Review of equations to predict methane emissions in dairy cows from milk fatty acid profiles and their application to commercial dairy farms

Greenhouse gas emission from the activities of all productive sectors is currently a topic of foremost importance. The major contributors in the livestock sector are ruminants, especially dairy cows. This study aimed to evaluate and compare 21 equations for predicting enteric methane emissions (EME) developed on the basis of milk traits and fatty acid profiles, which were selected from 46 retrieved through a literature review. We compiled a reference database of the detailed fatty acid profiles, determined by GC, of 992 lactating cows from 85 herds under 4 different dairy management systems. The cows were classified according to DIM, parity order, and dairy system. This database was the basis on which we estimated EME using the selected equations. The EME traits estimated were methane yield (20.63 ± 2.26 g/kg DMI, 7 equations), methane intensity (16.05 ± 2.76 g/kg of corrected milk, 4 equations), and daily methane production (385.4 ± 68.2 g/d, 10 equations). Methane production was also indirectly calculated by multiplying the daily corrected milk yield by the methane intensity (416.6 ± 134.7 g/d, 4 equations). We also tested for the effects of DIM, parity, and dairy system (as a correction factor) on the estimates. In general, we observed little consistency among the EME estimates obtained from the different equations, with exception of those obtained from meta-analyses of a range of data from different research centers. We found all the EME predictions to be highly affected by the sources of variation included in the statistical model: DIM significantly affected the results of 19 of the 21 equations, and parity order influenced the results of 13. Different patterns were observed for different equations with only some of them in accordance with expectations based on the cow's physiology. Finally, the best predictions of daily methane production were obtained when a measure of milk yield was included in the equation or when the estimate was indirectly calculated from daily milk yield and methane intensity.

Invited review: Advances in nutrition and feed additives to mitigate enteric methane emissions

Methane, both enteric and from manure management, is the most important greenhouse gas from ruminant livestock, and its mitigation can deliver substantial decreases in the carbon footprint of animal products and potentially contribute to climate change mitigation. Although choices may be limited, certain feeding-related practices can substantially decrease livestock enteric CH4 emission. These practices can be generally classified into 2 categories: diet manipulation and feed additives. Within the first category, selection of forages and increasing forage digestibility are likely to decrease enteric CH4 emission, but the size of the effect, relative to current forage practices in the United States dairy industry, is likely to be minimal to moderate. An opportunity also exists to decrease enteric CH4 emissions by increasing dietary starch concentration, but interventions have to be weighed against potential decreases in milk fat yield and farm profitability. A similar conclusion can be made about dietary lipids and oilseeds, which are proven to decrease CH4 emission but can also have a negative effect on rumen fermentation, feed intake, and milk production and composition. Sufficient and robust scientific evidence indicates that some feed additives, specifically the CH4 inhibitor 3-nitrooxypropanol, can substantially reduce CH4 emissions from dairy and beef cattle. However, the long-term effects and external factors affecting the efficacy of the inhibitor need to be further studied. The practicality of mass-application of other mitigation practices with proven short-term efficacy (i.e., macroalgae) is currently unknown. One area that needs more research is how nutritional mitigation practices (both diet manipulation and feed additives) interact with each other and whether there is synergism among feed additives with different mode of action. Further, effects of diet on manure composition and greenhouse gas emissions during storage (e.g., emission trade-offs) have not been adequately studied. Overall, if currently available mitigation practices prove to deliver consistent results and novel, potent, and safe strategies are discovered and are practical, nutrition alone can deliver up to 60% reduction in enteric CH4 emissions from dairy farms in the United States.

Effects of Dietary Crude Protein Level of Concentrate Mix on Growth Performance, Rumen Characteristics, Blood Metabolites, and Methane Emissions in Fattening Hanwoo Steers

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.

Sustainability of dairy systems through the lenses of the sustainable development goals

In this paper, we propose to view the sustainability of dairy farming as nested within the sustainability of agriculture, a subset of the sustainability of food systems, which in turn could be construed as a subset of the national commitments of a country to achieve the Sustainable Development Goals (SDGs). Disciplinary, multidisciplinary, and interdisciplinary research are essential to study bio-physical system components and their interactions. However, when dairy farming is viewed as nested within broader societal systems, the inclusion of human elements calls for transdisciplinary research. Few of the 17 SDGs are left untouched by the livestock sector. Research should aim at identifying relevant farm-level metrics that are in alignment with any of the 231 indicators supporting the SDGs. We used two examples to illustrate the approach. In the first, SDG 13 (Climate Action) is used as a reminder that despite the current emphasis on reducing milk carbon footprint (kg CO2-e/kg milk), the contribution of the sector to Climate Action depends on reducing its annual emission (kg CO2-e/year; indicator 13.2.2). In the second example, indicator 2.4.1 (land use for sustainable agriculture) of SDG 2 (Zero Hunger) is used to illustrate the potential tradeoffs between Milk N/Intake N as a metric of nitrogen use efficiency at the cow level and metrics such as the input:output ratio of human-edible protein (Milk N/Intake of human-edible N) that prioritize the use of human-inedible feed in dairy rations as a way to enhance efficiency and circularity at the food system level.

Feeding lower-protein diets based on red clover and grass or alfalfa and corn silage does not affect milk production but improves nitrogen use efficiency in dairy cows

