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The addition of methane-reducing compounds (MRCs) to livestock drinking water presents an alternative method for enteric methane mitigation in extensive systems where these compounds cannot be fed through the diet. This work evaluated several such compounds with the potential to be deployed in this manner. Methane-reducing compounds were selected based on the existing literature and likelihood of dissolution when combined with a commercially available water-based nutrient supplement (uPRO) (uPRO ORANGE®, DIT AgTech, QLD, Australia). This, in turn, would demonstrate the capacity for MRCs to be administered through animal drinking water when such supplements are in use. This technique requires the analysis of MRC solubility and stability in solution, which was completed via Fourier transform infrared-attenuated total reflectance spectroscopy. The uPRO supplement is comprised of urea, urea phosphate, and ammonium sulfate, providing nitrogen, phosphorus, and sulfur—limiting nutrients for ruminants grazing extensive systems during drier periods of the year. Accordingly, medium-quality Rhodes grass hay was used in fermentation runs to simulate a basal diet during the dry season. Methane-reducing compounds were assessed in accordance with each variable measured (gas/methane production, dry matter digestibility, stability under different environmental conditions) along with existing research in the field to determine the most suitable compound for co-administration. Whilst most compounds examined in this study appeared to retain their structure in solution with uPRO, fermentation results varied in terms of successful methane mitigation. The additive Agolin Ruminant L emerged as the most promising compound for further in vivo investigation. [ABSTRACT FROM AUTHOR]

In grazing systems in Northern Australia, crude protein (CP) and phosphorus (P) availability varies, affecting ruminant production due to voluntary reduced intake and therefore body weight (BW) gain. We were interested in understanding metabolic regulation in this model system, both in terms of a) identifying key tissues, and b) detecting any modifications in mitochondrial physiology, given the central role of this organelle in bioenergetic homeostasis. Merino wethers (n = 24) were subjected to three dietary regimens: High CP, High P, (Control), Low CP, Low P (Deficient), and High CP, High P, with restricted feed intake (Restricted). Mitochondrial DNA (mtDNA) copy numbers, indicative of mitochondrial content, were measured via qPCR. Transcriptomic analyses through RNA sequencing targeted mitochondriaassociated gene expression changes and pathways, using the MitoCarta 3.0 database. There was a significant decrease of mtDNA copy numbers in the liver of sheep under either Deficient and Restricted diets (P < 0.01), with as much as a 2-fold difference between the Control and Deficient diets. This may suggest reduced mitochondrial biogenesis as an adaptation to decreased energy intake. When compared with the Control group, both the Deficient and Restricted groups upregulated pathways related to vitamin metabolism (Log2FC: 0.231 and 0.449) and folate and 1-C metabolism (Log2FC: 0.409 and 0.706). However, impacted pathways shared between these two comparisons (Control v Deficient, Control v Restricted) also include choline and betaine metabolism, amino acid metabolism, and glycine metabolism, which suggests similar mechanisms being impacted by decreased energy intake, regardless of whether it is due to satiety from nutrient deficiency or restricted feed intake. Notably, the creatine metabolism pathway was uniquely upregulated in the Restricted group compared with the Deficient group (Log2FC: 0.114), although the CKMT2 gene was upregulated in the Restricted group compared with both the Control and Deficient group (Log2FC: 1.30 and 0.879). Additionally, the SLC25A family pathway, responsible for mitochondrial metabolite transport, was found to be upregulated in the Restricted group when compared with both Control and Deficient groups (Log2FC: 0.33 and 0.865). Overall, this study demonstrated a pronounced decrease in mitochondrial content in the liver of growing Merino wethers subjected to nutritional deficiencies and feed restriction. Multiple metabolic pathways were shared between the comparisons of the Control diet group to both Deficient and Restricted nutritional treatments. However, the SLC25A transporter family pathway was uniquely upregulated in the Restricted group compared with either an optimal or deficient diet. The regulation of these metabolic pathways is a subject of further study that may represent a systemic response to maintain homeostasis while undergoing significantly lower energy intake, with implications for animal growth, tissue deposition, and energetic maintenance. Understanding distinctions in the response to feed restriction and nutrient deficiency induced reduction in intake may help improve production strategies for ruminants grazing in these conditions. [ABSTRACT FROM AUTHOR]

Two experiments were conducted to determine the potential for the essential oil blend Agolin Ruminant L (Agolin) to reduce enteric methane (CH4) emissions from beef cattle when delivered via the drinking water. Experiment 1 evaluated aqueous solutions of Agolin (50 mg/L) and a non-protein nitrogen and mineral solution (uPRO ORANGE [uPRO]; 1.7 mL/L) individually and in combination, where Agolin was added to concentrated uPRO at 3, 4.5, 6% Agolin (w/w) prior to dilution with water at 1.7 mL/L, for a total of five treatments. These were incubated for 48 h with a medium-quality Rhodes grass (Chloris gayana) hay substrate, with gas production, CH4 concentration in gas, and digestibility measured in vitro. In Exp. 2, Droughtmaster steers (n = 24) were fed a basal diet of Rhodes grass hay and were allocated to one of three water treatments (n = 8/treatment) supplemented with either uPRO (2.27 mL uPRO/L water), or one of two inclusion rates of Agolin in combination with uPRO (2.27 mL uPRO and 6 µL Agolin/L water or 2.27 mL uPRO and 24 µL Agolin/L water) with enteric CH4 emissions, feed and water intake, and live weight gain (LWG) measured over 56 d. In Exp. 1, the inclusion of Agolin in uPRO at 6% w/w resulted in a reduction in CH4 production (15.8%; P = 0.003) and the proportion of CH4 in the gas produced (24.5%; P < 0.001). In Exp. 2, steers consuming the lower quantity of Agolin via drinking water had a 16.4% (P = 0.0027) reduction in CH4 production over the experiment, declining from 140 g/d during week 1 to 117 g/d in week 8. This inclusion rate of Agolin in the drinking water also resulted in a 25 g (17.6%) CH4/d decrease in emissions by steers compared to control steers (P = 0.0205). However, no significant differences in CH4 yield (g CH4/kg dry matter intake), or CH4 intensity (g CH4/kg LWG) by steers was observed between treatments. These results demonstrate that Agolin reduces CH4 emissions when mixed in aqueous solution under in vitro and in vivo conditions, providing a potential method to reduce enteric CH4 emissions from cattle in extensive production systems., (© The Author(s) 2024. Published by Oxford University Press on behalf of the American Society of Animal Science.)