Access to Emission Control Blocks for improved productivity and mitigation of enteric methane in smallholder cattle in Cambodia

Introduction

Sustainability of animal-sourced foods (ASF) increasingly needs identification and adoption of the multiple interventions required to achieve improved efficiencies in production (FAO 2018; Windsor 2024). With increasing emergence of global climate change concerns, attention has focused on the contribution of greenhouse gas emissions (GHGe) from global animal protein production, estimated to have contributed a total of 6.2 gigatonnes (Gt) of carbon dioxide equivalent (CO₂e) of emissions, or ~12% of the 50–52 Gt CO₂e total of anthropogenic emissions in 2015 (FAO 2023a). Cattle are by far the largest contributors to GHGe from ASFs, producing ~3.8 Gt CO₂e per annum (FAO 2023a). This is 62% of all livestock emissions and compares to contributions from pigs of 14%, chickens of 9%, buffaloes of 8% and small ruminants of 7% (FAO 2023a, 2023b).

There are variations in the carbon emissions of ASF production due to livestock management, species and breed productivity and feed availability (FAO 2023a). Strategies including improving nutrition, animal health and fertility have been suggested as offering potential pathways for reducing the carbon footprint of livestock systems (FAO 2023a) and meeting Global Methane Pledge (GMP 2024) agreements. This is the case for smallholder cattle production in countries where the emissions intensity (Ei; kg CO₂e/kg product) is highest. In the Greater Mekong Subregion (GMS), particularly Cambodia and Lao People’s Democratic Republic (Lao PDR; Laos), the estimated Ei for beef is 88.6 and 100.7 kg CO₂e/kg, respectively, compared to global estimates of Ei for beef of 28.3 kg CO₂e/kg (FAO 2023b).

Smallholder agricultural production in Cambodia is characterised as a low-input, low-output system. Livestock production is largely based on crop by-products, predominately rice straw, and ‘cut and carry’ of fodder or grazing (ACIAR 2013). Cattle raising is important in Cambodia, with a 2016 survey of the four agroecological regions (Samkol et al. 2015) finding an average cattle herd size of 3.7 (s.d. = 2.4). Indigenous Yellow cattle is the most common breed in Cambodia, with an increasing presence of Haryana and Brahman and their crosses (both originating from India). Yellow cattle are typically smaller (250–300 kg) than the Indian breeds (400–450 kg) and crosses between Haryana and Yellow cattle are the preferred breed for work in draft or sale (ACIAR 2013; FAO CAS 2021). Cattle in Cambodia are an important source of manure for fertiliser, energy from methane in household biodigesters, plus a financial asset or ‘bank’ that can be utilised by households when required (Windsor 2024). Constraints to cattle production in Cambodia include lack of quality feed resources, capital, concerns on breed quality and diseases (Samkol et al. 2015). However, longitudinal studies have demonstrated that the implementation of a ‘best practice’ program utilising forages and health interventions can increase average daily gains (ADG) from negative or zero production per day to approximately 50–125 g/day (Windsor 2011, 2024; Nampanya et al. 2012; ACIAR 2013; Bush et al. 2014b; Young et al. 2014; Ashley et al. 2018).

Cambodia is considered highly vulnerable to the impacts of climate change. The updated Cambodian Nationally Determined Contribution data (CNDC 2020) established a conditional target of 41.7% reduction of emissions by 2030 compared with a business-as-usual case. Most of the reductions are projected from forestry and land use change emissions abatement, although agriculture is also expected to contribute to this target. The CNDC targets are aligned to the National Strategic Development Plan (NSDP 2023) that reflects a development focus on reducing poverty and ensuring stable economic growth. Further, the Cambodia Climate Change Strategic Plan 2014–2023 (CCCSP 2013) was also developed to focus on economy wide adaptation through a gradual increase in mitigation actions aligned to economic development goals. Agriculture is a priority sector exposed to adaptation and mitigation, particularly for rice and other crop production. In addition, there are initiatives to increase the effectiveness and sustainability of agricultural land management techniques, manure management and research on improving animal agriculture productivity and resilience to climate change (e.g. genetics, breeding, feed).