Reducing the dietary crude protein (CP) concentration can decrease the financial cost and lower the environmental impact of milk production. Two studies were conducted to examine the effects of reducing the dietary CP concentration on animal performance, nutrient digestibility, milk fatty acid (FA) profile, and nitrogen use efficiency (NUE; milk N/N intake) in dairy cows fed legume silage-based diets. Thirty-six multiparous Holstein-Friesian dairy cows that were 76 ± 14 (mean ± SD) days in milk and 698 ± 54 kg body weight were used in a 3 × 3 Latin square design in each of 2 studies, with 3 periods of 28 d. In study 1, cows were fed diets based on a 50:50 ratio of red clover to grass silage [dry matter (DM) basis] containing 1 of 3 dietary CP concentrations: high (H) = 175 g of CP/kg of DM; medium (M) = 165 g of CP/kg of DM; or low (L) = 150 g of CP/kg of DM. In study 2, cows were fed 175 g of CP/kg of DM with a 50:50 ratio of alfalfa to corn silage (H50) or 1 of 2 diets containing 150 g of CP/kg of DM with either a 50:50 (L50) or a 60:40 (L60) ratio of alfalfa to corn silage. Cows in both studies were fed a total mixed ration with a forage-to-concentrate ratio of 52:48 (DM basis). All diets were formulated to meet the MP requirements, except L (95% of MP requirements). In study 1, cows fed L ate 1.6 kg of DM/d less than those fed H or M, but milk yield was similar across treatments. Mean milk protein, fat, and lactose concentrations were not affected by diet. However, the apparent total-tract nutrient digestibility was decreased in cows fed L. The NUE was 5.7 percentage units higher in cows fed L than H. Feeding L also decreased milk and plasma urea concentrations by 4.4 mg/dL and 0.78 mmol/L, respectively. We found no effect of dietary treatment on the milk saturated or monounsaturated FA proportion, but the proportion of polyunsaturated FA was increased, and milk odd- and branched-chain FA decreased in cows fed L compared with H. In study 2, DM intake was 2 kg/d lower in cows receiving L50 than H50. Increasing the alfalfa content and feeding a low-CP diet (L60) did not alter DMI but decreased milk yield and milk protein concentration by 2 kg/d and 0.6 g/kg, respectively, compared with H50. Likewise, milk protein and lactose yield were decreased by 0.08 kg/d in cows receiving L60 versus H50. Diet had no effect on apparent nutrient digestibility. Feeding the low-CP diets compared with H50 increased the apparent NUE by approximately 5 percentage units and decreased milk and plasma urea concentrations by 7.2 mg/dL and 1.43 mmol/L, respectively. Dietary treatment did not alter milk FA profile except cis-9,trans-11 conjugated linoleic acid, which was higher in milk from cows receiving L60 compared with H50. We concluded that reducing CP concentration to around 150 g/kg of DM in red clover and grass or alfalfa and corn silage-based diets increases the apparent NUE and has little effect on nutrient digestibility or milk performance in dairy cows.

Enteric methane emissions by lactating and dry cows in the high Andes of Peru

The objective of the study was to determine enteric methane emissions using the sulfur hexafluoride (SF₆) technique and comparing with The Intergovernmental Panel on Climate Change (IPCC) methodology in lactating cows (LC) and dry cows (DC) in the Peruvian highlands. Enteric methane (CH₄) emissions were measured on 5 LC and 6 DC Brown Swiss in a grazing system without concentrate. Forages samples were collected and analyzed for dry matter, crude protein, and neutral detergent fiber. Milk samples were collected and analyzed for fat, crude protein, and lactose to estimate energy-corrected milk. Animal intakes were measured using the external marker titanium dioxide (production of feces) and crude protein in feces (organic digestibility of the feed) and estimated by using performance data. The enteric methane emissions of LC were higher than methane emissions of DC (325 and 266 g CH₄/cow/day for LC and DC, respectively (P < 0.001)). Methane emissions were 358.5 g CH₄/day by SF₆ technique and 291.6 g CH₄/day by IPCC methodology for LC and 337.4 g CH₄/day by SF₆ technique and 195.8 g CH₄/day by IPCC methodology for DC. Methane yields measured by SF₆ were higher than methane yields estimated by IPCC methodology (29 g CH₄/kg DM and 22 g CH₄/kg DM using SF₆ technique and IPCC methodology, respectively (P < 0.001)). Methane yields were differently for all expressions by physiological stage and method. The methane conversion factor (Ym) was 9.7% for LC and 9.6% for DC. Methane intensities were similar by method (P > 0.05). It was concluded that IPCC's methodology underestimate the CH₄ emissions of dairy systems in the Peruvian Andes; therefore, in order to obtain precise Ym, direct measurements of enteric CH₄ in the different regions of Peruvian highlands are required.

Nitrogen use efficiency and soil chemical composition in small-scale dairy systems

In dairy production systems, the efficient use of resources is required to guarantee its sustainability. Worldwide, the efficiency of feed utilization and its effects have been widely studied. However, few studies have quantified animal nitrogen use and its corresponding soil contribution in small-scale production systems. Therefore, this study aimed to determine the efficiency of feed utilization and quantify the soil chemical composition in small-scale production systems using two different feeding strategies. Twelve dairy farms were evaluated from May 2016 to April 2017. Data analysis was performed using an ANOVA following a completely randomized model and using feeding strategies as treatment. Regarding the feeding systems' characteristics, significant differences (P < 0.05) were only observed in land surface and land used to produce mixed-grass and corn. Nitrogen (N) input and output in dairy cattle were significantly different (P < 0.05) for crude protein intake. The highest results were observed in grazing feeding systems. The cut and carry strategies excreted 71% of the consumed N in the manure; grazing strategies excreted 72%. The efficiency of feed utilization (EFU) is low; only 19% of the consumed N is recovered during milk production. As for the soil chemical composition, significant differences (P < 0.05) were observed in the percentage of total N and the carbon to nitrogen (C:N) ratio. The remaining components behaved similarly in both feeding systems. Systems that include crops and livestock can positively change the biophysical and socioeconomic dynamics of agricultural systems.

Effect of a Low-Methane Diet on Performance and Microbiome in Lactating Dairy Cows Accounting for Individual Pre-Trial Methane Emissions

This study examined the effects of partly replacing grass silage (GS) with maize silage (MS), with or without rapeseed oil (RSO) supplementation, on methane (CH₄) emissions, production performance, and rumen microbiome in the diets of lactating dairy cows. The effect of individual pre-trial CH₄-emitting characteristics on dietary emissions mitigation was also examined. Twenty Nordic Red cows at 71 ± 37.2 (mean ± SD) days in milk were assigned to a replicated 4 × 4 Latin square design with four dietary treatments (GS, GS supplemented with RSO, GS plus MS, GS plus MS supplemented with RSO) applied in a 2 × 2 factorial arrangement. Partial replacement of GS with MS decreased the intake of dry matter (DM) and nutrients, milk production, yield of milk components, and general nutrient digestibility. Supplementation with RSO decreased the intake of DM and nutrients, energy-corrected milk yield, composition and yield of milk fat and protein, and general digestibility of nutrients, except for crude protein. Individual cow pre-trial measurements of CH₄-emitting characteristics had a significant influence on gas emissions but did not alter the magnitude of CH₄ emissions. Dietary RSO decreased daily CH₄, yield, and intensity. It also increased the relative abundance of rumen Methanosphaera and Succinivibrionaceae and decreased that of Bifidobacteriaceae. There were no effects of dietary MS on CH₄ emissions in this study, but supplementation with 41 g RSO/kg of DM reduced daily CH₄ emissions from lactating dairy cows by 22.5%.

