Predicting CO2 production of lactating dairy cows from animal, dietary, and production traits using an international dataset.

Automated measurements of the ratio of concentrations of methane and carbon dioxide, [CH4]:[CO2], in breath from individual animals (the so-called "Sniffer-technique") and estimated CO2 production can be used to estimate CH4 production, provided that CO2 production can be reliably calculated. This would allow CH4 production from individual cows to be estimated in large cohorts of cows, whereby ranking of cows according to their CH4 production might become possible and their values could be used for breeding of low CH4 emitting animals. Estimates of CO2 production are typically based on predictions of heat production, which can be calculated from body weight (BW), energy-corrected milk yield, and days of pregnancy. The objectives of the present study were to develop predictions of CO2 production directly from milk production, dietary, and animal variables, and furthermore develop different models to be used for different scenarios, depending on available data. An international data set with 2,244 records from individual lactating cows including CO2 production and associated traits, as dry matter intake (DMI), diet composition, BW, milk production and composition, days in milk and days pregnant, was compiled to constitute the training data set. Research location and experiment nested within research location were included as random intercepts. The method of CO2 production measurement (respiration chamber (RC) or GreenFeed (GF)) was confounded with research location, and therefore excluded from the model. In total, 3 models were developed based on the current training data set: Model 1 ("Best Model"), where all significant traits were included, Model 2 ("On-Farm Model"), where DMI was excluded, and Model 3 ("Reduced On-Farm Model"), where both DMI and BW were excluded. Evaluation on test data sets either with RC data (n = 103), GF data without additives (n = 478) or GF data only including observations where nitrate, 3-nitrooxypropanol (3-NOP), or a combination of nitrate and 3-NOP were fed to the cows (GF+: n = 295), showed good precision of the 3 models, illustrated by low slope bias both in absolute values (-0.22 to 0.097) and in percentage (0.049 to 4.89) of mean square error (MSE). However, the mean bias (MB) indicated systematic over-prediction and under-prediction of CO2 production when the models were evaluated on the GF and the RC test data set, respectively. To address this bias, the 3 models were evaluated on a modified test data set, where the CO2 production (g/d) was adjusted by subtracting (where measurements were obtained by RC) or adding absolute MB (where measurements were obtained by GF) from evaluation of the specific model on RC, GF, and GF+ test data sets. By this modification, the absolute values of MB and MB as percentage of MSE became negligible. In conclusion, the 3 models were precise in predicting CO2 production from lactating dairy cows.

Effects of replacement of barley with oats on milk fatty acid composition in dairy cows fed grass silage-based diets.

This study consists of milk fatty acid (FA) data collected during 2 in vivo experiments. For this study, 8 cows from each experiment were included in a replicated 4 × 4 Latin square design. At the start of experiment 1 (Exp1) cows were at (mean ± standard deviation) 87 ± 34.6 d in milk, 625 ± 85.0 kg of body weight, and 32.1 ± 4.17 kg/d milk yield and at the start of experiment 2 (Exp2) cows were at 74 ± 18.2 d in milk, 629 ± 87.0 kg of body weight, and 37.0 ± 3.2 kg/d milk yield. In Exp1, we examined the effects of gradual replacement of barley with hulled oats (oats with hulls) on milk FA composition. The basal diet was grass silage and rapeseed meal (58 and 10% of diet DM, respectively), and the 4 grain supplements were formulated so that barley was gradually replaced by hulled oats at levels of 0, 33, 67, and 100% on dry matter basis. In Exp2, we examined (1) the effects of replacing barley with both hulled and dehulled oats (oats without hulls) and (2) the effects of gradual replacement of hulled oats with dehulled oats on milk FA composition. The basal diet was grass silage and rapeseed meal (60 and 10% of diet DM, respectively), and the 4 pelleted experimental concentrates were barley, hulled oats, a 50:50 mixture of hulled and dehulled oats, and dehulled oats on dry matter basis. In Exp1, gradual replacement of barley with hulled oats decreased relative proportions of 14:0, 16:0, and total saturated FA (SFA) in milk fat linearly, whereas proportions of 18:0, 18:1, total monounsaturated FA, and total cis unsaturated FA increased linearly. Transfer efficiency of total C18 decreased linearly when barley was replaced by hulled oats in Exp1. In Exp2, relative proportions of 14:0, 16:0, and total SFA were lower, whereas proportions of 18:0, 18:1, monounsaturated FA, and cis unsaturated FA were higher in milk from cows fed the oat diets than in milk from cows fed the barley diet. Moreover, in Exp2, gradual replacement of hulled oats with dehulled oats slightly decreased the relative proportion of 14:0 in milk fat but did not affect the proportions of 16:0, 18:0, 18:1, total SFA, monounsaturated FA, trans FA, or polyunsaturated FA. In Exp2, transfer efficiency of total C18 was lower when cows were fed the oat diets than when fed the barley diet and decreased linearly when hulled oats were replaced with dehulled oats. Predictions of daily CH4 emissions (g/d) using the on-farm available variables energy-corrected milk yield and body weight were not markedly improved by including milk concentrations of individual milk FA in prediction equations. In conclusion, replacement of barley with oats as a concentrate supplement for dairy cows fed a grass silage-based diet could offer a practical strategy to change the FA composition of milk to be more in accordance with international dietary guidelines regarding consumption of SFA.