A multi-intervention livestock development strategy involving a combination of nutritional and health interventions has been proposed as a ’scale-out’ strategy to assist smallholders in improving large ruminant livestock farming efficiency in countries in the GMS, with potential applications beyond and in developed countries (Windsor 2023, 2024). This strategy evolved from many years of local applied research that identified the positive impact of forage interventions in stimulating farmer learning and increasing receptivity to animal health and other interventions (Nampanya et al. 2012; Windsor 2024). However, as several years are required for forage production to provide an impact on farmer livelihoods, a method of hastening the process was required where the impacts are observable within several weeks of initiating the intervention (Windsor and Hill 2022).

A series of high-quality molasses blocks (MBs) incorporating anthelmintics were initially formulated to control endoparasites in Laos (Rast et al. 2014, 2017; BPP 2019; Olmo et al. 2020; Windsor et al. 2019, 2020, 2021a, 2021b; Windsor 2024). The improved productivity through nutrition and health from the various MB formulations used in these studies encouraged examination of the impacts on Ei. Calculations indicated that each 20-kg block indirectly reduced Ei by ~470 kg CO₂e through improved productivity and animal health (Windsor and Hill 2022). Importantly, Lao smallholder farmers described improved productivity, animal appearance and values, with declarations that the use of MBs greatly assisted animal management.

This current study aimed to trial a molasses-based 20 kg ‘emissions control block’ (ECB, AgCoTech Laos) as a feed supplement for cattle in Cambodia, and investigate changes in cattle productivity and abatement of methane (CH₄).

Materials and methods

This study incorporated three key components to calculate the impact on GHGe abatement of the ECB on Cambodian cattle. These components consisted of: (1) a field trial in Pursat Province to establish production impacts of the ECB; (2) modelling the results of the field trial and ECB feed inputs within the Intergovernmental Panel on Climate Change (IPCC) Tier 2 calculator tool (IPCC 2023) to establish the baseline GHGe of both trial groups; and (3) calculating the CH₄ abatement using a handheld methane monitor to assess breath methane concentration.

Results

Field experiment

The total number of farmers, gender and average age in the two villages are provided, in addition to the total cattle owned, average number of cattle per farm, and average cattle age (months) (Table 1). All cattle (n = 80) enrolled in the study were local Haryana cross animals (known as local breed). Of the initial 40 cattle enrolled in the study for each study group, farmers sold nine cattle prior to the end of the trial (four from the control group and five from the treatment group).

Table 1.Number of farmers, gender and their average age (years, in brackets) in each village, and total cattle, average number of cattle per farm, and average cattle age (months).

Village	Female farmers	Male farmers	Total farmers	Total cattle owned	Average per farm	Average cattle age (months)
						Treatment	Control
Svay Meas	6 (53)	16 (44)	22 (46)	107	4.86	16.5	17.7
Or Tbong	5 (53)	13 (48)	18 (49)	77	4.28	21.1	25.5
Total	11 (53)	29 (45)	40 (48)	184	4.60	18.6	21.2

Cattle body weight changes

The mean starting weight and end weight of cattle in the control group that completed the trial (n = 36) was 209.1 kg and 212.1 kg respectively, equating to an ADG of 42 g/day. The mean starting weight of treatment group cattle was 198.0 kg and final weight was 203.3 kg, equating to a ADG of 76 g/day (n = 35). For treatment cattle, a boxplot showing body weight of cattle during the trial by group at weeks 0, 5 and 10 is provided in Fig. 1. Note that at the start of the study (Day 0), there were no significant differences in the mean body weights between treatment and control animals (P = 0.10).

Fig. 1.

Boxplot of weight of trial groups at week 0, 5 and 10 (start, mid and end of trial). The horizontal line within the box indicates the median, and the limits of the box indicate upper and lower quartiles. Values shown as large dots may be considered outliers.

Summary statistics of average daily gain (ADG, kg/day)

Fig. 2 presents the ADG across the control and treatment groups during periods week 0–5 and 6–10.

Fig. 2.

Boxplot of average daily gain (kg/day) for each group over weeks 0–5 and 6–10. The horizontal line within the box indicates the median, and the limits of the box indicate upper and lower quartiles. Values shown as large dots may be considered outliers.

