Use of methane production data for genetic prediction in beef cattle: A review

Methane (CH4) is a greenhouse gas that is produced and emitted from ruminant animals through enteric fermentation. Methane production from cattle has an environmental impact and is an energetic inefficiency. In the beef industry, CH4 production from enteric fermentation impacts all three pillars of sustainability: environmental, social, and economic. A variety of factors influence the quantity of CH4 produced during enteric fermentation, including characteristics of the rumen and feed composition. There are several methodologies available to either quantify or estimate CH4 production from cattle, all with distinct advantages and disadvantages. Methodologies include respiration calorimetry, the sulfur-hexafluoride tracer technique, infrared spectroscopy, prediction models, and the GreenFeed system. Published studies assess the accuracy of the various methodologies and compare estimates from different methods. There are advantages and disadvantages of each technology as they relate to the use of these phenotypes in genetic evaluation systems. Heritability and variance components of CH4 production have been estimated using the different CH4 quantification methods. Agreement in both the amounts of CH4 emitted and heritability estimates of CH4 emissions between various measurement methodologies varies in the literature. Using greenhouse gas traits in selection indices along with relevant output traits could provide producers with a tool to make selection decisions on environmental sustainability while also considering productivity. The objective of this review was to discuss factors that influence CH4 production, methods to quantify CH4 production for genetic evaluation, and genetic parameters of CH4 production in beef cattle.

Effects of dietary fat, nitrate, and 3-nitrooxypropanol and their combinations on methane emission, feed intake, and milk production in dairy cows

The objective of the present study was to investigate the effect of individual and combined use of dietary fat, nitrate, and 3-nitrooxypropanol (3-NOP) on dairy cows' enteric methane (CH4) emission and production performance. Twenty-four primiparous and 24 multiparous Danish Holstein cows (111 ± 44.6 d in milk; mean ± standard deviation) were included in an incomplete 8 × 8 Latin square design with six 21-d periods. Dietary treatments were organized in a 2 × 2 × 2 factorial arrangement aiming for 2 levels of FAT (30 or 63 g of crude fat/kg of dry matter [DM]; LF or HF, respectively), 2 levels of NITRATE (0 or 10 g of nitrate/kg of DM; UREA or NIT, respectively), and 2 levels of 3-NOP (0 or 80 mg/kg DM; BLANK or NOP, respectively). Treatments were included in ad libitum-fed partial mixed rations in bins that automatically measured feed intake and eating behavior. Additional concentrate was offered as bait in GreenFeed units used for measurement of gas emission. For total DM intake (DMI), a FAT × NITRATE interaction showed that DMI, across parities and levels of 3-NOP, was unaffected by separate fat supplementation, but reduced by nitrate with 4.6% and synergistically decreased (significant 2-way interaction) with 13.0% when fat and nitrate were combined. Additionally, 3-NOP decreased DMI by 13.4% and the combination of 3-NOP with fat and nitrate decreased DMI in an additive way (no significant 3-way interaction). The decreasing effects on DMI were more pronounced in multiparous cows than in primiparous cows. For treatments with largest reductions in DMI, eating behavior was altered toward more frequent, but smaller meals, a slower eating rate and increased attempts to visit unassigned feed bins. Energy-corrected milk (ECM) yield increased by 6.3% with fat supplementation, whereas ECM yield did not differ among diets including nitrate (FAT × NITRATE interaction). Cows supplemented with 3-NOP had 9.0% lower ECM yield than cows fed no 3-NOP. Based on three 2-way interactions including FAT, NITRATE, and 3-NOP, the combined use of the additives resulted in antagonistic effects on CH4 reduction. A 6% to 7% reduction in CH4 yield (CH4/kg of DMI) could be ascribed to the effect of fat, a 12% to 13% reduction could be ascribed to the effect of nitrate and an 18% to 23% reduction could be ascribed to the effect of 3-NOP. Hence, no combinations of additives resulted in CH4 yield-reductions that were greater than what was obtained by separate supplementation of the most potent additive within the combination. The CH4 yield reduction potential of additives was similar between parities. Increased apparent total-tract digestibility of organic matter (OM) in cows fed combinations including nitrate or 3-NOP was a result of a NITRATE × 3-NOP interaction. Apparent total-tract digestibility of OM was also increased by fat supplementation. These increases reflected observed decreases in DMI. In conclusion, combined use of fat, nitrate, and 3-NOP in all combinations did not result in CH4 reductions that were greater than separate supplementation of the most potent additive within the combination (3-NOP > nitrate > fat). Additionally, separate supplementation of some additives and combined use of all additives reduced DMI.

3-Nitrooxypropanol supplementation of a forage diet decreased enteric methane emissions from beef cattle without affecting feed intake and apparent total-tract digestibility

