Abstract
The study evaluated enteric CH4 production, dry matter (DM) intake (DMI), and rumen fermentation in feedlot cattle supplemented with increasing concentrations of 3-nitrooxypropanol (3-NOP). A total of 100 crossbred steers (body weight, 421 ± 11 kg) was randomly assigned to one of 4 treatments (n = 25/treatment): control (no 3-NOP), or low (100 mg/kg DM), medium (125 mg/kg DM), and high (150 mg/kg DM) doses of 3-NOP. The study was comprised of 28 days of adaptation followed by three 28-d periods, with CH4 measured for 7-d per period and cattle remaining on their respective diets throughout the 112-d study. Each treatment group was assigned to a pen, with the cattle and diets rotated among pens weekly to allow the animals to access the GreenFeed emission monitoring (GEM) system stationed in one of the pens for CH4 measurement. Measured concentration (mg/kg DM) of 3-NOP in the total diet consumed (basal diet + GEM pellet) was 85.6 for low, 107.6 for medium, and 124.5 for high doses of 3-NOP. There was a treatment × period interaction (P < 0.001) for DMI; compared to control, the DMI was less for the low and high doses in periods 1, with no differences thereafter. Compared to control (10.78 g/kg DMI), CH4 yield (g/kg DMI) was decreased (P < 0.001) by 52%, 76%, and 63% for low, medium, and high doses of 3-NOP, respectively. A treatment × period effect (P = 0.048) for CH4 yield indicated that the low dose decreased in efficacy from 59% decrease in periods 1 and 2, to 37% decrease in period 3, while efficacy of the medium and high doses remained consistent over time. Irrespective of dose, hydrogen emissions increased by 4.9-fold (P < 0.001) and acetate:propionate ratio in rumen fluid decreased (P = 0.045) with 3-NOP supplementation, confirming that other hydrogen-utilizing pathways become more important in the CH4-inhibited rumen. The study indicates that supplementation of corn-based finishing diets with 3-NOP using a medium dose is an effective CH4 mitigation strategy for commercial beef feedlots with 76% decrease in CH4 yield. Further research is needed to determine the effects of 3-NOP dose on weight gain, feed conversion efficiency, and carcass characteristics of feedlot cattle at a commercial scale.
Generated Summary
This 112-day study investigated the impact of supplementing steam-flaked corn-based finishing diets with 3-nitrooxypropanol (3-NOP) on enteric methane (CH4) emissions in feedlot cattle. The research employed a completely randomized design, assigning 100 crossbred steers to four treatments: a control group (no 3-NOP), and groups receiving low (100 mg/kg DM), medium (125 mg/kg DM), and high (150 mg/kg DM) doses of 3-NOP. The study included an adaptation phase and three 28-day periods, with CH4 measurements taken over 7-day intervals in each period. The study’s methodology involved monitoring dry matter intake (DMI), rumen fermentation, and CH4 production. The aim was to assess the efficacy of 3-NOP in reducing CH4 emissions, a key aspect of mitigating the environmental impact of beef production. The study was conducted at a commercial feedlot, making the findings relevant to commercial practices.
Key Findings & Statistics
- A total of 100 crossbred steers (body weight, 421 ± 11 kg) were used in the study.
- The study comprised of 28 days of adaptation followed by three 28-d periods.
- Measured concentration (mg/kg DM) of 3-NOP in the total diet consumed (basal diet + GEM pellet) was 85.6 for low, 107.6 for medium, and 124.5 for high doses of 3-NOP.
- There was a treatment × period interaction (P < 0.001) for DMI.
- Compared to control (10.78 g/kg DMI), CH4 yield (g/kg DMI) was decreased (P < 0.001) by 52%, 76%, and 63% for low, medium, and high doses of 3-NOP, respectively.
- A treatment × period effect (P = 0.048) for CH4 yield indicated that the low dose decreased in efficacy from 59% decrease in periods 1 and 2, to 37% decrease in period 3.
- Irrespective of dose, hydrogen emissions increased by 4.9-fold (P < 0.001) and acetate:propionate ratio in rumen fluid decreased (P = 0.045) with 3-NOP supplementation.
- The nutrient composition of the basal diet is shown in Table 1. Analyzed chemical composition of the pellet used in the GEM system was (DM basis): 15.3 ± 0.55% CP, 43.6 ± 0.60% starch, 15.0 ± 2.27% NDF, and 7.3 ± 0.65% ADF.
- Overall, relative to the control treatment (11.46 kg/d), total DMI was 6.1% and 6.4% less (P < 0.001) for the low and high doses of 3-NOP, respectively.
- The observed variation in total DMI of cattle was due to the basal diet intake from the GrowSafe feed bunks (P < 0.001; Table 2).
