experiment 2, thirty-six Angus crossbred steers (332 ± 25 kg) were used in a generalized randomized block design grazing a mixed winter forage using wheat (Triticum aestivum), triticale (Triticosecale Wittmack), and rye (Secale cereale) for 48 d. The effects of CAN were evaluated on in vivo methane production, performance, supplement intake, and blood urea nitrogen (BUN) of beef steers. Cattle were blocked by BW (n = 3; 12 head/block) and randomly assigned to 1 of 3 treatments (4 steers/treatment in each block): 1) winter pasture + corn (0.3% of BW; PC), 2) WC + 328 mg/kg of BW encapsulated CAN (eCAN; PCN) and 3) PC + 124 mg/kg of BW urea (PCU). Treatments PCN and PCU were isonitrogenous. For experiment 2, data were analyzed as a generalized randomized block design, using the MIXED procedure of SAS. Steers was considered the experimental unit. The model included the fixed effects of treatment and the random effect of block. Blood urea nitrogen data were analyzed using the MIXED procedure of SAS with repeated measures. The model included the fixed effects of treatment, day, and treatment × day interaction and the random effect of block. The covariance structure used was compound symmetry. For both experiments significance was declared at P ≤ 0.05 and tendencies were discussed at 0.05 < P < 0.10. For experiment 1, a treatment effect was observed for IVOMD (P = 0.010), where IVOMD was greater (P ≤ 0.049) for WC and WCU versus W. An increase (P ≤ 0.005) in NH3-N was observed for WCN, and WCU treatments when compared to WC. Methane production in mM, mmol/g of substrate incubated, and mmol/g of substrate fermented were significantly reduced (P < 0.001) by WCN when compared to the other treatments. A treatment effect was observed for butyrate (P = 0.007) and valerate (P = 0.022), where butyrate was greater for WCU versus W (P = 0.043). While no differences were observed for acetate:propionate among treatments. For experiment 2, cattle consuming PC had a greater (P = 0.001) supplement intake versus NPN treatments. Concentrations of BUN were affected by day, d-24 (18.598 mg/dL) being greater compared to d-0 (8.215 mg/dL), d-35 (10.549 mg/dL) and d-49 (14.574 mg/dL). Methane production (g of CH4/d, g of CH4/kg of BW, and g of CH4/kg of MBW) was not different among treatments. Also, ADG was not affected by treatment (P = 0.984). The amount of eCAN consumed by steers grazing a mixed-winter forage did not improve performance or decrease enteric CH4 emissions.



Calcium-ammonium nitrate (CAN), Supplement intake, Average daily gain (ADG), Methane (CH4)