Evaluation of gallnut tannin and Lactobacillus plantarum as natural modifiers for alfalfa silage: Ensiling characteristics, in vitro ruminal methane production, fermentation profile and microbiota

AIMS

The potential of gallnut tannin (GT) and Lactobacillus plantarum (LP) on fermentation characteristics, in vitro ruminal methane (CH₄ ) production and microbiota of alfalfa silage was investigated.

METHODS AND RESULTS

Alfalfa was ensiled with GT (20 and 50 g kg^-1 dry matter [DM]) and LP (3 × 10⁸  CFU per gram fresh matter) alone or in combination for 60 days. The GT and LP alone or in combination decreased DM losses, pH and non-protein nitrogen contents of alfalfa silage. All additive treatments decreased ruminal CH₄ production, and increased propionic acid molar proportions and Fibrobacter succinogenes numbers. The LP treatment increased nutrient degradation, cellobiase, pectinase and protease activities, and Prevotella ruminicola abundance, whereas high-dose GT treatment inhibited these variables. Importantly, LP together with GT alleviated the adverse effects of high-dose GT supply alone by enhancing pectinase and protease activities as well as Rumincoccus flavefaciens and P. ruminicola growth.

CONCLUSIONS

Combination of GT and LP can be used as an efficient additive to improve silage quality and utilization by ruminants.

SIGNIFICANCE AND IMPACT OF THE STUDY

Using GT-LP combination has practical implications, particularly concerning effects of tannins on ruminal CH₄ mitigation, which may alleviate inhibitory effects of tannins on feed digestion through modulating ruminal microbiota.

Economic and environmental effects of revised metabolizable protein and amino acid recommendations on Canadian dairy farms

The objective of this research was to evaluate the potential economic and environmental effects of the formulation model used to balance dairy rations for metabolizable protein (MP) or 3 essential AA (EAA: His, Lys, and Met) in 3 regions of Canada with different farming systems. The Maritimes, Central Canada, and the Prairies reference dairy farms averaged 63, 71, 144 mature cows per herd and 135, 95, 255 ha of land, respectively. Using N-CyCLES, a whole-farm linear program model, dairy rations were balanced for (1) MP, based on National Research Council (NRC) requirements (MP_2001); (2) MP plus Lys and Met, based on NRC (AA_2001); (3) MP (MP_Rev); or (4) for His, Lys, and Met (AA_Rev), both based on a revised factorial approach revisiting both supply and requirements of MP and EAA. Energy was balanced to meet requirements based on NRC (2001). Assuming the requirements were met within each approach, it was considered that milk yield and composition were not affected by the type of formulation. Given the assumptions of the study, when compared with MP_2001 formulation, balancing dairy rations using the AA_Rev approach reduced calculated farm N balance by 3.8%, on average from 12.71 to 12.24 g/kg of fat- and protein-corrected milk; it also enhanced farm net income by 4.5%, from 19.00 to 19.70 $CAN/100 kg of fat- and protein-corrected milk, by reducing inclusion of protein concentrate in dairy rations. Calculated animal N efficiency was on average 4.3% higher with AA_Rev than with MP_2001 for mid-lactation cows. This gain in N efficiency would result in a reduction in N₂O emission by manure, contributing to a partial decrease of total greenhouse gas emission by 1.7%, through a reduction of N excreted in manure. With the AA_2001 formulation, farm N balance was 1% higher than with MP_2001 formulation while reducing farm net income by 6.4%, due to the need to purchase rumen-protected AA, with no effect on total greenhouse gas emission. Both MP formulations lead to fairly similar outputs. The AA_Rev formulation also indicated that His might be a co-limiting AA with Met in dairy rations balanced with ingredients usually included in Canadian dairy rations. Given the assumptions of the study, balancing dairy rations for 3 EAA (His, Lys, and Met) rather than MP, has some potential positive effects on Canadian dairy farms by increasing net incomes through a reduction of crude protein supply, leading to a decreased environmental effect.

Enteric and Fecal Methane Emissions from Dairy Cows Fed Grass or Corn Silage Diets Supplemented with Rapeseed Oil

Simple Summary

In this study, we evaluated methane emissions from dairy cows fed grass or corn silage diets supplemented with rapeseed oil. Enteric methane emissions decreased on adding rapeseed oil to the diet, but methane emissions from feces of dairy cows fed diets supplemented with rapeseed oil did not differ. Thus, no trade-offs were observed between enteric and fecal methane emissions due to forage type or addition of rapeseed oil to diets fed to Swedish dairy cows.

Abstract

This study evaluated potential trade-offs between enteric methane (CH₄) emissions and CH₄ emissions from feces of dairy cows fed grass silage or partial replacement of grass silage with corn silage, both with and without supplementation of rapeseed oil. Measured data for eight dairy cows (two blocks) included in a production trial were analyzed. Dietary treatments were grass silage (GS), GS supplemented with rapeseed oil (GS-RSO), GS plus corn silage (GSCS), and GSCS supplemented with rapeseed oil (GSCS-RSO). Feces samples were collected after each period and incubated for nine weeks to estimate fecal CH₄ emissions. Including RSO (0.5 kg/d) in the diet decreased dry matter intake (DMI) by 1.75 kg/d. Enteric CH₄ emissions were reduced by inclusion of RSO in the diet (on average 473 vs. 607 L/d). In 9-week incubations, there was a trend for lower CH₄ emissions from feces of cows fed diets supplemented with RSO (on average 3.45 L/kg DM) than cows with diets not supplemented with RSO (3.84 L/kg DM). Total CH₄ emissions (enteric + feces, L/d) were significantly lower for the cows fed diets supplemented with RSO. Total fecal CH₄ emissions were similar between treatments, indicating no trade-offs between enteric and fecal CH₄ emissions.

