Effect of 3-nitrooxypropanol on enteric methane emissions of feedlot cattle fed with a tempered barley-based diet with canola oil.

A dose-response experiment was designed to examine the effect of 3-nitrooxypropanol (3-NOP) on methane (CH4) emissions, rumen function and performance of feedlot cattle fed a tempered barley-based diet with canola oil. Twenty Angus steers of initial body weight (BW) of 356 ±â€…14.4 kg were allocated in a randomized complete block design. Initial BW was used as the blocking criterion. Cattle were housed in individual indoor pens for 112 d, including the first 21 d of adaptation followed by a 90-d finishing period when five different 3-NOP inclusion rates were compared: 0 mg/kg dry matter (DM; control), 50 mg/kg DM, 75 mg/kg DM, 100 mg/kg DM, and 125 mg/kg DM. Daily CH4 production was measured on day 7 (last day of starter diet), day 14 (last day of the first intermediate diet), and day 21 (last day of the second intermediate diet) of the adaptation period and on days 28, 49, 70, 91, and 112 of the finisher period using open circuit respiration chambers. Rumen digesta samples were collected from each steer on the day prior to chamber measurement postfeeding, and prefeeding on the day after the chamber measurement, for determination of rumen volatile fatty acids (VFA), ammonium-N, protozoa enumeration, pH, and reduction potential. Dry matter intake (DMI) was recorded daily and BW weekly. Data were analyzed in a mixed model including period, 3-NOP dose and their interaction as fixed effects, and block as a random effect. Our results demonstrated both a linear and quadratic (decreasing rate of change) effect on CH4 production (g/d) and CH4 yield (g/kg DMI) as 3-NOP dose increased (P < 0.01). The achieved mitigation for CH4 yield in our study ranged from approximately 65.5% up to 87.6% relative to control steers fed a finishing feedlot diet. Our results revealed that 3-NOP dose did not alter rumen fermentation parameters such as ammonium-N, VFA concentration nor VFA molar proportions. Although this experimental design was not focused on the effect of 3-NOP dose on feedlot performance, no negative effects of any 3-NOP dose were detected on animal production parameters. Ultimately, the knowledge on the CH4 suppression pattern of 3-NOP may facilitate sustainable pathways for the feedlot industry to lower its carbon footprint.

Livestock methane (CH4) is the main source of greenhouse gases (GHGs) in agriculture, contributing to 11.6% of global GHGs emissions from human-related activities. Therefore, mitigating CH4 emissions from ruminant animals is a great opportunity for meeting the current climate targets. In this experiment, increasing inclusion rates of a promising CH4-mitigating compound, 3-nitrooxypropanol (3-NOP, from 50 to 125 mg of 3-NOP/kg of dry matter [DM]), were added to a barley-based feedlot diet containing 25 ppm of monensin and 7% fat (DM-basis) and fed to Angus steers. Under these conditions, increasing inclusion rate of 3-NOP reduced both production and yield of CH4 by up to 90%. Rumen fermentation, feed intake, and average daily gain were not affected by the 3-NOP dose. Our results on the potential CH4 suppression of 3-NOP may assist the feedlot industry towards sustainability by lowering its GHG output.

Effects of dietary energy density and supplemental rumen undegradable protein on intake, viscera, and carcass composition of lambs recovering from nutritional restriction.

Variation in nutrition is a key determinant of growth, body composition, and the ability of animals to perform to their genetic potential. Depending on the quality of feed available, animals may be able to overcome negative effects of prior nutritional restriction, increasing intake and rates of tissue gain, but full compensation may not occur. A 2 × 3 × 4 factorial serial slaughter study was conducted to examine the effects of prior nutritional restriction, dietary energy density, and supplemental rumen undegradable protein (RUP) on intake, growth, and body composition of lambs. After an initial slaughter (n = 8), 124 4-mo-old Merino cross wethers (28.4 ± 1.8 kg) were assigned to either restricted (LO, 500 g/d) or unrestricted (HI, 1500 g/d) intake of lucerne and oat pellets. After 8 wk, eight lambs/group were slaughtered and tissue weights and chemical composition were measured. Remaining lambs were randomly assigned to a factorial combination of dietary energy density (7.8, 9.2, and 10.7 MJ/kg DM) and supplemental RUP (0, 30, 60, and 90 g/d) and fed ad libitum for a 12- to 13-wk experimental period before slaughter and analysis. By week 3 of the experimental period, lambs fed the same level of energy had similar DMI (g/d) and MEI (MJ/d) (P > 0.05), regardless of prior level of nutrition. Restricted-refed (LO) lambs had higher rates of fat and protein gain than HI lambs (P < 0.05) but had similar visceral masses (P > 0.05). However, LO lambs were lighter and leaner at slaughter, with proportionally larger rumens and livers (P < 0.05). Tissue masses increased with increasing dietary energy density, as did DMI, energy and nitrogen (N) retention (% intake), and rates of protein and fat gain (P < 0.05). The liver increased proportionally with increasing dietary energy density and RUP (P < 0.05), but rumen size decreased relative to the empty body as dietary energy density increased (P < 0.05) and did not respond to RUP (P > 0.05). Fat deposition was greatest in lambs fed 60 g/d supplemental RUP (P < 0.05). However, lambs fed 90 g/d were as lean as lambs that did not receive supplement (P0, P > 0.05), with poorer nitrogen retention and proportionally heavier livers than P0 lambs (P < 0.05). In general, visceral protein was the first tissue to respond to increased intake during refeeding, followed by non-visceral protein and fat, highlighting the influence of differences in tissue response over time on animal performance and body composition.