Supplementation of ruminant diets with the methane (CH4) inhibitor 3-nitrooxypropanol (3-NOP; DSM Nutritional Products, Switzerland) is a promising greenhouse gas mitigation strategy. However, most studies have used high grain or mixed forage-concentrate diets. The objective of this study was to evaluate the effects of supplementing a high-forage diet (90% forage DM basis) with 3-NOP on dry matter (DM) intake, rumen fermentation and microbial community, salivary secretion, enteric gas emissions, and apparent total-tract nutrient digestibility. Eight ruminally cannulated beef heifers (average initial body weight (BW) ± SD, 515 ± 40.5 kg) were randomly allocated to two treatments in a crossover design with 49-d periods. Dietary treatments were: 1) control (no 3-NOP supplementation); and 2) 3-NOP (control + 150 mg 3-NOP/kg DM). After a 16-d diet adaption, DM intake was recorded daily. Rumen contents were collected on days 17 and 28 for volatile fatty acid (VFA) analysis, whereas ruminal pH was continuously monitored from days 20 to 28. Eating and resting saliva production were measured on days 20 and 31, respectively. Diet digestibility was measured on days 38-42 by the total collection of feces, while enteric gas emissions were measured in chambers on days 46-49. Data were analyzed using the mixed procedure of SAS. Dry matter intake and apparent total-tract digestibility of nutrients (DM, neutral and acid detergent fiber, starch, and crude protein) were similar between treatments (P ≥ 0.15). No effect was observed on eating and resting saliva production. Relative abundance of the predominant bacterial taxa and rumen methanogen community was not affected by 3-NOP supplementation but rather by rumen digesta phase and sampling hour (P ≤ 0.01). Total VFA concentration was lower (P = 0.004) following 3-NOP supplementation. Furthermore, the reduction in acetate and increase in propionate molar proportions for 3-NOP lowered (P < 0.001) the acetate to propionate ratio by 18.9% as compared with control (4.1). Mean pH was 0.21 units lower (P < 0.001) for control than 3-NOP (6.43). Furthermore, CH4 emission (g/d) and yield (g/kg DMI) were 22.4 and 22.0% smaller (P < 0.001), respectively, for 3-NOP relative to control. Overall, the results indicate that enteric CH4 emissions were decreased by more than 20% with 3-NOP supplementation of a forage diet without affecting DM intake, predominant rumen microbial community, and apparent total-tract nutrients digestibility.

Effects of calcium ammonium nitrate fed to dairy cows on nutrient intake and digestibility, milk quality, microbial protein synthesis, and ruminal fermentation parameters

We evaluated the effects of supplemental calcium ammonium nitrate (CAN) fed to dairy cows on dry matter (DM) intake, nutrient digestibility, milk quality, microbial protein synthesis, and ruminal fermentation. Six multiparous Holstein cows at 106 ± 14.8 d in milk, with 551 ± 21.8 kg of body weight were used in a replicated 3 × 3 Latin square design. Experimental period lasted 21 d, with 14 d for an adaptation phase and 7 d for sampling and data collection. Cows were randomly assigned to receive the following treatments: URE, 12 g of urea/kg of DM as a control group; CAN15, 15 g of CAN/kg of DM; and CAN30, 30 g of CAN/kg of DM. Supplemental CAN reduced DM intake (URE 19.0 vs. CAN15 18.9 vs. CAN30 16.5 kg/d). No treatment effects were observed for apparent digestibility of DM, organic matter, crude protein, ether extract, and neutral detergent fiber; however, CAN supplementation linearly increased nonfiber carbohydrate digestibility. Milk yield was not affected by treatments (average = 23.1 kg/d), whereas energy-corrected milk (ECM) and 3.5% fat-corrected milk (FCM) decreased as the levels of CAN increased. Nitrate residue in milk increased linearly (URE 0.30 vs. CAN15 0.33 vs. CAN30 0.38 mg/L); however, treatments did not affect nitrite concentration (average: 0.042 mg/L). Milk fat concentration was decreased (URE 3.39 vs. CAN15 3.35 vs. CAN30 2.94%), and the proportion of saturated fatty acids was suppressed by CAN supplementation. No treatment effects were observed on the reducing power and thiobarbituric acid reactive substances of milk, whereas conjugated dienes increased linearly (URE 47.6 vs. CAN15 52.7 vs. CAN30 63.4 mmol/g of fat) with CAN supplementation. Treatments had no effect on microbial protein synthesis; however, molar proportion of ruminal acetate and acetate-to-propionate ratio increased with CAN supplementation. Based on the results observed, supplementing CAN at 30 g/kg of DM should not be recommended as an optimal dose because it lowered DM intake along with ECM and 3.5% FCM, although no major changes were observed on milk quality and ruminal fermentation.

Is it time to rethink our one-size-fits-all approach to nitrate toxicity thresholds in forages?

Annual forages provide a valuable grazing resource for cattle producers; however, annuals are prone to accumulating nitrate and have the potential to cause nitrate toxicity. Although these forages pose a risk of containing high nitrate concentrations, they can be a high-quality feed source. Understanding the factors that affect the potential for toxicity when using these forages is important to help nutritionists and producers make management decisions. This review describes the previous research, current guidelines for nitrate toxicity, and the potential for improvement in our current recommendations. Current extension toxicity guidelines appear to be founded primarily on drenching based studies and overestimate the nitrate toxicity potential of forages. Recommendations need to account for multiple factors that affect the threshold for toxicity. There is evidence that fresh forages have a lower risk of toxicity because of slower release of nitrate into the rumen and a slower rate of dry matter intake. Increased dietary energy and sulfur content reduce the potential for toxicity. Microbial adaptation can reduce the risk and allow use of potentially toxic forages. These factors should influence feeding recommendations. However, there is currently not enough data available to establish new guidelines that account for these main factors. Thus, there is a need for renewed research in this area. The limited number of studies grazing elevated nitrate forages seems to suggest that there is less risk in grazing situations, especially if animals graze selectively. There is a need to develop guidelines for nitrate toxicity and management recommendations when grazing. To accomplish this, there is a need for more studies to evaluate risk of toxicity in grazing situations. These grazing studies need to evaluate the effects of nitrate concentration, forage quality, and grazing management on the potential for nitrate toxicity. While the conservative guidelines that are currently in use reduce risk of nitrate toxicity, they may also cause a significant increase in feed costs for producers.