Comparison between the treatment and control group

Based on the fitted linear mixed model there was a significant Group × Week interaction for bodyweight (P = 0.026), with the effect of treatment differing between the two 5-week periods. In Week 10, treatment body weight means were significantly greater than control means by just over 4 kg (Table 2).

Table 2.Model-based mean body weight in the treatment and control groups from the linear mixed model.

Group	Week	Body weight (kg)
		Mean	s.e.	‘sig’A
Control	5	203	1.29	a
Treatment	5	205	1.28	a
Control	10	204	1.30	a
Treatment	10	208	1.29	b

^A Model-based means ± s.e., letter in ‘sig’ column indicates significant differences (P < 0.05) amongst all four means when letters differ.

There was a highly significant positive effect of initial weight on subsequent body weight, as expected (P < 0.001). For the ‘dose-response’ analysis of the effect of the amount of ECB consumed on body weight, there was a significant ECB × Week interaction (P < 0.001). This indicated that the linear effect of ECB (dose) was significant but differed between the two 5-week periods. In particular, ECB consumption during the first 5 weeks increased body weight at Week 5 by 0.33 kg/kg ECB consumed (P = 0.036). In the second 5-week period, the increase in body weight was 1.33 kg/kg ECB consumed (P < 0.001), as shown in Fig. 3, i.e. a much more substantial effect on growth in the second period. As with the previous analysis (treatment vs control), there was a highly significant positive effect of initial weight (P < 0.001).

Fig. 3.

Plot of model-based mean body weights at week 5 and week 10, showing dose-response of ECB consumption for weeks 1–5 and 6–10 respectively, based on the linear mixed model. Grey bands represent ± 1 s.e. At the bottom of the plot is a ‘rug plot’, indicating the observed ECB consumption values, for weeks 1–5 and 6–10.

Measurement of breath methane concentration

Assessing treatment and control groups for CH₄ output

Breath methane concentration tended to be lower in treatment cows (Fig. 4). In the formal analysis, this difference was found to be significant (P = 0.0019), with treatment cows on average producing 88.0 g/day compared with 106.0 g/day for control animals. This difference of 18 g/day CH₄ reduction represented a 17.0% decrease in daily CH₄ production and can be extrapolated to 6.57 kg CH₄ per animal per year, or 184 kg CO₂e per animal per year. There was also a significant effect of initial body weight (P = 0.038), with an increase by an average of 0.0014 g/day of CH₄, for each additional kg of body weight at Week 0.

Fig. 4.

Boxplot of CH₄ production (g/day) in the treatment and control groups. The horizontal line within the box indicates the median, and the limits of the box indicate upper and lower quartiles. Values shown as large dots may be considered outliers.

ECB dosage analysis

When the amount of ECB consumed by treatment animals is considered, there was a significant reducing effect on CH₄ for ECB consumption over the first 5 weeks (P = 0.041). However, there was no significant effect of ECB consumption over the second 5-week period (P = 0.72), although a reduction was observed. There was a significant increase in CH₄ with increasing body weight at Week 0 (P = 0.028).

Fig. 5 is a plot of the fitted model showing the effect of varying ECB consumption in the two 5-week periods. Note that the non-significant effect of consumption in the second 5-week period may be due to a limited range of ECB consumption in this period, compared to the first period. This is shown in the ‘rug plot’ at the bottom of Fig. 5: for the ECB consumption in the second 5-week period, the maximum consumption was 8.5 kg, but all other values were under 2.8 kg, with a very limited range of ECB values in the second period (Fig. 5). 

Fig. 5.

Plot of model-based mean CH₄ production showing dose-response of ECB consumption for weeks 1–5 and 6–10, based on the linear mixed model. Grey bands represent ± 1 s.e. At the bottom of the plot is a ‘rug plot’ indicating the observed ECB consumption values, for weeks 1–5 and 6–10.