Comparison of Molly and Karoline models to predict methane production in growing and dairy cattle.

Numerous empirical and mechanistic models predicting methane (CH4) production are available. The aim of this work was to evaluate the Molly cow model and the Nordic cow model Karoline in predicting CH4 production in cattle using a data set consisting of 267 treatment means from 55 respiration chamber studies. The dietary and animal characteristics used for the model evaluation represent the range of diets fed to dairy and growing cattle. Feedlot diets and diets containing additives mitigating CH4 production were not included in the data set. The relationships between observed and predicted CH4 (pCH4) were assessed by regression analysis using fixed and mixed model analysis. Residual analysis was conducted to evaluate which dietary factors were related to prediction errors. The fixed model analysis showed that the Molly predictions were related to the observed data (± standard error) as CH4 (g/d) = 0.94 (±0.022) × pCH4 (g/d) + 31 (±6.9) [root mean squared prediction error (RMSPE) = 45.0 g/d (14.9% of observed mean), concordance correlation coefficient (CCC) = 0.925]. The corresponding equation for the Karoline model was CH4 (g/d) = CH4 (g/d) = 0.98 (±0.019) × pCH4 (g/d) + 7.0 (±6.0) [RMSPE = 35.0 g/d (11.6%), CCC = 0.953]. Proportions of mean squared prediction error attributable to mean and linear bias and random error were 10.6, 2.2, and 87.2% for the Molly model, and 1.3, 0.3, and 98.6% for the Karoline model, respectively. Mean and linear bias were significant for the Molly model but not for the Karoline model. With the mixed model regression analysis RMSPE adjusted for random study effects were 10.9 and 7.9% for the Molly model and the Karoline model, respectively. The residuals of CH4 predictions were more strongly related to factors associated with CH4 production (feeding level, digestibility, fat concentrations) with the Molly model compared with the Karoline model. Especially large mean (underprediction) and linear bias (overprediction of low digestibility diets relative to high digestibility diets) contributed to the prediction error of CH4 yield with the Molly model. It was concluded that both models could be used for prediction of CH4 production in cattle, but Karoline was more accurate and precise based on smaller RMSPE, mean bias, and slope bias, and greater CCC. The importance of accurate input data of key variables affecting diet digestibility is emphasized.

Effects of ruminal protozoa on methane emissions in ruminants-A meta-analysis.

The effects of different ruminal protozoa (RP) on CH4 emissions from ruminants were evaluated in a meta-analysis, using 64 publications reporting data from 79 in vivo experiments. Experiments included in the database reported CH4 emissions (g/d) and total RP (TRP, log10 cells/mL) from the same group of animals. The relationship between CH4 emissions and RP (TRP, entodiniomorphids, and isotrichids), and TRP-, entodiniomorphid-, and isotrichid-based CH4 emission prediction models, were evaluated as mixed models with experiment as a random effect and weighted by the reciprocal of the standard error of the mean and centered around one. Positive associations existed between TRP and isotrichids with CH4 emissions but not between entodiniomorphids and CH4 emissions. A reduction in CH4 emissions was observed, averaging 7.96 and 4.25 g/d, per log unit reduction in TRP and isotrichid concentrations, respectively. Total RP and isotrichids were important variables in predicting CH4 emissions from ruminants. Isotrichid CH4 prediction model was more robust than the TRP, evidenciated by lower predicted sigma hat study (%), and error (%), and with higher concordance correlation coefficient. Both TRP and isotrichid models can accurately predict CH4 emissions across different ruminant types, as shown by the low square root of the mean square prediction error, with 6.59 and 4.08% of the mean of root of the mean square prediction error in the TRP and isotrichid models, respectively. Our results confirm that isotrichids are more important than entodiniomorphids in methanogenesis. Distinguishing these 2 populations yielded a more robust CH4 prediction model than combining them as total protozoa.

Prediction of nitrogen excretion from data on dairy cows fed a wide range of diets compiled in an intercontinental database: A meta-analysis.

Manure nitrogen (N) from cattle contributes to nitrous oxide and ammonia emissions and nitrate leaching. Measurement of manure N outputs on dairy farms is laborious, expensive, and impractical at large scales; therefore, models are needed to predict N excreted in urine and feces. Building robust prediction models requires extensive data from animals under different management systems worldwide. Thus, the study objectives were (1) to collate an international database of N excretion in feces and urine based on individual lactating dairy cow data from different continents; (2) to determine the suitability of key variables for predicting fecal, urinary, and total manure N excretion; and (3) to develop robust and reliable N excretion prediction models based on individual data from lactating dairy cows consuming various diets. A raw data set was created based on 5,483 individual cow observations, with 5,420 fecal N excretion and 3,621 urine N excretion measurements collected from 162 in vivo experiments conducted by 22 research institutes mostly located in Europe (n = 14) and North America (n = 5). A sequential approach was taken in developing models with increasing complexity by incrementally adding variables that had a significant individual effect on fecal, urinary, or total manure N excretion. Nitrogen excretion was predicted by fitting linear mixed models including experiment as a random effect. Simple models requiring dry matter intake (DMI) or N intake performed better for predicting fecal N excretion than simple models using diet nutrient composition or milk performance parameters. Simple models based on N intake performed better for urinary and total manure N excretion than those based on DMI, but simple models using milk urea N (MUN) and N intake performed even better for urinary N excretion. The full model predicting fecal N excretion had similar performance to simple models based on DMI but included several independent variables (DMI, diet crude protein content, diet neutral detergent fiber content, milk protein), depending on the location, and had root mean square prediction errors as a fraction of the observed mean values of 19.1% for intercontinental, 19.8% for European, and 17.7% for North American data sets. Complex total manure N excretion models based on N intake and MUN led to prediction errors of about 13.0% to 14.0%, which were comparable to models based on N intake alone. Intercepts and slopes of variables in optimal prediction equations developed on intercontinental, European, and North American bases differed from each other, and therefore region-specific models are preferred to predict N excretion. In conclusion, region-specific models that include information on DMI or N intake and MUN are required for good prediction of fecal, urinary, and total manure N excretion. In absence of intake data, region-specific complex equations using easily and routinely measured variables to predict fecal, urinary, or total manure N excretion may be used, but these equations have lower performance than equations based on intake.

