This study evaluated the effects of including fodder beet or swedes in a grass silage–fresh grass–concentrate diet on performance, rumen metabolism, nitrogen (N) excretion, selected health indicators, and profitability of early‑lactation dairy cows. Twelve multiparous Holstein‑Friesian cows (560 ± 22 kg BW; 30.0 ± 3.9 kg/d MY; 60 ± 11 DIM) were assigned to three diets in a replicated 3 × 3 Latin square: Control (CON; grass silage, fresh ryegrass, concentrate, ground corn and soybean meal), CON with 40% DM replaced by fodder beet (C-FB) or by swedes (C-Sw). Measurements included feed intake, feeding behaviour, milk yield and composition, rumen pH and volatile fatty acids (VFA), total N balance (intake, milk, faeces, urine), selected blood metabolites and income over feed cost. Total DMI, milk and energy‑corrected milk yields did not differ among treatments, whereas C-FB tended to increase milk crude protein concentration compared with CON, with C-Sw intermediate. Inclusion of both fodder crops in the diet increased ruminal butyrate molar proportion and reduced the proportion of branched‑chain VFA compared with CON, without affecting mean rumen pH, which remained ≥ 5.8 in all treatments. Swedes and fodder beet inclusion reduced ruminal NH₃ and milk urea concentrations, but only fodder beet improved nitrogen use efficiency. Haematology values and liver enzymes remained within physiological ranges in all treatments. Both C-FB and C-Sw reduced feeding cost per cow per day, and C-FB and C-SW increased income over feed cost relative to CON. Overall, inclusion of swedes or fodder beet at 40% of dietary DM maintained productive performance and improved profitability without evidence of adverse short-term health effects. Nevertheless, further long-term studies are required to evaluate the implications of the negative nitrogen balance observed in C-FB cows.

Reducing methane emissions from dairy goat production is essential for meeting sustainability targets and consumer expectations. Accurate quantification of enteric methane per unit of feed intake is a prerequisite for developing emission inventories and mitigation strategies. This pilot study developed and validated a methodology for measuring methane emissions from dairy goats using respiration chambers originally designed for cattle. Ten nonlactating Saanen dairy goats (mean +/- standard deviation liveweight: 63 +/- 9 kg) were group-housed for 2 days and, then paired and housed in small pens for 9 days to adapt to the diet and environment. They were fed pasture silage ad libitum, supplemented with 200 g of maize grain daily. Four pairs were selected for methane measurements in cattle chambers following a 2-day acclimation period. Methane emissions were recorded over 48 h at an airflow rate of 756 L/min. The mean methane yield was 22.9 +/- 1.4 g/kg dry matter intake, consistent with values reported for sheep and cattle. Power analysis indicated that six pairs per treatment group are required to detect a 10% difference in methane yield with 80% power. These findings establish a validated protocol for using cattle respiration chambers to measure methane emissions from dairy goats.

Dietary approaches that decrease ruminal pH may be combined with anti-methanogenic feed additives that prevent methane formation and consequently increase the dissolved hydrogen concentration. To evaluate the effect of pH and the effect of dissolved hydrogen concentration, two forages (forage rape and ryegrass) were incubated in vitro at two forage levels (FL 1% and 2% w/v) with or without bromoform (3 & micro;M). The combination of bromoform and FL 2% did not affect gas production or fermented hexose equivalents compared to both factors tested separately. The ratio of acetate-to-reduced products decreased greatly by combining FL 2% and bromoform (0.59 mmol.g-1/mmol.g-1) compared to FL 1% and bromoform (0.79 mmol.g-1/mmol.g-1). The production of reduced products increased by a similar proportion to the decrease in acetate. Ryegrass fermentation decreased by 8% with bromoform addition, while the forage rape fermentation was not impaired, even though the hydrogen released from forage rape (43.5 ml/g) was twice that released from ryegrass (21.5 ml/g). Results suggest that the combination of low pH and high hydrogen (achieved by 2% FL and bromoform addition) did not cause detrimental effects on feed fermentation in vitro, but ryegrass fermentation may be impacted by high dissolved hydrogen.

