Archivos Latinoamericanos de Producción Animal. 2023. 31 (1)

The carbon footprint of beef production from cull cows finished on

sown pastures in the savannas of the Colombian Orinoquía

Received 20210721; Accepted 20220224.

1Corresponding author: c.ramirez@creac.com.au

4Formely CIAT, Tropical Pastures Program, Km 17 CaliPalmira CP 763537, Apartado Aéreo 6713, Cali, Colombia.

5Formely Commonwealth Scientific and Industrial Research Organisation, (CSIRO) Agriculture, Australian Tropical Sciences and Innovation

Precint, James Cook University, Bebegu Yumba Campus, Townsville, QLD 4811, Australia.

1

Raul R. VeraInfanzón2,4

Carlos A. RamírezRestrepo1,4,5

Abstract. Neotropical savannas of the Colombian Orinoquía are largely dedicated to yearround beef production.

There is evidence of sustainable animal production in this savanna environment, but the links among animal

lifetime performance, greenhouse gas emissions, and soil organic carbon (SOC) accumulation at the system level

have been poorly studied to date. The objective of this study was to estimate the carbon (C) footprint of beef

production from Brahman (Bos indicus) cull cows finished on contrasting C4grassbased pastures in the Orinoco

River Basin. Longterm individual variations of liveweights and reproductive performance were used in an Excel®

dynamic model to estimate dry matter intake, methane (CH4) emissions, carcass traits, and the C footprint at the

farm gate. Values from the developed database were computed for cows born and raised on the savanna, bred on

Brachiaria decumbens, and later finished on B. humidicola [Scenario (SCE) 1, SCE 2]; B. decumbens (SCE 3); Andropogon

gayanus + Melinis minutiflora + Stylosanthes capitata (SCE 4); and A. gayanus + S. capitata (SCE 5) pastures. We

estimated the C footprints of SCE 1, SCE 3, and SCE 5 using published values of the rates of emission of CH4 and

nitrous oxide from the soil, feces, and urine; and accumulation of SOC in the soil during the fattening period. Most

of the estimated overall C footprint values at the system level were negative due to expected net SOC accumulation

during the fattening period. Depending on the expected quality of management, systems ranged from near

equilibrium in C balance to net increases in SOC accumulation.

Keywords: beef, methane, scenarios, soils, tropical forages

Huella de carbono en vacas de descarte cebadas en pasturas mejoradas de las

sabanas de la Orinoquia de Colombia

Resumen. Las sabanas Neotropicales de la Orinoquía de Colombia están dedicadas principalmente a la producción

de carne. Hay evidencias de que estos ecosistemas ganaderos pueden ser sostenibles, sin embargo, poco se conoce

acerca de las relaciones entre el desempeño animal, las emisiones de gases invernadero, y la acumulación de

carbono orgánico en el suelo (SOC) a nivel de sistema productivo. El objetivo del presente estudio fue estimar la

huella de C de la producción de carne, utilizando vacas (Bos indicus) de descarte cebadas en praderas contrastantes

de plantas C4. Se utilizaron variaciones reales e individuales y a largo plazo de peso y desempeño reproductivo de

las vacas a través de un modelo dinámico en EXCEL® para estimar el consumo de materia seca, las emisiones

entéricas de metano (CH4), las características productivas y ambientales de las carcasas, y la huella de carbono (C) a

nivel de finca. Las vacas nacidas, criadas y levantadas en sabana nativa, mantenidas en Brachiaria decumbens durante

su vida reproductiva fueron finalizadas en los siguientes escenarios (SCEs) modelados: Braquiaria humidicola (SCE 1

y SCE 2), B. decumbens (SCE 3), pastura mixta de Andropogon gayanus + Melinis minutiflora + Stylosanthes capitata (SCE

4) y pastura mixta de A. gayanus + S. capitata (SCE 5). La modelación se complementó con datos publicados de tasas

de emisión de CH4 y óxido nitroso del suelo, muestras de heces y orina, así como la acumulación de SOC en el

suelo durante la ceba. Las estimaciones de las huellas de C de los sistemas fueron mayoritariamente negativas

debido a la acumulación neta de SOC durante el período de finalización productiva. Dependiendo de la calidad del

manejo, los sistemas variaron entre equilibrio en el balance de C a aumentos netos de acumulación del SOC.

Palabras clave: carne, metano, escenarios, suelos, forrajes tropicales

www.doi.org/10.53588/alpa.310101

1CR Ecoefficient Agriculture Consultancy (CREAC®), Research and Education, 46 Bilbao Place, Bushland Beach, QLD 4818,

Australia. 2Consultant, 2 Norte 443, Viña del Mar, Chile. 3International Center for Tropical Agriculture (CIAT), Km 17 Cali

Palmira CP 763537, Apartado Aéreo 6713, Cali, Colombia.

Idupulapati M. Rao3

2

The world is facing challenges of population growth,

increased hunger, malnutrition, food and feed

insecurity, extreme events, and inequalities at multiple

scales [Food and Agriculture Organization of the

United Nations (FAO), 2009, 2015; Mora et al., 2018].

These challenges apply to Colombia with its growing

population, its allocation of resources, and the

vulnerability of its ecosystem services to climate

variability (Córdoba et al., 2019). The Neotropical

savannas environment of the Orinoco River Basin

represents 30.4 % of continental Colombia (Andrade et

al., 2009), and it is generally considered a major,

underutilized but fragile and biodiverse land resource

(RomeroRuiz et al., 2012). This socioculturalrich

region (Navas Ríos, 1999; RomeroRuiz et al., 2012) is

also believed to have considerable potential to satisfy

increased beef demand, stock turnover efficiency, and

farm profitability (RamírezRestrepo and Vera, 2019;

RamírezRestrepo et al., 2023) based on yearround

grazing on tropical pastures.

In this context, the reliability of evaluating pastoral

systems’ productivity and environmental impact lies in

the reproducibility and replicability of raw data to

refine concepts, hypotheses, and theories and assist in

comparing different development views (Eckard et al.,

2014; Colquhoun, 2017; RamírezRestrepo et al., 2019b,

2019c). On this basis, the preservation, reuse, and

repurposing of existing databases can address new

demands on science (Griffin, 2015; Murdy et al., 2015;

Wyborn et al., 2015). This also applies to environmental

metrics of cattle and their relationship with soil organic

C (SOC) accumulation at the system level (Rao et al.,

2015; RamírezRestrepo et al., 2019a; RamírezRestrepo

et al., 2023). To our knowledge, there are no studies

using longterm individual legacy data of cull cows

between birth and slaughter regarding land use, dry

matter intake (DMI), methane (CH4) emissions, and

animal performance to estimate the C footprint of cull

cows at the system level. Recent C footprint

estimations (RamírezRestrepo et al., 2020a) with year

round grazing of Brahman (Bos indicus) breeding herds

suggest that cull cows fattening phase may assist in

maintaining and even enhancing SOC stocks in

conservatively managed improved sown pastures.

We hypothesized that the fattening of cull cows

derived from tropical beef herds monitored over

several reproductive cycles would allow the estimation

of production efficiency and the C footprints of beef

produced from cull cows grazing on contrasting

tropical pastures. The objective of this study was to

estimate the C footprint of beef production from

Brahman cull cows finished on contrasting C4grass

based tropical pastures in the Orinoco River Basin of

Colombia.