Effect of source and level of forage in the diet on in vitro ammonia emission from manure of Holstein and Jersey dairy cows

Reducing overall reactive N losses from dairy production systems depends substantially on reducing the atmospheric emission of manure ammonia (NH₃). The objective of this study was to determine potential NH₃-N emission of reconstituted manure using an in vitro protocol. Feces and urine were collected from a companion study designed as a Latin square in which 4 Holstein and 4 Jersey cows were fed diets containing 2 levels of forage neutral detergent fiber (NDF) [low-forage NDF (19%) vs. high-forage NDF (24%; dry matter basis)] from either alfalfa silage or corn silage (70:30 vs. 30:70 ratio of alfalfa silage NDF:corn silage NDF) arranged as a 2 × 2 factorial. All diets contained similar levels of crude protein (17%) and starch (23%), and had forage-to-concentrate ratios of 55:45 and 68:32 for low- and high-forage NDF diets, respectively. Measurements of NH₃-N emission were conducted in a laboratory-scale chamber with 16 g of reconstituted manure (urine plus feces) incubated for 48 h at 15°C with sampling at 1, 3, 6, 12, 24, 36, and 48 h. Hourly NH₃-N emissions data were analyzed using a repeated-measures mixed model in R (https://www.r-project.org/). The fixed effects were breed, forage NDF level, forage NDF source, time of sampling, and all possible interactions; cow was included as a random term. The cumulative 48-h NH₃-N emissions and the scaled-up emissions accounting for daily output of manure from each cow were analyzed using the same model but without time of sampling. Level and source of forage in the diet tended to influence the pattern in hourly rate and 48-h cumulative emission, respectively. Accounting for daily manure volume differences, low-forage NDF diets led to lower estimates of daily NH₃-N emissions than high-forage NDF diets (20% on a cow basis, 15% on a raw manure basis, and 18% on a manure-N basis). Compared with Holsteins, Jerseys emitted 17% lower estimated NH₃-N on a cow basis, mainly due to lower manure excretion but tended to emit 15% more NH₃-N expressed on a manure-N basis. Findings of this study suggested that cow breed and dietary forage NDF level should be considered in the prediction of NH₃-N emission from the dairy industry.

In vitro degradability of corn silage and Leymus chinensis silage and evaluation of their mixed ratios on performance, digestion and serum parameters in beef cattle

This study investigated the degradability of corn silage (CS) and Leymus chinensis silage (LS) in vitro, and evaluated the effect of various ratios on growth performance, digestion and serum parameters in beef cattle. A 72-hr bath culture trial was performed to evaluate degradability and rumen fermentation characteristics of CS, LS and their combinations [67:33, 33:67, dry matter (DM) basis]. Forty Simmental steers, averaging 441.46 ± 4.45 kg of body weight (BW), were randomly allocated into four dietary treatments for 120-d period. Diets were given as total mixed rations with a forage-to-concentrate ratio of 60:40 and CS:LS ratios of 100:0, 67:33, 33:67 and 0:100 (DM basis). The in vitro trial showed that DM and neutral detergent fibre (NDF) degradability decreased linearly as LS proportion increased, whereas CP degradability increased linearly. Additionally, increased acid detergent fibre (ADF) degradability was detected at 48 hr of incubation. Increasing the proportion of LS increased rumen liquor pH and decreased volatile fatty acid linearly including acetate, propionate and butyrate, whereas the ammonia-N increased linearly at 12 and 72 hr of incubation. With increasing LS ratio, final BW, average daily gain and feed conversion ratio of steers decreased linearly, whereas DMI was not affected. Additionally, apparent digestibility of DM, organic matter, NDF and ADF linearly and quadratically decreased while ether extract apparent digestibility decreased linearly, and CP apparent digestibility was not affected. Serum glucose and urea nitrogen linearly and quadratically decreased while glutamic-pyruvic transaminase activity linearly decreased as the proportion of LS increased. Other serum parameters including total triglycerides, total cholesterol, total protein, albumin and glutamic-oxalacetic transaminease were not affected. Overall, enhancing ratio of LS caused inferior DM and NDF degradability but improved CP degradability in the combinations of LS and CS. A CS:LS ratio of 67:33 resulted in the best growth performance and nutrient utilization in steers.

The use of milk Fourier transform mid-infrared spectra and milk yield to estimate heat production as a measure of efficiency of dairy cows

Background

Transformation of feed energy ingested by ruminants into milk is accompanied by energy losses via fecal and urine excretions, fermentation gases and heat. Heat production may differ among dairy cows despite comparable milk yield and body weight. Therefore, heat production can be considered an indicator of metabolic efficiency and directly measured in respiration chambers. The latter is an accurate but time-consuming technique. In contrast, milk Fourier transform mid-infrared (FTIR) spectroscopy is an inexpensive high-throughput method and used to estimate different physiological traits in cows. Thus, this study aimed to develop a heat production prediction model using heat production measurements in respiration chambers, milk FTIR spectra and milk yield measurements from dairy cows.

Methods

Heat production was computed based on the animal’s consumed oxygen, and produced carbon dioxide and methane in respiration chambers. Heat production data included 168 24-h-observations from 64 German Holstein and 20 dual-purpose Simmental cows. Animals were milked twice daily at 07:00 and 16:30 h in the respiration chambers. Milk yield was determined to predict heat production using a linear regression. Milk samples were collected from each milking and FTIR spectra were obtained with MilkoScan FT 6000. The average or milk yield-weighted average of the absorption spectra from the morning and afternoon milking were calculated to obtain a computed spectrum. A total of 288 wavenumbers per spectrum and the corresponding milk yield were used to develop the heat production model using partial least squares (PLS) regression.