Fodder beet (FB; Beta vulgaris L.) is increasingly used in ruminant production systems, particularly in New Zealand. Its high content of readily fermentable carbohydrates and low crude protein content may reduce enteric methane emissions and nitrogen excretion when included in ruminant diets, provided that animal health and livestock performance are maintained. This study evaluated the effects of replacing pasture [a mixture of perennial ryegrass (Lolium perenne L.) and white clover (Trifolium repens L.)] with FB (1:1 on a dry matter basis, without rebalancing diets to equalise crude protein) on methane emissions and nitrogen partitioning in sheep. Thirty-two 12-month-old male sheep (mean liveweight 40 +/- 1.2 kg) were allocated to either an FB-based or a pasture diet (n = 16 each) and fed at 1.6 times their metabolisable energy requirements. Methane emissions (n = 12 each) were measured in respiration chambers in two experiments. Diets for the FB group contained 75% FB bulbs and 25% pasture (dry matter basis) in Experiment 1, and 90% FB and 10% pasture in Experiment 2. The 75% FB diet had greater digestibility and metabolisable energy value than pasture (n = 6 each; P < 0.05). Methane yield (g/kg dry matter intake) did not differ between the 75% FB and pasture diets, but was 13-16% lower when expressed per unit of digestible dry or organic matter. When FB formed 90% of the diet, methane yield decreased by over 60% (P < 0.05), but the abundance of rumen bacteria associated with acidosis increased. Feeding 75% FB reduced nitrogen intake, urinary nitrogen excretion, and microbial protein production, and altered rumen microbiota, with increased Sharpea and decreased Ruminococcus. While FB can reduce environmental emissions at the animal level, its inclusion should not exceed 75% of the dietary dry matter, and adequate protein supplementation is required to maintain rumen health and nutritional balance. Further research under grazing conditions is needed to confirm these findings and establish practical feeding guidelines.

Bromoform, a bioactive compound in certain seaweeds, has gained attention for its methane-mitigating effects in ruminants. Research is underway to use synthetic bromoform as an alternative for providing consistent and predictable dosing of the bioactive compound, but its inherent volatility and liquid form limit its application. To address these challenges, an investigational feed additive (IFA) in the form of a powder containing synthetic bromoform has been developed by Rumin8 Pty Ltd., West Perth, WA, Australia. The objective of this study was to evaluate the effect of the Rumin8 IFA on methane emissions from cattle fed fresh pasture. Sixteen 18-month-old Hereford × Friesian heifers (427 ± 11 kg; mean ± SD) were stratified by weight and randomly allocated to control and treatment groups using a randomised block design. Treatments included IFA doses at 100, 300, or 500 mg/d of bromoform per heifer, plus a placebo control. The heifers were fed fresh pasture twice daily with a total feed allowance set at a level of 1.6 to 1.8 times their maintenance energy requirements with 800 g of dried distiller's grain pellets containing treatments or placebo before each meal. After 16 d, the heifers' methane emissions were measured in open-circuit respiration chambers for 48 h. The results showed that pasture-fed heifers produced less methane when treated with the bromoform-containing IFA at every dose level (P < 0.05). Reductions of up to 50% in methane emissions were observed in the first 4 h after feeding (P < 0.05). Methane yield declined linearly with bromoform dose (P = 0.001), showing 16% (300 mg) and 24% (500 mg) reductions vs. control (P < 0.05). No treatment effect on feed intake or bromoform accumulation in muscle or fat was observed. In summary, the IFA containing synthetic bromoform significantly reduced methane emissions in pasture-fed heifers, with a clear dose–response relationship, no adverse effect on feed intake, and no detectable residues in muscle or fat. These results have significant implications for reducing the environmental impact of cattle production, offering a practical solution to the challenge of methane emissions in pasture-fed systems where animals have access to supplements.