Introduction

Pegada de carbono em vacas de descarte engordadas em pastagens melhoradas

nas savanas da região de Orinoquia da Colômbia

Resumo. As savanas Neotropicais da Orinoquia Colombiana são principalmente dedicadas à produção de carne. Há

evidências de que os ecossistemas pecuários podem ser sustentáveis, no entanto, pouco se sabe sobre as relações

entre o desempenho animal, as emissões de gases de efeito estufa e o acúmulo de carbono orgânico en el suelo

(SOC) no nível do sistema de produção. O objetivo do presente estudo foi estimar a pegada C da produção de carne,

utilizando vacas de descarte (Bos indicus) terminadas em pastagens melhoradas (C4) da região de Orinoquia.

Variações reais, individuais e de longo prazo para peso e desempenho reprodutivo dessas vacas foram usadas em

um modelo dinâmico do EXCEL® para estimar o consumo de matéria seca, emissões de metano entérico (CH4),

características produtivas e ambientais de vacas, carcaças e pegada de carbono (C) ao nível de fazenda. Os valores

da base de dados foram calculados para vacas nascidas e criadas em pastagens de Brachiaria decumbens e

posteriormente as vacas foram terminadas em B. humidicola (Cenário (SCE) 1, SCE 2); B. decumbens (SCE 3);

Andropogon gayanus + Melinis minutiflora + Stylosanthes capitata (SCE 4); e A. gayanus + S. capitata (SCE 5). Nós

estimamos a pegada de C nos cenários SCE 1, SCE 3 e SCE 5 utilizando valores de literatura para níveis de emissão

de CH4 e óxido nitroso do solo, fezes e urina; e acumulação de SOC no solo durante o período de engorda. A

maioria dos valores globais estimados para a pegada C ao nível do sistema foram negativos devido à acumulação

líquida esperada de SOC durante o período de engorda. A maioria dos valores globais estimados para a pegada C

ao nível do sistema foram negativos devido à acumulação líquida esperada de SOC durante o período de engorda.

Dependendo da qualidade do manejo, os sistemas variaram entre equilíbrio no balanço de C a aumentos líquidos

no acúmulo de SOC.

Palavraschave: carne, metano, cenários, solos, forrageiras tropicais

RamírezRestrepo et al.

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Material and Methods

The database used for modeling

Heritage files generated from longterm grazing

experiments carried out at Carimagua Research Centre

(CRC: latitude 4o36’44.6” N, longitude 74o08’42.2” W)

in the Neotropical savannas (Llanos) environment of

Colombia were used as a source of animal data. The

constructed large database included individual

liveweight (LW), LW gains (LWG), and reproductive

performance records from birth to the end of cow’s

reproductive performance in Brahman breeding herds

over six continued reproductive cycles (RCs;

conceptionweaning; Vera et al., 2002; Ramírez

Restrepo et al., 2020a) lasting up to 10 ± 0.13 years.

Females had two provenances, the first one consisting

of animals born and raised on native savannas up to

272.6 ± 2.94 kg LW (25.87 ± 0.635 months), and the

second one was born and raised on wellmanaged

Brachiaria decumbens Stapf (syn. Urochloa decumbens)

cultivar (cv) Basilisk pastures with higher LWG up to

comparable initial breeding LW. In this paper, only

cows initially raised on savanna were included as the

production system represents the more

environmentally costly path and the most common

practice. Comparable shorterterm observations in

several commercial ranches of the region (Vera and

Seré, 1989; Astigarraga and Ingrand, 2011), although

not used in the present study, further support the

magnitudes and trends of the assembled dataset.

Soil properties and environmental conditions

Mean values for soil physi

cal and chemical charac

teristics (020 cm depth) before pasture establishment

(details given below) were 19.8 % sand, 40.2 % clay, 2.9

% organic matter, 4.78 pH, 90.1 % Al saturation, 1.46

µg/g available P (BrayII), and 0.17, 0.08 and 0.06 cmol/

kg of exchangeable Ca, Mg and K, respectively. These

values are similar to the subgroup of farms located on

relatively heavier soils monitored by Vera and Hoyos

(2019) and for which animal outputs were available.

Mean values of 2.202 mm of annual rainfall and 26.5

°C of ambient temperature were recorded at CRC

between 1979 and 1991. The wet season occurred

during the April to November period, while across the

years, January and June were the driest and wettest

months; and July and March were the coldest and

hottest months, respectively (Figure 1).

Pastures and forage quality characteristics

The pastures used to fatten cull cows, and their

botanical composition (%) on offer were as follows: B.

humidicola cv Llanero (Rendle) Schweick (syn. Urochloa

humidicola); B. decumbens; A. gayanus Kunth cv

Carimagua + M. minutiflora P. Beauv + S. capitata

Vogel cv Capica (~ 70: 20: 10); and A. gayanus + S.

capitata (~ 95: 5). The pastures were established with

the recommended level of fertilizer application (kg/

ha) of 20 P, 20 K, 48 Ca, 14 Mg and 10 S, while a third

of that rate was used as maintenance fertilization

every third year (RamírezRestrepo and Vera, 2019;

RamírezRestrepo et al., 2020a; VeraInfanzón and

RamírezRestrepo, 2020). At the beginning of the

experiments, pastures were 34 years old, thus largely

excluding the rapid decline in animal productivity

reported by Vera and Hoyos (2019) in the initial years

following pasture establishment.

Pasture management during the fattening period

consisted of continuous grazing during the rainy

season. Cull cows were sold towards the end of the

rainy season (Figure 1). All pastures were managed to

conserve adequate soil cover and aboveground

biomass as described by Vera and RamírezRestrepo

(2017).

Measurements of the forage biomass and its botani

cal composition in the field during pregrazing and

postgrazing herbage periods were carried out

approximately every two months according to the

BOTANAL procedure (Jones and Tothill, 1985). Forage

on offer in the A. gayanus pastures exceeded 6500 kg

DM/ha, and at the end of the rainy season standing

forage always exceeded 3000 kg DM/ha. Equivalent

forage biomass values for B. humidicola and B.

decumbens pastures were 3500 and 1200 kg DM/ha,

respectively.

Total crude protein (CP) and neutral detergent fiber

(NDF) concentrations (g/kg DM) during the wet

period were derived from the CRC grazingforage

database constructed by RamírezRestrepo and Vera

(2019). Nutritive values (CP vs NDF) were 7337 vs

825785, 75110 vs 710650, 8590 vs 740746, and 101

66 vs 757760 for the B. humidicola, B. decumbens, A

gayanus + M. minutiflora + S. capitata, and A. gayanus +

S. capitata pastures, respectively

3

Sustainable fattening of cull beef cows

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4

Modeling approach

The LWs of cull cows with different past repro

ductive performances were used to derive longterm

trends in LWs, CH4 emissions, and DMI, and these

were expanded by using recorded cumulative LWGs

(kg) over varied fattening periods (RamírezRestrepo

and Vera, 2019). In the original field experiment, cows

served as the experimental units. However, when

cows were grouped in a paddock for fattening

scenarios, those fattening scenarios represent the

experimental units rather than individual cows

themselves.

