The breeding herd dataset (Vera et al., 2002) extended by Ramírez-Restrepo et al. (2023) was integrated with the herd’s unpublished seventh reproductive cycle (RC; i.e., conception-weaning) at Carimagua Research Centre (latitude 4°36’44.6” N, longitude 74°08’42.2” W) in the Colombian WNSE. Data from 30 cows provided individual liveweight (LW) and age fluctuations across male (n = 55) and heifer (n = 75) calves from birth [28.6 ± 0.50 vs 27.8 ± 0.42 kg (least-squares means ± SEM)] to weaning (183.9 ± 4.80 vs 162.5 ± 4.10 kg and 8.5 ± 0.18 vs 8.4 ± 0.15 months) up to 10.3 ± 0.49 years. Details of the breeding herd on year-round grazing of B. decumbens cultivar Basilisk pastures outlining long-term reproductive efficiency and the allocation of GHG costs to cows and cow-calf pairs were described by Ramírez-Restrepo et al. (2020).

Calving events were daily recorded on the paddock while at approximately 4 month intervals, cow’s rectal palpation, and visual body condition score [on a scale of 1 (poor) to 5 (fat)], LWs, branding, and castration of males (steers) at weaning were performed in the yard. Briefly, animals were adequately restrained in cattle crushes to minimize the risk to the welfare of cattle, particularly stress while also ensuring the field staff’s well-being. Branding irons were well maintained and heated correctly to perform a 2-3 seconds blue-hot-iron branding [CIAT’s symbol, and two and three numbers to identify the year of birth and stock sequence, respectively] on a dry hide (near the left side rump) of the animal. Surgical removal of testicles involving enough twist of the spermatic cord and the severed scraping of it to allow quick blood clotting was performed through the implementation of good hygiene practices related to the use of an antiseptic solution in a bucket for hands, scrotum disinfection handling, and instruments (scalpel handles-No 3 and sterile disposable scalpel blades-No 10 changed regularly). Post-surgical healing was also facilitated by the use of antibacterial fly powder and antiseptic spray on the incision before releasing weaners from the yard, monitoring on a clean paddock for 14 days, the use of anti-inflammatory drugs, and previous tetanus (Clostridium tetani) vaccination. In both, branding and castration practices pain minimization strategies were followed.

Weaners from different provenance at Carimagua became stockers and yearlings (i.e., backgrounding) on native savanna (Ramírez-Restrepo and Vera-Infanzón, 2019) and experimental pastures (Lascano and Estrada, 1989; Lascano, 1991) whereas surplus heifers and yearling steers were sold to regional farms. Among the livestock categories, pooled stockers-yearlings extended the efficient utilization of low-input pastures based on the relevance of replacement heifers (Vera-Infanzón and Ramírez-Restrepo, 2020; Vera-Infanzón and Ramírez-Restrepo, 2022) and the association of mixed ages and stock classes (Ramírez-Restrepo and Vera, 2019) of farming systems.

In all cases, cattle had always free access to fresh water plus a commercial mineral supplement containing as-kg fed 137 g Ca, 269 g Cl, 0.01 g Co, 1.038 Cu, 0.076 g I, 175 g Na, 80 g P, 20 g S, and 3.5 g Zn. Supplement intake was recorded on a fortnightly basis. Trial design and implementation were done by accredited Colombian Doctors of Veterinary Medicine according to Colombian husbandry and animal welfare standards and guidelines (MINEDUCATION, 1985).

The climate recorded during the research period at Carimagua’s weather station was humid-very humid (April-November) and dry (December-March) with annual precipitation of 3,300 mm in 1986, dropping to an average of 2,202 mm between 1979 and 1991. Thirteen-year minimum and maximum ambient temperatures were 25.2°C to 28.1°C, respectively (Vera and Ramírez-Restrepo, 2017).

Soils at the site were well-drained clay loam Oxisols (tropeptic haplustox isohyperthermic) with 4.78 pH and 90.1% Al saturation. The 0-20 cm soil layer contained 2.9% organic matter, 40.2% clay, 19.8% sand, 1.46 µg/g available P (Bray-II), and exchangeable (cmol/kg) Ca (0.17), Mg (0.08), and K (0.06; Ramírez-Restrepo et al., 2020).