Replacement of barley with oats and dehulled oats: Effects on milk production, enteric methane emissions, and energy utilization in dairy cows fed a grass silage-based diet.

Sixteen Nordic Red dairy cows, at 80 ± 4.6 d in milk and with an average body weight of 624 ± 91.8 kg, were used in a replicated 4 × 4 Latin square design to investigate the effects of different concentrate supplements on milk production, enteric CH4 emissions, ruminal fermentation, digestibility, and energy utilization. The cows were blocked into 4 groups based on parity and milk yield and randomly assigned to 1 of 4 experimental concentrates: (1) barley, (2) hulled oats, (3) an oat mixture consisting of hulled and dehulled oats, 50:50 on dry matter basis, and (4) dehulled oats; canola meal was a protein supplement in all 4 concentrates. The cows were fed grass silage and experimental concentrate (forage-to-concentrate ratio 60:40 on dry matter basis) ad libitum. To compare the effects of barley and oats, the barley diet was compared with the overall mean of the hulled oat, oat mixture, and dehulled oat diets. To investigate the effects of gradual replacement of hulled oats with dehulled oats, linear and quadratic contrasts were specified. Milk and energy-corrected milk (ECM) yield were higher on the oat diets compared with the barley diet but were not affected by the type of oats. Concentrations of milk constituents were not affected by grain species or type of oats, except for protein concentration, which was lower on the oat diets than on the barley diet. Feeding the oat diets led to higher milk protein yield and higher milk urea N concentrations. Feed efficiency tended to be higher on the oat diets, and linearly increased with increased inclusion of dehulled oats. Methane emissions (g/d) and CH4 yield (g/kg of dry matter intake) were unaffected by grain species but increased linearly with increasing inclusion of dehulled oats in the diet. Because of higher ECM yield, CH4 intensity (g/kg of ECM) was on average 5.7% lower from cows on the oat diets than on the barley diet. Ruminal fermentation was not affected by dietary treatment. Total-tract apparent digestibility of organic matter, crude protein, and neutral detergent fiber was unaffected by grain species but linearly increased with increasing inclusion of dehulled oats. Gross energy content was higher on the oat diets and linearly increased with increasing inclusion of dehulled oats. Feeding the oat diets led to a lower ratio of CH4 energy to gross energy intake, greater milk energy and heat production but no change in energy balance. Gradual replacement of hulled oats with dehulled oats linearly increased gross energy digestibility, CH4 energy, metabolizable energy intake, heat production, and energy balance. We observed no effect of dietary treatment on efficiency of metabolizable energy use for lactation. In conclusion, replacing barley with any type of oats increased milk and ECM yield, which led to a 5.7% decrease in CH4 intensity. In addition, dehulling of oats before feeding is unnecessary because it did not significantly improve production performance of dairy cows in positive energy balance.

The effects of gradual replacement of barley with oats on enteric methane emissions, rumen fermentation, milk production, and energy utilization in dairy cows.

This study evaluated the effects of gradual replacement of barley with oats on enteric CH4 emissions, rumen fermentation, diet digestibility, milk production, and energy utilization in dairy cows fed a grass silage-based diet. Sixteen lactating Nordic Red dairy cows received a total mixed ration [58:42 forage:concentrate on dry matter (DM) basis]. Grass silage (Phleum pratense) was the sole forage with canola meal (10% of diet DM) as a protein supplement. The effects of gradual replacement of barley with oats on DM basis were evaluated using a replicated 4 × 4 Latin square design with 21 d periods. The grain supplements (30% of diet DM) consisted of 100% barley, 67% barley and 33% oats, 33% barley and 67% oats, and 100% oats. In addition to intake, milk production, and digestibility measurements, CH4 emissions were measured by the GreenFeed system (C-Lock Inc.). The energy metabolism was estimated from the gas exchange measurements recorded by the GreenFeed unit. The last 10 d of each period were used for recordings of gas exchanges, feed intake and milk production. Dry matter intake, body weight, milk yield, and energy-corrected milk yield were not affected by gradual replacement of barley with oats in the diet. Increased inclusion of oats linearly decreased CH4 emissions from 467 to 445 g/d, and CH4 intensity from 14.7 to 14.0 g/kg energy-corrected milk. In addition, the ratio of CH4 to CO2 decreased with increasing inclusion of oats in the diet. Digestibility of organic matter, neutral detergent fiber, and potentially digestible neutral detergent fiber decreased linearly with increasing inclusion of oats. Increased inclusion of oats linearly increased fecal energy from 121 to 133 MJ/d, whereas urinary energy and heat production were not affected by dietary treatment. This resulted in a linear decrease in metabolizable energy intake. However, increased levels of oat in the diet did not significantly affect energy balance or efficiency of metabolizable energy utilization for lactation. This study concludes that barley could be replaced with oats in the diet of dairy cows fed a grass silage-based diet to mitigate CH4 emissions without having any adverse effects on productivity or energy balance. However, the effect of replacing barley with oats on CH4 emissions is dependent on the differences between barley and oats in the concentrations of indigestible neutral detergent fiber and fat.