Discussion

Interestingly, the CH₄ eructation data indicated a significant effect of the ECB (P = 0.0019) with ‘treatment’ on average producing 88.0 g/day compared with 106.0 g/day for ‘control’, a 17.0% decrease in daily CH₄ breath concentration. The handheld, portable LaserMethane device was developed to detect gas leaks in industry from a safe distance but has increasingly been used to measure the methane concentration in the expired air of cattle, sheep, and goats to quantify their emissions (Sorg 2022). Whilst it has been observed that there is no consensus on a uniform measurement and data-analysis protocol with the device, it is well recognised that several aspects, including the distance to the animal or the activity of the animals, should be fixed for all measurements of an experiment or at least be documented and considered as fixed effects in the statistical analysis (Sorg 2022). In this trial, the phenotype of the animals was matched, and a single point of repeated measurement was used, timed at the peak of eructation, assisting repeatability and enabling analysis to compare the average CH₄ concentration of the ‘treatment’ group with the ‘control’. Using the IPCC calculator, the modelled indirect abatement was calculated as 220 kg CO₂e per animal and methane breath abatement at 184 kg CO₂e. This study supports that ECBs can lead to a reduction in methane output for cattle consuming the ECB.

Whilst access to the ECB avoided weight loss in the ‘treatment’ group compared to the ‘control group’, the modest ADG likely reflected the low daily ECB consumption rates. ECB consumption rates (range: 21–94 g/day) were considerably less than expected and well below the target (160–200 g/day) of previous trials (Windsor and Hill 2022). This reflected excessive firmness in this ‘cooked’ batch of ECBs, suggesting a minor modification of the ‘hardener’ in the formulation was required to obtain the optimal consumption typical of MB, and more recently ECB, use in Laos (Windsor and Hill 2022; Windsor 2024). Despite this concern, it was concluded that ECBs for cattle offers GHGe abatement implications that could be capable of supporting Cambodia in meeting Nationally Determined Contributions and the commitment to the Global Methane Pledge.

When assessing antimethanogenic feed additives, tailored approaches are needed. The IPCC calculations for methane emissions change only consider the emissions of an animal either under business-as-usual (BAU) (baseline) or the animal that is now performing at a different plane of production; for example, a change in weight gain through better efficiency of conversion of feed. The IPCC Tier 2 calculators are not designed to consider direct abatement of GHGe using a CH₄ mitigant, as the animal is considered as being managed under BAU conditions. However, when a direct CH₄ mitigant is added (as in this case with lemongrass in the ECBs) the CH₄ emissions are reduced, but there are no (significant) changes in animal performance due to the mitigant alone. Therefore, if we used the IPCC calculator to determine if there has been an impact on methane emissions, it would report a negligible change. Therefore, the IPCC calculator would not account for both impacts due to improved production and the direct abatement from the methanogenic compound. Similarly, if the study only measured the breath methane concentration, the analysis would not account for any Ei changes due to the ECBs components that led to the productivity gains (molasses, minerals and vegetable oils etc.).

A multi-intervention livestock development strategy that can achieve ‘scale-out’ has been proposed as a pathway for improving smallholder large ruminant livestock farming efficiency in developing countries (AgCoTech Global 2023; Windsor 2023; Windsor 2024). The strategy involves the initial provision of high-quality MBs, now redesigned as ECBs, with their use potentially reducing the carbon footprint of the livestock agrifood system (FAO 2007, 2023a; Windsor 2024). Importantly, ECBs improve rumen digestion efficiency with reduced Ei of production, and inclusion of GHGe-reducing compounds provides direct abatement of rumen methane (Windsor 2024). Widespread adoption of this strategy would enable numerous countries to better align with the aspirations of the Global Methane Pledge (GMP 2024). Using high-quality ECBs may be the catalyst for adoption of the proposed ‘scale-out’ strategy that includes forage and health interventions. ECBs offer a relatively simple method for improving rural livelihoods and food security whilst reducing GHGe from ruminants, yet offering numerous socioeconomic benefits that may improve the resilience of poor rural communities (Windsor 2024).

