The effects of feeding cut plantain and perennial ryegrass-white clover pasture on dairy heifer feed and water intake, apparent nutrient digestibility and nitrogen excretion in urine

Could natural phytochemicals be used to reduce nitrogen excretion and excreta-derived N2O emissions from ruminants?

Ruminants play a critical role in our food system by converting plant biomass that humans cannot or choose not to consume into edible high-quality food. However, ruminant excreta is a significant source of nitrous oxide (N2O), a potent greenhouse gas with a long-term global warming potential 298 times that of carbon dioxide. Natural phytochemicals or forages containing phytochemicals have shown the potential to improve the efficiency of nitrogen (N) utilization and decrease N2O emissions from the excreta of ruminants. Dietary inclusion of tannins can shift more of the excreted N to the feces, alter the urinary N composition and consequently reduce N2O emissions from excreta. Essential oils or saponins could inhibit rumen ammonia production and decrease urinary N excretion. In grazed pastures, large amounts of glucosinolates or aucubin can be introduced into pasture soils when animals consume plants rich in these compounds and then excrete them or their metabolites in the urine or feces. If inhibitory compounds are excreted in the urine, they would be directly applied to the urine patch to reduce nitrification and subsequent N2O emissions. The phytochemicals' role in sustainable ruminant production is undeniable, but much uncertainty remains. Inconsistency, transient effects, and adverse effects limit the effectiveness of these phytochemicals for reducing N losses. In this review, we will identify some current phytochemicals found in feed that have the potential to manipulate ruminant N excretion or mitigate N2O production and deliberate the challenges and opportunities associated with using phytochemicals or forages rich in phytochemicals as dietary strategies for reducing N excretion and excreta-derived N2O emissions.

Varying plantain content in temperate ryegrass-white clover pastures affects urinary-nitrogen excretion of non-lactating dairy cows

Dairy cow urine patches contain high rates of nitrogen (N; >500 kg N/ha) and represent the main source of N loss from grazed pastoral systems. Emerging research has identified plantain (Plantago lanceolata) as a key forage to potentially reduce urine N (UN) losses from dairy cows. This experiment examined the effect of increasing proportions of plantain in the diet of dairy cows on UN excretion relative to a ryegrass-white clover diet. Twenty mixed aged non-lactating dairy cows were randomly assigned to one of five treatment diets; 0 %, 20 %, 40 %, 60 % or 100 % plantain (dry matter basis), with the remainder comprised of ryegrass-white clover pasture and grass-silage. Cows were fitted with urine sensors to measure urination event N concentration, volume and frequency. Daily N intake increased with increasing proportions of plantain in the diet due to the greater N concentration of plantain. Conversely, mean UN concentration was reduced as the proportion of plantain in the diet increased. Urine-N concentration was >40 % lower for cows on 100 % plantain compared with 0 % plantain (0.46 and 0.81 % N respectively). There was no treatment effect on the total daily amount of UN excreted, indicating a dilution effect of plantain as total daily urine volumes markedly increased with increasing plantain diets. Nitrogen load per urination event was lower for cows on 100 % plantain than 0 % despite greater N intake, with no significant difference for the intermediate treatment groups. The reduced N load per event for cows on >60 % plantain could help to reduce N leaching losses at the urine patch level. This experiment suggests that a reduction in UN concentration can be achieved on low levels of plantain (20 % of the diet), but >60 % plantain diets are required to reduce N load per event.

A Review: Plant Carbohydrate Types—The Potential Impact on Ruminant Methane Emissions

Carbohydrates are the major component of most ruminant feeds. The digestion of carbohydrates in the rumen provides energy to the ruminants but also contributes to enteric methane (CH₄) emissions. Fresh forage is the main feed for grazing ruminants in temperate regions. Therefore, this review explored how dietary carbohydrate type and digestion affect ruminant CH₄ emissions, with a focus on fresh forage grown in temperate regions. Carbohydrates include monosaccharides, disaccharides, oligosaccharides, and polysaccharides. Rhamnose is the only monosaccharide that results in low CH₄ emissions. However, rhamnose is a minor component in most plants. Among polysaccharides, pectic polysaccharides lead to greater CH₄ production due to the conversion of methyl groups to methanol and finally to CH₄. Thus, the degree of methyl esterification of pectic polysaccharides is an important structural characteristic to better understand CH₄ emissions. Apart from pectic polysaccharides, the chemical structure of other polysaccharides per se does not seem to affect CH₄ formation. However, rumen physiological parameters and fermentation types resulting from digestion in the rumen of polysaccharides differing in the rate and extent of degradation do affect CH₄ emissions. For example, low rumen pH resulting from the rapid degradation of readily fermentable carbohydrates decreases and inhibits the activities of methanogens and further reduces CH₄ emissions. When a large quantity of starch is supplemented or the rate of starch degradation is low, some starch may escape from the rumen and the escaped starch will not yield CH₄. Similar bypass from rumen digestion applies to other polysaccharides and needs to be quantified to facilitate the interpretation of animal experiments in which CH₄ emissions are measured. Rumen bypass carbohydrates may occur in ruminants fed fresh forage, especially when the passage rate is high, which could be a result of high feed intake or high water intake. The type of carbohydrates affects the concentration of dissolved hydrogen, which consequently alters fermentation pathways and finally results in differences in CH₄ emissions. We recommend that the degree of methyl esterification of pectic polysaccharides is needed for pectin-rich forage. The fermentation type of carbohydrates and rumen bypass carbohydrates should be determined in the assessment of mitigation potential.