Animal performance is determined by the combined effects of both prior and current nutrition. The present study used a 2 × 3 × 4 factorial to examine the effects of prior feeding level (HI or LO) on subsequent ad-libitum intake of diets varying in energy density (7.8, 9.2, 10.7 MJ/kg DM) and level of supplemental rumen undegradable protein (RUP; 0, 30, 60, and 90g/d). By week 3 of refeeding, LO and HI lambs had similar feed intake, but LO lambs had proportionally more gut and liver tissue and were lighter and leaner at final slaughter. As dietary energy density increased, the rumen became proportionally smaller while the liver became proportionally larger. Liver size increased with increasing RUP, and lambs fed 30 and 60 g/d were fatter than other lambs. However, lambs fed 90 g/d RUP had less fat than other lambs, as the increased energy requirements of a larger liver and of disposing of excess nitrogen appeared to outweigh any nutritional benefits. Understanding how prior nutrition affects current performance, as well as how tissues vary in their response to the same diet, is key to improving our understanding of animal performance and response to change.

Meta-analysis quantifying the potential of dietary additives and rumen modifiers for methane mitigation in ruminant production systems.

Increasingly countries are seeking to reduce emission of greenhouse gases from the agricultural industries, and livestock production in particular, as part of their climate change management. While many reviews update progress in mitigation research, a quantitative assessment of the efficacy and performance-consequences of nutritional strategies to mitigate enteric methane (CH4) emissions from ruminants has been lacking. A meta-analysis was conducted based on 108 refereed papers from recent animal studies (2000-2020) to report effects on CH4 production, CH4 yield and CH4 emission intensity from 8 dietary interventions. The interventions (oils, microalgae, nitrate, ionophores, protozoal control, phytochemicals, essential oils and 3-nitrooxypropanol). Of these, macroalgae and 3-nitrooxypropanol showed greatest efficacy in reducing CH4 yield (g CH4/kg of dry matter intake) at the doses trialled. The confidence intervals derived for the mitigation efficacies could be applied to estimate the potential to reduce national livestock emissions through the implementation of these dietary interventions.

Genetic variance and covariance components for carbon dioxide production and postweaning traits in Angus cattle.

This experiment investigated phenotypic and genetic relationships between carbon dioxide production, methane emission, feed intake, and postweaning traits in Angus cattle. Respiration chamber data on 1096 young bulls and heifers from 2 performance recording research herds of Angus cattle were analyzed to provide phenotypic and genetic parameters for carbon dioxide production rate (CPR; n = 425, mean 3,010 ± SD 589 g/d) and methane production rate (MPR; n = 1,096, mean 132.8 ± SD 25.2 g/d) and their relationships with dry matter intake (DMI; n = 1,096, mean 6.15 ± SD 1.33 kg/d), body weight (BW) and body composition traits. Heritability estimates were moderate to high for CPR (0.53 [SE 0.17]), MPR (0.31 [SE 0.07]), DMI (0.49 [SE 0.08]), yearling BW (0.46 [SE 0.08]), and scanned rib fat depth (0.42 [SE 0.07]). There was a strong phenotypic (0.83 [SE 0.02]) and genetic (0.75 [SE 0.10]) correlation between CPR and MPR. The correlations obtained for DMI with CPR and with MPR were high, both phenotypically (rp) and genetically (rg) (rp: 0.85 [SE 0.01] and 0.71 [SE 0.02]; rg (0.95 [SE 0.03] and 0.83 [SE 0.05], respectively). Yearling BW was strongly correlated phenotypically (rp ≥ 0.60) and genetically (rg > 0.80) with CPR, MPR, and DMI, whereas scanned rib fat was weakly correlated phenotypically (rp < 0.20) and genetically (rg ≤ 0.20) with CPR, MPR, and DMI. The strong correlation between both CPR and MPR with DMI confirms their potential use as proxies for DMI in situations where direct DMI recording is not possible such as on pasture.