Brachiaria decumbens cultivar Basilisk pastures were established 2-3 years before cow-calf grazing following the recommended application (kg/ha) of Ca (48), P (20), K (20) Mg (14), and S (10) (Ramírez-Restrepo et al., 2020). Every 3 years and for ~ 60 days, cattle were shifted to identical B. decumbens pastures that were used strategically for adult steers fattening to allow pasture renewal practices including two light disking plus the spread of a third of the establishment fertilization (Vera et al., 2002).

The field experiment used a stocking rate of 1.5 head/ha to ensure conservative grazing management that balanced forage growth and use and maintained full soil cover and land conditions to minimize erosion. Pasture performance was monitored six times per year following the BOTANAL procedure (Jones and Tothill, 1985). Forage mass was between 1,500 and 3,500 kg dry matter (DM)/ha with contents (g/100 g DM) of crude protein (CP, 7.1-11.0), neutral detergent fiber (65.0-71.0), ash (8.5-10.0), and fat (1.0) while in vitro DM digestibility (IVDMD; g/100 g) of the whole plant was 63.7 and 55.0, in the wet and dry season, respectively. (Values derived from a Carimagua grazing-forage database assembled by Ramírez-Restrepo and Vera, 2019).

The basic structure of the modeling framework is one of beef production in which the benefits of plausible growth (Ramírez-Restrepo and Vera-Infanzón, 2019) and fattening (Ramírez-Restrepo et al., 2023) practices were estimated using least-squares regressions concerning LW-derived CH₄ emissions (Eq. 1) and DM intake (DMI; Eq. 2) from 56 days of age. These functional relationships (y = a + bx) are derived from the Commonwealth Scientific and Industrial Research Organisation (CSIRO) calibrated (0.99 pure CH₄ gas recovery) open-circuit chambers measurements using Brahman (Ramírez-Restrepo et al., 2016a) and Belmont Red Composite [Africander (African Sanga) x Brahman x Hereford-Shorthorn (3/4 B. taurus; Ramírez-Restrepo et al., 2014; Ramírez-Restrepo et al., 2016b) steers fed ad libitum on a daily DM basis (2.1% of total LW; Fisher et al., 1987).

r² = 0.663, P < 0.0001; CV = 16.78; r.s.d = 30.82; r = 0.814, P < 0.0001

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

The second strategy in the model was to link weaning LW differences (P < 0.0001) between heifers and steers with on-farm low (0.428 kg) and high (0.516 kg) post-weaning on-farm daily LW gains (DLWGs) in heifers and steers (0.516 kg) on B. decumbens pastures (Vera and Hoyos, 2019), respectively to reach target slaughter LW SCEs that are representative of those used in the industry (Wiedemann et al., 2015; Ramírez-Restrepo and Vera, 2019). Under this rationale, the model is implicitly ensuring that individual preweaning LW variations within each sex category are maintained up to slaughter at variable ages and grazing times to capture temporal and spatial beef-herd transactions, and existing regional land uses (Vera-Infanzón et al., 2023). The third strategy paired the slaughterhouse LWs with hot (0.4992) and chilled (0.4772) carcass dressing-outs (Velásquez and Ríos, 2010), accumulated CH₄ emissions, and DMIs.

The post-weaning combination in heifers [confidence limits for weaning 154.4-170.6 kg] of non-feed supplemented low and high DLWGs allowed them to simultaneously reach an early breeding status (272.7 ± 0.01 kg) and the simulation of four target LW SCEs (i.e., 405, 414, 438, and 453 kg representing SCE 1, SCE 2, SCE 3, and SCE 4, respectively ( Figure 1 ). In parallel, assuming a single DLWG, the backgrounding-fattening period of steers (weaning confidence limits 174.4-193.5 kg) to achieve butcher LWs of 435, 474, and 574 kg was represented by SCEs 5, 6, and 7, respectively ( Figure 1 ). Hence, derived carcass carbon dioxide equivalent (CO₂-eq) efficiency intensities constituted the specific system’s boundary cut-off criteria ( Figure 1 ). An underlying assumption in using a post-weaning dataset partitioned into male and female sets is that LWGs of young steers are larger than in heifers grazing the same tropical pastures year-round (Ramírez-Restrepo and Vera, 2019). Thus, in the suckling herd, this study considered calves and heifers as experimental units while post-weaning sex-grouped animals represented the experimental units over the simulated fattening SCEs.