The agricultural sector is vital for food security and economic well-being, but is a major contributor to global greenhouse gas (GHG) emissions. Within the agricultural sector, reducing emissions from livestock is essential, especially as emissions of enteric methane from ruminants represent a sizable proportion of agricultural methane. Efforts to reduce GHG emissions from livestock systems must balance climate needs with the contribution of the ruminant industries to high-quality food products, which are important for local economies. Improving the efficiency of ruminant production systems is still the most practical way to reduce emissions per unit of food produced. In systems operating at high levels of efficiency, such as those in New Zealand and parts of Latin America, interventions that directly abate emissions at the source (i.e. the rumen) will be required. Feed additives with proven efficacy are becoming available for intensive systems, but their application in grazing systems is limited. The variation between individuals in methane emissions is being exploited to produce low-GHG flocks and herds. Other mitigation options under development, such as anti-methane vaccines, are promising in terms of wider applicability across production systems, but are yet to produce unambiguous evidence of efficacy in animal trials. Future research will need to shift from the discovery of technologies towards determining their long-term efficacy and understanding synergies, co-benefits, and trade-offs.

Milk is a fundamental food matrix that is widely consumed. Milk fat is important for producing dairy products such as butter, cream, cheese and whole milk powder. Aside from flavour, it has been linked to human health and its chemistry can be modulated by various means towards a more healthy fatty acid profile. Industry and stakeholders have different interests in milk fat, based on specific policies which reflect the type of research and funding initiatives currently performed in different countries. This position paper summarizes the current state-of-the-art with regards to milk fat research and industry as well as stakeholder initiatives, and then highlights new developments based on information gathered from North America (United States and Mexico), Europe (United Kingdom, Spain, Italy, and Finland), Africa (Egypt), Asia (China and Bangladesh) and Oceania (New Zealand). South America is an important contributor to the dairy industry but will not be considered here and thus this paper must be considered cross-continental rather than global. This manuscript intends to show a wide 'picture' of milk fat from different angles in different parts of the globe.

Rumen microbiota enable ruminants to grow on fibrous plant materials, but also produce methane, driving 5% of global greenhouse gas emissions and leading to a loss of gross energy content. Methanogenesis inhibitors such as 3-nitrooxypropanol (3-NOP) decrease methane emissions in ruminants when supplemented in feed. Yet we lack a system-wide, species-resolved understanding of how the rumen microbiota remodels following inhibition and how this influences animal production. Here, we conducted a large-scale trial with 51 dairy calves to analyze microbiota responses to 3-NOP, pairing host performance, emissions, and nutritional profiles with genome-resolved metagenomic and metatranscriptomic data. 3-NOP supplementation decreased methane emissions by 62%, modulated short-chain fatty acid and H2 levels, and did not affect dietary intake or animal performance. We created a rumen microbial genome catalogue (27,884 genomes) that mapped to the meta-omic data at high rates. There was a strong reduction of methanogens and stimulation of reductive acetogens, primarily uncultivated lineages such as "Candidatus Faecousia." However, there was a shift in major fermentative communities away from acetate production in response to hydrogen gas accumulation. In vitro incubations recapitulated these results and showed an enrichment of acetate from reductive acetogenesis. Altogether, the divergent responses of the fermentative and hydrogenotrophic communities lead to net hydrogen build-up and limit potential productivity gains from methane reduction. By linking ruminant greenhouse gas emissions and productivity to specific microbial species, this study emphasizes the importance of microbiota-wide analysis for optimizing methane mitigation strategies and identifies promising strategies to simultaneously reduce emissions while increasing animal production.

