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The hand-held laser methane detector (LMD) technique has been suggested as an alternative method for measuring methane (CH4) emissions from enteric fermentation of ruminants in the field. This study aimed to establish a standard procedure for using LMD to assess CH4 production in cattle and evaluate the efficacy of the protocol to detect differences in CH4 emissions from cattle fed with diets of different forage-to-concentrate (FC) ratios. Experiment 1 was conducted with four Hanwoo steers (584 ± 57.4 kg body weight [BW]) individually housed in metabolic cages. The LMD was installed on a tripod aimed at the animal's nostril, and the CH4 concentration in the exhaled gas was measured for 6 min every hour for 2 consecutive days. For the data processing, the CH4 concentration peaks were identified by the automatic multi-scale peak detection algorithm. The peaks were then separated into those from respiration and eructation by fitting combinations of two of the four distribution functions (normal, log-normal, gamma, and Weibull) using the mixdist R package. In addition, the most appropriate time and number of consecutive measurements to represent the daily average CH4 concentration were determined. In experiment 2, 30 Hanwoo growing steers (343 ± 24.6 kg BW), blocked by BW, were randomly divided into three groups. Three different diets were provided to each group: high FC ratio (35:65) with low-energy concentrate (HFC-LEC), high FC ratio with high-energy concentrate (HFC-HEC), and low FC ratio (25:75) with high-energy concentrate (LFC-HEC). After 10 d of feeding the diets, the CH4 concentrations for all steers were measured and analyzed in duplicate according to the protocol established in experiment 1. In experiment 1, the mean correlation coefficient between the CH4 concentration from respiration and eructation was highest when a combination of two normal distributions was assumed (r = 0.79). The most appropriate measurement times were as follows: 2 h and 1 h before, and 1 h and 2 h after morning feeding. Compared with LFC-HEC, HFC-LEC showed 49% and 57% higher CH4 concentrations in exhaled gas from respiration and eructation (P < 0.01). In conclusion, the LMD method can be applied to evaluate differences in CH4 emissions in cattle using the protocol established in this study., (© The Author(s) 2022. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

Simple Summary: This study investigated the effect of varying the levels of dietary crude protein (CP) in concentrate mixes on growth performance, rumen characteristics, digestibility, blood metabolites, and methane emissions in fattening Hanwoo steers. The experiment was conducted for 12 weeks by feeding four concentrate mixes with different levels of dietary CP (15, 18, 19, and 21% of CP dry matter basis). There was a linear increasing trend in the average daily gain (ADG) with increasing dietary CP (p = 0.066). The increase in CP levels also influenced the characteristics of the rumen fluid, leading to increased concentrations of rumen ammonia and an increase in the proportion of butyrate and valerate (p < 0.05) while decreasing the propionate proportion (p = 0.004). The blood urea increased (p < 0.001) and the blood non-esterified fatty acids and cholesterol decreased (p ≤ 0.003) as the dietary CP increased. The methane concentration from eructation per intake (ppm/kg), forage neutral detergent fiber (NDF) intake, total NDF intake, and ADG exhibited linear decreases (p ≤ 0.014) across diets. In summary, increasing the dietary CP to 21% in concentrates tended to increase the ADG, reduce the propionate, and increase the butyrate. The methane from eructation showed a tendency to linearly decrease with higher CP. This study aimed to investigate the effect of varying levels of dietary crude protein (CP) on growth performance, rumen characteristics, blood metabolites, and methane emissions in fattening Hanwoo steers. Twenty-four steers, weighing 504 ± 33.0 kg (16 months old), were assigned to four dietary treatments with different CP concentrations (15, 18, 19, and 21% of CP on a dry matter (DM) basis). A linear increasing trend in the average daily gain (ADG) was observed (p = 0.066). With increased dietary CP levels, the rumen ammonia concentration significantly increased (p < 0.001), while the propionate proportion linearly decreased (p = 0.004) and the proportions of butyrate and valerate linearly increased (p ≤ 0.003). The blood urea exhibited a linear increase (p < 0.001), whereas the blood non-esterified fatty acids and cholesterol showed a linear decrease (p ≤ 0.003) with increasing dietary CP. The methane concentration from eructation per intake (ppm/kg), forage neutral detergent fiber (NDF) intake, total NDF intake, and ADG exhibited linear decreases (p ≤ 0.014) across the treatments. In conclusion, increasing the dietary CP up to 21% in concentrates demonstrated a tendency to linearly increase the ADG and significantly decrease the propionate while increasing the butyrate. The methane concentration from eructation exhibited a tendency to linearly decrease with increasing dietary CP. [ABSTRACT FROM AUTHOR]

Simple Summary: This study investigated the effect of varying levels of dietary fat in concentrate mixes on growth performance, rumen characteristics, digestibility, blood metabolites, and methane emissions in growing Hanwoo steers. The experiment was conducted for 12 weeks by feeding three concentrate mixes with different levels of dietary fat (i.e., 48, 74, 99 g/kg dry matter [DM] of concentrate mix). Increasing fat levels in the concentrate mix significantly reduced the intake of concentrate mix (p < 0.01); however, there were no significant adverse effects on the growth rate, feed efficiency, and digestibility (p > 0.05). Increasing fat levels also affected the characteristics of rumen fluid, increasing the proportion of propionate (p < 0.01) and decreasing the proportion of butyrate and acetate to propionate in the total volatile fatty acids (p < 0.01). Cholesterol in blood serum increased significantly with increasing fat levels (p < 0.01). The highest fat level showed 18% lower methane concentration in exhaled gas from eructation than the lowest (basal) fat level (p < 0.05). In conclusion, increasing the fat level up to 100 g/kg DM in the concentrate mix reduced methane concentration in the exhaled gas from eructation without altering growth performance in growing Hanwoo steers. This study investigated the effect of different dietary fat levels in concentrate mixes on the growth performance, rumen characteristics, digestibility, blood metabolites, and methane emissions in growing Hanwoo steers. Thirty steers (386 ± 24.6 kg of body weight [BW]; 12 months old), blocked by BW, were randomly assigned to three dietary treatments with varying fat concentrations in concentrate mix (48, 74, and 99 g of ether extract per kg dry matte [DM]). The fat intake of the low-fat treatment represented 4.15% of the total dry matter intake (DMI), while the medium- and high-fat treatments accounted for 5.77% and 7.23% of total DMI, respectively. Concentrate mix DMI decreased with increasing fat level (p < 0.01). The growth rate and digestibility did not significantly differ based on the fat level (p > 0.05). As the fat level increased, propionate in the total ruminal volatile fatty acids increased, and butyrate and acetate-to-propionate decreased (p < 0.01). Cholesterol in blood serum increased significantly with increasing dietary fat levels (p < 0.01). Methane emissions exhibited a linear decrease with increasing fat level (p < 0.05). In conclusion, elevating fat content in the concentrates up to 100 g/kg DM reduced methane emissions without compromising the growth performance of growing Hanwoo steers. [ABSTRACT FROM AUTHOR]