Results

Measured heat production of studied animals ranged between 712 and 1470 kJ/kg BW^0.75. The coefficient of determination for the linear regression between milk yield and heat production was 0.46, whereas it was 0.23 for the FTIR spectra-based PLS model. The PLS prediction model using weighted average spectra and milk yield resulted in a cross-validation variance of 57% and a root mean square error of prediction of 86.5 kJ/kg BW^0.75. The ratio of performance to deviation (RPD) was 1.56.

Conclusion

The PLS model using weighted average FTIR spectra and milk yield has higher potential to predict heat production of dairy cows than models applying FTIR spectra or milk yield only.

Enteric methane, lactation performances, digestibility, and metabolism of nitrogen and energy of Holsteins and Jerseys fed 2 levels of forage fiber from alfalfa silage or corn silage

Our objective was to determine the effects of replacing alfalfa silage (AS) neutral detergent fiber (NDF) with corn silage (CS) NDF at 2 levels of forage NDF (FNDF) on enteric methane (CH₄), lactation performance, ruminal fluid characteristics, digestibility, and metabolism of N and energy in Holstein and Jersey cows. Twelve Holstein and 12 Jersey cows (all primiparous and mid-lactation) were used in a triplicated split-plot 4 × 4 Latin square experiment, where breed and diet formed the main and subplots, respectively. The 4 iso-nitrogenous and iso-starch dietary treatments were arranged as a 2 × 2 factorial with 2 levels of FNDF [19 (low FNDF, LF) and 24% (high FNDF, HF) of dry matter] and 2 sources of FNDF (70:30 and 30:70 ratio of AS NDF to CS NDF). Soyhull (non-forage NDF) and corn grain were respectively used to keep dietary NDF and starch content similar across diets. Total collection of feces and urine over 3 d was performed on 8 cows (1 Latin square from each breed). The difference in dry matter intake (DMI) between Holsteins and Jerseys was greater when fed AS than CS. Compared with Jerseys, Holstein cows had greater body weight (48%), DMI (34%), fat- and protein-corrected milk (FPCM; 31%) and CH₄ production (22%; 471 vs. 385 g/d). However, breed did not affect CH₄ intensity (g/kg of FPCM) or yield (g/kg of DMI), nutrient digestibility, and N partitioning. Compared with HF, LF-fed cows had greater DMI (10%), N intake (8%), and FPCM (5%), but they were 5% less efficient (both FPCM/DMI and milk N/intake N). Compared with HF, LF-fed cows excreted 11 and 17% less urinary N (g/d and % of N intake, respectively). In spite of lower (2.5%) acetate and higher (10%) propionate (mol/100 mol ruminal volatile fatty acids) LF-fed cows had greater (6%) CH₄ production (g/d) than did HF-fed cows, most likely due to increased DMI, as affected mainly by the soyhulls. Compared with AS, CS-fed cows had greater DMI (7%) and FPCM (4%), but they were less efficient (5%), and CH₄ yield (g/kg of DMI) was reduced by 8%. In addition, per unit of gross energy intake, CS-fed cows lost less urinary energy (15%) and CH energy (11%) than did AS-fed cows. We concluded that, in contrast to level and source of FNDF, breed did not affect digestive and metabolic efficiencies, and, furthermore, neither breed nor dietary treatments affected CH₄ intensity. The tradeoff between CH₄ and N losses may have implications in future studies assessing the environmental effects of milk production when approached from a whole-farm perspective.

Methane emissions of manure from dairy cows fed red clover- or corn silage-based diets supplemented with linseed oil

The objective of this study was to investigate the effects of forage source (red clover silage: RCS vs. corn silage: CS) and diet supplementation with linseed oil (LO) on CH₄ emissions of manure from dairy cows. For this purpose, 12 lactating cows were used in a 2 × 2 factorial arrangement of treatments. Cows were fed (ad libitum) RCS- or CS-based diets (forage:concentrate ratio 60:40; dry matter basis) without or with LO addition (4% dry matter). Feces and urine were collected from each cow and mixed with residual sludge obtained from a manure storage structure. Manure was incubated for 17 wk at 20°C under anaerobic conditions (O₂-free N₂) in 500-mL glass bottles. Methane emissions and changes in chemical composition of the manure were monitored during the entire incubation period. The total amount of feces and urine excreted by cows was not affected by dietary treatments and averaged 6.6 kg/d of volatile solids (VS). Compared with manure from cows fed RCS-based diets, maximum CH₄ production potential of manure from cows fed CS-based diets was 54% higher (182 vs. 118 L/kg of VS) throughout the incubation period. Maximum CH₄ production potential from manure also increased (by 17%) when cows were fed LO-supplemented diets compared with those fed nonsupplemented diets. Similar to maximum CH₄ production potential, VS degraded during incubation (i.e., VS loss) was higher from manure from cows fed CS-based diets versus cows fed RCS-based diets (30.6 vs. 22.5%), and increased (+3 percentage units, on average) with the addition of LO to the diets. Ammonia concentration in manure was higher when cows were fed CS-based diets compared with RCS-based diets, and declined with LO supplementation to CS and RCS diets. It is concluded that both dietary forage source and fat supplementation affect maximum CH₄ production potential from manure and this should be taken into account when such dietary options are recommended to mitigate enteric CH₄ emissions from dairy cows.

Are dietary strategies to mitigate enteric methane emission equally effective across dairy cattle, beef cattle, and sheep?

The digestive physiology of ruminants is sufficiently different (e.g., with respect to mean retention time of digesta, digestibility of the feed offered, digestion, and fermentation characteristics) that caution is needed before extrapolating results from one type of ruminant to another. The objectives of the present study were (1) to provide an overview of some essential differences in rumen physiology between dairy cattle, beef cattle, and sheep that are related to methane (CH₄) emission; and (2) to evaluate whether dietary strategies to mitigate CH₄ emission with various modes of action are equally effective in dairy cattle, beef cattle, and sheep. A literature search was performed using Web of Science and Scopus, and 94 studies were selected from the literature. Per study, the effect size of the dietary strategies was expressed as a proportion (%) of the control level of CH₄ emission, as this enabled a comparison across ruminant types. Evaluation of the literature indicated that the effectiveness of forage-related CH₄ mitigation strategies, including feeding more highly digestible grass (herbage or silage) or replacing different forage types with corn silage, differs across ruminant types. These strategies are most effective for dairy cattle, are effective for beef cattle to a certain extent, but seem to have minor or no effects in sheep. In general, the effectiveness of other dietary mitigation strategies, including increased concentrate feeding and feed additives (e.g., nitrate), appeared to be similar for dairy cattle, beef cattle, and sheep. We concluded that if the mode of action of a dietary CH₄ mitigation strategy is related to ruminant-specific factors, such as feed intake or rumen physiology, the effectiveness of the strategy differs across ruminant types, whereas if the mode of action is associated with methanogenesis-related fermentation pathways, the strategy is effective across ruminant types. Hence, caution is needed when translating effectiveness of dietary CH₄ mitigation strategies across different ruminant types or production systems.