Plantain (PL) contains plant secondary metabolites (PSM), such as acteoside, aucubin, and catalpol, known for their bioactive properties. While acteoside and aucubin have been linked to reducing nitrogen losses in grazed pastures, their effects on enteric methane (CH4) emissions remain unexplored. Three in vitro batch culture experiments were conducted to assess the effects of PSM on rumen fermentation, using PL pastures with varying PSM concentrations, purified PSM compounds, and/or their combinations added to ryegrass (Lolium perenne, RG), which does not contain these PSM. Aucubin addition to RG extended the time to reach halftime for gas production (GP) and CH4 by 15-20% due to its antimicrobial effects. Acteoside, alone or with aucubin, promoted propionate production, an alternative hydrogen sink, which reduced the acetate to propionate ratio, increased GP by up to 13%, and decreased CH4 proportion in gas by 5-15%. Aucubin reduced ruminal net ammonia (NH3) production by up to 46%, with a similar reduction observed when combined with acteoside. This study highlights the potential of PSM to mitigate CH4 emissions and reduce nitrogen losses from dairy cows, warranting in vivo evaluation of PSM and targeted breeding of PL pastures with increased PSM content.

Context. Plantain (PL) is recognised for reducing nitrate leaching and nitrous oxide emissions in pastoral systems. Evidence has shown that cows fed pure PL produced less methane (CH4) than cows fed ryegrass. However, it is unclear if the CH4 reduction can be achieved with PL in mixed pasture. Aim. The study evaluated the in vitro rumen fermentation profiles of ryegrass-white clover (RWC) and medium-level PL (PLM, containing similar to 40% PL) pasture collected during different climatic seasons, to determine whether this inclusion level influences CH4 and rumen ammonia (NH3) production. Methods. Substrates were selected from samples with various proportions of PL. Samples were categorised into three climatic seasons (i.e. spring, summer and autumn) and two pasture types (PLM and RWC). Representative samples for these scenarios were tested in an automated in vitro rumen batch culture system for gas, CH4 (mL/g DM) and NH3 (mM/g DM) production. Key results. In summer samples, PLM produced approximately 8%, 14% and 19% less CH4 at 12 h, 24 h and potential CH4 production (PCH4), respectively. Although gas production (GP) was similar at 12 and 24 h, PLM had 13% lower potential GP than RWC (P < 0.05). In spring samples, PLM had approximately 11% greater GP and CH4 production at 12 h. For the autumn samples, GP and CH4 production were similar between PLM and RWC (P > 0.05). Net NH3 production from PLM substrates was significantly lower in spring (27%) and autumn (17%) samples, with no differences in summer, despite higher crude protein levels in the selected PLM. Conclusions. Compared with RWC, PLM changed rumen fermentation parameters that could translate to potential environmental benefits: PLM produced less net NH3 in spring and autumn samples (27% and 17%, respectively), and up to 19% less CH4 production in summer samples. Implications. Incorporating similar to 40% PL into RWC pasture showed a promising reduction of CH4 emissions and nitrogen losses in vitro. If the in vitro results translate to cows grazing pasture, this could offer greater environmental benefits with minimal input costs. In vitro results suggest that PLM's potential to mitigate CH4 emissions can be influenced by seasonal variations in pasture quality compared with RWC. However, further animal studies are needed to fully comprehend the CH4 mitigation potential of this forage.

