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Ruminants produce one-third of the anthropogenic methane ( CH 4 ) emissions worldwide, and 47% of the CH 4 emissions result from ruminants under grazing conditions. However, there is limited information regarding the appropriate number of visits to accurately determine enteric CH 4 emissions using the automated head-chamber system ( AHCS ) from growing beef cattle under intensive grazing conditions. Data from one experiment were analyzed to determine the number of visits to assess gas flux (CH 4 , carbon dioxide [ CO 2 ], and oxygen [ O 2 ]) from Angus-crossbreed steers grazing in a pivot-irrigated improved pasture. A total of 110 steers (324 ± 37.3 kg initial body weight) were selected and divided into two blocks. Steers were under intensive grazing management for 84 d. Depending on forage availability, steers were rotated at 2- to 4-d intervals. Pastures were predominately composed of cool-season forages. Two different databases using the same animals ( n  = 16) were defined to calculate the gas flux using the first 100 visits to an AHCS with 2 or more or 3 or more minutes of visitation length. The mean gas flux was estimated as the average for increasing (forward) or decreasing (reverse) the gas flux of 5-visit intervals starting with the first or the last 5 visits and increasing or decreasing until the full 100-visit dataset was utilized, respectively. Spearman and Pearson correlations were computed between the maximum visits and each shortened visit interval. Concurrently, the residual variance and the residual variance change were determined for each interval by fitting a mixed model. The minimum number of visits was defined when correlations with the total visits were greater than 0.95, and the residual variance was stabilized. The results indicated that the minimum number of visits needed to determine CH 4 production varied between 45 and 70, while CO 2 production and O 2 consumption varied between 45 and 50 according to the visitation length. Additionally, steers that visited the AHCS for 2 or more minutes in visit duration required a greater number of visits than those that visited for 3 or more minutes. Thus, based on the average daily visitation in this experiment (1.4 visit/d), the assessment of CH 4 emissions requires 32 d, while CO 2 production and O 2 consumption require between 32 and 36 d using 3 or more minutes of visit length from growing steers under intensive grazing conditions., Competing Interests: None declared., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science.)

Non-protein nitrogen ( NPN ) supplements improve animal performance in backgrounding diets. However, there is scarce information regarding the effect of different NPN sources and combinations on ruminal fermentation profile. The current study aimed to evaluate the effect of different NPN sources and their combinations on in vitro fermentation, microbial N synthesis, and methane (CH 4 ) production in a backgrounding diet. Incubations were conducted on three separate days for 24 h using corn silage and cotton gin byproduct (70% and 30% of DM, respectively) as substrate. Treatments were control (without NPN), urea, and five different proportions of urea-biuret and nitrate (100:0, 75:25, 50:50, 25:75, and 0:100). Each treatment, except control, was formulated to be isonitrogenous and equivalent to 1% urea inclusion. Ruminal fluid was collected from two ruminally cannulated Angus crossbred steers fed ad libitum corn silage and cotton gin byproduct plus 100 g of a urea-biuret-nitrate mixture. The concentration of volatile fatty acids ( VFAs ) and ammonia nitrogen ( NH 3 -N ) were determined at 12 and 24 h of incubation. Final pH, in vitro dry and organic matter digestibility, total gas production, and concentration of CH 4 were determined at 24 h. The supplementation of NPN increased ( P  < 0.05) the concentration of NH 3 -N at 12 and 24 h. Although NPN supplementation increased ( P  < 0.05) the concentration of total VFA and acetate at 12 h, treatments did not differ ( P  > 0.05) at 24 h. Supplementation of NPN increased ( P  < 0.05) the proportion of acetate at 12 and 24 h but tended to reduce ( P  = 0.054) the proportion of propionate only at 12 h. Digestibility and pH were not different ( P  > 0.05) among treatments. Increasing nitrates in the NPN supplement increased ( P  < 0.05) the proportion of acetate and reduced ( P  < 0.05) the proportion of butyrate at 12 and 24 h. The supplementation of NPN increased ( P  < 0.05) microbial N synthesis. Furthermore, increasing nitrate proportion in the NPN supplement increased ( P  < 0.05) the microbial N synthesis and efficiency of N use. Supplementation of NPN did not modify ( P  > 0.05) total gas or CH 4 production. However, increasing nitrate proportion in the NPN supplement linearly reduced ( P  < 0.05) CH 4 production. Supplementation of NPN increased NH 3 -N concentration and microbial N while increasing the inclusion of nitrate decreased the production of CH 4 and increased the microbial N synthesis in a corn silage-based substrate under in vitro conditions., Competing Interests: Isabel Ruiz-Ascacibar works in the R&D department of YARA Industrial Solutions. The other authors declare no real or perceived conflicts of interest., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science.)

Data from three experiments was analyzed to determine the number of visits and days to assess gas flux (CH 4 , CO 2 , and O 2 ), dry matter intake (DMI), and average daily gain (ADG) from growing animals under confined conditions. In experiment 1, 213 animals (461 ± 91 kg initial body weight [BW]) were fed a backgrounding diet and evaluated for 60 d. In experiment 2, 169 steers (488 ± 37 kg initial BW) were fed a finishing diet and assessed for 70 d. In experiment 3, 64 steers (514 ± 42 kg initial BW) were fed a finishing diet and evaluated for 80 d. In each experiment, animals were placed in one pen with one Greenfeed and five SmartFeeds to collect gas flux and feed intake simultaneously. Gas flux was analyzed using data from 161 animals from the three experiments with 100 visits for 2 or more min or 3 or more min. Also, metabolic heat production (MHP) was estimated using the individual gas flux. Daily DMI was calculated as the daily feed intake corrected by the dry matter concentration. ADG was computed as the slope of the regression of the shrunk BW (96% BW) throughout each of the experimental periods. The mean gas flux and MHP were estimated for increasing or decreasing 5-visit intervals starting with the first or the last 5 visits and increasing or decreasing until the full 100-visit dataset was utilized, respectively. Intervals of DMI were estimated for increasing or decreasing 5-d intervals starting with the first or the last 5 d and increasing or decreasing until the end of the experimental period, respectively. Intervals of ADG were estimated for increasing or decreasing measurement period intervals until the end of the experimental period, respectively. Pearson and Spearman correlations were computed between the maximum visits or days and each shortened visit or day interval. The minimum number of visits and days was determined when correlations with the total visits were greater than 0.95. The results indicated that the minimum number of visits needed to quantify CO 2 , O 2 , and MHP accurately was 40, while CH 4 was 60. A visitation length of 2 min or more or 3 min or more did not modify the gas flux determination. Thus, based on the average daily visitation in these experiments, gas flux data could be collected for 25 d. Additionally, the required days to determine DMI was 30, while ADG could not be assessed in a shorter than 60-d period., Competing Interests: The authors declare no real or perceived conflicts of interest., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science.)