The use of an upgraded GreenFeed system and milk fatty acids to estimate energy balance in early-lactation cows.

Measurements of energy balance (EB) require the use of respiration chambers, which are quite expensive and laborious. The GreenFeed (GF) system (C-Lock Inc.) has been developed to offer a less expensive, user friendly alternative. In this study, we used the GF system to estimate the EB of cows in early lactation and compared it with EB predicted from energy requirements for dairy cows in the Finnish feeding standards. We also evaluated the association between milk fatty acids and the GF estimated EB. The cows were fed the same grass silage but supplemented with either cereal grain or fibrous by-product concentrate. Cows were followed from 1 to 18 wk of lactation, and measurements of energy metabolism variables were taken. Data were subjected to ANOVA using the mixed model procedure of SAS (SAS Institute Inc.). The repeatability estimates of the gaseous exchanges from the GF were moderate to high, presenting an opportunity to use it for indirect calorimetry in EB estimates. Energy metabolism variables were not different between cows fed different concentrates. However, cows fed the grain concentrate produced more methane (24.0 MJ/d or 62.9 kJ/MJ of gross energy) from increased digestibility than cows fed the by-product concentrate (21.3 MJ/d or 56.5 kJ/MJ of gross energy). Nitrogen metabolism was also not different between the diets. Milk long-chain fatty acids displayed an inverse time course with EB and de novo fatty acids. There was good concordance (0.85) between EB predicted using energy requirements derived from the Finnish feed table and EB estimated by the GF system. In conclusion, the GF can accurately estimate EB in early-lactating dairy cows. However, more data are needed to further validate the system for a wide range of dietary conditions.

Ruminal metabolism of ammonia N and rapeseed meal soluble N fraction.

The present study was conducted to investigate ruminal N metabolism in dairy cows using 15N labeled N sources [ammonia N (AN), soluble non-ammonia N (SNAN) from rapeseed meal, and insoluble non-ammonia N (NAN) from rapeseed meal]. To describe the observed pattern of 15N transactions in the rumen, dynamic compartmental models were developed. The experiment consisted of 3 experimental treatments allocated to 4 cows according to a changeover design. The results from 2 treatments (AN and rapeseed meal SNAN) are reported in this paper. Ammonia N and rapeseed SNAN, both labeled with 15N, were administered intraruminally. Rumen evacuations in combination with grab samples from the rumen contents were used to determine ruminal N pool sizes. The 15N-atom% excess was determined in N fractions of rumen digesta samples that were distributed between 0 and 82 h after dosing. For the AN treatment, a 2-compartment model was developed to describe the observed pattern in 15N-atom% excess pool sizes of AN and bacterial N and to estimate kinetic parameters of ruminal 15N transactions. For the SNAN treatment, an additional compartment of SNAN was included in the model. Model simulations were used to estimate N fluxes in the rumen. Both models described the observed pattern of 15N-atom% excess pool sizes accurately, based on small residuals between observed and predicted values. Immediate increases in 15N-atom% excess of bacterial N with AN treatment suggested that microbes absorbed AN from extracellular pools rapidly to maintain sufficient intracellular concentrations. Proportionally 0.69 of the AN dose was recovered as NAN flow from the rumen. A rapid disappearance of labeled SNAN from rumen fluid and appearance in bacterial N pool indicated that, proportionally, 0.56 of SNAN was immediately either adsorbed to bacterial cell surfaces or taken up to intracellular pools. Immediate uptake of labeled SNAN was greater than that of AN (proportionally 0.56 vs. 0.16 of the dose). Degradation rate of SNAN to AN was relatively slow (0.46/h), but only 0.08 of the SNAN dose was estimated to escape ruminal degradation because of rapid uptake by the bacteria. Overall, losses of the 15N dose as AN absorption and outflow from the rumen were higher (P < 0.01) for the AN than the SNAN treatment (0.31 and 0.11 of the dose, respectively). Consequently, recovery as NAN flow was greater for SNAN than for AN treatment (0.89 vs. 0.69 of the dose). Estimated rate of bacterial N recycling to AN was on average 0.006/h, which suggests that N losses due to intraruminal recycling are small in dairy cows fed at high intake levels. We conclude that SNAN isolated from rapeseed meal had better ruminal N utilization efficiency than AN, as indicated by smaller ruminal N losses as AN (0.11 vs. 0.31 of the dose) and greater bacterial N flow (0.81 vs. 0.69 of the dose). Furthermore, the current findings indicate that rapid adsorption of soluble proteins to bacterial cells plays an important role in ruminal N metabolism.