Effects of bismuth subsalicylate and calcium-ammonium nitrate on ruminal in vitro fermentation of bahiagrass hay with supplemental molasses

There is a need to increase efficiency of beef production. Decreasing losses of CH₄ and improving byproduct utilization are popular strategies. Two feed additives were tested to find potential solutions. Three randomized complete block design experiments were performed using batch culture systems to evaluate the effects of bismuth subsalicylate (BSS) and calcium-ammonium nitrate (CAN) on in vitro ruminal fermentation of bahiagrass hay and supplemental molasses. The first experiment contained four treatments: (1) basal substrate; (2) basal substrate with 0.75% urea (DM basis); (3) basal substrate with 1.2% CAN and 0.38% urea (DM basis); and (4) basal substrate with 2.4% CAN (DM basis). Treatments 2, 3, and 4 were isonitrogenous. The second experiment had a 4 × 3 factorial arrangement of treatments with 4 concentrations of BSS (0.00, 0.33, 0.66, and 1.00%; DM basis) and 3 concentrations of CAN (0.0, 1.2, and 2.4%; DM basis). The third experiment had the following treatments: (1) basal substrate; (2) basal substrate with 0.05% BSS (DM basis); (3) basal substrate with 0.10% BSS (DM basis); and (4) basal substrate with 0.33% BSS (DM basis). For all experiments, basal substrate consisted of Pensacola bahiagrass hay (Paspalum notatum Flüggé; 80% substrate DM) and molasses (20% substrate DM). All data were analyzed using the MIXED procedure of SAS. In Exp. 1, in vitro organic matter (OM) digestibility (IVOMD) was linearly reduced (P < 0.001) with the inclusion of CAN, and CH₄, in mmol/g OM fermented, was decreased linearly (P < 0.001). The volatile fatty acid (VFA) profile was not impacted by the inclusion of nonprotein nitrogen (NPN) or CAN (P > 0.05). In Exp. 2, except for CH₄ production (P < 0.05), there were no BSS × CAN interactions. Linear reductions in total gas production (P < 0.001), IVOMD (P < 0.001), and total concentration of VFA (P = 0.007) were observed with the inclusion of BSS up to 1%. The inclusion of BSS decreased H₂S production in a quadratic manner (P = 0.024). In Exp. 3, IVOMD was not impacted by the inclusion of BSS (P > 0.05); however, production of H₂S was linearly decreased (P = 0.004) with the inclusion of BSS up to 0.33%. In conclusion, in vitro fermentation was negatively impacted by the inclusions of BSS, up to 1%, and CAN, up to 2.4%; however, BSS decreased production of H₂S when included up to 0.33% without impeding fermentation, while CAN decreased CH₄ production.

Changes in hematological, biochemical, and blood gases parameters in response to progressive inclusion of nitrate in the diet of Holstein calves

Background and Aim:

Nitrate (NO₃^-) reduces enteric methane emissions and could be a source of non-protein nitrogen in ruminant feeds. Nonetheless, it has a potential toxic effect that could compromise animal health and production. The purpose of this study was to determine the effects of progressive inclusion of NO₃^- in the diet on the hematological, biochemical, and blood gases parameters, in turn, the effects on feed intake and live weight gain (LWG) in Holstein calves.

Materials and Methods:

Eighteen Holstein heifers and steers (nine animals/treatment) were maintained in individual pens for 45 days. Animals were randomly allocated to either a control or nitrate diet (ND) (containing 15 g of NO₃^-/kg of dry matter [DM]). The biochemical parameters and blood gases were analyzed only in the NO₃^- group on days: -1, 1, 7, 13, 19, and 25 corresponding to 0, 20, 40, 60, 80, and 100% of the total inclusion of NO₃^- in the diet, respectively. In addition, DM intake (DMI) and LWG were evaluated among dietary treatments.

Results:

Feeding the ND did not influence DMI or LWG (p>0.05). Methemoglobin (MetHb) and deoxyhemoglobin increased according to the NO₃^- concentrations in the diet (p<0.05), while an opposite effect was observed for oxyhemoglobin and carboxyhemoglobin (p<0.05). Hematocrit levels decreased (p<0.05), while albumin, alanine aminotransferase, and gamma-glutamyl transpeptidase concentrations were not modified (p>0.05). However, glucose, urea, aspartate aminotransferase (AST), and retinol concentrations increased (p<0.05) according to the NO₃^- concentrations in the diet.

Conclusion:

This study confirmed that the progressive inclusion of 123 g of NO₃^-/animal/day in the diet could be safe without affecting DMI and LWG of Holstein calves. In turn, a dose-response effect of the MetHb, glucose, urea, AST, and retinol was observed, but these values did not exceed reference values. These results highlighted the importance of using a scheme of progressive inclusion of NO₃^- in the diet of calves to reduce the risks of NO₃^- toxicity.

The effect of molasses nitrate lick blocks on supplement intake, bodyweight, condition score, blood methaemoglobin concentration and herd scale methane emissions in Bos indicus cows grazing poor quality forage

Context The Australian government has approved a greenhouse gas (GHG) offset method that requires cattle to consume nitrate in the form of a lick block. Field studies demonstrating the effectiveness of this methodology have not been previously reported. Aims This experiment was conducted to determine the effects on productivity and health when nitrate lick blocks were provided as a supplement to grazing beef cattle. We hypothesised that beef cattle given access to nitrate lick blocks would have similar productivity compared with cattle offered urea lick blocks. Methods Bos indicus breeding cows (n = 76) grazed a 467-ha paddock near Charters Towers, Queensland, between May and November 2014. A two-way remote automatic drafting system enabled allocation of cattle to different treatments while grazing in a common paddock. Treatments were 30% urea lick blocks (30U), or molasses nitrate lick blocks (MNB). At monthly intervals liveweight (LW), body condition score (BCS), and blood methaemoglobin concentration were recorded. Estimates of individual supplement intake were made on three separate occasions using a lithium marker technique. Results Mean daily supplement intake (±s.e.m.) of 30U (122 ± 13 g) was greater (P &lt; 0.001) than MNB (67 ± 8 g). Lesser MNB intake was associated with greater variability for individual supplement intake, a greater proportion of non-consumers of supplement during July (P &lt; 0.05) and reduced voluntary supplement intake until October (P &lt; 0.001). Increasing MNB consumption during October and November was accompanied by elevated blood methaemoglobin concentration (P &lt; 0.001). It was estimated that cattle offered MNB had insufficient supplementary nitrogen intake throughout the study to resolve rumen degradable nitrogen deficiency from grazed forage. Consequently, cattle provided access to MNB demonstrated conceptus free liveweight loss and lesser BCS compared with cattle treated with 30U (P &lt; 0.001). Conclusion Nitrate lick blocks were ineffective as a dual-purpose non-protein nitrogen supplement and methane mitigant for beef cattle grazing poor quality forage. Further field experiments are required to determine if there may be situations where this GHG offset methodology is efficacious. Implications Caution is advised in implementing GHG mitigation methods that involve the use of nitrate lick blocks.