Effect of Grape Marc Added Diet on Live Weight Gain, Blood Parameters, Nitrogen Excretion, and Behaviour of Sheep

Simple Summary

This experiment explored how feeding grape wine production waste product grape marc impacts on sheep production. Forty merino sheep were divided into two groups; one group received a sheep industry standard diet (control), and one group received a treatment diet which had 20% of the control diet replaced by grape marc. The results showed that the grape marc diet led to a higher intake and faecal nitrogen/urinary nitrogen ratio, but no difference in sheep live weight gain, behaviour, and parasitic egg count compared with control diet-fed sheep. Overall, the results showed that feeding grape wine production waste product grape marc as a cheap feed, to replace 20% of the control ration, can maintain sheep productivity, health, and environmental sustainability.

Abstract

A 39-day field experiment was conducted to assess the effect of grape marc (GM) feeding on sheep productivity, health, and environmental sustainability. Forty merino sheep were divided into two dietary groups, each having five replications (n = 4 sheep/replication). Experimental diet consisted of: (i) control: 55% lucerne hay + 40% wheat grain + 5% faba bean; (ii) GM treatment: control diet with 20% replaced by GM on a dry matter (DM) basis. The GM treatment contained 2–10% higher phytochemical contents than the control. The DMI from the GM treatment was 15% higher than the control (p < 0.001). No difference was found in sheep live weight gain, behaviour, and quality between groups (p > 0.05). No difference was found in total faecal production, faecal organic matter, and nitrogen contents (p > 0.05) and parasitic egg count. The GM treatment led to higher nitrogen intake (23.1 vs. 27.2 g/d) and faecal nitrogen excretion (6.3 vs. 8.7 g/d) compared to the control. Urinary creatinine, allantoin, and purine derivatives were lower in the GM treatment than control (p < 0.05). However, both groups had similar purine derivatives/DMI (i.e., indicator of rumen microbial protein synthesis efficiency; p > 0.05). Overall, the results showed that GM can replace 20% of the control ration to maintain sheep productivity, health, and environmental sustainability.

Uncertainties in direct N2O emissions from grazing ruminant excreta (EF3PRP) in national greenhouse gas inventories

Excreta deposition onto pasture, range and paddocks (PRP) by grazing ruminant constitute a source of nitrous oxide (N₂O), a potent greenhouse gas (GHG). These emissions must be reported in national GHG inventories, and their estimation is based on the application of an emission factor, EF_3PRP (proportion of nitrogen (N) deposited to the soil through ruminant excreta, which is emitted as N₂O)_. Depending on local data available, countries use various EF_3PRPs and approaches to estimate N₂O emissions from grazing ruminant excreta. Based on ten case study countries, this review aims to highlight the uncertainties around the methods used to account for these emissions in their national GHG inventories, and to discuss the efforts undertaken for considering factors of variation in the calculation of emissions. Without any local experimental data, 2006 the IPCC default (Tier 1) EF_3PRPs are still widely applied although the default values were revised in 2019. Some countries have developed country-specific (Tier 2) EF_3PRP based on local field studies. The accuracy of estimation can be improved through the disaggregation of EF_3PRP or the application of models; two approaches including factors of variation. While a disaggregation of EF_3PRP by excreta type is already well adopted, a disaggregation by other factors such as season of excreta deposition is more difficult to implement. Empirical models are a potential method of considering factors of variation in the establishment of EF_3PRP. Disaggregation and modelling requires availability of sufficient experimental and activity data, hence why only few countries have currently adopted such approaches. Replication of field studies under various conditions, combined with meta-analysis of experimental data, can help in the exploration of influencing factors, as long as appropriate metadata is recorded. Overall, despite standard IPCC methodologies for calculating GHG emissions, large uncertainties and differences between individual countries' accounting remain to be addressed.