- Although the total DMI for the low and high doses was less than that of control, intake of GEM pellet was actually 22-25% greater (P = 0.045) for these treatments relative to the control treatment (0.49 kg/d).
- When only the cattle used to measure CH4 emissions were considered, the effect of 3-NOP on intakes of total DM and basal diet was similar to that of all cattle, but with a tendency (P = 0.06) for treatment × period interaction for basal diet.
- Of a possible 25 cattle per treatment, 48% to 68% of animals in period 1, 60% to 80% in period 2 and 68% to 84% in period 3 visited the GEM system, depending upon the treatment group.
- Calculated concentration of 3-NOP in the total DMI, which accounts for intake of basal diet and pellet, was 85.6, 107.6, and 124.5 mg/kg DM for the low, medium and high doses, respectively.
- Recovery of 3-NOP ranged between 88.8% and 91.2% of the target concentration.
- Feeding 3-NOP decreased (P < 0.001) CH4 yield (g/kg DMI), CH4 production (g/d) and percentage of GEI lost as CH4 (Table 4). Compared to the CH4 yield (11.32 g/kg DMI) of the control treatment, the greatest decrease (76.0%) occurred for the medium dose followed by high (63.3%) and low (52.2%) doses.
- The average hourly CH4 emissions after feeding were substantially less for cattle fed 3-NOP compared with control cattle (Fig. 5).
- Hydrogen production and yield increased (P < 0.001) with the level of 3-NOP inclusion in the diet, with period (P < 0.001) and treatment × period interactions (P ≤ 0.004) effects (Table 4).
- Rumen fermentation was altered by 3-NOP supplementation. Total VFA concentration tended (P = 0.060) to be affected by 3-NOP supplementation, with a slight decrease for the medium dose.
- Molar proportion of acetate was less (P < 0.001) for cattle fed 3-NOP compared with control, while molar proportion of propionate only tended (P = 0.059) to be greater for cattle receiving 3-NOP supplementation.
- Isobutyrate was greater (P = 0.001) for medium and high doses of 3-NOP, but there was no treatment effect on butyrate, valerate, isovalerate, or caproate (P > 0.115).
- Acetate:propionate ratio was 30.5% less (P = 0.045) for low and medium doses compared with control.
Other Important Findings
- The study indicates that supplementation of corn-based finishing diets with 3-NOP using a medium dose is an effective CH4 mitigation strategy for commercial beef feedlots.
- The low dose decreased in efficacy from 59% decrease in periods 1 and 2, to 37% decrease in period 3, while efficacy of the medium and high doses remained consistent over time.
- The diurnal pattern of CH4 emissions that occurred post-morning feeding was not evident when cattle were fed 3-NOP.
- The average diurnal pattern of H2 production by treatment (Fig. 6) generally followed a pattern similar to that of CH4 production (Fig. 5).
- The observed decrease in CH4 yield as affected by dose in the present study was assessed relative to the literature for beef cattle fed high grain diets supplemented with 3-NOP (Fig. 3).
- For all treatments there was large variation in CH4 production (g/d) among animals (Fig. 4), with an average coefficient of variation (cv) of 19.9%, 78.1%, 39.6% and 85.4% for the control, low, medium and high treatments, respectively.
Limitations Noted in the Document
- The levels of 3-NOP in the final diets consumed (basal diet + pellets) were expected to be less than the concentrations of 3-NOP in the basal diet alone.
- The reason for the lack of response to 3-NOP in the study by Kim et al. (2019) is not clear, but may relate to the type of grain fed (corn versus barley) and the degree of processing (whole versus processed).
- In addition, only a small number of animals (n = 9) was used in the study of Kim et al. (2019), which was a replicated 3 × 3 Latin Square design with limited emission measurements taken over 3 days.
- The efficacy of 3-NOP for CH4 reduction declined for the low dose in period 3 indicating a possible rumen adaptation at low levels of supplementation.
Conclusion
The study’s findings highlight the potential of 3-NOP, particularly at a medium dose, in reducing methane emissions in feedlot cattle. The 76% reduction in CH4 yield with the medium dose underscores its effectiveness as a mitigation strategy. The study’s conclusions emphasize the need for further research to determine the optimum dose of 3-NOP for performance and carcass characteristics of feedlot cattle. The study’s results suggests that the medium dose of 3-NOP is the most effective. The decrease in CH4 yield with 3-NOP supplementation is supported by previous research. However, the variation in individual animal responses and the decline in efficacy of the low dose over time point to the need for a more nuanced understanding of 3-NOP’s effects. The study’s focus on commercial feedlot conditions enhances the applicability of its findings to real-world scenarios. The observed increase in hydrogen emissions and the shift in rumen fermentation patterns suggest the involvement of alternative hydrogen-utilizing pathways. These findings contribute to the growing body of knowledge on strategies to reduce the environmental impact of beef production, and suggest that further studies are needed.