The laser methane detector (LMD) has been proposed as a method to characterize enteric methane (CH₄) emissions from animals in a natural environment. To validate LMD use, its CH₄ outputs (LMD-CH₄), were compared against CH₄ measured with respiration chambers (chamber-CH₄). The LMD was used to measure CH₄ concentration (µL/L) in the exhaled air of 24 lactating ewes and 72 finishing steers. In ewes, LMD was used on 1 d for each ewe, for 2-min periods at 5 hourly observation periods (P1 to P5, respectively) after feeding. In steers fed either low- or high-concentrate diets, LMD was used once daily for a 4-min period for 3 d. The week after LMD-CH₄ measurement, ewes or steers entered respiration chambers to quantify daily CH₄ output (g/d). The LMD outputs consisted of periodic events of high CH₄ concentrations superimposed on a background of oscillating lower CH₄ concentrations. The high CH₄ events were attributed to eructation and the lower background CH₄ to respiration. After fitting a double normal distribution to the data set, a threshold of 99% of probability of the lower distribution was used to separate respiration from eructation events. The correlation between mean LMD-CH₄ and chamber-CH₄ was not high, and only improved correlations were observed after data were separated in 2 levels. In ewes, a model with LMD and DMI (adjusted R² = 0.92) improved the relationship between DMI and chamber-CH₄ alone (adjusted R² = 0.79) and between LMD and chamber-CH₄ alone (adjusted R² = 0.86). In both experiments, chamber-CH₄ was best explained by models with length of eructation events (time) and maximum values of CH₄ concentration during respiration events (µL/L; P < 0.01). Correlation between methods differed between observation periods, indicating the best results of the LMD were observed from 3 to 5 h after feeding. Given the short time and ease of use of LMD, there is potential for its commercial application and field-based studies. Although good indicators of quantity of CH₄ were obtained with respiration and eructation CH₄, the method needed to separate the data into high and low levels of CH₄ was not simple to apply in practice. Further assessment of the LMD should be performed in relation to animal feeding behavior and physiology to validate assumptions of eructation and respiration levels, and other sources of variation should be tested (i.e., micrometeorology) to better investigate its potential application for CH₄ testing in outdoor conditions. Copyright © 2014. American Society of Animal Science .

A modeling study based on a dataset from a large-scale grazing study was used to identify the potential impact of grazing behavior and performance of diverse cow genotypes on predicted methane (CH₄) emissions. Lactating cows grazing extensive seminatural grassland and heath vegetation were monitored with Global Positioning System collars and activity sensors. The diet selected by cows of 3 different genotypes, Aberdeen Angus cross Limousin (AxL), Charolais (CHA), and Luing (LUI), was simulated by matching their locations during active periods with hill vegetation maps. Measured performance and activity were used to predict energy requirements, DMI, and CH₄ output. The cumulative effect of actual performance, diet selection, and actual physical activity on potential CH₄ output and yield was estimated. Sensitivity analyses were performed for the digestibility of intake, energy cost of activity, proportion of milk consumed by calves, and reproductive efficiency. Although with a better performance (P < 0.05), LUI required less total energy than the other genotypes (P < 0.001) as the other 2 spent more energy for maintenance (P < 0.001) and activity (P < 0.001). By selecting a better quality diet (P < 0.03), estimated CH₄ of CHA cow–calf pairs was lower than AxL (P = 0.001) and slightly lower than LUI (P = 0.08). Energy lost as CH₄ was 0.17 and 0.58% lower for LUI than AxL and CHA (P < 0.002). This study suggests for the first time that measured activity has a major impact on estimated CH₄ outputs. A 15% difference of the cow–calf pair CH₄ was estimated when using different coefficients to convert actual activity into energy. Predicted CH₄ was highly sensitive to small changes in diet quality, suggesting the relative importance of diet selection on heterogeneous rangelands. Extending these results to a farm systems scale, CH₄ outputs were also highly sensitive to reductions in weaning rates, illustrating the impact on CH₄ at the farm-system level of using poorly adapted genotypes on habitats where their performances may be compromised. This paper demonstrates that variations in grazing behavior and grazing choice have a potentially large impact on CH₄ emissions, illustrating the importance of including these factors in calculating realistic national and global estimates. Copyright © 2014. American Society of Animal Science .