The scope of this computation considered the interconnected CF of GHG dynamics on B. decumbens portrayed by Ramírez-Restrepo et al. (2020); Ramírez-Restrepo et al. (2023), and to the extent possible, parameters used in this study have been reviewed. Briefly, fecal CH₄ assumed the predicted DMI, IVDMD (55 g/100 g), and the 0.112 emission factor (EF; Zhu et al., 2018). Nitrogen excretion assumed DMI, N concentration (1.488 g/100 g), nutrient digestibility (71.62 g/100 g; Vercoe and Frisch, 1970), and the kg N₂O-kg N EF of 0.0014 (Lessa et al., 2014) and 0.016 (Chirinda et al., 2019) for feces and urine, respectively. Intakes of DM and CP met the LW-related requirements of female and male B. indicus cattle raised on pasture in Brazil (Rotta et al., 2016). The factor used for a kg of the mineralized supplement was 0.800 kg CO₂-eq (C-equivalent; KLIMATMÄRKING FÖR MAT, 2009) while supplement intake assumed the 0.124 g/kg LW factor derived from the expected consumption of 60 g/day by a 500 kg Brahman in the foothills region of the Colombian Llanos (Rincón et al., 2018).

The estimation of the overall C balance was mainly adapted from contemporary studies on soil-plant relations conducted at Carimagua (Fisher et al., 1994; Rondón et al., 2006; Trujillo et al., 2006). Soil organic C values to 1 m depth considered data from Fisher et al. (1994); Rondón et al. (2006), and Fisher et al. (2007). The standing above and belowground DM biomass values used were from published reports (Fisher et al., 1998; Rao, 1998; Kanno et al., 1999; Rao et al., 2001a, b; Grace et al., 2006; Trujillo et al., 2006). Soil CH₄ and N₂O emissions were estimated from the review studies done by Castaldi et al. (2006) and Rondón et al. (2006). The CO₂-eq footprint from pasture establishment and maintenance was assumed on a prorated basis considering 15 years of on-farm productive grazing (Vera and Hoyos, 2019). Fertilizer and tillage imprints were computed from Edwards-Jones et al. (2009); Kim et al. (2011), and the University of Arkansas (2019) while the estimated range of CO₂-eq SOC accumulation rate was based on published reports (Fisher et al., 1994; Rao, 1998; Fisher et al., 1998; Rondón et al., 2006; Fisher et al., 2007; Costa et al., 2022; Hyman et al., 2022).

The study used the horizon global warming potential (GWP)_100-34 value for CH₄ that includes climate-C feedbacks (Gasser et al., 2017; Mueller and Mueller, 2017; Allen et al., 2018) whilst the _GWP100-298 value for N₂O (Ramírez-Restrepo et al., 2019b). This is consistent with previous studies on GHGE conducted by Vera et al. (2023) that were aimed to assist possible BFS intensification on the WNSE, as well as discussions, and policy-making efforts focusing on environmental trade-offs, planning, natural resources management, rural livelihoods, market chains, and research for development (Latawiec et al., 2014; Cunha Malafaia et al., 2021).

The variances associated with age and LW fluctuations, CH₄ emissions, dynamics of the relationships between LWs and CH₄ emissions, DMI, and carcass measurements were tested using the GLM procedure within the Statistical Analysis System (SAS®, 2021) including the upper and lower confidence limits for each mean observation and the confidence level for the parameter estimation methods. The model considered the fixed effects of breeding-herd RCs (i.e., 1 to 7) and fattening-slaughter SCEs (i.e., 1 to 7), and their interaction. Results are presented as least-squares means ± standard errors of the mean (SEM) while differences between the main factors were reported if significant at P ≤ 0.05.