Initial and final cold carcass weights (CCW) of all

animals were estimated at the start and the end of the

fattening phase using a 0.4772 ratio of CW to LW

(Velásquez and Ríos, 2010) to determine CCW gains

(CCWG). These specifications allowed the model to

estimate final LWs, carcass traits, the full cycle of

production, production efficiency, and the C footprint

at the system level. This study does not include any

quantification from calves’ data that were analyzed in

detail by RamírezRestrepo et al. (2020a).

Developing scenarios

A similar stocking rate (SR; 1.3 UA/ha, 585 kg LW/

ha) was used to compare five fattening scenarios

(SCEs). Confidence intervals across all SCs and RCs

were calculated for initial LWs (360.6403.4 kg); daily

LWGs (0.3840.573 kg); target LWs (439493 kg); and

age (98.49109.08 months) at slaughter. Following the

methodology reported by Velásquez and Ríos (2010),

carcass attributes of cull cows were calculated to

estimate the interaction among LW, age and DMI

dynamics, partial and lifetime CH4 emissions, and

slaughter data (RamírezRestrepo and Vera, 2019). To

derive carcass CO2eq efficiency indices, for CH4

estimation, the century horizon global warming

potential (GWP) of 34 with the inclusion of climateC

feedback was used (Gasser et al., 2017; Mueller and

Mueller, 2017; Allen et al., 2018) to allow for

compatibility with authors’ previously published work

(RamírezRestrepo and VeraInfanzón, 2019; Ramírez

Restrepo et al., 2019a, 2020a, 2023).

The first and second scenarios (SCE 1, SCE 2)

represent the performance of cull cows on an

overgrazed versus a wellmanaged B. humidicola

pasture to yield low and high daily LWGs,

respectively as reported by VeraInfanzón and

RamírezRestrepo (2020). Scenario 3 refers to the

performance of cull cows on B. decumbens pasture that

serves as local control and was initially reported by

RamírezRestrepo et al. (2020a). Based on Ramírez

Restrepo and Vera (2019), SCE 4 and SCE 5

represented the performance of cull cows grazed on

grasslegume associations of A. gayanus + M.

minutiflora + S. capitata, and A. gayanus + S. capitata

pastures, respectively. All sown pastures were 5 to 9

years old when the cows were culled.

Figure 1. Average monthly precipitation (∆) and ambient air temperature (●) recorded over 12 years by the meteorological

station at Carimagua Research Centre in the eastern plains of Colombia.

RamírezRestrepo et al.

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5

Animals

As indicated before, females were monitored from

birth (26.2 ± 0.12 kg) and were weaned (157 ± 2.82 kg;

Rivera, 1988), and raised on savanna until mating (241

± 9.76 g/day; Vera and Hoyos, 2019). Cows were

offered ad libitum access to fresh water and a standard

mineral formulation of 175 Na, 269 Cl, 137 Ca, 80 P, 20

S, 1.04 Cu, 3.5 Zn, and mg of 10 Co and 76 I g/kg of a

commercial product. Registered Colombian Doctors of

Veterinary Medicine ensured animal welfare

regulations across all livestock manipulations in the

field (Law 73, MINEDUCATION, 1985).

Calculating intakes

Dry matter intake was calculated as an LW function

of feeding daily ad libitum on a DMI basis (i.e., 2.1 % of

total LW; Fisher et al., 1987) from measurements in

opencircuit chambers in tropical Australia (Ramírez

Restrepo and Vera, 2019) using a leastsquares

interceptslope regression (Equation 1) specified as:

DMI kg/day = 2.216 (± 1.315) + 0.014 (± 0.003) LW

(kg)

r2 = 0.491, P < 0.01; CV = 18.94; r.s.d = 1.34; r = 0.701,

P < 0.01

Predictions of DMI with Equation 1 fall within the

range of field measurements by Hess (1995), and

Pereira et al. (2009) for B. humidicola.

Estimating ruminant CH4 emissions

Using the structured daily DMI regression form,

individual estimations of CH4 emissions were based

on the simple relationship between LW per animal and

CH4 emissions per day in calibrated (pure CH4 gas 0.99

recoveries) opencircuit chambers (Equation 2). This

was recorded from wellcared and trained Brahman

(RamírezRestrepo et al., 2016b) and Belmont Red

Composite [Brahman x Africander (African Sanga) x

HerefordShorthorn (3/4 B. taurus); RamírezRestrepo

et al., 2014, 2016a] steers fed ad libitum.

CH4 g/day = 16.176 (± 21.087) + 0.324 (± 0.057) LW

(kg)

r2 = 0.663, P < 0.0001; CV = 16.78; r.s.d = 30.82;

r = 0.814, P < 0.0001

Thus, predicted CH4 emissions are consistent with

the estimations of Cottle and Eckard (2018) and are

also consistent with recently published reports

(RamírezRestrepo and Vera, 2019; RamírezRestrepo

et al., 2019a, 2020a, 2023). As expected, this allows the

present results also to be comparable with other

tropical cattle system values (KuVera et al., 2018).

Lastly, we deliberately ignored issues related to CO2

eq costs involving transportation, supply chains, the

slaughterhouse, and the retail meat market.

Estimating CO2eq CH4 footprint, C stocks, rate of

SOC accumulation, and overall C footprint

Greenhouse gas emissions and C footprints were

calculated for three contrasting scenarios (SCE 1, SCE

3, and SCE 5) that were chosen to represent a wide

range of cattle fattening systems currently in use.

Some required parameters were obtained from

adjoining, mostly contemporary, paddocks (Rao, 1998;

Fisher et al., 1998; Rondón et al., 2006). These were

complemented when required with data obtained

under comparable Neotropical savannas, including

abundant data from the Venezuelan savannas

reviewed by Castaldi et al. (2006). Emissions from soils,

feces, and urine were estimated using the published

values on emission factors from the literature, and in

all cases, we used the maximum positive values

reported. Soil emission factors used for CH4 and

nitrous oxide (N2O) were adopted from Castaldi et al.

(2006) of the Venezuelan savannas. Although acid

savanna soils have been reported to act as a seasonal

sink, rather than a source, particularly for CH4, this

was not considered in the present estimations. Values

on N intake by animals were calculated from the

predicted DMI as explained above, and forage N

contents were reported in several grazing experiments

by Lascano and Thomas (1990), Lascano and Euclides

(1996), and from our data. Nitrogen digestibility was

calculated as in Glover et al. (1957), and urinary N

output as per Equation 1 reported by Waldrip et al.

(2013). The resulting animal N balance was checked

for compatibility with the observed LWG against the

requirements suggested by Rotta et al. (2016) for

tropical cattle in Brazil. Maximal fecal emissions were

estimated from the emission factors derived by Zhu et

al (2018), whereas those for fecal and urinary N2O

emissions were derived from Lessa et al. (2014).