There is a need for rigorous and scientifically-based testing standards for existing and new enteric methane mitigation technologies, including antimethanogenic feed additives (AMFA). The current review provides guidelines for conducting and analyzing data from experiments with ruminants intended to test the antimethanogenic and production effects of feed additives. Recommendations include study design and statistical analysis of the data, dietary effects, associative effect of AMFA with other mitigation strategies, appropriate methods for measuring methane emissions, production and physiological responses to AMFA, and their effects on animal health and product quality. Animal experiments should be planned based on clear hypotheses, and experimental designs must be chosen to best answer the scientific questions asked, with pre-experimental power analysis and robust post-experimental statistical analyses being important requisites. Long-term studies for evaluating AMFA are currently lacking and are highly needed. Experimental conditions should be representative of the production system of interest, so results and conclusions are applicable and practical. Methane-mitigating effects of AMFA may be combined with other mitigation strategies to explore additivity and synergism, as well as trade-offs, including relevant manure emissions, and these need to be studied in appropriately designed experiments. Methane emissions can be successfully measured, and efficacy of AMFA determined, using respiration chambers, the sulfur hexafluoride method, and the GreenFeed system. Other techniques, such as hood and face masks, can also be used in short-term studies, ensuring they do not significantly affect feed intake, feeding behavior, and animal production. For the success of an AMFA, it is critically important that representative animal production data are collected, analyzed, and reported. In addition, evaluating the effects of AMFA on nutrient digestibility, animal physiology, animal health and reproduction, product quality, and how AMFA interact with nutrient composition of the diet is necessary and should be conducted at various stages of the evaluation process. The authors emphasize that enteric methane mitigation claims should not be made until the efficacy of AMFA is confirmed in animal studies designed and conducted considering the guidelines provided herein.

The objective of this study was to determine the effect of including forage rape, chicory, or irrigated pasture in the diet of mid-lactation dairy cows on performance, rumen metabolism and microbiome, milk quality, CH4 emissions and N excretion. Twelve multiparous lactating dairy cows (527 +/- 40 kg BW; 24.8 +/- 2.5 kg /d milk production and 140 +/- 20 DIM at the beginning of the study; mean +/- SD) were randomly allocated to three dietary treatments in a replicated 3 x 3 Latin square design. The treatments were diets based on grass silage and concentrate plus irrigated pasture (IP), chicory (Ch), and forage rape (Fr). The IP diet was composed of 500 g/kg grass silage, 300 g/kg fresh perennial ryegrass irrigated pasture and 200 g/kg commercial grain-based concentrate; the Ch diet was composed of 500 g/kg grass silage, 300 g/kg fresh chicory and 200 g/kg commercial grain-based concentrate; and FR diet composed of 500 g/kg grass silage, 300 g/kg fresh forage rape, 150 g/kg commercial grain-based concentrate and 50 g/kg of soybean meal. Cows fed diets containing forage rape and chicory had greater dry matter intake than those fed diet with irrigated pasture (P < 0.001). There were no differences in time spent eating among the treatments (P > 0.05), but cows fed the diet containing chicory spent less time ruminating. Milk protein production was greater for the forage rape diet (P = 0.047), compared to the chicory diet. Treatments did not affect the ammonia (NH3) concentration in the rumen. Cows on the forage rape diet had a greater concentration of ruminal total VFA compared to the chicory diet (P = 0.036) and greater valerate concentration compared with cows fed the irrigated pastures diet (P = 0.029). Succinivibrionaceae UCG-001 was more prevalent in cows fed the irrigated pasture diet (all FDR < 0.05). Cows fed diets containing irrigated pasture or forage rape excreted more fecal N compared to cows fed diets containing chicory (P = 0.003), whereas cows fed the chicory diet excreted less N (urinary plus fecal), than cows fed forage rape diets (P = 0.004). No differences (P > 0.05) were observed between treatments for total methane (CH4) production (g/day), nor for the intensity (CH4/kg milk), but CH4 yield was lower in cows fed diets with forage rape and chicory. Overall, using chicory and forage rape in the diet may be a viable option to maintain productivity on dairy farms during the summer. Inclusion of either chicory or forage rape in the diet reduced CH4 yield; however, considering the lower nitrogen excretions of cows fed chicory, the environmental impact due to ammonia, nitrate losses, and N2O emissions might be lower compared with cows fed forage rape.