The predicted chilled carcass weights (CCWs) in the range of 193-210 kg for heifers and 208-274 kg for steers at 24-31 and 24-33 months of age, respectively, can be compared with the results of León-Llanos et al. (2022) who reported in the Llanos a range of 259-269 kg CCWs at 34-35 months from seven commercial Brahman crosses fattened rotationally for 24 months on B. decumbens and B. humidicola pastures. Although León-Llanos et al. (2022) and the present study used animals from experimental cow-calf systems, differences between the present calculations and León-Llanos et al. (2022) can be explained by the higher initial age (10-11 months), initial LW (246 kg), and stocked paddocks (2.8 head/ha) used by the latter authors which in turn reflected in lower DLWGs (0.442 kg). It is also important to note that León-Llanos et al. (2022) did not assess heifers and used a crop-based supplement during the dry season period.

Rincón and Villalobos (2021) raised Brahman yearlings (18 months of age - 240-280 kg) on rotationally grazed B. decumbens pastures or mixed with the tannin-containing legumes [Lascano et al., 1990; International Center for Tropical Agriculture (CIAT), 2016] including Centrosema molle (accession CIAT 15160), C. macrocarpum (accession CIAT 15799), and Grona heterocarpa subsp. ovalifolia (syn. Desmodium ovalifolium cultivar Maquenque) that yielded average daily liveweight gains (DLWGs) of 0.437, 0.687, 0.396, and 0.440 kg, respectively in Experiment 1 (22 months). A second, shorter experiment (14 months) on the same pastures, resulted in mean DLWGs of 0.545, 0.744, 0.563, and 0.573 kg, respectively. Thus, the final LWs (495-504 kg) recorded by Rincón and Villalobos (2021) fall within the present scenario (SCE) 6 and SCE 7 estimations and these values reflect the model’s mean steers’ target processing LW (494 kg). Similarly, the mean DLWG (0.487 kg), across heifers and steers set by the model, and the overall DLWG (0.486 kg) on B. decumbens after 36 months of grazing (Rincón and Villalobos, 2021) emphasize the predictive capability of the model considering the continuous growth rate from weaning to slaughter approach. However, carcass traits and CO₂-eq CH₄ concentration in carcass yields were not estimated by Rincón and Villalobos (2021).

The methodology employed in this research provided strong evidence to support the view that LWGs, grazing management, and processing LW frameworks exert an impact on intensification in the beef farming systems (BFS) of the well-drained native savanna ecosystem (WNSE). Slaughtering cattle at a younger age will play a significant role in commodity markets for homogenous products within gender groups or in supply chains where there is much likelihood of heterogeneous quality products from adult cattle. Nevertheless, emphasis on plant characteristics that relate to nutritional and feeding values, and persistence to address increasing climate extremes, shifts, and changes from seasons to years should provide long-term benefits and future opportunities for research and development of the industry. This may require the integration of fodder resources such as trees and shrubs to supply protein, energy, and other nutrients into tropical grazing systems (Vandermeulen et al., 2018a).

Previous studies from WNSE (Ramírez-Restrepo and Vera, 2019) reported that Brahman-influenced cull cows (10-13 years) and steers (3-5 years) can achieve CCWs of 169-193 kg and 202-226 kg, respectively when grazed on Andropogon gayanus plus Stylosanthes capitata pastures after 144-201 days of fattening, while CCWs of 176-194 kg (cull cows) and 187-211 kg (steers) were observed on B. humidicola pastures during 146-181 days. Therefore, as the choice of cattle categories for fattening on improved pastures and/or fodder resources is an important consideration for farmers, further appropriate modeling studies are required to determine the benefits of complementary fattening of young and adult cattle practices to diversify farm outputs while meeting consumers’ expectations and delivering increased economic returns to producers.