Conversion of native savanna to sown pastures

slightly modifies soil emissions as reviewed by

Castaldi et al. (2006) for the seasonally dry Neotropical

savannas. Data from GarcíaMontiel et al. (2001) and

Castaldi et al. (2006) showed an average value of soil

CH4 emissions during the wet season as 1.18 mg/m2

day, but it is noted that soils under these conditions

may also be a net CH4 sink (Sanhueza et al., 1994a,

Sustainable fattening of cull beef cows

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6

Animal performance and CH4 emission metrics

The effects of SCEs on calculated DMI, LWGs,

slaughter age, carcass traits, daily CH4, CH4 yield (CH4

g/kg DMI), periodCH4 emissions, and CO2eq CH4

concentration in carcass yields are shown in Table 1.

Compared to cull cows on the mixed A. gayanus + S.

capitata pasture (SCE 5), cows on the first B. humidicola

pasture (SCE 1) had the lowest DMI, however, cows

grazed on the second B. humidicola (SCE 2), the B.

decumbens (SCE 3), and the A. gayanus + M. minutiflora

+ S. capitata pasture (SCE 4) performed similarly to cull

cows in the SCE 5. Accordingly, the model yielded

total DMIs of 1.20, 1.51, 1.46, 1.39, and 1.65 ± 0.026 t of

DMI from the first to the fifth fattening SCEs.

Relative to the B. humidicola low LWG scenario

(SCE 1), the remaining SCEs had higher numerical

LWGs and CCWGs of 19, 27, 46, and 49 %, and 46, 50,

63, and 95 %, respectively. This trend was repeated in

terms of lean meat and edible protein carcass gain

(LMCG, EPCG, Table 1).

Daily CH4 and CH4 yield emissions per animal for

the B. humidicola (SCE 1) were significantly (P ≤ 0.05)

lower than those of the A. gayanus + S. capitata (SCE 5),

but enteric emissions were similar among the other

SCEs (Table 1). Furthermore, the emission of CH4/kg

LWG decreased linearly from SCE 1 to SCE 5 (r2 =

0.88, P = 0.02, r = 0.93), amounting to a difference of

28 % between the two extreme SCEs. Hence, the

magnitude of CH4 emissions for the finishing period in

terms of kg CO2eq/kg CCWG, LMCG, and EPCG

decreased (P ≤ 0.0001) between SCE 1 and SCE 5 by 29

% (Table 1).

The effect of successive RCs on systems performan

ce is given in Table 2. There were significant

differences in DMI values between some RCs (P ≤

0.0001). Lifetime DMIs (t DM) differed (P ≤ 0.0001)

among the consecutive RCs evaluated (12.19 ± 0.884 vs

17.65 ± 0.395 vs 23.38 ± 0.316 vs 25.10 ± 0.334 vs 27.39 ±

0.266). Emissions between RCs during the fattening

practice differed when expressed in kg CO2eq/kg

CCWG, with the largest difference amounting to 18 %

between RC 4 and RC 6 (P ≤ 0.0001). However, over

the lifetime of the animals, there was at most an 11 %

difference (P ≤ 0.0001) between RC 1 and RC 6, such

that the ranking of the RCs depends on the carcass

parameter used for the comparisons.

Estimated C footprint of beef production of cull

cows

Enteric emissions increased 30 % from SCE 1 to

SCE 5 (Table 3), but the magnitude of the changes in

1994b). Similarly, soil N2O emissions averaged 0.32 mg/

m2 per day, but the range of values includes negative

values as well. However, we followed a conservative

approach and used relatively high values for soil

emissions. Pasture establishment and maintenance

incur in GHG emission costs related to machinery use,

and the use of fertilizers, and these were calculated as

in RamírezRestrepo et al. (2020a). Pasture

establishment costs were prorated over the assumed

persistence of wellmanaged pastures for 15 years, as it

was documented for onfarm pastures by Vera and

Hoyos (2019) for similarly managed onfarm sown

grasslands.

The aboveground and belowground C stocks and SOC

accumulation rates from improved pastures were

estimated for the three contrasting SCEs to reflect

differences that are not usually captured by animal

performance variables and static characteristics.

Values on SOC accumulation derived from

contemporaneous experiments at CRC and nearby to

the current study area were used (Fisher et al., 1994;

Rao, 1998; Trujillo et al., 2006; Costa et al., 2022; Hyman

et al., 2022). The methods used to determine SOC

stocks in different pastures were described by Fisher et

al. (1994). Values used to show the range of pasture

biomass production of both aboveground (Fisher et al.,

1998; Rao, 1998; Grace et al., 2006) and belowground

(Fisher et al., 1998; Rao, 1998; Trujillo et al., 2006) are

summarized in Table 3.

Statistical analyses

Data were analyzed with the GLM procedure of

the Statistical Analysis System (SAS, 2016; version 3.5)

including the upper and lower confidence limits

(CLM) for each mean observation and CL for the

parameter estimates (CLPARM) methods. Models for

LW and age dynamics, DMI, CH4 emissions, carcass

features, and carcassrelated indices considered the

fixed effects of breedingherd RCs and animal

fattening SCEs and their interaction. The relationships

between total LWG and CH4 emissions per kg LWG

during the fattening process were performed using the

CORR and REG procedures. Significant differences

between leastsquares means ± standard errors of the

mean were declared when P ≤ 0.05.

Results

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fecal CH4 production was less. On the contrary and

associated with the increased N intake of SCE 5,

urinary N2O emission rose considerably. Gains in the

carcass, lean meat, and edible protein weights (Table 1)

differed between SCEs, with SCE 5 nearly doubling the

gains in SCE 1, and emissions per kg of gain in carcass

parameters diminished from SCE 1 to SCE 5 by 29 %.

Over the lifetime of the animals, differences between

SCEs in emissions per kg of the final carcass, lean meat

and edible protein weights were less pronounced, with

at most 12 % higher emissions in SCE 1 than in SCE 5

(Table 2). As before, the remaining SCEs showed

intermediate values between the two extremes. Thus,

the magnitude of the differences between SCEs

depended very much on the denominator used for the

comparisons, while LW determined the final point for

sales of cows.

The estimated CO2eq CH4 emission values from the

feces of SCE 3 were 9.2 % higher while SCE 5 was 13.7

% larger compared to SCE 1. Estimated CO2eq N2O

emission values from the feces of SCE 3 were 30 %

higher, while SCE 5 was 44 % higher compared to SCE

1. The CO2eq N2O emission values estimated from the

urine of SCE 3 were 2.11fold greater, while SCE 5 was

2.87fold greater compared to SCE 1. The contribution

of the mineral supplement consumed by cows to CO2

eq GHG emission was also greater for SCE 5 than SCE

3 and SCE 1. The estimated values of total CO2eq

GHG emissions (kg/ha) during the grazing period,

including CH4 from animals, CH4 and N2O from feces,

and N2O from urine together with the mineral

supplement consumed were 1.232; 1.483 and 1.640 for

SCE 1, SCE 3, and SCE 5, respectively. Total values of

CO2eq GHG emissions (kg/ha) during the grazing

period at the system level were 1.345; 1.613 and 1.781

for SCE 1, SCE 3, and SCE 5, respectively (Table 3).

Nevertheless, differences between SCEs are con

founded with the different final LWs (Table 1) and

consequently different lengths of the fattening period,

and these differences disappear if expressed per day,

with an average for total GHG emissions of 8.4 kg

CO2eq/ha day.

