Complementary use of neotropical savanna and grass-legume pastures for early weaning and effects on growth and metabolic status of weaners and inter-calving intervals of dams

Abstract

Extensive, rangeland-based beef production systems that predominate in the neotropical savannas of northern South America are low input-low output beef breeding systems, and their intensification faces major hurdles due to their location, soil, water and topographic constraints. Intensification requires the introduction of improved pastures strategically managed to complement the native savannas, to improve production and to allow opportunities for a wider range of associated ecosystem services. This study assessed the feasibility of early weaning of beef calves onto small areas of sown pastures to aid system intensification. Weaning calves at 90 days of age and grazing on Andropgon gayanus, A. gayanus-Pueraria phaseoloides, A. gayanus-Centrosema acutifolium and Brachiaria humidicola-Arachis pintoi sown tropical pastures stocked at 6 animals/ha was compared with conventional weaning on native savanna over 4 consecutive years. The reproductive performance of their Brahman (Bos indicus) and crossbred [Brahman x San Martinero (native; B. taurus)] dams grazing savanna (0.2 cows/ha) was monitored in comparison with control cow-calf systems, where calves were weaned onto savanna between 240 and 270 days of age. Post-weaning weight gains of early weaned calves on sown pasture (0.1‒0.2 kg/d) were much lower than those of unweaned animals on savanna (0.31‒0.35 kg/d), but compensatory gains realized after the end of the weaning experiments allowed early weaned calves to reach weights similar to those of control animals 400 days after the end of the pasture phase. As expected, early weaned cows achieved higher live weights and had shorter inter-calving intervals than their counterparts. Trade-offs between performance of calves and of cows are discussed, but it is suggested that the strategic use of small areas of sown pastures for early weaned calves may productively complement large areas of native savannas. It is hypothesized that the improved quality, frequency and intensity of management required by these intensified systems may place a burden on these low-input primary enterprises, which may also challenge the productive and environmental adaptive capacity of primary resource users.Keywords: Cattle, extensive systems, intensification, rangelands, sustainability, tropical pastures.