Effects of bismuth subsalicylate and encapsulated calcium ammonium nitrate on ruminal fermentation of beef cattle

A replicated 5 × 5 Latin square design with a 2 × 2 + 1 factorial arrangement of treatments was used to determine the effects of bismuth subsalicylate (BSS) and encapsulated calcium ammonium nitrate (eCAN) on ruminal fermentation of beef cattle consuming bahiagrass hay (Paspalum notatum) and sugarcane molasses. Ten ruminally cannulated steers (n = 8; 461 ± 148 kg of body weight [BW]; average BW ± SD) and heifers (n = 2; 337 ± 74 kg of BW) were randomly assigned to one of five treatments as follows: 1) 2.7 g/kg of BW of molasses (NCTRL), 2) NCTRL + 182 mg/kg of BW of urea (U), 3) U + 58.4 mg/kg of BW of BSS (UB), 4) NCTRL + 538 mg/kg of BW of eCAN (NIT), and 5) NIT + 58.4 mg/kg of BW of BSS (NITB). With the exception of NCTRL, all treatments were isonitrogenous. Beginning on day 14 of each period, ruminal fluid was collected and rectal temperature was recorded 4× per day for 3 d to determine ruminal changes every 2 h from 0 to 22 h post-feeding. Ruminal gas cap samples were collected at 0, 3, 6, 9, and 12 h on day 0 of each period followed by 0 h on days 1, 2, 3, and 14. Microbial N flow was determined using Cr-Ethylenediaminetetraacetic acid, YbCl3, and indigestible neutral detergent fiber for liquid, small particle, and large particle phases, respectively. Data were analyzed using the MIXED procedure of SAS. Orthogonal contrasts were used to evaluate the effects of nonprotein nitrogen (NPN) inclusion, NPN source, BSS, and NPN source × BSS. There was no treatment effect (P > 0.05) on concentrations of H2S on day 0, 1, 2, or 14; however, on day 3, concentrations of H2S were reduced (P = 0.018) when NPN was provided. No effect of treatment (P = 0.864) occurred for ruminal pH. There was an effect of NPN source on total concentrations of VFA (P = 0.011), where a 6% reduction occurred when eCAN was provided. There were effects of NPN (P = 0.001) and NPN source (P = 0.009) on the concentration of NH3-N, where cattle consuming NPN had a greater concentration than those not consuming NPN, and eCAN reduced the concentration compared with urea. Total concentrations of VFA and NH3-N were not affected (P > 0.05) by BSS. There was an effect of BSS (P = 0.009) on rectal temperature, where cattle not consuming BSS had greater temperatures than those receiving BSS. No differences for NPN, NPN source, nor BSS (P > 0.05) were observed for microbial N flow. In conclusion, eCAN does not appear to deliver equivalent ruminal fermentation parameters compared with urea, and BSS has limited effects on fermentation.

Risk assessment of nitrate and nitrite in feed

The European Commission asked EFSA for a scientific opinion on the risks to animal health related to nitrite and nitrate in feed. For nitrate ion, the EFSA Panel on Contaminants in the Food Chain (CONTAM Panel) identified a BMDL 10 of 64 mg nitrate/kg body weight (bw) per day for adult cattle, based on methaemoglobin (MetHb) levels in animal's blood that would not induce clinical signs of hypoxia. The BMDL 10 is applicable to all bovines, except for pregnant cows in which reproductive effects were not clearly associated with MetHb formation. Since the data available suggested that ovines and caprines are not more sensitive than bovines, the BMDL 10 could also be applied to these species. Highest mean exposure estimates of 53 and 60 mg nitrate/kg bw per day in grass silage-based diets for beef cattle and fattening goats, respectively, may raise a health concern for ruminants when compared with the BMDL 10 of 64 mg nitrate/kg bw per day. The concern may be higher because other forages might contain higher levels of nitrate. Highest mean exposure estimates of 2.0 mg nitrate/kg bw per day in pigs' feeds indicate a low risk for adverse health effects, when compared with an identified no observed adverse effect level (NOAEL) of 410 mg nitrate/kg bw per day, although the levels of exposure might be underestimated due to the absence of data on certain key ingredients in the diets of this species. Due to the limitations of the data available, the CONTAM Panel could not characterise the health risk in species other than ruminants and pigs from nitrate and in all livestock and companion animals from nitrite. Based on a limited data set, both the transfer of nitrate and nitrite from feed to food products of animal origin and the nitrate- and nitrite-mediated formation of N-nitrosamines and their transfer into these products are likely to be negligible.