The stocks of SOC to 1 m soil depth for the medium

textured soils of all three scenarios (SCE 1, SCE 3, and

SCE 5) were estimated to be in the range of 130 to 160

Mg/ha based on the published reports cited in Table 3.

The range of values of the standing aboveground

biomass estimated from published reports of SCE 1

was 1.2 to 3.5 Mg/ha and this was markedly lower

than those of SCE 3 (5.15 to 9.07) and SCE 5 (3.0 to 6.5).

Standing belowground biomass values (Mg/ha)

estimated from published reports ranged from 2.8 to

9.3, 8.3 to 10.5, and 6.0 to 9.0 for SCE 1, SCE 3, and SCE

5, respectively. We assumed the same values for CO2

eq CH4 (3.2 x 34 kg/ha/year) and N2O (1.05 x 298 kg/

ha/year) emission from the soil for all three SCEs to

estimate differences among the three SCEs based on

the number of days of the grazing period.

The estimated emission values from fertilizers and

tillage were the same among the three SCEs since

pasture establishment methods were the same. Using

the published values of above and belowground

biomass and their contribution to the SOC

accumulation, we estimated a range of rate of SOC

accumulation from 1.0 to 3.0 Mg/ha/year (Table 3).

The estimated overall C footprint values at the

system level in CO2eq in Mg/ha were 0.140 to 3.110;

0.154 to 3.688; and 0.167 to 4.059 for SCE 1, SCE 3,

and SCE 5, respectively. These negative values imply

that all three systems showed small to high values of

net SOC accumulation after correcting for GHG

emissions from animals, soil, and external inputs to

the system.

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Table 2. Influence of computed finishing scenarios (SCEs)† on dry matter intake (DMI), methane (CH4) emissions, and carbon

dioxide equivalent (CO2eq)CH4 carcass efficiency indices of consecutive reproductive cycles (RCs), and on CO2eqCH4 lifetime

emissions of carcass traits in multiparous commercial Brahman (Bos indicus) cull cows‡

2RC 3RC 4RC 5RC 6RC

Fattening phase

Number of animals 30 29 24 18 11

DMI, kg/head/day 8.469 ± 0.345ab 8.727 ± 0.154a 7.717 ± 0.140c 7.981 ± 0.130bc 8.848 ± 0.104a

CH4, g/head/day 159.1 ± 7.88ab 165.0 ± 3.52a 141.9 ± 3.21c 147.9 ± 2.97bc 167.2 ± 2.37a

CH4, g/kg DMI 18.78 ± 0.173ab 18.89 ± 0.077a 18.33 ± 0.070c 18.50 ± 0.065b 18.91 ± 0.052a

Period CH4, kg/head 27.59 ± 1.374ab 28.61 ± 0.614a 24.61 ± 0.561c 25.66 ± 0.519bc 29.09 ± 0.414a

kg CO2eq/kg CCWG 23.48 ± 1.185ab 24.32 ± 0.530a 20.91 ± 0.483c 21.80 ± 0.447bc 24.73 ± 0.357a

kg CO2eq/kg LMCG 38.60 ± 1.950ab 40.03 ± 0.872a 34.41 ± 0.796c 35.88 ± 0.737bc 40.70 ± 0.588a

kg CO2eq/kg EPCG 148.46 ± 7.500ab 153.98 ± 3.354a 132.37 ± 3.062c 138.02 ± 2.835bc 156.57 ± 2.261a

SCE 1 SCE 2 SCE 3 SCE 4 SCE 5

Lifetime emissions

Number of animals 30 30 30 30 30

kg CO2eq/kg CCW 65.06 ±1.851a 61.82 ± 1.851ab 61.30 ± 1.851ab 60.01 ± 1.851b 58.22 ± 1.851b

kg CO2eq/kg LM 107.05 ± 3.046a 101.73 ± 3.046ab 100.87 ± 3.046ab 98.75 ± 3.046b 95.81 ± 3.046b

kg CO2eq/kg EP 411.76 ± 11.715a 391.29 ± 11.715ab 387.99 ± 11.715ab 379.82 ± 11.715b 368.50 ± 11.715b

Table 1. Dry matter intake (DMI), liveweight (LW) gain, slaughter age, carcass attributes, methane (CH4) emissions, and carbon

dioxide equivalent (CO2eq)CH4 carcass efficiency indices of commercial Brahman (Bos indicus) cull cows continuously mated

on B. decumbens pastures‡ and fattened on grass alone Brachiaria humidicola (SCE 1, SCE 2), B. decumbens (SCE 3), and grass

legume association pastures of Andropogon gayanus + Melinis minutiflora + Stylosanthes capitata (SCE 4) and A. gayanus + S.

capitata (SCE 5)

SCE 1 SCE 2 SCE 3 SCE 4 SCE 5 Pooled s.e.m.

Number of animals 30 30 30 30 30

DMI, kg/head day 8.093b 8.337ab 8.342ab 8.419ab 8.551a 0.153

LW gain, kg/day † 0.384 0.457 0.486 0.561 0.573 0.014

Final LW, kg 439c 465b 467b 475a 493a 10.8

Age at slaughter, months 103.0 103.0 103.9 103.6 104.5 2.30

Cold carcass weight gain (CCWG, kg)T 27.20 39.60 40.84 44.37 52.96 4.164

Lean meat carcass gain (LMCG, kg) 16.52 24.06 24.82 26.96 32.18 2.885

Edible protein carcass gain (EPCG, kg) 4.29 6.25 6.45 7.01 8.36 0.658

CH4 emission metrics

CH4, g/head day 150.6b 156.0ab 156.2ab 157.9ab 160.9a 3.50

CH4, g/kg DMI 18.57b 18.68ab 18.69ab 18.72ab 18.78a 0.077

Period CH4, kg/head 22.34e 28.35bc 27.50c 26.17d 31.20a 0.610

kg CO2eq/kg CCWG 27.98a 24.33b 22.88c 20.04de 19.99e 0.526

kg CO2eq/kg LMCG 46.05a 40.04b 37.66c 32.98de 32.90e 0.886

kg CO2eq/kg EPCG 177.12a 154.03b 144.85c 126.85de 126.55e 3.332

Adapted from Velásquez and Ríos (2010), †RamírezRestrepo and Vera (2019), and ‡Vera et al. (2002) and RamírezRestrepo et al. (2020a).

The leastsquares means values in the same row bearing different letters between SCEs are significantly different (a,e: P ≤ 0.05). Standard error of the mean (s.e.m.).

†Brachiaria humidicola (SCE 1, SCE 2), B. decumbens (SCE 3), Andropogon gayanus + Melinis minutiflora + Stylosanthes capitata (SCE 4) and A. gayanus + S. capitata (SCE 5)

pastures.

Adapted from † RamírezRestrepo and Vera (2019), and ‡ Vera et al. (2002) and RamírezRestrepo et al. (2020a). EPCG: Edible protein carcass gain. CCWG: Cold

carcass weight gain. LMCG: lean meat carcass gain. The leastsquares means (LSM) ± standard error of the mean in the same row bearing different letters are

significantly different (ad: P ≤ 0.05).