Invited review: Nitrogen in ruminant nutrition: A review of measurement techniques

Nitrogen is a component of essential nutrients critical for the productivity of ruminants. If excreted in excess, N is also an important environmental pollutant contributing to acid deposition, eutrophication, human respiratory problems, and climate change. The complex microbial metabolic activity in the rumen and the effect on subsequent processes in the intestines and body tissues make the study of N metabolism in ruminants challenging compared with nonruminants. Therefore, using accurate and precise measurement techniques is imperative for obtaining reliable experimental results on N utilization by ruminants and evaluating the environmental impacts of N emission mitigation techniques. Changeover design experiments are as suitable as continuous ones for studying protein metabolism in ruminant animals, except when changes in body weight or carryover effects due to treatment are expected. Adaptation following a dietary change should be allowed for at least 2 (preferably 3) wk, and extended adaptation periods may be required if body pools can temporarily supply the nutrients studied. Dietary protein degradability in the rumen and intestines are feed characteristics determining the primary AA available to the host animal. They can be estimated using in situ, in vitro, or in vivo techniques with each having inherent advantages and disadvantages. Accurate, precise, and inexpensive laboratory assays for feed protein availability are still needed. Techniques used for direct determination of rumen microbial protein synthesis are laborious and expensive, and data variability can be unacceptably large; indirect approaches have not shown the level of accuracy required for widespread adoption. Techniques for studying postruminal digestion and absorption of nitrogenous compounds, urea recycling, and mammary AA metabolism are also laborious, expensive (especially the methods that use isotopes), and results can be variable, especially the methods based on measurements of digesta or blood flow. Volatile loss of N from feces and particularly urine can be substantial during collection, processing, and analysis of excreta, compromising the accuracy of measurements of total-tract N digestion and body N balance. In studying ruminant N metabolism, nutritionists should consider the longer term fate of manure N as well. Various techniques used to determine the effects of animal nutrition on total N, ammonia- or nitrous oxide-emitting potentials, as well as plant fertilizer value, of manure are available. Overall, methods to study ruminant N metabolism have been developed over 150 yr of animal nutrition research, but many of them are laborious and impractical for application on a large number of animals. The increasing environmental concerns associated with livestock production systems necessitate more accurate and reliable methods to determine manure N emissions in the context of feed composition and ruminant N metabolism.

Bacterial Community Diversity Associated With Different Utilization Efficiencies of Nitrogen in the Gastrointestinal Tract of Goats

The objective of this study was to examine the association between bacterial community structure and the utilization efficiency of nitrogen (UEN) phenotypes by determining the bacterial community in the gastrointestinal tract (GIT) of goats that differ in UEN using high-throughput 16S rRNA gene sequencing. Thirty Nubian goats were selected as experimental animals, and their UEN was determined in a metabolic experiment. Subsequently, eight individuals were grouped into the high nitrogen utilization (HNU) phenotype, and seven were grouped into the low nitrogen utilization (LNU) phenotype. The bacterial 16S rRNA gene amplicons from the rumen, abomasum, jejunum, cecum and colon contents of these animals were sequenced using next-generation high-throughput sequencing technology. Two hundred thirty-nine genera belonging to 23 phyla in the rumen, 319 genera belonging to 30 phyla in the abomasum, 248 genera belonging to 36 phyla in the jejunum, 248 genera belonging to 25 phyla in the colon and 246 genera belonging to 23 phyla in the cecum were detected, with Bacteroidetes and Firmicutes predominating. In addition, a significant correlation was observed between the UEN and the genera Succiniclasticum, Bacteroides, Ruminobacter, Methanimicrococcus, Mogibacterium, Eubacterium_hallii_group and Ruminococcus_1 in the rumen; Bacteroidales_S24-7_group, Bacteroidales_RF16_group, Bacteroidales_UCG-001 and Anaerovibrio in the abomasum; Ruminococcus_2, Candidatus_Saccharimonas, Candidatus_Arthromitus and Coprococcus_1 in the jejunum; Erysipelotrichaceae_UCG-004, Akkermansia, Senegalimassilia, Candidatus_Soleaferrea and Methanocorpusculum in the colon; and Ruminococcaceae_UCG-002, Anaerovibrio and Ruminococcaceae_UCG-007 in the cecum. Furthermore, the real-time PCR results showed that the ruminal copies of Fibrobacter_succinogenes, Butyrivibrio_fibrisolvens, Ruminococcus_sp._HUN007, Prevotella ruminicola and Streptococcus bovis in the HNU animals were significantly higher than those in the LNU animals. This study suggests an association of GIT microbial communities as a factor that influences UEN in goats.