The effects of energy metabolism variables on feed efficiency in respiration chamber studies with lactating dairy cows.

The objective of the present study was to investigate factors related to variation in feed efficiency (FE) among cows. Data included 841 cow/period observations from 31 energy metabolism studies assembled across 3 research stations. The cows were categorized into low-, medium-, and high-FE groups according to residual feed intake (RFI), residual energy-corrected milk (RECM), and feed conversion efficiency (FCE). Mixed model regression was conducted to identify differences among the efficiency groups in animal and energy metabolism traits. Partial regression coefficients of both RFI and RECM agreed with published energy requirements more closely than cofficients derived from production experiments. Within RFI groups, efficient (Low-RFI) cows ate less, had a higher digestibility, produced less methane (CH4) and heat, and had a higher efficiency of metabolizable energy (ME) utilization for milk production. High-RECM (most efficient) cows produced 6.0 kg/d more of energy-corrected milk (ECM) than their Low-RECM (least efficient) contemporaries at the same feed intake. They had a higher digestibility, produced less CH4 and heat, and had a higher efficiency of ME utilization for milk production. The contributions of improved digestibility, reduced CH4, and reduced urinary energy losses to increased ME intake at the same feed intake were 84, 12, and 4%, respectively. For both RFI and RECM analysis, increased metabolizability contributed to approximately 35% improved FE, with the remaining 65% attributed to the greater efficiency of utilization of ME. The analysis within RECM groups suggested that the difference in ME utilization was mainly due to the higher maintenance requirement of Low-RECM cows compared with Medium- and High-RECM cows, whereas the difference between Medium- and High-RECM cows resulted mainly from the higher efficiency of ME utilization for milk production in High-RECM cows. The main difference within FCE (ECM/DMI) categories was a greater (8.2 kg/d) ECM yield at the expense of mobilization in High-FCE cows compared with Low-FCE cows. Methane intensity (CH4/ECM) was lower for efficient cows than for inefficient cows. The results indicated that RFI and RECM are different traits. We concluded that there is considerable variation in FE among cows that is not related to dilution of maintenance requirement or nutrient partitioning. Improving FE is a sustainable approach to reduce CH4 production per unit of product, and at the same time improve the economics of milk production.

Between-cow variation in the components of feed efficiency.

A meta-analysis based on an individual-cow data set was conducted to investigate between-cow variations in the components and measurements of feed efficiency (FE) and to explore the associations among these components. Data were taken from 31 chamber studies, consisting of a total of 841 cow/period observations. The experimental diets were based on grass or corn silages, fresh grass, or a mixture of fresh grass and straw, with cereal grains or by-products as energy supplements, and soybean or canola meal as protein supplements. The average forage-to-concentrate ratio across all diets on a dry matter basis was 56:44. Variance component and repeatability estimates of FE measurements and components were determined using diet, period, and cow within experiment as random effects in mixed procedures of SAS (SAS Institute Inc., Cary, NC). The between-cow coefficient of variation (CV) in gross energy intake (GE; CV = 0.10) and milk energy (El) output as a proportion of GE (El/GE; CV = 0.084) were the largest among all component traits. Similarly, the highest repeatability estimates (≥0.50) were observed for these 2 components. However, the between-cow CV in digestibility (DE/GE), metabolizability [metabolizable energy (ME)/GE], methane yield (CH4E/GE), proportional urinary energy output (UE/GE), and heat production (HP/GE), as well as the efficiency of ME use for lactation (kl), were rather small. The least repeatable component of FE was UE/GE. For FE measurements, the between-cow CV in residual energy-corrected milk (RECM) was larger than for residual feed intake (RFI), suggesting a greater possibility for genetic gain in RECM than in RFI. A high DE/GE was associated with increased CH4E/GE (r = 0.24), HP/GE (r = 0.12), ME/GE (r = 0. 91), energy balance as a proportion of GE (EB/GE; r = 0.35), and kl (r = 0.10). However, no correlation between DE/GE and GE intake or UE/GE was observed. Increased proportional milk energy adjusted to zero energy balance (El(0)/GE) was associated with increases in DE/GE, ME/GE, EB/GE, and kl but decreases in UE/GE, CH4E/GE, and HP/GE, with no effect on GE intake. In conclusion, several mechanisms are involved in the observed differences in FE among dairy cows, and reducing CH4E yield (CH4E/GE) may inadvertently result in reduced GE digestibility. However, the selection of dairy cows with improved energy utilization efficiencies offers an effective approach to lower enteric CH4 emissions.

Short communication: Variation in feed efficiency hampers use of carbon dioxide as a tracer gas in measuring methane emissions in on-farm conditions.