The effects of dietary nitrate on plasma glucose and insulin sensitivity in sheep.

Nitrate (NO3 ¯ ) is an effective non-protein nitrogen source for gut microbes and reduces enteric methane (CH4 ) production in ruminants. Nitrate is reduced to ammonia by rumen bacteria with nitrite (NO2 ¯ ) produced as an intermediate. The absorption of NO2 ¯ can cause methaemoglobinaemia in ruminants. Metabolism of NO3 ¯ and NO2 ¯ in blood and animal tissues forms nitric oxide (NO) which has profound physiological effects in ruminants and has been shown to increase glucose uptake and insulin secretion in rodents and humans. We hypothesized that absorption of small quantities of NO2 ¯ resulting from a low-risk dose of dietary NO3 ¯ will increase insulin sensitivity (SI ) and glucose uptake in sheep. We evaluated the effect of feeding sheep with a diet supplemented with 18 g NO3 ¯ /kg DM or urea (Ur) isonitrogenously to NO3 ¯ , on insulin and glucose dynamics. A glucose tolerance test using an intravenous bolus of 1 ml/kg LW of 24% (w/v) glucose was conducted in twenty sheep, with 10 sheep receiving 1.8% supplementary NO3 ¯ and 10 receiving supplementary urea isonitrogenously to NO3 ¯ . The MINMOD model used plasma glucose and insulin concentrations to estimate basal plasma insulin (Ib ) and basal glucose concentration (Gb ), insulin sensitivity (SI ), glucose effectiveness (SG ), acute insulin response (AIRg) and disposition index (DI). Nitrate supplementation had no effect on Ib (p > .05). The decrease in blood glucose occurred at the same rate in both dietary treatments (SG ; p = .60), and there was no effect of NO3 ¯ on either Gb , SI , AIRg or DI. This experiment found that the insulin dynamics assessed using the MINMOD model were not affected by NO3 ¯ administered to fasted sheep at a low dose of 1.8% NO3 ¯ in the diet.

Genetic variation in residual feed intake is associated with body composition, behavior, rumen, heat production, hematology, and immune competence traits in Angus cattle1.

This experiment was to evaluate a suite of biological traits likely to be associated with genetic variation in residual feed intake (RFI) in Angus cattle. Twenty nine steers and 30 heifers bred to be divergent in postweaning RFI (RFIp) and that differed in midparent RFIp-EBV (RFIp-EBVmp) by more than 2 kg DMI/d were used in this study. A 1-unit (1 kg DM/d) decrease in RFIp-EBVmp was accompanied by a 0.08 kg (SE = 0.03; P < 0.05) increase in ADG, a 0.58 kg/d (0.17; P < 0.01) decrease in DMI, a 0.89 kg/kg (0.22; P < 0.001) decrease in FCR, and a 0.62 kg/d (0.12; P < 0.001) decrease in feedlot RFI (RFIf). Ultrasonically scanned depths of subcutaneous fat at the rib and rump sites, measured at the start and end of the RFI test, all had strong positive correlations with RFIp-EBVmp, DMI, and RFIf (all r values ≥0.5 and P < 0.001). Variation in RFIp-EBVmp was significantly correlated (P < 0.05) with flight speed (r = -0.32), number of visits to feed bins (r = 0.45), and visits to exhaled-emission monitors (r = -0.27), as well as the concentrations of propionate (r = -0.32) and valerate (r = -0.31) in rumen fluid, white blood cell (r = -0.51), lymphocyte (r = -0.43), and neutrophil (r = -0.31) counts in blood. RFIp-EBVmp was also correlated with the cellular immune response to vaccination (r = 0.25; P < 0.1) and heat production in fasted cattle (r = -0.46; P < 0.001). Traits that explained significant variation (P < 0.05) in DMI over the RFI test were midtest metabolic-BW (44.7%), rib fat depth at the end of test (an additional 18%), number of feeder visits (additional 5.7%), apparent digestibility of the ration by animals (additional 2.4%) and white blood-cell count (2.1%), and the cellular immune response to vaccine injection (additional 1.1%; P < 0.1), leaving ~23% of the variation in DMI unexplained. The same traits (BW excluded) explained 33%, 12%, 3.6%, 3.7%, and 3.1%, and together explained 57% of the variation in RFIf. This experiment showed that genetic variation in RFI was accompanied by variation in estimated body composition, behavior, rumen, fasted heat production, hematology, and immune competence traits, and that variation in feedlot DMI and RFIf was due to differences in BW, scanned fatness, and many other factors in these cattle fed ad libitum and able to display any innate differences in appetite, temperament, feeding behavior, and activity.