This study aimed to determine dry matter intake, ruminal fermentation, health-related blood metabolites, and production responses of early-lactation dairy cows fed two inclusion levels (30 and 45 %) of low SMCO swedes in the diet. Twelve pregnant multiparous lactating HolsteinFriesian dairy cows (24.1 +/- 0.72 kg milk/d, 540 +/- 7.3 kg BW, and 142 +/- 3.9 DIM at the start of the study) were used in this study. Cows were randomly allocated to three dietary treatments in a replicated 3 x3 Latin square design. The experiment lasted 63 d and was divided into three 21d periods. Inclusion of swedes at 30 and 45% in the diet had no effect on DMI, but increased milk, protein and fat yields, as well as CP concentration in milk. This was due to changes in VFA patterns with greater molar proportions of propionate and butyrate, as well as a greater utilisation of dietary N that was converted to microbial N. No negative effects on haematological and biochemical blood parameters, except for increased BHB concentrations. Fatty acids composition in milk was modified, with a greater proportion of saturated FA and lower n-3 FA. Overall, low SMCO swedes can be included up to 45 % in the diet of pasture fed dairy cows during winter.

With dairy cattle farming under pressure to lower its environmental footprint it is important to find effective on-farm proxies for evaluation and monitoring of management practices aimed at reducing the risk of nitrogen (N) losses and optimizing N use efficiency of dairy farm systems. Urinary N (UN) is regarded as the most potent source of N emissions. In contrast to confinement systems, there have been few studies from pasture-based systems associating on-farm animal and nutritional factors with UN output. Thus, the aims of this meta-analysis were to collate a database from pasture-based research to: (a) investigate the associations of management, dietary, and animal variables with MUN concentration, and daily UN output; (b) describe the MUN-UN association; and (c) assess whether animal, management, and dietary factors influence the relationship. We developed a data set consisting of 95 observations representing 919 lactating dairy cattle fed pasture-based diets, which was compiled from 32 unique research publications that reported both MUN and UN output. Multi-level, mixed meta-analysis regression techniques were used to analyze the data. Initially, all variables were assessed as the sole fixed effect in a 2-level random effects model, accounting for within publication heterogeneity. Meta-regression techniques were then used to assess the relationship of all variables with MUN and UN output, respectively, accounting for 3 sources of variability: the sampling error of the individual observation, within publication heterogeneity, and among publication heterogeneity. At the univariable level, despite more than 10 dietary, animal, or management variables being significantly associated with MUN, none explained a large amount of the MUN variation. The variables that explained the greatest amount of variation were dietary crude protein (CP) content and the nitrogen: metabolizable energy content ratio, which explained about 33% and 31% of the variation in MUN concentrations, respectively. Combining factors in multiple regressions improved the model fit, such that the variation within publications explained by dietary CP and N intake increased to 40.0% in the final multiple meta-regression model. For UN output, individual variables explained a greater proportion of variance reported among observations, compared with MUN, whereby diet CP content (pseudo R2 = 66.1%), N to metabolizable energy intake ratio (pseudo R2 = 64.0%), N intake (pseudo R2 = 58.3%), and MUN (pseudo R2 = 43.5%) explained the greatest amount of the total variation. Milk urea nitrogen, N intake and dry matter intake were associated with UN output in the final multiple meta-regression model. Substantial heterogeneity existed in both MUN and UN among publications, with among publication heterogeneity accounting for 73.4% of all the variation noted in MUN, and 88.6% of all the variation in UN output. As such, the meta-analyses could not predict MUN and UN to any great extent. It is recommended that a consistent approach to measuring and reporting MUN concentrations and UN output is carried out for all future research in pasture-based systems.