Short-Term Eating Preference of Beef Cattle Fed High Forage or High Grain Diets Supplemented with 3-Nitrooxypropanol

Two experiments were conducted to examine eating preference of beef cattle for diets with or without the investigative enteric methane inhibitor 3-nitrooxypropanol (3-NOP). Nine beef steers were housed in individual stalls, each equipped with two feed bunks. The first experiment (Exp. 1) was conducted with a high forage diet and each animal received a diet without 3-NOP (CON) in one bunk and a diet with 3-NOP (dNOP) in the other bunk. The second study (Exp. 2) was conducted with the same animals about 6 months after Exp. 1 where a high grain diet without (CON) or with 3-NOP (dNOP) was offered. In Exp. 1, animals initially preferred CON compared with dNOP. Feed consumption from 0 to 3, 3 to 6, and 6 to 12 h after feeding was lower for dNOP compared with CON. However, dry matter intake (DMI) and feed consumption of dNOP gradually increased during Exp. 1 such that there was no preference between CON and dNOP on day 7. In Exp. 2, there was no preference for or against dNOP. Average DMI was greater for dNOP vs. CON, but interactions between diet and day for DMI and feed consumption rates indicated that daily preference between CON and dNOP was variable. In conclusion, beef steers initially detected a difference between CON and dNOP and selected in favor of CON rather than dNOP when they had not previously been exposed to 3-NOP. However, the animals rapidly acclimatized to a diet with 3-NOP (Exp. 1) and showed no eating preference between CON and dNOP within 7 days. This lack of preference was maintained throughout Exp. 2 when the same animals were fed a high grain diet.

Effects of 3-nitrooxypropanol on enteric methane production, rumen fermentation, and feeding behavior in beef cattle fed a high-forage or high-grain diet1

The objective of the study was to determine whether feeding a diet supplemented with 3-nitrooxypropanol (3-NOP) affects feeding behavior altering intake and rumen fermentation. Two experiments were conducted with 9 rumen-cannulated beef steers in a replicated 3 × 3 Latin square design where animals received a high-forage or high-grain diet. Treatments were 1) a basal diet (CON), the CON diet supplemented with 3-NOP (dNOP; 100 mg/kg in dietary DM or 1 g/d), or the CON diet with 3-NOP (1 g/d) infused into the rumen (infNOP). Each experimental period consisted of 14-d diet adaptation and 7-d sample collection. A 7-d washout period was provided between experiment periods. All data were analyzed as a Latin square design using Mixed Procedure of SAS. In Exp. 1 (high-forage diet), methane yield (measured by the Greenfeed system) was lowered by 18% (18.6 vs. 22.7 g/kg DMI; P < 0.01) by dNOP compared with CON. Rumen fermentation was altered similarly by both NOP treatments compared with CON where dNOP and infNOP increased (P < 0.01) rumen pH at 3 h and decreased (P < 0.01) proportion of acetate in total VFA. However, DMI, feed consumption rate (0 to 3, 3 to 6, 6 to 12, and 12 to 24 h after feeding), particle size distribution of orts, and feeding behavior (videotaped for individual animals over 48 h) were not affected by dNOP and infNOP compared with CON. In Exp. 2 (high-grain diet), methane production was not affected by dNOP or infNOP compared with CON. Dry matter intake, feed consumption rate, particle size distribution of orts, and feeding behavior were not altered by dNOP and infNOP compared with CON. However, both dNOP and infNOP affected rumen fermentation where total VFA decreased (P = 0.04) and acetate proportion in total VFA tended to decrease (P = 0.07) compared with CON. In conclusion, dietary supplementation of 3-NOP did not affect feeding behavior of beef steers fed a high-forage or high-grain diet. However, rumen fermentation was similarly changed when 3-NOP was provided in the diet or directly infused in the rumen. Thus, observed changes in rumen fermentation with 3-NOP were not due to changes in feeding behavior indicating no effects on the organoleptic property of the diets. In addition, according to small or no changes in DMI in both experiments and relatively small changes in rumen fermentation in Exp. 2, a greater dosage level of 3-NOP than 100 mg/kg (dietary DM) may need further examination of its effects on feeding behavior of beef cattle.

Effect of Encapsulated Nitrate and Microencapsulated Blend of Essential Oils on Growth Performance and Methane Emissions from Beef Steers Fed Backgrounding Diets

A long-term study (112 days) was conducted to examine the effect of feeding encapsulated nitrate (NO₃-), microencapsulated blend of essential oils (EO), and their combination on growth performance, feeding behavior, and enteric methane (CH₄) emissions of beef cattle. A total of 88 crossbred steers were purchased and assigned to one of four treatments: (i) control, backgrounding high-forage diet supplemented with urea (1.17% in dietary DM); (ii) encapsulated NO₃- (EN), control diet supplemented with 2.5% encapsulated NO₃- as a replacement for urea (1.785% NO₃- in the dietary DM); (iii) microencapsulated blend of EO (MBEO), control diet supplemented with 150 mg/kg DM of microencapsulated blend of EO and pepper extract; and (iv) EN + MBEO, control diet supplemented with EN and MBEO. There was no interaction (p ≥ 0.080) between EN and MBEO on average dry matter intake (DMI), average daily gain (ADG), gain to feed ratio (G:F), feeding behavior, and CH₄ emission (using GreenFeed system), implying independent effects of feeding EN and MBEO. Feeding MBEO increased CH₄ production (165.0 versus 183.2 g/day; p = 0.005) and yield (18.9 versus 21.4 g/kg DMI; p = 0.0002) but had no effect (p ≥ 0.479) on average DMI, ADG, G:F, and feeding behavior. However, feeding EN had no effect on ADG and G:F (p ≥ 0.119) but reduced DMI (8.9 versus 8.4 kg/day; p = 0.003) and CH₄ yield (21.5 versus 18.7 g/kg DMI; p < 0.001). Feeding EN slowed (p = 0.001) the feeding rate (g of DM/min) and increased (p = 0.002) meal frequency (events/day). Our results demonstrate that supplementing diets with a blend of EO did not lower CH₄ emissions and there were no advantages of feeding MBEO with EN. Inclusion of EN as a replacement for urea reduced CH₄ emissions but had no positive impact on animal performance.