Integrating Plantain (Plantago lanceolata L.) and Italian Ryegrass (Lolium multiflorum Lam.) into New Zealand Grazing Dairy System: The Effect on Farm Productivity, Profitability, and Nitrogen Losses

A two-year farm system study was conducted at Canterbury, New Zealand to evaluate the effects on farm productivity, profitability, and nitrogen (N) losses of integrating plantain (Plantago lanceolate L.) and Italian ryegrass (Lolium multiflorum Lam.) into a ryegrass and white clover (RGWC)-based dairy system. Three farm systems were compared: (1) a lower input RGWC-based system (LIRG) with stocking rate of 3.5 cow/ha, annual N fertiliser rate of 150 kg/ha, and imported feed level of <1.2 t DM/cow/year; (2) a lower input ryegrass + plantain-based system (LIRG + PL) with a stocking rate of 3.5 cow/ha, annual N fertiliser rate of 150 kg/ha, and imported feed level of <1.2 t DM/cow/year; and (3) a higher input RGWC-based system (HIRG) with a stocking rate of 5.0 cow/ha, annual N fertiliser rate of 300 kg/ha, and imported feed level of >1.2 t DM/cow/year. Cows in the LIRG + PL system grazed a diverse mix of Italian ryegrass, perennial ryegrass, white clover, and plantain (60% of farmlet area), and a mixed sward of plantain-white clover (40% of farmlet area). The average annual herbage harvested was similar between LIRG + PL and LIRG (11.7 t DM/ha), but greater in HIRG (12.7 t DM/ha) with the increased N fertiliser rate. During the calving to dry-off period, the average imported supplement feed per ha was higher in HIRG (8.0 t DM) compared with LIRG (3.2 t DM) and LIRG + PL (3.7 t DM). Average milk solid production (MS; fat + protein) was similar in LIRG + PL (1640 kg/ha) and LIRG (1622 kg/ha), but greater in HIRG (2130 kg/ha). Estimated profitability (NZD/ha) at milk price of NZD 6.5/kg MS was 10% greater for HIRG than LIRG + PL and LIRG, and similar (<1.5% numerical difference) between LIRG + PL and LIRG. The average estimated annual N leaching loss from the LIRG and LIRG + PL was 31% and 56% less than the loss from the HIRG. These large reductions in N leaching loss were achieved without a large decrease in profitability (i.e., LIRG and LIRG + PL compared to HIRG). In addition, the estimated reduction in N losses from the LIRG + PL system compared to LIRG suggests that an Italian ryegrass + plantain-based dairy system is a viable strategy to reduce the environmental footprint while maintaining farm profitability. However, the environmental benefits of plantain and Italian ryegrass estimated in this study require further confirmation through direct measurements at full farm level.

Does Brachiaria humidicola and dicyandiamide reduce nitrous oxide and ammonia emissions from cattle urine patches in the subtropics?

Nitrous oxide (N₂O) emissions from pasture-based livestock systems represent 34% of Brazil's agricultural greenhouse gas emissions. The forage species Brachiaria humidicola is known for its biological nitrification inhibition (BNI) capacity and N₂O emissions reduction ability from urine patches under tropical conditions. However, there is little information about the effect of BNI on N₂O emission and ammonia (NH₃) volatilisation in the subtropics. This study aimed to: (i) evaluate the potential of Brachiaria humidicola, compared with Panicum maximum (Jacq. cv. Áries; guinea grass), a broadly used grass (with no BNI capacity), to reduce N₂O emissions under subtropical conditions; (ii) determine the efficacy of nitrification inhibitor dicyandiamide (DCD) to decrease N₂O emissions; and (iii) determine the effect of brachiaria and DCD application on NH₃ volatilisation. A field experiment was carried out using a Cambisol, where cattle urine ± DCD was applied to brachiaria and guinea grass. Over the 67-day measurement period, cumulative N₂O emissions were 20% lower from urine patches in the brachiaria treatment (1138 mg N m^-2, Emission factor = 1.06%) compared to guinea grass (1436 mg N m^-2, Emission factor = 1.33%) (P < .10). A greenhouse experiment, using pots with the same treatments as in the field experiment, suggested that this could have been due to lower soil nitrate levels under brachiaria forage compared to guinea grass, indicating that BNI could be a possible mechanism for lower N₂O emissions from brachiaria. The DCD application was effective in both forage species, decreasing N₂O emissions by 40-50% (P < .10) compared with the urine only treatment. Approximately 25% of the urine applied N was lost via NH₃ volatilisation, however the NH₃ loss was not affected by forage species or DCD application (P > .10). Overall, the results demonstrated that brachiaria and DCD use are strategies that can reduce N₂O emissions from urine patches.

How does stage of lactation and breeding worth affect milk solids production and production efficiency of grazing dairy cows?

The study investigated the effect of stage of lactation and Breeding Worth (BW) index on estimated dry matter intake (DMI), milk solids (MS) production, energy use efficiency (EUE) and feed conversion efficiency (FCE) of grazing cows. Two hundred crossbred cows with similar calving date (14 August ± 9.97 days), live weight (471.5 ± 44.02) and age (7.5 ± 1.25 years) were separated into five groups (n = 40) based on New Zealand BW index: Low BW (BW = 63.1); Medium Low BW (BW = 88.2); Medium BW (BW = 19.1); Medium High BW (BW = 128.9); and High BW (BW = 146.9). Milk samples were collected in early, mid and late lactation and herbage samples were taken the day before milk sampling. The DMI was estimated by back-calculation based on metabolizable energy requirement for maintenance and production. The MS production, herbage DMI, EUE and FCE declined from early to late lactation. The overall results suggest regardless of the stage of lactation, cows with higher BW had a higher DMI, MS production and FCE.