Relevance of sward structure and forage nutrient contents in explaining methane emissions from grazing beef cattle and sheep.

Forage nutrient contents are an important factor explaining the dry matter intake (DMI), average daily gain (ADG), and methane emissions (CH4) of ruminants fed indoors. However, for grazing animals, the forage nutrient contents might be limited in explaining such response variables. We aimed to verify the explanatory power of forage nutrient contents and sward structure on daily intake, performance, and CH4 emissions by sheep and beef cattle grazing different grassland types in southern Brazil. We analyzed data from five grazing trials using sheep and beef cattle grazing on Italian ryegrass (Lolium multiflorum), mixed Italian ryegrass and black oat (Lolium multiflorum + Avena strigosa), pearl millet (Pennisetum americanum), and multispecies native grassland. We used mixed models, including the forage nutrient contents [crude protein (CP), neutral detergent fiber (NDF), and acid detergent fiber (ADF)], sward structure (sward height and herbage mass) and their interactions, as fixed effects and trial, season, methodologies, animal species, grassland type, and paddock, as random effects. The model for DMI (kg DM/LW0.75) had an adjusted coefficient of determination (R2adj) of 71.6 %, where 11.3, 23.1, and 37.2 % of the R2adj were explained by the forage nutrient contents, sward structure, and their interaction, respectively. The ADG (kg/LW0.75) model presented an R2adj of 74.2 %, with 12.5 % explained by forage nutrient contents, 29.3 % by sward structure, and 32.4 % by their interaction. The daily CH4 emission (g/LW0.75) model had a lower adjusted coefficient of determination (R2adj = 47.6 %), with 16.8 % explained by forage nutrient contents and 30.8 % explained by sward structure, but no effect of the interaction. Our results show that in grazing ecosystems, the forage nutrient contents explain a small fraction, and the greater explanatory power for DMI, ADG, and CH4 emissions models is related to sward structure descriptors, such as sward height and herbage mass. Moreover, the interaction between these variables explains most of the variation. In conclusion, forage nutrient contents and sward structure have different influences on DMI, ADG, and CH4 emissions by grazing ruminants. Because of its relevance to daily CH4 emissions, offering an optimal sward structure to grazing animals is a major climate-smart strategy to improve animal production and mitigate CH4 emissions in pastoral ecosystems.

Feed intake, methane yield, and efficiency of utilization of energy and nitrogen by sheep fed tropical grasses.

Forage allowance impacts dry matter (DM) intake and the use of nutrients by ruminants. The efficient use of protein and energy from pasture is related to better livestock performance and lower environmental impacts. The aims of this study were to evaluate the effect of forage allowance levels on intake, digestibility, nitrogen (N) and energy balance, and methane (CH4) emissions by lambs fed fresh pearl millet [Pennisetum americanum (L.) Leeke]. An indoor trial was performed using lambs in a completely randomized design with four treatments [forage allowance at 1.5, 2.0, 2.5 kg DM/100 kg of live weight (LW), and ad libitum allowing 20% of refusals] and four replicates (lambs). Forage intake, digestibility, total urine and feces excretion, and CH4 emission were measured to calculate N and energy balances. An increase in forage allowance resulted in a linear increase in lamb forage intake, N retention, and metabolizable energy intake. Moreover, lamb CH4 emission (g/day) also increased with greater forage allowance, while CH4 yield decreased linearly as forage allowance increased. Our results indicate that maximizing forage intake improves N and energy use efficiency and mitigates CH4 yield and decreases CH4 conversion factor (Ym) by lambs fed pearl millet forage. Thus, management strategies that optimize intake of tropical forages by ruminants improve the use of nutrients ingested and mitigates negative impacts to the environment.

Low-Intensity, High-Frequency Grazing Strategy Increases Herbage Production and Beef Cattle Performance on Sorghum Pastures.

We assessed the effects of high-intensity and low-frequency (HILF) vs. low-intensity and high-frequency (LIHF) grazing on herbage production and performance of beef cattle grazing sorghum pastures. The experimental design was a complete randomized block with two treatments and four replicates (paddocks), carried out in 2014/15. The management target of 50 and 30 cm for pre- and post-grazing, respectively, a LIHF grazing management strategy oriented to maximize beef cattle herbage intake per unit time, was compared with a HILF grazing management strategy of 80 and 20 cm for pre- and post-grazing, respectively, aiming to maximize herbage accumulation and harvest efficiency. Sixteen Brangus steers of 15-month-old and 265 ± 21 kg of live weight (LW) were randomly distributed to paddocks (experimental units). The LIHF resulted in shorter rest periods when compared with the HILF. The greater leaf lamina mass in LIHF allowed greater sward light interception at post-grazing, resulting in greater total herbage production than HILF (7581 and 4154 kg DM/ha, respectively). The average daily gain (ADG) of steers was greater for the LIHF than for the HILF treatment (0.950 and 0.702 kg/animal, respectively); however, even with a greater stocking rate in the HILF, there was no difference for LW gain per ha, with an average of 4 kg LW/ha/day. Our findings demonstrated that the LIHF strategy that is based on offering to the animals an optimal sward structure to favor the maximum herbage intake rate fosters greater herbage production, harvesting efficiency, and ADG without compromising LW gain per area of beef steers, despite the lower herbage harvested per stocking cycle.