Including soybean hulls (SH) in ruminant diets increase the carbon circularity of livestock systems. We evaluated whether SH could partially replace corn grain (CG) in the diet of lactating cows (≈7.5% of the total diet). Six Holstein multiparous cows were fed a 50:50 (dry matter basis) corn-silage to concentrate diet for two 25-day periods in three replicated 2 × 2 Latin Squares using linear mixed models. Feed intake, milk yield and composition, N excretion, CH₄ production, and ruminal microbial profiles were measured. Enteric CH₄ was measured in respiration chambers. The DMI of cows fed SH (28 kg DM/d) was greater (p = 0.034) than those fed CG (26 kg DM/d), but no differences were observed in milk production (p = 0.557) or enteric CH₄ emission intensity (g/kg milk, p = 0.387). Enteric CH₄ emissions tended to be greater in SH-fed cows (484 g/d) than CG-fed cows (456 g/d; p = 0.075), and N excretion was significantly greater in SH than CG cows (p < 0.001). No mayor shifts in ruminal microbiota or overall ruminal environment were observed. In conclusion, SH can partially replace CG in diets of lactating dairy cows without affecting production, but potential negative environmental impacts should be considered.

While livestock production is a significant source of greenhouse gas emissions, it remains vital for fulfilling the growing global demand for animal protein. Including by-products in ruminant diets can enhance food circularity and reduce competition for human food, while also increasing the likelihood of reducing methane (CH₄) emissions. This study aimed to evaluate the impact of fully replacing corn grain and urea in the control diet with local by-products, specifically corn distillers’ grains combined with either barley brewed grains or with wheat middlings, on enteric CH₄ emissions and performance of sheep. Diets were balanced to be isoproteic and isoenergetic with 2.6 Mcal ME/kg of dry matter (DM) and 160 g crude protein/kg DM, respectively. Corn silage is the only source of forage in the diet, and the forage-to-concentrate ratio was maintained to 60:40 on a DM basis. Twelve Highlander female sheep of 35.9 ± 3.12 kg initial body weight (BW, mean ± standard deviation), were used in a Completely Randomized Block design, with four sheep per treatment and two measurement periods under the same treatment. Experiment lasted 60 d, 30 d acclimatization and 30 d measurements. Dry matter intake (DMI) was restricted to 2.5% of BW. Enteric CH₄ emissions of individual sheep were quantified in respiration chambers over a 48 h period. Dietary treatments did not have a significant effect either on DMI or BW gain. The diet containing barley brewed grains significantly reduced total daily CH₄ production by 22.3%, CH₄ emissions per kg of DMI by 34% and energy loss as CH₄ by 38% compared to the control diet. In conclusion, the agro-industrial by-products combinations evaluated in this study effectively replaced corn grain and urea without compromising feed intake or animal performance. Additionally, the diet containing barley brewed grains significantly reduced CH₄ yield, and energy loss compared to the control diet.

Grass-based beef cattle systems have limited opportunities to adopt novel input-based greenhouse gas (GHG) mitigation options. Furthermore, these systems are highly susceptible to extreme weather events, triggering large fluctuations in the quality and quantity of forage supplies. Early weaning is a common management practice used in grazing beef cattle systems, a climate change adaptation measure to reduce economic and productivity risks. However, there is little information regarding its impact on GHG emissions intensity at the farm level in complete beef cattle operations. This study aimed to compare early versus traditional weaning on GHG emissions intensity of a complete beef cattle operation from the southeastern Pampas region of Argentina. The total GHG emissions, productivity, and GHG emissions intensity were estimated based on IPCC Tier 2, considering on-farm and off-farm GHG embedded emissions of inputs. Two production systems with alternative weaning management (early vs. traditional) were modeled based on observed animal performance under actual field conditions along with data from the literature. Early weaning reduced total GHG emissions by 10%, beef production by 3%, and GHG emissions intensity of the production system by 8%. Results suggest that early weaning, a useful management practice during extreme weather events, can reduce GHG emissions in grass-based beef production systems.