Effects of encapsulated nitrate on growth performance, carcass characteristics, nitrate residues in tissues, and enteric methane emissions in beef steers: Finishing phase

A finishing feedlot study was conducted with beef steers to determine effects of encapsulated nitrate (EN) on growth performance, carcass characteristics, methane production, and nitrate (NO) residues in tissues. The 132 crossbred steers were backgrounded in a feedlot for 91 d and transitioned for 28 days to the high-concentrate diets evaluated in the present study, maintaining the treatment and pen assignments designated at the start of the backgrounding period. The steers were initially assigned to 22 pens (6 animals per pen) in a randomized complete block design with BW (18 pens) and animals designated for methane measurement (4 pens) as blocking factors. Five animals in each pen designated for methane measurement (total of 20 animals) were monitored for methane emissions in respiratory chambers twice during the experiment. Pens received 3 dietary treatments (7 pens each): Control, a finishing diet supplemented with urea; 1.25% EN, control diet supplemented with 1.25% encapsulated NO in dietary DM that partially replaced urea; and 2.5% EN, control diet supplemented with 2.5% EN (DM basis) fully replacing urea. The final pen designated only for methane measurement received a fourth dietary treatment, 2.3% UEN, the control diet supplemented with unencapsulated NO (UEN) fully replacing urea. The cattle weighed 449 ± SD 32 kg at the start of the 150-d finishing period. The 2.5% EN diet decreased ( < 0.01) DMI compared with Control and 1.25% EN diets. Feeding EN tended to increase ( = 0.092) ADG compared with Control, and G:F was improved ( < 0.01) for EN compared with Control. No differences in methane production (g/d) and yield (g/kg DMI) were observed among treatments. Inclusion of EN in the diets increased ( ≤ 0.03) sorting in favor of large and medium particles and against small and fine particles. Plasma NO and NO concentrations were elevated ( < 0.01) with EN in a dose-response manner, but total blood methemoglobin levels for all treatments were low, below the detection limit. Feeding EN increased ( < 0.01) NO concentrations of samples from muscle, fat, liver, and kidney; NO concentrations of these tissues were similar between 1.25% EN and 2.3% UEN. In conclusion, inclusion of 2.5% EN in a finishing diet (DM basis; about 2% NO) did not cause NO toxicity or any health problems in the long term. In comparison with supplemental urea, feeding EN improved feed efficiency despite increases in sorting against dietary EN.

Effects of encapsulated nitrate on growth performance, nitrate toxicity, and enteric methane emissions in beef steers: Backgrounding phase

A long-term experiment was conducted to examine the effects of feeding encapsulated nitrate (EN) on growth, enteric methane production, and nitrate (NO) toxicity in beef cattle fed a backgrounding diet. A total of 108 crossbred steers (292 ± 18 kg) were blocked by BW and randomly assigned to 18 pens. The pens (experimental unit; 6 animals per pen) received 3 dietary treatments: Control, a backgrounding diet supplemented with urea; 1.25% EN, control diet supplemented with 1.25% encapsulated calcium ammonium NO (i.e., EN) in dietary DM, which partially replaced urea; or 2.5% EN, control diet supplemented with 2.5% EN (DM basis) fully replacing urea. Additionally, 24 steers were located in 4 pens and randomly assigned to 1 of the above 3 dietary treatments plus a fourth treatment: 2.3% UEN, control diet supplemented with 2.3% unencapsulated calcium ammonium NO (UEN) fully replacing urea. Animals in the additional 4 pens were used for methane measurement in respiratory chambers, and the pens (except UEN) were also part of the performance study (i.e., = 7 pens/treatment). The experiment was conducted for 91 d in a randomized complete block design. During the experiment, DMI was not affected by inclusion of EN in the diet. Feeding EN had no effect on BW, ADG, and G:F ( ≥ 0.57). Methane production (g/d) tended to decrease ( = 0.099) with EN and UEN, but yield (g/kg DMI) did not differ ( = 0.56) among treatments. Inclusion of EN in the diet increased ( ≤ 0.02) sorting of the diets in favor of large and medium particles and against small and fine particles, resulting in considerable increases in NO concentrations of orts without affecting DMI. Plasma NO-N and NO-N concentrations increased ( ≤ 0.05) for EN compared with Control in a dose response manner, but blood methemoglobin levels were below the detection limit. Nitrate concentration in fecal samples slightly increased (from 0.01% to 0.14% DM; < 0.01) with increasing levels of EN in the diet. In conclusion, EN can be used as a feed additive replacing urea in beef cattle during a backgrounding phase in the long term without NO intoxication or any negative effects on growth performance. In addition, the study confirmed that feeding EN tended to decrease enteric methane production in the long term.

Effect of stocking density on performance, diet selection, total-tract digestion, and nitrogen balance among heifers grazing cool-season annual forages

Grazing annual cool-season forages after oat grain harvest in South Dakota may allow an opportunity to increase efficient use of tillable land. However, data are limited regarding effects of stocking density on diet selection, nutrient digestion, performance, and N retention by cattle grazing annual cool-season forage. Heifers were blocked by initial BW (261 ± 11.7 kg) and randomly assigned to 1 of 12 paddocks (1.1 ha) to graze a mixture of grass and brassica for 48 d. Each paddock contained 3, 4, or 5 heifers to achieve 4 replicates of each stocking density treatment. Ruminally cannulated heifers were used to measure diet and nutrient intake. Effects of stocking density on diet and nutrient selection were measured after 2, 24, and 46 d of grazing, and BW was measured at the beginning, middle, and end of the experiment as the average of d 1 and 2, d 22 and 23, and d 47 and 48 BW, respectively. Measures of DMI and DM, OM, NDF, and ADF digestion were collected from d 18 to 23. Increased stocking density increased intake of brassica relative to grass on d 24 (quadratic, = 0.02), but increased stocking density decreased (linear, ≤ 0.01) intake of brassica compared with grass on d 48 (stocking density × time, < 0.01). Increased stocking density increased DM (quadratic, < 0.01), OM (quadratic, = 0.01), and NDF (quadratic, = 0.05) digestion, and stocking density tended to increase DMI (quadratic, = 0.07). Additionally, increased stocking density quadratically increased ( = 0.05) N retention but did not affect overall BW gains. Increased stocking density did, however, contribute to linearly decreased ( = 0.05) BW gains from d 1 to 22 of grazing, but BW gains during the latter half of the experiment were greater than BW gains from d 1 to 22. Ruminal concentration of acetate:propionate was least on d 24 of grazing, and ruminal nitrate concentration tended to linearly decrease ( = 0.06) with greater amounts of time on pasture. Ruminal liquid and particulate fill and amounts of VFA were less (quadratic, ≤ 0.01) with greater amounts of time on pasture. Apparently, binary mixtures of brassica and grass planted after oat grain harvest can provide an opportunity to increase efficient use of land by providing forage resources. Increased stocking density may facilitate a more rapid adaptation to and intake of brassica among cattle grazing brassica-grass-based pastures.