Measuring the methane to carbon dioxide ratio (CH4/CO2) from animals could be useful to predict CH4 yield when dry matter intake (DMI) cannot be measured. The objectives were to (1) evaluate the relationship of CH4/CO2 with CH4 yield; (2) compare the CH4/CO2 of 10-60 simulated spot-samples with the CH4/CO2 calculated with data from 48-h of respiration chamber measurements. The DMI and CH4 and CO2 emissions measured every 5-6 min in respiration chambers from a previous experiment with 70 lambs fed ryegrass substituted with 0%, 25%, 50%, 75% and 100% of forage rape were retrieved. Emission data were used to perform simulations of 10, 20, 30, 40, 50 and 60 randomly selected spot-samples per lamb. The CH4/CO2 of 20 or more spot-samples was useful to predict CH4 yield and detect differences between dietary treatments, while the precision of the prediction increased when increasing the number of spot-samples up to 50 samples per lamb. Twenty spot-samples were sufficient to obtain accurate CH4/CO2 estimates; however, variance decreased (precision improved) with an increasing number of spot-samples per lamb up to 50 spot-samples. The CH4/CO2 of 10-60 simulated spot-samples explained 61% to 66% of variation in the 48-h measured CH4 yield.

BACKGROUND:Low rumen pH is proposed to be a major mechanism for low methane (CH4) emissions from sheep fed forage rape. However, it is difficult to separate this from other in vivo factors, such as rumen passage rate. The objective of this study was to determine the effect of pH alone on CH4 production in vitro using different pH buffers. Ryegrass, white clover and forage rape were incubated in vitro using three different incubation buffers with starting pH values of 5.5, 6.2 and 6.8. RESULTS:Decreasing pH reduced overall in vitro CH4 emission relative to fermented hexoses (CH4/FHex) by up to 54% and overall fermentation by 40%. pH also changed fermentation profiles where the acetate + butyrate to propionate + valerate ratio decreased when pH decreased. Within the three forages, forage rape led to the lowest CH4/FHex, but only in pH 5.5 and 6.2 buffer, and this was enhanced when the pH fell below 6. CONCLUSION:Reducing pH in vitro decreased CH4 production and overall fermentation across all forages. The lower pH reached by forage rape compared to ryegrass and white clover appears to drive the lower CH4 production relative to the extent of fermentation from forage rape compared to the other forages. © 2024 The Author(s). Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Urinary nitrogen (UN) excretion and milk production traits of 35 groups of 15 grazing cows each were measured over two years. Urine volume and N concentration were measured with urine sensors and daily UN excretion was calculated for four consecutive days. Milk yield, composition and cow liveweight (LW) were used to estimate daily dry matter intakes (DMI) based on back-calculated animal energy requirements and feed metabolisable energy (ME). Different N fractions in the diet were estimated using laboratory data and protein digestion equations. Mean estimates of N intake and UN excretion were 460 and 227 g N/d, respectively. Urinary-N represented 52% of the N consumed, which aligns with indoor N balance studies. Urinary N excretion was weakly correlated (r = 0.29) with dietary N intake, but moderately correlated (r = 0.63-0.67) with diet N concentration, diet N:ME ratio, and diet effective rumen degradable protein (ERDP). The ERDP balance had moderate to strong correlations with N utilisation efficiency (r = -0.89) and the UN expressed relative to N intake (r = 0.59) and N in milk (r = 0.78). These relationships illustrate the potential of urine sensors and energy-based estimations of intake to assess the influence of dietary management strategies to mitigate UN excretion from grazing animals.

Nitrogen (N) concentration in the diet is the best sole predictor of the contribution of urinary N to total N in excreta. A large database was compiled containing feed and excreta variables from dairy cattle, beef cattle, sheep and deer, to evaluate the predictive ability of five linear models and four non-linear models to calculate the contribution of urinary N to total N in excreta. Species-specific linear models for beef cattle and sheep did not result in better predictions than those obtained from a generic linear model developed for all ruminant species. The predictive ability of a non-linear dairy cattle model was noticeably better than that of a linear model. The poor performance of a linear model along with a smaller number of observations from deer studies points to the merit of the construction of a new deer-specific model. This study provides support for the robustness of N partitioning towards urinary N in the animal sub-model of OverseerFM™ for a comprehensive range of diets with varying N concentration for beef cattle and sheep. In the future, the use of more sophisticated modelling approaches that involve partitioning of data for model development and evaluation may be required.

