Bodyweight performance, estimated carcass traits and methane emissions of beef-cattle categories grazing Andropogon gayanus, Melinis minutiflora and Stylosanthes capitata mixed swards and Brachiaria humidicola pasture

Abstract

Cow–calf operations constitute the main land-use system in the 18 million ha of well drained tropical savannas of Colombia located in the Orinoco basin. There, numerous sex and age animal categories are present, ranging from suckling calves to old cull cows and steers, which in variable proportions are stocked at one animal unit (AU)/5–10 ha, depending on the ranch and distance from markets. In parallel, early-on farm observations showed that when sown pastures are introduced, graziers recur to opportunistic partial fattening of cull animals for a rapid economic return. The paper reports animal weight gains of cull cows, old steers, and young heifers and yearlings over seven consecutive years grazing on a low fertiliser-input well managed Andropogon gayanus-based pasture and four contemporary years on Brachiaria humidicola. The first 2 years involved three stocking rates (SR; 1.38, 1.85 and 2.32 animal units/ha), whereas a single SR of 1.33 animal units/ha was used for the remainder. A large database that included chemical, and in vitro and in vivo digestibility, values for all forages involved, was used as an input to a mathematical model to estimate methane (CH4) emissions. Estimations were compared with weight-based predictions derived from chamber measurements recorded recently in tropical Australia. Faecal mineral concentration varied little (not significantly) among SR and animal categories. Weight gains of old steers were 4–24% larger than those of cull cows, which, in turn, were larger than those of young steers and heifers (P < 0.01). Excepting one year, the performance of cull cows and old steers did not differ between pastures, confirming earlier on-ranch observations of reasonable weight gains of adult cattle on both pastures. The predicted carcass composition of cull cows and old steers did not differ between pastures either. Over the length of the experiment, cull cows emitted significantly less CH4 than did old steers (129 vs 141 g/day) on A. gayanus, while emissions on B. humidicola amounted to 128 and 137 g/day respectively. Despite between-year differences in animal performance, they are indicative of well managed pasture sustainability. They also show some of the trade-offs involved in the use of contrasting animal categories and pastures in terms of weight performance and predicted carcass composition and CH4 production. The authors expect that the present results will contribute to a rational, science-based discussion of the role of beef systems vis-à-vis environment in a region with limited production alternatives.

Dynamics of animal performance, and estimation of carbon footprint of two breeding herds grazing native neotropical savannas in eastern Colombia

“…Overall, this scientific reasoning on LW ensures, reproducibility and applicability of research outcomes as it has been previously demonstrated by Allard et al (2007), Ramírez-Restrepo et al (2017) and Ramírez-Restrepo and Vera (2019). However, to reflect differences not captured by the initial explanatory characteristics of the Excel spread mechanistic model, particular equations used to derive DMI and CH 4 emissions (Ramírez-Restrepo and Vera 2019) have been included between lines 194 and 199 in the revised manuscript.…”

“…In this context, McAuliffe et al (2018) noted that emissions, C balances and life cycle assessments of animal production systems are most frequently carried out based on aggregate data from farm surveys (Gaitán et al, 2016) or stochastic simulation approaches (Toro et al, 2017). On the contrary, analyses are seldom based on actual, individual, animal performance (McAuliffe et al, 2018) and even less frequently, on observations of individual animals replicated over long periods of time (Ramírez-Restrepo and Vera, 2019), an approach that allows assessment of within herd, and between years, variability (Tables 1-5 and supplementary material 1).…”

“…Cows may represent up to 63% of the females in the herd, but only half of them raise a calf in any given year under extensive management (Corporación Colombiana de Investigación Agropecuaria [CORPOICA, 1998];De Armas, 2005;Ezanno, 2005) and calved, lactating cows contribute the most to herd emissions (Casey and Holden, 2006). A somewhat more accurate figure for CO 2 -eq emissions of the full breeding herd can be estimated using the figures presented above for bred cows and empty, non-lactating cows, and those of Velásquez and Ríos (2010) and Ramírez-Restrepo and Vera (2019) for replacement heifers and cull cows, yielding 153 kg C ha over the full RC for a herd with 63% of breeding cows. These estimates should be considered relatively high and conservative values for herds bred and maintained exclusively on savannas based on clay-loam soils and SRs of 0.20 cows ha -1 .…”

Tropical Grasslands-Forrajes Tropicales Vol.7 No.1 [January 2019]

“…Lascano and Euclides (1996) reported a marked decrease in performance with age in an experimental Brachiaria humidicola pasture located in Carimagua. On the other hand, using large paddocks, Ramírez-Restrepo and Vera (2018) reported limited variation between years in an equally old pasture of B. humidicola located only 1 km away from the long-term experiments summarized by Lascano and Euclides (1996). These contrasting results explain in part the large variation between farms and years found in our database, all of which contributed to relatively large random and experimental residuals.…”

“…and Ph.D. theses (Grazing Ecology Research Group at UFRGS, Brazil) to develop 'rules of thumb' for FA, which would provide an optimal combination of ADG and stocking rate (Table 1). For beef cows, we developed FA standards based on research developed from 2007 (Do Carmo et al 2016;2018) plus previous information that recommended target forage height and BCS of cows during the lactation-gestation cycle (Soca et al 2007; see Table 1). For fattening animals we were unable to locate grazing experiments for Campos grassland, and for this reason standards presented are a mixture of beef cow values and empirical experience collected in this project (Table 1).…”