A meta-analysis of nutrient intake, feed efficiency and performance in cattle grazing on tropical grasslands
Résumé
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, R2 = 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, R2 = 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.