Dietary fat sources affect feed intake, digestibility, rumen microbial populations, energy partition and methane emissions in different beef cattle genotypes

Abstract

The mitigation of enteric methane emission in beef cattle production is important for reducing feed energy loss and increasing environmental sustainability. The main objective of this study was to evaluate the effect of different oilseeds included in fermented total mixed rations (whole soyabean seed (SBS, control), whole kapok seed (KPS) and cracked oil palm fruit (OPF)) on feed intake, digestibility, rumen microbial populations, energy partition and methane emissions in different cattle genotypes (Charolais crossbred v. Japanese Black crossbred). Three Charolais crossbred and three Japanese Black crossbred bulls were studied in a replicated 3×3 Latin square experimental design; genotypes were analysed in separate squares including three periods of 21 days each and three dietary oilseed treatments fed ad libitum. The cattle were placed in a metabolic cage equipped with a ventilated head box respiration system for evaluating digestibility and energy balance. As compared with Charolais crossbred individuals, Japanese Black crossbred bulls showed consistently lower dry matter intake (15.5%, P<0.01), metabolisable energy (ME) intake (13.8%, P<0.05), ME requirement for maintenance (10.3%; 386 v. 430 kJ/kg metabolic BW, respectively), faeces energy loss (19.2%, P<0.001) and enteric methane emissions (18.5%, P<0.001). However, these two genotypes did not differ in energy retention (ER) (P=0.80). Among the three dietary oilseed treatments, OPF exhibited higher NDF intake (P<0.01) and digestibility (P<0.01), which was associated with a larger (P<0.05) total number of bacteria in the rumen. In addition, the OPF diet contributed to higher ME intake and ER than that of the KPS diet, whereas the SBS diet presented intermediate values (P<0.05). The methane conversion factor of these crossbreds was not significantly affected by genotype (P>0.05) or diet (P>0.05) under the experimental conditions and ranged from 5.8% to 6.0% of gross energy intake. This value is lower than that reported by the Intergovernmental Panel on Climate Change (6.5%) for cattle fed with low-quality crop residues or by-products. Thus, our results imply that the Japanese Black crossbred cattle consume less feed and emits less enteric methane than the Charolais crossbred does, mainly owing to its lower ME requirement for maintenance. The OPF diet could be used to replace SBS for high beef production, although further studies are required to evaluate their application across a wide range of beef production systems.