The model interpolation of LWs and CH₄ emissions between weaning, slaughter, and lifespan proportions allowed the differentiation in CF of young BFS. The analysis indicated that weaning LW to slaughter LW ratios of 0.3932, 0.3848, 0.3634, and 0.3517 ± 0.0076 were achieved in heifers’ SCEs 1, 2, 3, and 4, respectively whilst ratios of 0.4194, 0.3850, and 0.3179 ± 0.0089 corresponded to steers’ SCEs 5, 6, and 7, respectively. Likewise, it was shown that significant differences in the overall growth from birth to weaning between heifers (0.533 ± 0.004 kg) and steers (0.620 ± 0.007 kg), their birth LW to weaning LW ratios (0.1799 ± 0.001 vs 0.1612 ± 0.002), and their cumulative CH₄ emissions before fattening (7.73 ± 0.300 kg vs 9.20 ± 0.351 kg) can be linked to the differential significant magnitudes of weaning to slaughter and weaning to lifespan CH₄ ratios in heifers (0.1301 ± 0.001 vs 0.1443 ± 0.003) and steers (0.1137 ± 0.001 vs 0.1241 ± 0.002). In particular, the pattern of LWGs during the rearing period in a pasture-based system corresponds to the value of LW at 12 months as a proportion of 21 months of age on cumulative production (Handcock et al., 2020) while LWs and DLWGs in real-time can be predicted in B. indicus cattle during growing and finishing phases (Comminotte et al., 2020).

Taken together, these results indicate that the within and between individual animal variability and herd-level variation in the LW recorded database and the predicted DMI and CH₄ emissions were also coupled with the natural variation in measured LWs, DMIs, and CH₄ outputs from cattle while in accurate respiratory chambers (Ramírez-Restrepo and Vera, 2019; Zhang et al., 2021). It is important to observe that we hypothesized that suckling growth paths would affect lifetime production and the sustainable efficiency of carcass yields. The mathematical output supports this hypothesis, as we provided insights into the implications of measurements obtained at differential LW and age at slaughter that can be caused by the same variation from birth to weaning on the same pasture with a pivotal effect on the overall CF at the system level. Connectedly, Foote et al. (2016) indicated that in ad libitum-fed beef-finishing heifers and steers, their differential appetite, DLWGs, and feed efficiency are consistently regulated by the circadian-blood expression of levels of acyl ghrelin (gut-peptide hormone), total ghrelin (acyl and desacyl), and ghrelin ratio (acyl: total ghrelin). Hence the current model can be used as part of a whole-farm model to predict the effects of pasture intensification strategies on production dynamics and the environmental footprint of beef herds in the Llanos (Vera et al., 2023).

This study also contributes to current knowledge by documenting the range of values on lifetime CH₄ emissions from finished heifers (60.03 to 88.15 ± 0.470 kg) and steers (67.30 to 116.23 ± 0.593 kg) and the subsequent carcass metric implications. This is shown from the calculated CH₄ yield ranges of 18.1-18.4 (heifers) and 17.9-18.5 (steers) that match the values from open-circuit respiration chambers values with B. indicus influenced heifers (18.07) and steers (18.4-19.0) that were with fed fresh grasses as reported by Ku-Vera et al. (2018) and Meat and Livestock Australia (MLA, 2020), respectively. Although in agreement with Skidmore et al. (2022), the present modeling effort followed a single-issue life cycle assessment approach across a wide range of slaughter regimes, the current predictive values for steers (24.2-32.9 months) are well below the estimated steers’ lifetime CH₄ emissions of 151.23 kg (36 months) and 201.83 kg (48 months) from Brazilian pasture-based BFS. Interestingly, while using the Intergovernmental Panel on Climate Change (IPCC) Tier 2 methodology Skidmore et al. (2022) argued that it is practicable to slaughter lifetime grazing heifers with 168.12 kg of CH₄ emissions at 36 months of age while the present modeling showed that un-supplemented younger heifers (23.9-30.7 months) can be slaughtered at a reduced time to lower enteric CH₄ emissions by ~44%.

