A meta-analysis of nutrient intake, feed efficiency and performance in cattle grazing on tropical grasslands

It is essential to quantify the potential of tropical grasslands to allow significant feed efficiency for grazing livestock in controlled conditions such as at pasture. We conducted a quantitative analysis of published studies reporting the experimental results of average daily gains (ADG) and diet characteristics obtained specifically under grazing conditions (17 publications and 41 experiments), which have been less studied compared with controlled conditions in stalls. The database was analyzed to determine the average and range of values obtained for ADG (g/kg BW), dry matter digestibility, intake (DMI) and digestible DMI (DDMI, g/kg BW) and feed conversion efficiencies (FCE), as well as to predict the response of these parameters to the main strategies investigated in the literature - that is, mainly the stocking rate (SR) and the concentrate intake (CI). The ADG reached 1.2 kg BW per day and was directly linked to DDMI (ADG=-1.63+0.42 DDMI -0.0084 DDMI2, n=90, r.m.s.e=0.584, R 2=0.93). The DDMI, which was representative of the nutrient input, was driven mainly by DMI rather than dry matter digestibility, whereas these two parameters did not correlate (r=0.068, P=0.56). The average global FCE (0.11 g ADG/g DDMI) showed a greater association with the metabolic FCE (0.17 g ADG/g DMI) than the digestive FCE (0.62). The CI (g DM/kg BW) increased ADG (ADG=2376+CI 56.1, n=16, r.m.s.e.=441, R 2=0.95). The SR expressed as kg BW/ha decreased the individual ADG by 1.19 g/kg BW per additional ton of BW/ha, whereas the global ADG calculated per ha increased by 0.57 per additional ton BW/ha. When the SR was expressed as kg BW/ton DM and per ha rather than as kg BW/ha, the impact on the individual ADG decreased by 0.18 or 0.86 g per additional ton BW/ha, depending on the initial BW of the cattle. These results provide a better view of the potential performance and feeding of cattle in tropical grasslands. The results provide an improved quantification of the relationships between diet and performance, as well as the overall quantitative impact of SR and supplementation.

The northern Australian beef industry, a snapshot. 5. Land and pasture development practices

The land and pasture development practices of 375 northern Australian beef properties in 8 regions were surveyed during 1996–97. These properties represented a broad cross-section of the beef industry in terms of geographical location, enterprise and herd size, and ownership structures. Both tree clearing and killing were more common in Queensland than in the Northern Territory or northern Western Australia. In all regions where trees were poisoned, native pasture was more widely used than sowing introduced grass and/or legume species. In contrast, tree clearing was most often accompanied by sowing pastures (either an introduced grass only or introduced grass and legume species together), rather than using native pastures. Central coastal Queensland had the highest use of poisoning trees for pasture development. Tree clearing and using native pasture was most important in central Queensland regions and the Maranoa South West. Sowing introduced pasture species under live trees was more commonly practiced in northern Queensland, the Northern Territory and northern Western Australia than in other regions. A considerable number of introduced grass and legume species were sown by producers. Most of the sown species were grasses. Many of the sown grass and legume species were spreading naturally. Buffel grass was spreading in all areas with < 1000 mm average annual rainfall, but most sown species were spreading only in wetter regions. Stylosanthes spp. were the most commonly spreading legume species in regions with > 500 mm average annual rainfall. The results are discussed in relation to contemporary natural resource management issues and how this may affect land and pasture development activities in the future.