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Table 3. Estimated greenhouse gas (GHG) emissions and overall carbon (C) footprint of commercial Brahman (Bos indicus) cull

cows fattened on B. humidicola (SCE 1), B. decumbens (SCE 3), and Andropogon gayanus + Stylosanthes capitata (SCE 5) pastures

Scenarios Observations, data sources, and

emission factors

Parameters SCE 1 SCE 3 SCE 5

Days on a grazing system 148 176 194

Cows 30 30 30

SR, cows/ha 1.42 1.38 1.34 Average onranch and onstation SR values on

MTAC

Mean final LW, kg/head 439 467 493 Table 1 of this paper

CO2eq enteric CH4, kg/ha 1082 1289 1418

CO2eq CH4 from feces, kg/ha

113.8

124

.3 129.4 Zhu et al. (2018): EF dry season = 0.001, rainy =

0.003

CO2eq N2O from feces, kg/ha 6.17 8.02 8.87 Lessa et al. (2014): EF = 0.0014

CO2eq N2O from urine, kg/ha 28.44

59.96 81.71 Chirinda et al. (2019): EF = 0.016; Lessa et al.

(2014): EF = 0.0193

CO2eq of mineral supplement consu

med, kg/ha 1.52 1.75 1.87 Cardoso et al. (2010) cited by Cerri et al. (2016)

Total CO2eq GHG emissions, kg/ha 1232 1483 1640

Estimation of overall C balance

SOC to 1 m depth, medium texture

soil, Mg/ha 130  160 130  160 130  160 Fisher et al. (1994); Rondón et al. (2006); Ramírez

Restrepo et al. (2019a)

Standing aboveground (shoot) biomass,

DM Mg/ha 1.2  3.5 5.1  9.1 3.0  7.0 Fisher et al. (1998); Kanno et al. (1999); Rao et al.

(2001a); Grace et al. (2006)

Standing belowground (root) biomass,

DM Mg/ha 2.8  9.3 8.3  10.5 6.0  9.0 Fisher et al. (1998); Rao (1998); Kanno et al.

(1999); Rao et al. (2001b); Trujillo et al. (2006)

Total aboveground and belowground

biomass, DM Mg/ha 4.0  12.8 13.4  19.6 9.0  15.0

CO2eq CH4 emission from the soil, kg/ha 2.74 3.20 3.59 Castaldi et al. (2006)

CO2eq N2O emission from the soil, kg/ha 91.23 108.49 119.59 Castaldi et al. (2006)

CO2eq emission from fertilizer inputs and

tillage, kg/ha 24.64 24.64 24.64 EdwardsJones et al. (2009); Kim et al. (2011);

University of Arkansas (2019)

CO2eq total GHG emissions at the system

level, kg/ha 1345 1613 1781

SOC accumulation rate, Mg/ha/year

1.0 to 3.0

1.0 to 3.0 1.0 to 3.0 Fisher et al. (1994); Rao et al. (1998); Fisher et al.

(1998); Rondón et al. (2006); Fisher et al. (2007);

Costa et al. (2022); Hyman et al. (2022)

SOC accumulation, kg/ha 405 to

1215

482 to 1446 531 to 1593 SOC accumulation during the grazing period

CO2eq soil C accumulation, kg/ha

1485 to 4445

1767 to 530

1

1948 to 5840

SOC accumulation in CO2eq during the

grazing period

Overall C footprint at the system level in

0.140 to 3110

0.154 to 3688

0.167 to 4059

Estimated from the difference between GHG

CO2eq, Mg/ha emissions and the soil C accumulation during

the grazing period

CH4: Methane. CO2eq: Carbon dioxide equivalent. EF: Emission factor. Mg: megagram. LW: Liveweight. N2O: Nitrous oxide. MTAC: Medium texture acid soils.

SOC: Soil organic carbon. SR: Stocking rate. Negative CO2eq values for soil C for overall C footprint imply SOC accumulation. CO2eq emission values are

expressed for the total duration of the grazing period.

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Discussion

The use of legacy data in the present paper aligns

well with the views of many authors that reviewed the

issue by taking into consideration of reduced funding

and the need to take a fresher, and more

comprehensive view of longterm results from studies

on grazing systems (Rouquette et al., 2009; Black 2014,

2018). Some authors have even questioned the

occasional excess of collecting “futile data” (Tedeschi,

2019), rather than making fuller and more innovative

use of existing information. The present inclusion of

cull cows’ emissions adds to the need to consider full

cattle production cycles as discussed by Eckard et al.

(2014). Lastly, current cattle systems in the region

continue to be dominated by breeding herds grazed on

traditional lowinput Brachiaria spp. pastures [Romero

et al., 2018; AGROSAVIA, 2019; Encuesta Nacional

Agropecuaria (ENA), 2019].

Grazing systems and animal production

Early onfarm studies (Vera and Seré, 1989) noted

that the fattening of cull cows in extensive ranches

constitutes an opportunistic use of recently established

sown pastures and provides a quick and profitable

return on investments. Fat cull cows constitute 32 % of

the cattle market in the study region (Romero et al.,

2018), whereas males account for 53 % of the total, and

all of them are mostly raised and fattened on sown

tropical grass pastures. A recent survey (Romero et al.,

2018) revealed that the most important grasses during

the study were B. dictyoneura, B. humidicola, and B.

decumbens. Another survey (Díaz et al., 2018) carried

out in both the Orinoco River Basin and the Atlantic

coast of Colombia, verified the continued popularity of

those three grass species. The present study, therefore,

includes pastures that represent a range of current

alternatives for grass pastures differing in quality and

management demands. B. humidicola (SCE 1)

constitutes the lowest limit of that range, while the A.

gayanus + S. capitata (SCE 5) represents a higher quality

pasture that is admittedly more demanding of

management, particularly under conditions of

extensive production.

In this study, we used a combination of onstation

mid to longterm grazing data to estimate the C

footprint of beef production from cull cows finished on

contrasting C4grassbased pastures. To our

knowledge, this is the first such integrated analysis in

the Orinoco River Basin. In this context, the results

presented in Tables 2 and 3 show evidence for the

varying links between CH4 emissions, LWs, carcass

metrics, and SOC accumulation. Scenario 1 relied on

an intensively grazed B. humidicola pasture, a

management technique that is most frequently

observed on commercial ranches, whereas SCE 3

represents a traditional approach to fattening, and SCE

5 indicates the potential of a stable grasslegume

pasture which could be feasible under muchimproved

management and production conditions.

Animal performance, CH4 emissions, and carcass

measures

The cumulative emissions (Table 2) would justify

culling cows after the third weaning as emissions

subsequently increase again. The effects of this practice

might be an increased number of heifers (Vera

Infanzón and RamírezRestrepo, 2020) for earlier

breeder replacement and specialized farming systems

(RamírezRestrepo, et al., 2023) resulting in more stable

temporal emissions. Culling of older mature breeding

dams should result in more efficient cowcalf

operations with lower environmental impact. In

contrast, Roberts et al. (2015) suggested the opposite

view when applied to temperate, more intensive,

breeding systems. Nevertheless, given the diversity of

pastoralbeef farming systems in the Llanos

(CORPOICA, 2010; Vera and Hoyos, 2019), further

data and ruminant modelmediated predictions would

be desirable. A small further refinement of the carcass

analyses could be made if additional estimates of the

carcass: LW ratio, as opposed to the fixed 0.4772 value,

become available for cull cows in the study region.