The results from this study point out that at different levels of intensification, the lifespan C footprint at the farm gate is in the range of 5.040 to 6.616 kg CO₂-eq/kg FLW in heifers and 5.254 to 6.883 kg CO₂-eq/kg FLW in steers. On average, these values are 43.4%, 45.4%, 51.0%, 55%, and 77% lower than the Australian methodologically-variable cradle to farm-gate life cycle assessment estimates of 10.5 CO₂-eq/kg beef LW (Eady et al., 2013; 2016), 10.9 CO₂-eq/kg beef LW (Ridoutt, 2021), 12.2 CO₂-eq/kg beef LW (Wiedemann et al., 2016), 13.3 kg CO₂-eq/kg beef LW (MLA, 2022), and 25.8 CO₂-eq/kg beef LW sold (Eady et al., 2016). Furthermore, present lifetime means of 6.179 kg CO₂-eq/kg LWG for heifers and 6.314 kg CO₂-eq/kg LWG for steers are 42% and 80% lower than the CO₂-eq/kg LWG fattening range indices of 10.9 and 30.9 suggested by the cradle to farm-gate life cycle assessment estimations for the Colombian piedmont plains using 2019 refined IPCC parameters (González-Quintero et al., 2022). Alternatively, if a CH₄ GWP_100-28 metric (Myhre et al., 2013) is introduced to compare with the assumed CH₄ EF of 1.5 t CO₂-eq/animal equivalent (AE; 455 kg LW)/year which is used to estimate the C balance of the Queensland beef industry (QLD Government, 2019) or the 1.56 t CO₂-eq/AE/year for farm C accounting (Ekonomou et al., 2020), constant heifers’ LWs of 438 and 453 kg, emit 1.365 vs 1.390 t CO₂-eq/year while 1.225, 1.289, and 1.451 t CO₂-eq/year emissions, respectively equate to stable steers’ LWs of 435, 474, and 574 kg. These disparities provide the foundation to simulate the environmental impacts of alternative finishing LWs by choosing the assessment methodology and production option that makes sense in the context of sustainable productivity at the BFS level for assisting a low-C emission future. It is also relevant to recognize that 33% and 47% of the variation in predicted CO₂-eq emissions per kg LW in BFS is explained by weaning percentage and averaged DLWGs, respectively (Wiedemann et al., 2016).

On the other hand, the model predicted a range of values of 10.5-13.8, 17.3-22.8, and 66.8-87.4 kg CO₂-eq/kg of CW, lean meat, and edible protein for heifers and 11.0-14.4, 18.1-23.7, and 69.9-91.2 for steers, respectively for steers. Overall, they represent 19.9% for heifers and 20.7% for steers from the total (cumulative) carcass-reference values of CH₄ emission that would be expected from multiparous Brahman cull cows (8.7 years) that were continuously bred and fattened for 86 days on B. decumbens pasture (Ramírez-Restrepo et al., 2023). These estimated values are in contrast with Ridoutt’s (2021) estimate of 25.5 kg CO₂-eq/kg of edible beef. Nevertheless, such estimations underscore the value of 16.7 CO₂-warming-eq (CO₂-w.e.)/kg of edible beef (Ridoutt, 2021) which aligns the future warming with the permanent change in the rate of short-lived GHGE like CH₄ (Lynch et al., 2020). Hence, results from the model used in this study may support published values by the potential use of the new GWP* CO₂-w.e. metrics to further review the CF of the beef industry of the WNSE.

The present study estimated the enhancement of soil organic carbon (SOC) storage at different stages of the BF system. First, the long periods of grazing by heifers (677 days) and steers (756 days) strike a positive balance between on-farm productivity, CO₂-eq SOC accumulation, and climate change mitigation. The notion that conservatively managed grazing of tropical BFS negatively imprints the environment is not tenable. Indeed, positive trade-offs are involved, and farmers may need to make sensible resource management decisions regarding the appropriate allocation of pastures and animal stocks to ensure red meat target-setting and choose the relative contribution of pastoral abatement strategies.

This is consistent with the view that in the Colombian Orinoquía, increased SOC storage at deep soil layers (30-100 cm), reduced N₂O emissions from beef urine deposition, and viable land-based agendas of CO₂ removal from the atmosphere can be achieved through the ability of biological nitrification inhibition, N uptake from the ammonium source, and the deep rooting of B. humidicola (Costa et al., 2022). Hyman et al. (2022) showed a large potential for SOC storage in Colombia’s Eastern High Plains. They found less SOC storage than Fisher et al. (1994) and indicated that earlier high levels of SOC accumulation in well-managed pastures returned to a lower equilibrium value under inadequate management conditions. Thus, these two recent reports on SOC stocks in the Llanos not only highlight the need for improving the management of native savanna and degraded pastures across the 1 million ha study but also infer that land-use changes in the WNSE can vary widely in the balance between beef outputs and the overall CF at the farming system level (Vera-Infanzón et al., 2023).