Starch and dextrose at 2 levels of rumen-degradable protein in iso-nitrogenous diets: Effects on lactation performance, ruminal measurements, methane emission, digestibility, and nitrogen balance of dairy cows

Our objectives were to determine the effects of readily rumen-available carbohydrate source (refined starch vs. dextrose), the level of rumen-degradable protein (RDP), and their interaction on lactation performance, ruminal measurements, enteric methane (CH4) emission, nutrient digestibility, and nitrogen (N) balance in lactating dairy cows. Eighteen mid-lactation multiparous Holstein cows were used in this split-plot study. The main plots were created by randomly assigning 9 cows to diets of 11 or 9% RDP obtained by altering the percentage of soybean meal, expeller soybean meal, and blood meal in the diet. All diets included 16.4% crude protein. In the subplots, the effects of 0:10, 5:5, and 10:0 refined starch:dextrose ratio (% of dietary dry matter) were determined in three 3 × 3 Latin squares by randomly assigning the 9 cows in each RDP level into squares. Each period lasted 4 wk, with the last 2 wk allotted for sample collection. Carbohydrate source × RDP level interaction tended to influence dry matter intake (DMI), the concentration of urinary N, and urinary urea-N. Replacing refined starch with dextrose increased DMI, the molar percentage of ruminal butyrate and valerate, daily CH4 production (g/d), and fecal N and decreased the molar percentage of ruminal branched-chain volatile fatty acids, feed efficiency (fat- and protein-corrected milk/DMI), and N use efficiency (milk N/intake N) but did not influence nutrient digestibility. Enteric CH4 production was negatively related to the molar percentage of ruminal propionate but positively related to the molar percentage of ruminal butyrate. Treatments did not influence milk production responses, but cows fed 9% RDP diets had lower ruminal ammonia concentration (7.2 vs. 12.3 mg/dL) and tended to excrete less urinary purine derivatives (428 vs. 493 mmol/d) compared with cows fed 11% RDP diets, suggesting lower ruminal synthesis of microbial protein. Reducing the level of RDP in iso-nitrogenous diets had no effect on nutrient apparent total-tract digestibility, manure excretion and composition, N balance, and CH4 production. In this study, treatments did not affect yield (20.0 g of CH4/kg of DMI) or intensity (13.1 g of CH4/kg of fat- and protein-corrected milk), but methane production (g of CH4/d) was 7.0% lower and N use efficiency (conversion of intake N into milk protein) was 7.8% higher for cows fed a diet of 28.1% starch and 4.6% water-soluble carbohydrate compared with diets with lower starch and higher water-soluble carbohydrate contents.

Nitrogen utilisation efficiency in small-scale dairy systems in the highlands of Central Mexico

Nitrogen (N) plays an important role in small-scale dairy systems, both in production costs and as an indicator of environmental impact. The objective of this study was to quantify nitrogen inputs and outputs to identify areas for improvement in nitrogen utilisation efficiency (NUE). Evaluation was in 12 small-scale dairy farms with different feeding strategies. Six followed the traditional cut and carry of irrigated temperate pastures (CUT), and six have implemented grazing of pastures (GRZ), quantifying N inputs and outputs from May 2016 to April 2017. Data were analysed by ANOVA following a split-plot model with season (rainy or dry) as main plots and feeding strategy (CUT or GRZ) as split-plots, with results in kilograms N per hectare and kilograms N per cow. There were differences (P < 0.05) between seasons and strategies in N inputs from purchased N fertilisers and purchased feeds as concentrates and roughages, showing different N inputs and outputs whether in CUT or GRZ strategies. There were also significant interactions between seasons and strategies as in the sale of animals, where GRZ sell throughout the year, while CUT sell at the beginning of the dry season. N balance ranged from 33.9 to 183.0 kg N/ha, and 37.8 to 111.0 as kilograms N per cow with an interaction (P < 0.05) between season and strategies. There was a larger N surplus in GRZ during the rainy season from fertiliser inputs, which reduced N utilisation efficiency (NUE). Mean NUE in kilograms N per hectare and kilograms N per cow was 19%, with the higher efficiency for GRZ in the dry season. Farms with the best NUE had lower use of fertilisers and purchased feeds.

Effects of concentrate crude protein content on nutrient digestibility, energy utilization, and methane emissions in lactating dairy cows fed fresh-cut perennial grass

Although many studies have investigated mitigation strategies for methane (CH₄) output from dairy cows fed a wide variety of diets, research on the effects of concentrate crude protein (CP) content on CH₄ emissions from dairy cows offered fresh grass is limited. The present study was designed to evaluate the effects of cow genotype and concentrate CP level on nutrient digestibility, energy utilization, and CH₄ emissions in dairy cows offered fresh-grass diets. Twelve multiparous lactating dairy cows (6 Holstein and 6 Holstein × Swedish Red) were blocked into 3 groups for each breed and assigned to a low-, medium-, or high-CP concentrate diet [14.1, 16.1, and 18.1% CP on a dry matter (DM) basis, respectively], in a 3-period changeover study (25d per period). Total diets contained (DM basis) 32.8% concentrates and 67.2% perennial ryegrass, which was harvested daily. All measurements were undertaken during the final 6d of each period: digestibility measurements for 6d and calorimetric measurements in respiration chambers for 3d. Feed intake and milk production data were reported in a previous paper. We observed no significant interaction between concentrate CP level and cow genotype on any parameter. Concentrate CP level had no significant effect on any energy utilization parameter, except for urinary energy output, which was positively related to concentrate CP level. Similarly, concentrate CP content had no effect on CH₄ emission (g/d), CH₄ per kg feed intake, or nutrient digestibility. Cross breeding of Holstein cows significantly reduced gross energy, digestible energy, and metabolizable energy intake, heat production, and milk energy output. However, cow genotype had no significant effect on energy utilization efficiency or CH₄ parameters. Furthermore, the present study yielded a value for gross energy lost as CH₄ (5.6%) on fresh grass-based diets that was lower than the widely accepted value of 6.5%. The present findings indicate that reducing concentrate CP content from 18.1 to 14.1% may not be a successful way of alleviating CH₄ emissions from lactating dairy cows offered good-quality fresh grass, but grazing cows could be offered a low-CP concentrate without compromising energy utilization efficiency. Further research is needed to investigate whether larger differences in dietary CP content may yield positive results.