Feed intake, growth, and body and carcass attributes of feedlot steers supplemented with two levels of calcium nitrate or urea

Nitrate supplementation has been shown to be effective in reducing enteric methane emission from ruminants, but there have been few large-scale studies assessing the effects of level of nitrate supplementation on feed intake, animal growth, or carcass and meat quality attributes of beef cattle. A feedlot study was conducted to assess the effects of supplementing 0.25 or 0.45% NPN in dietary DM as either urea (Ur) or calcium nitrate (CaN) on DMI, ADG, G:F, and carcass attributes of feedlot steers ( = 383). The levels of NPN inclusion were selected as those at which nitrate has previously achieved measurable mitigation of enteric methane. The higher level of NPN inclusion reduced ADG as did replacement of Ur with CaN ( < 0.01). A combined analysis of DMI for 139 steers with individual animal intake data and pen-average intakes for 244 bunk-fed steers showed a significant interaction between NPN source and level ( = 0.02) with steers on the high-CaN diet eating less than those on the other 3 diets ( < 0.001). Neither level nor NPN source significantly affected cattle G:F. There was a tendency ( = 0.05) for nitrate-supplemented cattle to have a slower rate of eating (g DMI/min) than Ur-supplemented cattle. When adjusted for BW, neither NPN source nor inclusion level affected cross-sectional area of the LM or fatness measured on the live animal. Similarly, there were no significant main effects of treatments on dressing percentage or fat depth or muscling attributes of the carcass after adjustment for HCW ( > 0.05). Analysis of composited meat samples showed no detectable nitrates or nitrosamines in raw or cooked meat, and the level of nitrate detected in meat from nitrate-supplemented cattle was no higher than for Ur-fed cattle ( > 0.05). We conclude that increasing NPN inclusion from 0.25 to 0.45% NPN in dietary DM and replacing Ur with CaN decreased ADG in feedlot cattle without improving G:F.

Effects of feed consumption rate of beef cattle offered a diet supplemented with nitrate ad libitum or restrictively on potential toxicity of nitrate

The objective of the study was to investigate the effects of feed consumption rate on potential toxicity, rumen fermentation, and eating behavior when beef heifers were fed a diet supplemented with nitrate (NI). Twelve ruminally cannulated heifers (827 ± 65.5 kg BW) were used in a randomized complete block design. The experiment consisted of 10-d adaptation, 8-d urea-feeding, and 3-d nitrate-feeding periods. All heifers were fed a diet supplemented with urea (UR) during the adaptation and urea-feeding periods, whereas the NI diet (1.09% NO in dietary DM) was fed during the nitrate-feeding period. After adaptation, heifers were randomly assigned to ad libitum or restrictive feeding (about 80% of ad libitum intake) for the urea- and nitrate-feeding periods. Ad libitum DMI decreased (14.1 vs. 15.1 kg/d; < 0.01) when heifers were fed the NI diet compared with the UR diet. The amount of feed consumed increased ( < 0.01) at 0 to 3 h and decreased ( ≤ 0.03) at 3 to 24 h for restrictive vs. ad libitum feeding of both the UR and NI diets. Compared to the UR diet, the NI diet decreased ( < 0.01) feed consumption at 0 to 3 h and increased ( < 0.02) feed consumption at 3 to 24 h (except feed consumption at 9 to 12 h; = 0.90), indicating nitrate feeding changed the consumption pattern (a more even distribution of feed intake over the day). The increased feed consumption from 0 to 3 h after feeding the NI diet restrictively vs. ad libitum numerically decreased ( = 0.11) rumen pH and numerically or significantly increased ( = 0.01 to 0.28) rumen ammonia, NO, and NO; blood methemoglobin; and plasma NO and NO at 3 h. Regression analysis indicated that increased feed consumption (0 to 3 h) exponentially elevated ( < 0.01; = 0.75) blood methemoglobin, and plasma NO + NO among other rumen and blood variables had the greatest correlation (sigmoid response; < 0.01, = 0.47) with feed consumption (0 to 3 h). Particle size distribution of orts was partially altered ( = 0.02 to 0.40) when the NI diet was fed compared with the UR diet. During the nitrate-feeding period, the nitrate content of orts on d 2 and 3 was greater ( = 0.02) than that on d 1. In conclusion, the increased consumption rate of a diet supplemented with nitrate was an important factor influencing risk of nitrate toxicity based on blood methemoglobin and plasma NO. In addition, the pattern of daily feed consumption was altered by nitrate (creating a "nibbling" pattern of eating) in beef heifers.

