Autores
L. F. Oliveira , A. C. Ruggieri, R. H. Branco, O. L. Cota C , R. C. Canesin, H. J. U. Costa and M. E. Z. Mercadante
Resumo
The objective of the present
study was to assess the relationship between residual feed intake (RFI)
evaluated in a feedlot-performance test and on pasture, and to
determine the effect of feedlot RFI classification on enteric methane
(CH4) production in the feedlot and on pasture. Seventy-three
animals (25 with a low RFI, 24 with a medium RFI and 24 with a high
RFI) classified in a feedlot performance test were subjected to
performance testing on Brachiaria brizantha cv. Marandu pasture. Enteric CH4 was measured in a sample of these animals (n
= 47, with high and low RFI) by the sulfur hexafluoride tracer-gas
technique after the feedlot-performance test and during the performance
test on pasture. In the feedlot-performance test, dry-matter intake
(DMI) of low-RFI animals was 9.4% and 19.7% lower (P < 0.05)
than that of medium- and high-RFI animals respectively. However, there
was no difference in DMI and, consequently, in RFI on pasture among
animals classified as low, medium and high RFI. Accordingly, there is
evidence of re-ranking of animals for RFI performance tested in the
feedlot after weaning and, subsequently, on pasture. During the period
of enteric CH4 measurement in the feedlot and on pasture, the
DMI, neutral detergent-fibre intake and gross-energy intake of low-RFI
animals were lower than those of high-RFI animals, and low-RFI animals
exhibited greater DM and neutral detergent fibre digestibility only in
the feedlot. Enteric CH4 production did not differ between low- and high-RFI animals either in the feedlot (101 and 107 g CH4/day) or on pasture (101 and 95.9 g CH4/day). A significant difference in CH4 yield (CH4/kg DMI) was observed on pasture between animals with low and high RFI (17.6 and 13.7 g CH4/kg
DMI respectively). The results did not support the hypothesis that an
increase in feed efficiency, evaluated in growing animals in
feedlot-performance tests, decreases enteric CH4 production (g/day) proportionally to the lower DMI.
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