Our results suggest a need to strategically switch

fertile heifers from grazing on native savanna or low

quality B. humidicola pastures to superior nutritive

value B. decumbens pastures and other types of grass

pastures in the mid to longterm (Vera et al., 2002;

RamírezRestrepo et al., 2020a). Previous Australian

studies (Marshall, 2010; Marshall and Smajgl, 2013;

Marshall et al., 2014) indicated that delaying emissions

would facilitate adaptation to climatedriven changes.

Furthermore, there is evidence from consumer

research in Colombia (Charry et al., 2019) that buyers

have preferences for beef welfare and ecofriendly

certified beef production. This means that some

consumer segments would pay about 52 % more when

in addition to welfare and ecofriendly labels, certified

reduction in GHG emissions of the marketed beef is

available (Charry et al., 2019).

The analysis of the present C balance at the system

level is conservative, and we avoided dealing with

current controversies on the biogenic C cycle in

grazing systems that have been previously addressed

by Adegosan et al. (2015) and Wiloso et al. (2016). This

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also includes the possible shortlife effect of emitted

enteric CH4 (GWP 020year average vs GWP 0100

year average; Mueller and Mueller, 2017; Allen et al.,

2018) from animals. Consistent with these views, we

have reported the actual amounts of CH4 and

discussed our calculations based on the CO2eq values

at 100 years’ average horizon that we consider to be a

conservative approach to emissions.

Cull cows in the present study, raised on savanna as

heifers, and bred and fattened on B. decumbens showed

average carcass CO2eq stores 1.1 times the amount of

CO2eq accumulated in their counterparts grazing

lifetime on only B. decumbens pastures (detailed data

not shown). These estimated values indicated that

although the same beef product is produced, the CO2

eq overhead of cull cows across their lives varies

considerably according to management in early life.

This differs from FAO (2013)’s beef production data

that showed a global life cycle analysis (LCA) value of

67.8 kg CO2eq/kg CW), or the LCA annual

estimations of Cardoso et al. (2016) on degraded

Brachiaria pastures (51.66 kg CO2eq/kg CW). These

contrasting differences suggest the need to evaluate

beef systems relative to culling strategies since the

present results showed that culling over the second or

third weaning is a practical farming management

response to mitigate climate change. Opencircuit

respiration chamber studies (Grandl et al., 2016) with

Brown Swiss cattle (B. taurus) have shown that CH4

production in heifers increases with age, while in

multiparous cows the highest emissions are linked to

their second and third lactations (4 to 6.5 years). This

was followed by slightly lower CH4 production in

older cows. In parallel, the highest magnitude of that

CH4 emission response from B. indicus cows in

lactation (1 to 6) was found by RamírezRestrepo et al.

(2020a) during the fourth lactation (9 years).

Estimated C footprints

Extensive grazing systems can accumulate SOC

under different soil, climate, and management

systems, as shown by metaanalysis and synthesis of

published results (Conant et al., 2017; Viglizzo et al.,

2019). Several practices, including proper grazing

management, fertilization, sowing of improved grass

and/or legume species, irrigation, and conversion

from cultivation, could contribute to an increase in

SOC accumulation to a range of 0.105 to more than 1

Mg C/ha/year (Conant et al., 2017) over the longer

time but as yet the undefined length of years. Results

from longterm grazing experiments conducted in

wellwatered tropical areas, using wellmanaged

Brachiaria grassbased pastures indicated that it is

possible to not only improve animal production but

also increase SOC stocks (da Silva et al., 2017; Segnini et

al., 2017; dos Santos et al., 2019) over the medium

term.

Tropical pastures with sown grasses with deep root

systems, such as B. humidicola and A. gayanus when

wellmanaged (Fisher et al., 2007) with proper grazing

and maintenance fertilizer application (Braz et al.,

2013; Saravia et al., 2014) can increase SOC stocks in

deep soil layers up to 1 m depth, while soils under

poorly managed or degraded pastures may lose SOC

over time (Boddey et al., 2010). In this study, our

assumed values of SOC accumulation rates of 1 to 3

Mg/ha/year were based on the published reports on

above and belowground net primary productivity

(NPP; Fisher et al., 1998; Kanno et al., 1999; Rao et al.,

2001a; Trujillo et al., 2006) and SOC accumulation in

longterm pastures in Colombia and Brazil (Fisher et

al., 1994, 2007; Bustamante et al., 2006; Braz et al., 2013;

Saravia et al., 2014; Baptistella et al., 2020; Hyman et al.,

2022).

Pasture utilization by grazing cattle under tropical

conditions is in the range of 20 to 30 % and 4050 % of

the consumed DM is returned as feces, so that the

annual amount of litter and feces returned to the soil

surface is in the range of 33.5 to 40.5 Mg/ha/year

(Fisher et al., 1998, 2007). This C return to soil depends

on the level of pasture utilization in the range of 13 to

16 Mg C/ha/year, assuming a value of 40 % C in DM.

The NPP of the aboveground biomass of A. gayanus

pastures in the eastern plains was estimated to be as

much as 43 Mg/ha/year (Fisher et al., 1998). Trujillo et

al. (2006) found that the NPP of belowground biomass

of wellmanaged grass alone (B. dictyoneura) pasture

was 30.0 Mg/ha/year, while the grasslegume (B.

dictyoneura + S. capitata) association was 31.34 Mg/ha

year. Brachiaria dictyoneura grass has been recently

classified as B. humidicola and it is similar in growth

habits to the B. humidicola grass used in this study.

Kanno et al. (1999) compared five different tropical

grasses in their differences in root distribution under

continuous grazing with low amounts of fertilizer

application in the Cerrados of Brazil. Although they

measured the total root biomass only up to 40 cm soil

depth, the values of different grasses ranged between

6 to 16 Mg/ha. Urquiaga et al. (1998) estimated that 54

% and 62 % of root C from A. gayanus and B. decumbens

pastures, respectively will be nondecomposable

thereby contributing to an increase in SOC

accumulation. The belowground root biomass and its

functional activity in tropical pastures result from root

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production, growth, mortality, and decomposition

processes (i.e., root turnover), which occur

simultaneously and fluctuate widely under grazing

conditions and the age of the pasture (Rao, 1998; Fisher

et al., 2007; Siqueira da Silva et al., 2019).

Root turnover in the grass was estimated to be 2.2

times in both grass alone (B. dictyoneura) and grass +

legume (B. dictyoneura + Arachis pintoi) pastures (Rao et

al., 2001b). If one assumes that the NPP of

belowground DM is similar to aboveground DM, the

total C inputs to a grazed pasture are estimated to be

in the range of 26 to 32 Mg/ha/year (Fisher et al.,

1998). Improved grasses used in this study differ in

their growth habits and values for both above and

belowground DM production as well as in litter

decomposition. Andropogon gayanus is an erect,

tussockforming tall grass, B. decumbens is low

growing, erect or decumbent, rhizomatous and

stoloniferous grass while B. humidicola is a strongly

stoloniferous and rhizomatous grass. The rate of litter

decomposition reported was lower for B. humidicola

and A. gayanus compared to B. decumbens. The legume

litter of S. capitata decomposes much faster than that of

the three grasses (Thomas and Asakawa, 1993).