Effect of dietary nitrate level on enteric methane production, hydrogen emission, rumen fermentation, and nutrient digestibility in dairy cows

Nitrate may lower methane production in ruminants by competing with methanogenesis for available hydrogen in the rumen. This study evaluated the effect of 4 levels of dietary nitrate addition on enteric methane production, hydrogen emission, feed intake, rumen fermentation, nutrient digestibility, microbial protein synthesis, and blood methemoglobin. In a 4×4 Latin square design 4 lactating Danish Holstein dairy cows fitted with rumen, duodenal, and ileal cannulas were assigned to 4 calcium ammonium nitrate addition levels: control, low, medium, and high [0, 5.3, 13.6, and 21.1g of nitrate/kg of dry matter (DM), respectively]. Diets were made isonitrogenous by replacing urea. Cows were fed ad libitum and, after a 6-d period of gradual introduction of nitrate, adapted to the corn-silage-based total mixed ration (forage:concentrate ratio 50:50 on DM basis) for 16d before sampling. Digesta content from duodenum, ileum, and feces, and rumen liquid were collected, after which methane production and hydrogen emissions were measured in respiration chambers. Methane production [L/kg of dry matter intake (DMI)] linearly decreased with increasing nitrate concentrations compared with the control, corresponding to a reduction of 6, 13, and 23% for the low, medium, and high diets, respectively. Methane production was lowered with apparent efficiencies (measured methane reduction relative to potential methane reduction) of 82.3, 71.9, and 79.4% for the low, medium, and high diets, respectively. Addition of nitrate increased hydrogen emissions (L/kg of DMI) quadratically by a factor of 2.5, 3.4, and 3.0 (as L/kg of DMI) for the low, medium, and high diets, respectively, compared with the control. Blood methemoglobin levels and nitrate concentrations in milk and urine increased with increasing nitrate intake, but did not constitute a threat for animal health and human food safety. Microbial crude protein synthesis and efficiency were unaffected. Total volatile fatty acid concentration and molar proportions of acetate, butyrate, and propionate were unaffected, whereas molar proportions of formate increased. Milk yield, milk composition, DMI and digestibility of DM, organic matter, crude protein, and neutral detergent fiber in rumen, small intestine, hindgut, and total tract were unaffected by addition of nitrate. In conclusion, nitrate lowered methane production linearly with minor effects on rumen fermentation and no effects on nutrient digestibility.

Insights on Alterations to the Rumen Ecosystem by Nitrate and Nitrocompounds

Nitrate and certain short chain nitrocompounds and nitro-oxy compounds are being investigated as dietary supplements to reduce economic and environmental costs associated with ruminal methane emissions. Thermodynamically, nitrate is a preferred electron acceptor in the rumen that consumes electrons at the expense of methanogenesis during dissimilatory reduction to an intermediate, nitrite, which is primarily reduced to ammonia although small quantities of nitrous oxide may also be produced. Short chain nitrocompounds act as direct inhibitors of methanogenic bacteria although certain of these compounds may also consume electrons at the expense of methanogenesis and are effective inhibitors of important foodborne pathogens. Microbial and nutritional consequences of incorporating nitrate into ruminant diets typically results in increased acetate production. Unlike most other methane-inhibiting supplements, nitrate decreases or has no effect on propionate production. The type of nitrate salt added influences rates of nitrate reduction, rates of nitrite accumulation and efficacy of methane reduction, with sodium and potassium salts being more potent than calcium nitrate salts. Digestive consequences of adding nitrocompounds to ruminant diets are more variable and may in some cases increase propionate production. Concerns about the toxicity of nitrate's intermediate product, nitrite, to ruminants necessitate management, as animal poisoning may occur via methemoglobinemia. Certain of the naturally occurring nitrocompounds, such as 3-nitro-1-propionate or 3-nitro-1-propanol also cause poisoning but via inhibition of succinate dehydrogenase. Typical risk management procedures to avoid nitrite toxicity involve gradually adapting the animals to higher concentrations of nitrate and nitrite, which could possibly be used with the nitrocompounds as well. A number of organisms responsible for nitrate metabolism in the rumen have been characterized. To date a single rumen bacterium is identified as contributing appreciably to nitrocompound metabolism. Appropriate doses of the nitrocompounds and nitrate, singly or in combination with probiotic bacteria selected for nitrite and nitrocompound detoxification activity promise to alleviate risks of toxicity. Further studies are needed to more clearly define benefits and risk of these technologies to make them saleable for livestock producers.

Nitrate and Inhibition of Ruminal Methanogenesis: Microbial Ecology, Obstacles, and Opportunities for Lowering Methane Emissions from Ruminant Livestock

Ruminal methane production is among the main targets for greenhouse gas (GHG) mitigation for the animal agriculture industry. Many compounds have been evaluated for their efficacy to suppress enteric methane production by ruminal microorganisms. Of these, nitrate as an alternative hydrogen sink has been among the most promising, but it suffers from variability in efficacy for reasons that are not understood. The accumulation of nitrite, which is poisonous when absorbed into the animal’s circulation, is also variable and poorly understood. This review identifies large gaps in our knowledge of rumen microbial ecology that handicap the further development and safety of nitrate as a dietary additive. Three main bacterial species have been associated historically with ruminal nitrate reduction, namely Wolinella succinogenes, Veillonella parvula, and Selenomonas ruminantium, but others almost certainly exist in the largely uncultivated ruminal microbiota. Indications are strong that ciliate protozoa can reduce nitrate, but the significance of their role relative to bacteria is not known. The metabolic fate of the reduced nitrate has not been studied in detail. It is important to be sure that nitrate metabolism and efforts to enhance rates of nitrite reduction do not lead to the evolution of the much more potent GHG, nitrous oxide. The relative importance of direct inhibition of archaeal methanogenic enzymes by nitrite or the efficiency of capture of hydrogen by nitrate reduction in lowering methane production is also not known, nor are nitrite effects on other members of the microbiota. How effective would combining mitigation methods be, based on our understanding of the effects of nitrate and nitrite on the microbiome? Answering these fundamental microbiological questions is essential in assessing the potential of dietary nitrate to limit methane emissions from ruminant livestock.