'Rotatinuous' stocking as a climate-smart grazing management strategy for sheep production.

We aimed to evaluate the effect of different grazing management strategies on carcass characteristics traits, meat quality and CH4 intensity and yield of lambs grazing Italian ryegrass pastures in Southern Brazil. A grazing trial was performed (2014 and 2015) in a randomized complete block design with two grazing management targets and four replicates. Treatments were traditional rotational stocking (RT), with pre- and post-grazing sward heights of 25 and 5 cm, respectively, and 'Rotatinuous' stocking (RN), with pre- and post-grazing sward heights of 18 and 11 cm, respectively. Castrated crossbred Texel and Polwarth lambs were used. Results indicated that diet cost per kg of dry matter (p = 0.001) and per hectare (p < 0.001) were lower for RN than for RT treatment. Final live weight (p = 0.022) and hot and cold carcass weight (p = 0.006) were greater for the RN treatment. All commercial cuts were greater for RN than for RT treatment. The RN treatment presented greater (p < 0.001) production of carcass, edible food and crude protein. Feed efficiency and feed cost conversion were better for RN than for RT treatment. CH4 intensity per kg of carcass, edible food and crude protein gain were 2.6, 2.7 and 2.1 times lower (p < 0.001) for RN. Moreover, CH4 yield was lower (p = 0.014) for RN than for RT treatment, with an average of 7.6 and 8.3% of the gross energy intake, respectively. We conclude that the 'Rotatinuous' stocking results in a greater carcass production, carcass quality and lower diet cost, and CH4 intensity and yield of grazing lambs. Adopting this grazing management strategy could enhance both lamb production and mitigation of CH4 intensity and yield in grazing ecosystems, which could be considered a good example of climate-smart livestock production.

Does grazing management provide opportunities to mitigate methane emissions by ruminants in pastoral ecosystems?

Agriculture, and livestock production in particular, is criticized for being a contributor to global environmental change, including emissions of greenhouse gases (GHG). Methane (CH4) from grazing ruminants accounts for most of livestock's carbon footprint because a large share of them are reared under suboptimal grazing conditions, usually resulting in both low herbage intake and animal performance. Consequently, the CH4 quota attributed to animal maintenance is spread across few or no animal outputs, increasing the CH4 intensity [g CH4/kg live weight (LW) gain or g CH4/kg milk yield]. In this review, the generalized idea relating tropical pastures with low quality and intrinsically higher CH4 intensity is challenged by showing evidence that emissions from animals grazing tropical pastures can equal those of temperate grasses. We demonstrate the medium-to-high mitigation potential of some grazing management strategies to mitigate CH4 emissions from grazing ruminants and stress the predominant role that sward canopy structure (e.g., height) has over animal behavioral responses (e.g., intake rate), daily forage intake and resulting CH4 emissions. From this ecological perspective, we identify a grazing management concept aiming to offer the best sward structure that allows animals to optimize their daily herbage intake, creating opportunities to reduce CH4 intensity. We show the trade-off between animal performance and CH4 intensity, stressing that mitigation is substantial when grazing management is conducted under light-to-moderate intensities and optimize herbage intake and animal performance. We conclude that optimizing LW gain of grazing sheep and cattle to a threshold of 0.14 and 0.7 kg/day, respectively, would dramatically reduce CH4 intensity to approximately 0.2 kg CH4/kg LW gain, as observed in some intensive feeding systems. This could represent a mitigation potential of around 55% for livestock commodities in pasture-based systems. Our results offer new insights to the debate concerning mitigation of environmental impacts of pastoral ecosystems.

Prediction of biogas and pressure from rumen fermentation using plant extracts to enhance biodigestibility and mitigate biogases.

Improving digestibility, fermentation characteristics, and reducing greenhouse biogases to protect the environment without the use of synthetic materials is an important goal of modern-day farming and nutritionist. Plant extracts are capable of solving these. This is due to the digestive enzymes and the bioactive components capable of performing antimicrobial functions inherent in these plants. This study was aimed to investigate the effect of standard maize substrate treated with selected herbs and spices extracts on ruminal environmental biogas production and pressure during fermentation via biogas production technique. Herbs (Azadirachta indica leaves (T1), Moringa oleifera leaves (T2), Ocimum gratissimum leaves (T3) and spices (Allium sativum bulb (T4), Zingiber officinale rhizome (T5)) were harvested, air dried, and milled using standard procedures. Methanolic extracts of the herbs and spices were prepared and used as additives at different concentrations (50, 100, and 150 µL) to the maize substrate for in vitro biogas production. Data were analyzed using regression analysis. There were significant (P < 0.05) differences across all the treatments on the volume and pressure of biogas. The pressure and volume of biogas when compared with the levels tested showed differences (P < 0.05) across all the treatments for the prediction of volume from pressure of biogas. The pressure and volume of gas produced in vitro increased (P < 0.05) and biogases decreased (P < 0.05) by the substrate treated with herbs and spices but for the drum stick leaves which was similar for the levels of concentration tested. This means that the level tested had a pronounced mitigation effect on pressure of biogas and volume of biogas produced. It was concluded that the herb and spice extracts have the potential to improve rumen fermentation and reduce the production of biogases in ruminant diet.