Furthermore, results from this study suggest that early weaning-fattening systems in the tropics may also offer the opportunity for climate mitigation by transferring C credits within or outside the BFS involving land transactions and promoting C markets. Brahman-influenced cow-calf herd systems in the WNSE may be not only close to C neutral under estimated conventional and early weaning management practices (583 vs 579 kg CO₂-eq/ha/year; Ramírez-Restrepo et al., 2019b) but also may act as C sinks at the system level by removing atmospheric CO₂ across six consecutive RCs by grazing on B. decumbens pastures during the cow-calf-bull breeding phase (-1,180 to -8,513 kg CO₂-eq/ha/year; Ramírez-Restrepo et al., 2020). These C sinks may also contribute toward SOC storage imbalances caused by land use change, cropland use, or complementary routine animal feed supplementation locally or elsewhere. Therefore, climate stabilization may be nurtured from land use efficiency through pasture management and the adoption of a climate-neutral target strategy with improved production from the meat industry (MLA, 2021).

The current predictions from this study provide dimensional insights to reduce slaughter age while monitoring GHGE at the system level. However, this approach did not assess the effect of B. decumbens pastures mixed with legumes that contain secondary metabolites that may influence even more on sustainable ruminant intensification (Ramírez-Restrepo and Barry, 2005). Therefore, it is suggested that year-round productivity should not underestimate the feeding value of forage resources containing secondary compounds (Ramírez-Restrepo and Charmley, 2015; Durmic et al., 2017; Vandermeulen et al., 2018b) to further reduce the impact on the C cycle by using the present fattening framework. This argument is strengthened by the counter-balancing effect of LWs and age targets on animal GHGE vs the reduction in GHGE from shorter fattening periods, especially considering not only that CP concentration in B. decumbens plus legumes swards can be 33% higher than in B. decumbens alone pastures (Rincón and Villalobos, 2021) but also the effect of condensed tannins-containing legumes shifting N digestion and increasing fecal N concentration (Waghorn et al., 1987), thereby mitigating CH₄, CO₂, and N₂O emission from excreta in the soil (van Cleef et al., 2022), and increasing soil N retention in grazed pastures (Slebodnik, 2020).

The present estimates also suggest that replacement heifers raised on B. decumbens pastures may favor lifetime breeding systems grazing higher-quality pastures or if transferred, could positively impact extensive cow-calf operations that are subject to improved decision-making (Vera-Infanzón and Ramírez-Restrepo, 2020; Vera-Infanzón and Ramírez-Restrepo, 2022). Nevertheless, defining the physiological and genomic limits on selection pressure on beef genotypes that may have a significant environmental effect remains to be an intriguing issue if grazing low CH₄ emitters and efficient producers are targeted. Interestingly, our understanding is limited in many basic details related to the physiological systemic effects of blood CH₄ concentration in Brahman cattle (Ramírez-Restrepo et al., 2016a).

Likewise, the current early breeding and backgrounding stages may offer a potential window of opportunity for the transition to other BFS practices that may reduce the GWP of the national GHG inventory. This can be achieved through the finishing of beef cattle on feedlots that are potentially driven by the feed supplementation of ecologically relevant compounds (Tedeschi et al., 2021). Nevertheless, as feed-intensive practices are inevitably linked to the provision of high-concentrated diets, plausible BFS should consider that a kg of feed-milled supplement at the farm gate may represent 0.93 kg CO₂-eq under a life cycle assessment methodology (Adom et al., 2013). Relatedly, the evaluation of trade-offs, synergies, and challenges between land use, breeding goals, plant by-products, profitability, environmental stability, and consumers’ recognition of WNSE-BFS in a circular planet-friendly food system should be similarly addressed (Oosting et al., 2022). Hence, as the transformation of finishing BFS on the WNSE is not well documented, future advances will depend on research focused on the integration of beef genotypes, grazing systems with an emphasis on deep-rooted pasture grass and legume species, and several fattening-supplemented practices under grazing or feed yard conditions to assist decision-making and to address environmental policy issues.