Breeding cows for low CH4 emissions requires that the trait is variable and that it can be recorded with low cost from an adequate number of individuals and with high precision, but not necessarily with high accuracy if the trait is measured with high repeatability. The CH4:CO2 ratio in expired breath is a trait often used as a tracer with the production of CO2 predicted from body weight (BW), energy-corrected milk yield, and days of pregnancy. This approach assumes that efficiency of energy utilization for maintenance and production is constant. Data (307 cow-period observations) from 2 locations using the same setup for measuring CH4 and CO2 in respiration chambers were compiled, and observed production of CH4 and CO2 was compared with the equivalent predicted production using 2 different approaches. Carbon dioxide production was predicted using a previously reported model based on metabolic BW and energy-corrected milk production and a currently developed model based on energy requirements and the relationship between observed CO2 and heat production (models 1 and 2, respectively). Animals used were categorized (low, medium, and high efficiency) according to (1) residual feed intake and (2) residual milk production. Model 1 underestimated CH4 production by 15%, whereas model 2 overestimated CH4 by 1.4% for the whole database. Model 1 underestimated CO2 production by 2.8 and 0.9 kg/d for low- and high-efficiency cows, respectively, whereas model 2 underestimated CO2 production by 0.9 kg/d for low-efficient animals but overestimated it by 1.2 kg/d for high-efficiency cows. Efficient cows produce less heat, and consequently CO2, per unit of metabolic body weight and energy-corrected milk than inefficient cows, challenging the use of CO2 as a tracer gas. Because of biased estimates of CO2 production, the models overestimated CH4 production of high-efficiency cows by, on average, 17% relative to low-efficiency cows, respectively. Selecting low CH4-emitting cows using a CO2 tracer method can therefore favor inefficient cows over efficient cows.

Effects of different barley and oat varieties on methane production, digestibility, and fermentation pattern in vitro.

The objective of this in vitro study was to determine the effects of different barley and oat varieties on CH4 production, digestibility, and rumen fermentation patterns in dairy cows. Our hypothesis was that oat-based diets would decrease CH4 production compared with barley-based diets, and that CH4 production would differ between varieties within grain species. To evaluate this hypothesis, we conducted an in vitro experiment using a fully automated gas production technique, in which the total gas volume was automatically recorded by the system. The experiment consisted of triplicate 48-h incubations with 16 treatments, including 8 different varieties of each grain. The grain varieties were investigated as a mix with an early-cut grass silage (1:1 ratio of grain to silage on a dry matter basis) and mixed with buffered rumen fluid. We estimated predicted in vivo total gas production and CH4 production by applying a set of models to the gas production data obtained by the in vitro system. We also evaluated in vitro digestibility and fermentation characteristics. The variety of grain species did not affect total gas production, CH4 production, or fermentation patterns in vitro. However, in vitro-determined digestibility and pH were affected by variety of grain species. Grain species affected total gas and CH4 production: compared with barley-based diets, oat-based diets decreased total gas production and CH4 production by 8.2 and 8.9%, respectively, relative to dry matter intake. Grain species did not affect CH4 production relative to in vitro true dry matter digestibility. Oat-based diets decreased digestibility and total volatile fatty acid production, and maintained a higher pH at 48 h of incubation compared with barley-based diets. Grain species did not affect fermentation patterns, except for decreased molar proportions of valerate with oat-based diets. These results suggest that replacing barley with oats in dairy cow diets could decrease enteric CH4 production.

Effects of ensiling time on corn silage neutral detergent fiber degradability and relationship between laboratory fiber analyses and in vivo digestibility.

Accurate analysis of degradability of silage neutral detergent fiber (NDF) is important for diet formulation and to predict lactational performance of dairy cows. In this study, 5 corn silage hybrids ensiled for 0 (unfermented), 30, 60, 120, and 150 d were used to determine the effects of ensiling time on silage neutral detergent fiber degradability (NDFD) and to assess the relationships between near-infrared reflectance spectroscopy (NIR) NDF-related analyses and in situ NDFD variables. In addition, the relationships between dietary concentration of indigestible NDF, 288-h incubation (iNDF288), or undegraded NDF, 240-h incubation (uNDF240), and in vivo total-tract apparent organic matter and NDF digestibility were studied in total mixed ration samples from 16 experiments with lactating dairy cows. Ensiling time had no effect on silage NDF concentration; however, the ratio of acid detergent fiber ÷ NDF increased, and estimated hemicellulose concentration decreased quadratically with ensiling time. Also, concentration of NDF-bound protein decreased, and that of lignin increased linearly with ensiling time. These changes in silage fiber composition resulted in a linear decrease in in situ effective degradability of silage NDF with increasing ensiling time. The indigestible fraction of NDF and concentration of structural carbohydrates were not affected by ensiling time. Correlations of in situ NDFD variables with laboratory NIR NDFD analyses were weak to moderate. The relationship of corn silage uNDF240 with lignin concentration or 30-h NDFD (all NIR analyses) was remarkably good (R2 = 0.73 and 0.88, respectively). The relationship between in situ iNDF288 concentration (but not uNDF240) and in vivo total-tract apparent digestibility of dietary organic matter and NDF was good (R2 = 0.72 and 0.80, respectively). In conclusion, in situ degradability of silage NDF linearly decreased from 0 to 150 d ensiling time, primarily caused by a decrease in concentrations of hemicellulose and NDF-bound protein. In situ NDF degradability measurements and common laboratory NIR NDF-related analyses were generally poorly correlated. We found a good relationship between in vivo NDF digestibility and dietary concentration of iNDF288 determined in situ, but the relationship with uNDF240 was poor.

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.

Effects of intraruminal urea-nitrogen infusions on feed intake, nitrogen utilization, and milk yield in dairy cows.