Nutritional and Environmental Effects on Ammonia Emissions from Dairy Cattle Housing: A Meta-Analysis

Nitrogen excreted in dairy manure can be potentially transformed and emitted as NH, which can create livestock and human respiratory problems and be an indirect source of NO. The objectives of this study were to: (i) investigate environmental factors influencing NH emissions from dairy housing; and (ii) identify key explanatory variables in the NH emissions prediction from dairy housing using a meta-analytical approach. Data from 25 studies were used for the preliminary analysis, and data from 10 studies reporting 87 treatment means were used for the meta-analysis. Season and flooring type significantly affected NH emissions. For nutritional effect analysis, the between-study variability (heterogeneity) of mean NH emission was estimated using random-effect models and had a significant effect ( < 0.01). Therefore, random-effect models were extended to mixed-effect models to explain heterogeneity regarding the available dietary and animal variables. The final mixed-effect model included milk yield, dietary crude protein, and dry matter intake separately, explaining 45.5% of NH emissions heterogeneity. A unit increase in milk yield (kg d) resulted in a 4.9 g cow d reduction in NH emissions, and a unit increase in dietary crude protein content (%) and dry matter intake (kg d) resulted in 10.2 and 16.3 g cow d increases in NH emissions, respectively, in the scope of this study. These results can be further used to help identify mitigation strategies to reduce NH emissions from dairy housing by developing predictive models that could determine variables with strong association with NH emissions.

Assessing quality of Medicago sativa silage by monitoring bacterial composition with single molecule, real-time sequencing technology and various physiological parameters

The present study applied the PacBio single molecule, real-time sequencing technology (SMRT) in evaluating the quality of silage production. Specifically, we produced four types of Medicago sativa silages by using four different lactic acid bacteria-based additives (AD-I, AD-II, AD-III and AD-IV). We monitored the changes in pH, organic acids (including butyric acid, the ratio of acetic acid/lactic acid, γ-aminobutyric acid, 4-hyroxy benzoic acid and phenyl lactic acid), mycotoxins, and bacterial microbiota during silage fermentation. Our results showed that the use of the additives was beneficial to the silage fermentation by enhancing a general pH and mycotoxin reduction, while increasing the organic acids content. By SMRT analysis of the microbial composition in eight silage samples, we found that the bacterial species number and relative abundances shifted apparently after fermentation. Such changes were specific to the LAB species in the additives. Particularly, Bacillus megaterium was the initial dominant species in the raw materials; and after the fermentation process, Pediococcus acidilactici and Lactobacillus plantarum became the most prevalent species, both of which were intrinsically present in the LAB additives. Our data have demonstrated that the SMRT sequencing platform is applicable in assessing the quality of silage.

Replacement of grass and maize silages with lucerne silage: effects on performance, milk fatty acid profile and digestibility in Holstein-Friesian dairy cows

In total, 20 multiparous Holstein-Friesian dairy cows received one of four diets in each of four periods of 28-day duration in a Latin square design to test the hypothesis that the inclusion of lucerne in the ration of high-yielding dairy cows would improve animal performance and milk fatty acid (FA) composition. All dietary treatments contained 0.55 : 0.45 forage to concentrates (dry matter (DM) basis), and within the forage component the proportion of lucerne (Medicago sativa), grass (Lolium perenne) and maize silage (Zea mays) was varied (DM basis): control (C)=0.4 : 0.6 grass : maize silage; L20=0.2 : 0.2 : 0.6 lucerne : grass : maize silage; L40=0.4 : 0.6 lucerne : maize silage; and L60=0.6 : 0.4 lucerne : maize silage. Diets were formulated to contain a similar CP and metabolisable protein content, with the reduction of soya bean meal and feed grade urea with increasing content of lucerne. Intake averaged 24.3 kg DM/day and was lowest in cows when fed L60 (P0.05) by dietary treatment. Digestibility of DM, organic matter, CP and fibre decreased (P<0.01) with increasing content of lucerne in the diet, although fibre digestibility was similar in L40 and L60. It is concluded that first cut grass silage can be replaced with first cut lucerne silage without any detrimental effect on performance and an improvement in the milk FA profile, although intake and digestibility was lowest and plasma urea concentrations highest in cows when fed the highest level of inclusion of lucerne.

Feed conversion efficiency in dairy cows: Repeatability, variation in digestion and metabolism of energy and nitrogen, and ruminal methanogens

The objective was to study repeatability and sources of variation in feed conversion efficiency [FCE, milk kg/kg dry matter intake (DMI)] of lactating cows in mid to late lactation. Trials 1 and 2 used 16 cows (106 to 368 d in milk) grouped in 8 pairs of 1 high- and 1 low-FCE cow less than 16 d in milk apart. Trial 1 determined the repeatability of FCE during a 12-wk period. Trial 2 quantified the digestive and metabolic partitioning of energy and N with a 3-d total fecal and urine collection and measurement of CH4 and CO2 emission. Trial 3 studied selected ruminal methanogens in 2 pairs of cows fitted with rumen cannulas. Cows received a single diet including 28% corn silage, 27% alfalfa silage, 17% crude protein, and 28% neutral detergent fiber (dry matter basis). In trial 1, mean FCE remained repeatedly different and averaged 1.83 and 1.03 for high- and low-FCE cows, respectively. In trial 2, high-FCE cows consumed 21% more DMI, produced 98% more fat- and protein-corrected milk, excreted 42% less manure per kilogram of fat- and protein-corrected milk, but emitted the same daily amount of CH4 and CO2 compared with low-FCE cows. Percentage of gross energy intake lost in feces was higher (28.6 vs. 25.9%), but urinary (2.76 vs. 3.40%) and CH4 (5.23 vs. 6.99%) losses were lower in high- than low-FCE cows. Furthermore, high-FCE cows partitioned 15% more of gross energy intake toward net energy for maintenance, body gain, and lactation (37.5 vs. 32.6%) than low-FCE cows. Lower metabolic efficiency and greater heat loss in low-FCE cows might have been associated in part with greater energy demand for immune function related to subclinical mastitis, as somatic cell count was 3.8 fold greater in low- than high-FCE cows. As a percentage of N intake, high-FCE cows tended to have greater fecal N (32.4 vs. 30.3%) and had lower urinary N (32.2 vs. 41.7%) and greater milk N (30.3 vs. 19.1%) than low-FCE cows. In trial 3, Methanobrevibacter spp. strain AbM4 was less prevalent in ruminal content of high-FCE cows, which emitted less CH4 per unit of DMI and per unit of neutral detergent fiber digested than low-FCE cows. Thus lower digestive efficiency was more than compensated by greater metabolic efficiencies in high- compared with low-FCE cows. There was not a single factor, but rather a series of mechanisms involved in the observed differences in efficiency of energy utilization of the lactating cows in this study.