Boddey et al. (2020) indicated that the amount of N

being recycled through aboveground plant litter could

be over 100 kg N/ha/year for the grasslegume

association; and they also pointed out that

belowground N recycling may be of the same

magnitude as the aboveground N (Trujillo et al., 2006).

Root tissue of higher C: N ratios in tropical grasses

(109224) could lead to slower decomposition and

formation of fewer microbial byproducts (Rao, 1998,

Trujillo et al., 2006; Dietzel et al., 2017). Root C: N ratios

could play a key role in contributing to a larger

proportion of SOC that is found in deeper soil layers

below 20 cm soil depth (Fisher et al., 2007). Under

pasture (B. brizantha) land use treatment, de Figueiredo

et al. (2010) reported that 48 % of the total SOC was in

the form of particulate organic carbon (POC), and a

high value of C: N ratio of 47.8 was observed with this

POC by these authors. Clearly, all of the above factors

may influence the range of the assumed values of SOC

accumulation.

The amount of SOC accumulation in longterm (up

to 9 years old) pure grass pastures in the eastern plains

of Colombia was about 3.0 Mg/ha/year but it was

markedly increased with a legume component in the

pasture (Fisher et al., 1994). The use of legume

components in association with grasses can not only

improve N supply to the grass but also considerably

enhance soil biological activity. This is through an

increase not only in terms of earthworm biomass and

soil aggregation (Lavelle et al., 2014) but also in the

rate of N mineralization (Rao et al., 1994). Proper

grazing management together with maintenance

fertilizer application every two to three years could

sustain both aboveground and belowground NPP

leading to significant amounts of SOC accumulation in

improved pastures in the eastern plains of Colombia.

We do not assume that SOC accumulation in

introduced pastures will either be constant or be

continued indefinitely. But two recent studies from the

Brazilian agroecosystems presented some interesting

observations. Durrer et al. (2021) used a 100year

observational chronosequence spanning primary

foresttopasture conversion and subsequent

secondary forest succession in the Amazon region and

observed a surprising increase in topsoil SOC

concentrations in pastures at 60 years following

conversion. To predict longterm changes in SOC

stocks after pasture intensification and diversification,

Damian et al. (2021) used the DayCent model and

simulated the effects of converting poorly managed

pastures (PMP) to more intensive and diversified

systems of pasture management, including fertilized

pasture (FP). They used field data collected from three

regions with contrasting climatic conditions. The

DayCent model estimated that the conversion of PMP

to FP increases the soil C stocks by 0.95 Mg/ha/year.

The model also estimated that the fertilization of the

pasture every year (FP) could result into higher SOC

stocks.

The differences in overall C footprint estimates

among SCE1, SCE 3, and SCE 5 were not that marked

at the lower range, but at the higher range, those were

larger due to a greater number of grazing days and the

resultant SOC accumulation. The overall C footprint

values shown in Table 3 include an interval of possible

values that range from near neutrality to high net soil

C accumulation (negative values). They reflect the

natural variability encountered due to soils,

management strategies, betweenyears variability, and

variation in the potential growth of different species.

The three different tropical grasses included in the

SCEs generally exhibit high belowground

productivity, thus accumulating large amounts of

organic C in depths up to 2 meters, a contribution

frequently underestimated in the past due to only

superficial soil measurements (Qi et al., 2019). The

values estimated for B. humidicola in SCE 1 are

particularly interesting since this germplasm accession

CIAT 679 has been consistently demonstrated to have

RamírezRestrepo et al.

ISSNL 10221301. Archivos Latinoamericanos de Producción Animal. 2023. 31 (1): 1  20

Conflicts of interest: The authors declare that there has been no interest(s) that might raise the question of bias in

the reported research or the manuscript's inferences, opinions, or conclusions.

13

a high root growth rate, and very slow decay rate of

stored biomass, even in visually degraded, overgrazed

pastures (Chirinda et al., 2019). This greater ability of

B. humidicola pastures with lower values of

digestibility and N content may be associated with the

ability of biological nitrification inhibition (BNI), a trait

that even extends to inhibition of N release from urine

patches (Byrnes et al., 2017). These BNI effects were not

accounted for in our calculations, so the corresponding

overall C footprint values may be a conservative

estimate. On the contrary, generalizations of results for

SCE 5 based on A. gayanus grass are narrower, as there

is limited information on its environmental impact,

this species has a smaller niche, and it is more

demanding of adequate grazing management than

generally practiced in extensive systems. Nevertheless,

SCE 5 constitutes a prototype of a productive grass

legume pasture that has persisted well under good

management in onstation trials and a small number of

commercial ranches.

Conclusions

This study elaborates on realistic simulated SCEs of

beef production by culling cows in the Llanos of the

Colombian Orinoquía. It was made possible by the

intensive use of longterm onstation legacy data of

animal production and studies related to animal GHG

emissions and dynamics of plant biomass, both above

and belowground, complemented with data on soil

emissions and SOC accumulation. Large and

practically important differences were found in

emissions and footprints between the tropical pasture

systems studied. These differences were particularly

notable during the fattening phase of cull cows on the

three systems chosen to represent two widely used

production practices with grassalone pastures,

compared to one promising grasslegume pasture. The

results clearly demonstrated that given a fixed

fattening period during the wet season, system

performance depends very much on the daily weight

gains allowed for by the pastures used. Furthermore,

the present estimates of emissions and footprints

suggest that cows’ age at culling may significantly

impact system performance, an issue that deserves

further longterm research. The estimates of C

footprints based on substantiated rates of SOC

accumulation over the mediumterm show that the

tested system may compensate for animal and soil

GHG emissions. However, the net values may vary

over a relatively wide range and demand above

average grazing management strategies relative to

current practices.

Ethics statement: The research did not require ethical review and approval because the animal data that were used

in the study were repurposed from legacy files recorded ethically at the Carimagua Research Station (CRC).

Author contributions: CARR: Investigation, Data curation, Conceptualization, Methodology, Model development,

Writing, Review, and Editing. RRVI: Investigation, Data curation, Conceptualization, Methodology, Model

development, Writing, Review, and Editing. IMR: Methodology, Writing, Review, and Editing.

Funding: The original pastoral research conducted at the CRC was financially supported between 1979 and 1991 by

a core budget from the International Center for Tropical Agriculture (CIAT). This manuscript and model develop

ment were funded from 2017 to 2021 by CR Ecoefficient Agriculture Consultancy (CREAC©) and R. R. Vera

Infanzón Private Consultant Services.

Acknowledgments: We would like to thank the technical assistance given by many staff at the CRC and CIAT years

ago. Special thanks are extended to the Commonwealth Scientific and Industrial Research Organisation (CSIRO) for

allowing C.A. RamírezRestrepo to review, collate, and analyze the original dataset between 2016 and 2017.

Edited by Dr. Ana María Herrera Angulo and Dr. Claudia Faverin.

Sustainable fattening of cull beef cows

ISSNL 10221301. Archivos Latinoamericanos de Producción Animal. 2023. 31 (1): 1  20

14

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