Use of dietary fermentation modifiers containing a high content of secondary plant ingredients, including tannins and saponins, are of increasing interest in efforts to achieve CH₄ abatement from cattle feeding. Saponins form complexes in cell membranes, causing the death of rumen protozoa, whereas tannins can be either hydrolysing, forming complexes with proteins that inhibits the growth of methane-forming microorganisms, or acting as condensed tannins, reducing the degradability of fibre components of the feed (Goel and Makkar 2012; Guggenberger 2021). A diet with 1.5% extract containing a mixture of hydrolysed and condensed tannins was found to have a significant methane-reducing effect, as was the feeding of lemongrass with 60 g condensed tannins/kg DM to cattle in two trials (Aboagye et al. 2018; Vázquez-Carillo et al. 2020). A recent study from Austria (Beauchemin et al. 2020) on the effect of feeding of 100 g lemongrass as feed supplement on CH₄ concentration in the respiratory air of beef cattle, indicated reductions in expired CH₄ of 14.6% (range 7.8–23.4%). These findings stimulated interest in the provision of a chopped feed mix supplement containing plant tannins and citral extract from readily available local vegetable materials to beef cattle and dairy buffalo, demonstrating reductions in CH₄ concentration at eructation of 18% and 30% respectively (Windsor et al. 2023). This success prompted incorporation of this condensed tannin material (such as lemongrass) into MBs to create ECBs, now extensively used in Laos (Windsor 2024). Numerous trials with ECBs have been occurring in Indonesia (MLRB 2024), with this initial trial now completed in Cambodia indicating the strategy has merit.

Farmers describe improved productivity, animal appearance and values, with declarations that the ECBs greatly assisted the management of their animals (MLRB 2023). In the larger herds, cattle and buffalo return from grazing in the fields and forests more readily to seek access to the blocks and farmers regularly commented that their animals were calmer, fatter, shinier and much more valuable (MLRB 2023). Further, ECBs can provide an important source of energy support for animals during potentially fatal hypothermia episodes (Khounsy et al. 2012), assisting climate change adaptation. The very positive impacts of ECBs encouraged the development of an MB manufacturing facility in northern Laos near Luang Prabang that opened in April 2023 and is now producing ~3000 blocks per month. The ECBs are distributed free to farmers in exchange for the verified carbon credits accrued (Windsor and Hill 2022), and it is estimated that the plant will contribute ~150,000 ECBs in 2024, with a likely minimum abatement contribution of between 75,000 and 100,000 t of CO₂e (Windsor 2024).

An important aspect of the ECB delivery process is the extension knowledge required by farmers to utilise the ECBs efficiently and ensure animal health issues do not compromise the positive impacts of ECBs on GHGe. Animal health surveillance and management requires vigilant disease prevention programs, with reporting and emergency responsiveness, including appropriate therapy and biosecurity interventions, particularly for transboundary animal diseases and One Health concerns (Windsor 2024). Use of ECBs offers an increasingly ‘informed’ role for community animal health workers, working closely with government animal production and health authorities in supporting these processes, delivering both improved nutrition through ECBs in combination with forages, plus improved disease surveillance and therapy, as previously advocated (Windsor et al. 2020; MacPhillamy et al. 2022; Sieng et al. 2022; Windsor 2024). The recent ongoing success of ECB delivery with appropriate extension interventions, although preliminary, likely increases the motivations of farmers to adopt ‘risk management’, including disease preventive vaccines and therapies, plus potentially adopting biosecurity and, hopefully, animal welfare interventions (Windsor 2024).

A ‘whole of village’ strategy that utilises the distribution of ECBs has been proposed. It includes a field audit of production and a disease risk assessment, enabling issues to be addressed that could compromise the performance of the ECBs. The use of highly visible interventions capable of creating rapid system change by motivated farmers and other stakeholders, and that overcomes resistance to change, are urgently required in the GMS (Young et al. 2015). Access to ECBs to increase productivity and improve management can precipitate this change. This should be accompanied by leveraging targeted health surveillance and disease prevention strategies, including vaccination, biosecurity and endoparasite control to reduce disease risk (Windsor 2024). All have the potential to help drive practice changes and create a more receptive environment for the change management required to progress both animal health and welfare through productivity innovations, assisting GHGe mitigation from the currently inefficient livestock systems, particularly in developing countries in the GMS and beyond.