Dairy cows’ urinary nitrogen (N) excretion (UN; g/d) represents a significant environmental concern due to their contribution to nitrate leaching, nitrous oxide (a potent greenhouse gas), and ammonia emissions (contributor to N deposition). The first objective of the current study was to determine the adequacy of existing models to predict UN from total mixed ration (TMR)-fed and fresh forage (FF)-fed cows. Next, we aimed to develop equations to predict UN based on animal factors [milk urea nitrogen (MUN; mg/dL) and body weight (BW, kg)] and to explore how these equations are improved when dietary factors, such as diet type, dry matter intake (DMI), or dietary characteristics [neutral detergent fiber (NDF) and crude protein (CP) content], are considered. A dataset was obtained from 51 published experiments composed of 174 treatment means. The whole dataset was used to evaluate the mean and linear biases of three existing equations including diet type as an interaction term; all models had significant linear and mean biases and two of the three models had poor predictive capabilities as indicated by their large relative prediction error (RPE; root mean square error of prediction as a percent of the observed mean). Next, the complete data set was split into training and test sets, which were used to develop and to evaluate new models, respectively. The first model included MUN and BW, and there was a significant interaction between diet type and the coefficients. This model had the worst 1:1 agreement [Lin’s concordance correlation coefficient (CCC) = 0.50] and largest RPE (24.7%). Models that included both animal and dietary factors performed the best, and when included in the model, the effect of diet type was no longer significant (p > 0.10). These models all had very good agreement (CCC ≥ 0.86) and relatively low RPE (≤13.1%). This meta-analysis developed precise and accurate equations to predict UN from dairy cows in both confined and pasture-based systems.

The temporal profile of methane (CH4) emissions from ruminants is affected by feed composition and forage type. This study aimed to 1) describe and compare the post-feeding pattern of CH4 emissions from lambs fed fresh ryegrass substituted with graded levels of forage rape, and 2) to evaluate the association between the magnitude of the variation in CH4 emission patterns and organic fermentation products quantified in pre- and- post- feeding rumen content samples. Methane emissions were measured at approximately 6 min intervals in respiration chambers from 70 lambs (n = 14 per treatment) fed ryegrass only (FR0) or as a proportion, 0.25 forage rape + 0.75 ryegrass (FR25), 0.50 forage rape + 0.50 ryegrass (FR50), 0.75 forage rape + 0.25 ryegrass (FR75), and forage rape only (FR100). The magnitude of the variability in CH4 emissions was defined as the ratio of maximum to minimum CH4 emissions in a 24 h period. This ratio was correlated (P < 0.05) with the proportions of major short chain fatty acids, and calculated hydrogen (H-2) available per unit of glucose fermented (H-2/GEF), quantified in rumen content samples collected pre- and- post- feeding. The CH4 emission profile after each feeding followed an asymmetrical positively skewed shape for FR0 to FR75, but not in lambs fed FR100. The lowest CH4 emission rates were observed before morning feeding which was followed by a CH4 peak within the 2 h after feeding, and then the CH4 emissions decreased until the next feeding. In FR100 lambs, the CH4 emission rate was, unexpectedly, relatively constant after feeding, without any clear CH4 peaks. The magnitude of the variability in the CH4 emission rate increased when the pH of rumen contents and H-2/GEF measured in pre-feeding samples decreased. Including forage rape at 0.75, or greater proportion, in the diet of lambs drastically changed the CH4 emissions pattern, likely due to a continuous low pH in the rumen which is detrimental for methanogenesis. In conclusion, the daily variation in CH4 emissions decreased with increasing forage rape inclusion in the diet of sheep and this was associated with a decreasing acetate proportion in the rumen liquid.