The objective of this study was to determine the effects of supplementation of protein deficient diet with increasing amounts of urea-N on feed intake, milk yield, rumen fermentation, and nutrient digestibility in dairy cows. The hypothesis was that low rumen ammonia-N concentrations provide suboptimal conditions for rumen microbes and these conditions can be alleviated by urea-N that increases rumen ammonia-N concentrations. To evaluate this hypothesis, the diet was formulated slightly deficient with respect to rumen-degradable protein. To supplement the diet with rumen degradable N, 5 levels of urea-N (0, 17, 33, 49, and 66 g/d) were continuously infused into the rumen of 5 dairy cows according to a 5 × 5 Latin square. Increasing levels of urea-N infusion increased N intake and N excretion in urine and feces in a linear manner and tended to increase milk and milk protein yields. Feed intake and fiber digestibility were not affected by urea-N infusion levels. Rumen ammonia-N concentrations remained low (3.5 mg/100 mL) and did not respond to urea-N infusions levels between 0 to 49 g/d, whereas the highest level of urea-N (66 g/d) increased rumen ammonia-N concentration to 5.1 mg/100 mL (quadratic effect). These observations suggested that rumen microbes efficiently captured ammonia-N from rumen fluid until sufficient intracellular ammonia-N concentrations were attained, after which ammonia-N concentrations started to increase in extracellular rumen fluid. In contrast, milk urea-N concentrations increased in a curvilinear manner (cubic effect) from 4.4 to around 6 mg/100 mL for the medium levels of urea-N and then to 7.9 mg/100 mL for the highest level of urea-N infusion. The current results indicated that 18% of supplementary N intake was secreted in milk and 53% in urine. In spite of low rumen ammonia-N concentrations observed for the basal diet, it was estimated that only 43% of supplementary N was captured by rumen microbes. Estimated true digestibility for supplementary N (93%) provided further evidence that urea-N stimulated microbial N synthesis. The current results indicate that rumen ammonia-N concentration was an insensitive indicator of N deficiency at low levels of diet CP, whereas milk urea-N was responsive to diet CP concentrations at all urea-N infusion levels.

Ruminal metabolism of grass silage soluble nitrogen fractions.

The present study was conducted to investigate ruminal N metabolism in dairy cows using 15N-labeled N sources and dynamic models. The data summarized in this study were obtained from 2 of 4 treatments whose effects were determined in a 4 × 4 Latin square design. Soluble N (SN) isolated from timothy grass silage labeled with 15N and ammonia N (AN) labeled with 15N were administered into the rumen contents of 4 ruminally cannulated dairy cows. Ruminal N pool sizes were determined by manual evacuation of rumen contents. The excess 15N-atom% was determined in N-fractions of rumen digesta grab samples that were collected frequently between 0 to 72 h and used to determine 15N metabolism in the rumen. Calculations of area under the curve ratios of 15N were used to estimate proportions of N fractions originating from precursor N pools. A model including soluble nonammonia N (SNAN), AN, bacterial N, and protozoal N pools was developed to predict observed values of 15N atomic excess pool sizes. The model described the pool sizes accurately based on small residuals between observed and predicted values. An immediate increase in 15N enrichment of protozoal N suggests physical attachment of bacteria pool to protozoa pool. The mean proportions of bacterial N, protozoal N, and feed N in rumen solid phase were 0.59, 0.20, and 0.21, respectively. These observations suggest that protozoal N accounted for 0.25 of rumen microbial N. About 0.90 of the initial dose of AN was absorbed or taken up by microbes within 2 h. Faster 15N enrichment of bacterial N with SN than with AN treatment indicates a rapid adsorption of SNAN to microbial cells. Additionally, the recovery of 15N as microbial and feed N flow from the rumen was approximately 0.36 greater for SN than for the AN treatment, indicating that SNAN was more efficiently used for microbial growth than AN. The present study indicated that about 0.15 of microbial N flowing to the duodenum was of protozoal origin and that 0.95 of the protozoal N originated from engulfed bacterial N. The kinetic variables indicated that 0.125 of SNAN escaped ruminal degradation, which calls into question the use of in situ estimations of protein degradation to predict the flow of rumen undegradable protein.

Predicting omasal flow of nonammonia N and milk protein yield from in vitro-determined utilizable crude protein at the duodenum.

This study evaluated the relationship between utilizable crude protein (uCP) at the duodenum estimated in vitro and omasal flow of crude protein (CP; omasal flow of nonammonia N × 6.25) measured in lactating dairy cows. In vivo data were obtained from previous studies estimating omasal digesta flow using a triple-marker method and 15N as microbial marker. A total of 34 different diets based on grass and red clover silages were incubated with buffered rumen fluid previously preincubated with carbohydrates for 3 h. The buffer solution was modified to contain 38 g of NaHCO3 and 1 g of (NH4)HCO3 in 1,000 mL of distilled water. Continuous sampling of the liquid phase for determination of ammonia-N was performed at 0.5, 4, 8, 12, 24, and 30 h after the start of incubation. The ammonia N concentrations after incubation were used to calculate uCP. The natural logarithm of uCP [g/kg of dry matter (DM)] at time points 0.5, 4, 8, 12, 24, and 30 h of incubation was plotted against time to estimate the concentration of uCP (g/kg of DM) at time points 16, 20, and 24 h using an exponential function. Fixed model regression analysis and mixed model regression analysis with random study effect were used to evaluate the relationships between predicted uCP (supply and concentration) and observed omasal CP flow and milk protein yield. Residual analysis was also conducted to evaluate whether any dietary factors influenced the relationships. The in vitro uCP method ranked the diets accurately in terms of total omasal CP flow (kg/d) or omasal CP flow per kilogram of DM intake. We also noted a close relationship between estimated uCP supply and adjusted omasal CP flow, as demonstrated by a coefficient of determination of 0.87, although the slope of 0.77 indicated that estimated uCP supply (kg/d) was greater than the value determined in vivo. The linear bias with mixed model analysis indicated that uCP supply overestimated the difference in omasal CP flow between the diets within a study, an error most likely related to study differences in feed intake, animals, and methodology. Predicting milk protein yield from uCP supply showed a positive relationship using a mixed model (coefficient of determination = 0.79), and we observed no difference in model fit between the time points of incubation (16, 20, or 24 h). The results of this study indicate that the in vitro method can be a useful tool in evaluating protein value of ruminant diets.

Effects of replacement of late-harvested grass silage and barley with early-harvested silage on ruminal digestion efficiency in lactating dairy cows.

The objective of this experiment was to quantify the effects of graded replacement of late-harvested grass silage and barley with early-harvested silage on nutrient digestion and rumen fermentation. Four experimental diets were fed to 4 multiparous rumen-cannulated Nordic Red cows in 4 × 4 Latin square design with 21-d periods. Dietary treatments consisted of late-cut grass silage (LS) and rolled barley, which was gradually replaced with early-cut grass silage [ES; 0, 33, 67, and 100% of the forage component (ES + LS) of the diet]. With increased proportion of ES in the diet, the proportion of barley decreased from 47.2 to 26.6% on a dry matter basis. Early- and late-cut silages were harvested at 2-wk intervals (predicted concentrations of metabolizable energy 11.0 and 9.7 MJ/kg of dry matter). The 4 diets were formulated to support the same milk production. Nutrient flows were quantified using omasal sampling technique applying the triple-marker method (Cr, Yb, and indigestible neutral detergent fiber) and 15N as a microbial marker. Feed intake decreased with graded replacement of LS and barley with ES, but milk production was not influenced by diet. Digestibility of nutrients improved with graded addition of ES in the diet with the greatest difference observed in digestibility of neutral detergent fiber (NDF) and potentially digestible NDF (pdNDF). The results suggested that improved cell wall digestibility with graded level of ES in the diet was partly related to higher intrinsic digestibility of ES than LS, and partly due to negative associative effects with an increased proportion of LS and barley in the diet. Efficiency of microbial N synthesis was not influenced by the diet, but ruminal protein degradability increased with ES in the diet. Rumen fermentation pattern was not affected by the diet despite large difference in the profile of dietary carbohydrates. Rumen pool size of NDF and pdNDF, and ruminal turnover time of NDF decreased with graded addition of ES in the diet, whereas digestion rate of pdNDF improved. The results of this study indicate that increased CH4 yield in a parallel production study with graded addition of ES in the diet were more related to greater ruminal and total digestibility of organic matter than to the changes in rumen fermentation pattern.

Effect of dietary fish oil supplements alone or in combination with sunflower and linseed oil on ruminal lipid metabolism and bacterial populations in lactating cows.

Fish oil (FO) alters ruminal biohydrogenation causing trans fatty acid (FA) intermediates to accumulate, but the effects of 18-carbon polyunsaturated FA supply on ruminal long-chain FA metabolism and microbial communities in cattle fed FO are not well established. Four cows fitted with rumen cannula were used in a 4 × 4 Latin square with 21-d experimental periods to evaluate the effects of FO alone or in combination with plant oils high in 18:2n-6 or 18:3n-3 on rumen microbial ecology and flow of FA at the omasum. Treatments comprised a basal grass silage-based diet containing no additional oil (control) or supplements of FO (200 g/d) or FO (200 g/d) plus 500 g/d of sunflower oil (SFO) or linseed oil (LFO). Flow of FA was determined using the omasal sampling technique. The relative abundance of key biohydrogenating bacteria was assessed by quantitative PCR on 16S rRNA genes in omasal digesta. Fish oil-supplemented treatments increased the amounts of trans-18:1, trans-18:2, and 20- to 22-carbon polyunsaturated FA escaping the rumen. Relative to the control, oil supplements had no effect on the amount of 18:0 leaving the rumen, but LFO decreased the flow of 18:0 at the omasum compared with SFO. Both SFO and LFO increased trans-18:1 relative to FO, whereas LFO resulted in the highest trans-18:2 and 20- to 22-carbon FA flow. Supplements of FO plus plant oils shifted biohydrogenation toward trans-10 18:1 formation. Compared with FO alone, the ruminal metabolism of 22:6n-3 in the rumen of lactating cows is more extensive on diets containing higher amounts of 18-carbon polyunsaturated FA. However, the biohydrogenation of 22:5n-3 was less extensive in LFO than SFO, but showed no difference between FO and diets containing plant oils. Ruminal outflow of 20:5n-3 was not altered when plant oils were added to FO. Alterations in the amount of intermediates at the omasum or ruminal biohydrogenation pathways were not accompanied by major changes in analyzed bacterial populations. In conclusion, dietary supplements of FO alone or in combination with plant oils increase the amount of biohydrogenation intermediates containing 1 or more trans double bonds escaping the rumen, which may have implications for host metabolism and the nutritional quality of ruminant foods.