6 August 2013

4 minute read

Research staff at the Tecnological University of Lisbon have shed more light on the area of fat deposition and the role genetics and finishing system has to play in Alentejana and Barrosa bulls. 

Ana SH da Costa, Virgínia MR Pires, Carlos MGA Fontes and José A Mestre Prates gathered data from a pool of forty bulls of Portugese origin.  

An analysis was then undertaken looking at the differential between genetics and finishing diet on subcutaneous adipose tissue and longissmus lumborum. 

The team give a summary of their paper and findings below.

Background

Both genetic background and finishing system can alter fat deposition, thus indicating their influence on adipogenic and lipogenic factors. However, the molecular mechanisms underlying fat deposition and fatty acid composition in beef cattle are not fully understood.

This study aimed to assess the effect of breed and dietary silage level on the expression patterns of key genes controlling lipid metabolism in subcutaneous adipose tissue (SAT) and longissimus lumborum (LL) muscle of cattle.

To that purpose, forty bulls from two genetically diverse Portuguese bovine breeds with distinct maturity rates, Alentejana and Barrosã, were selected and fed either low (30 per cent maize silage/70 per cent concentrate) or high silage (70 per cent maize silage/30 per cent concentrate) diets.

Results

The results suggested that enhanced deposition of fatty acids in the SAT from Barrosã bulls, when compared to Alentejana, could be due to higher expression levels of lipogenesis (SCD and LPL) and β-oxidation (CRAT) related genes.

Our results also indicated that SREBF1 expression in the SAT is increased by feeding the low silage diet. Together, these results point out to a higher lipid turnover in the SAT of Barrosã bulls when compared to Alentejana.

In turn, lipid deposition in the LL muscle is related to the expression of adipogenic (PPARG and FABP4) and lipogenic (ACACA and SCD) genes.

The positive correlation between ACACA expression levels and total lipids, as well trans fatty acids, points to ACACA as a major player in intramuscular deposition in ruminants.

Moreover, results reinforce the role of FABP4 in intramuscular fat development and the SAT as the major site for lipid metabolism in ruminants.

Conclusions

The results herein presented suggest that, at 18 months old, Barrosã bulls might have more differentiated adipocytes and lipids deposited in SAT than Alentejana animals.

Moreover, both lipogenesis (SCD and LPL) and β-oxidation (CRAT) related genes had higher levels of mRNA in the SAT from Barrosã animals when compared to Alentejana bulls.

These data indicate a higher storage/removal ratio of TAG and a greater dynamics of lipid turnover in the SAT of Barrosã breed relative to Alentejana bulls.

The fatty acid deposition in the SAT is mainly influenced by dietary silage level, whereas the effect of breed is mostly associated with the expression level of the transcription factor SREBF1. Combined effects of breed and diet were obtained for the de novo fatty acid synthesis (ACACA) and fatty acid transport in adipocytes (FABP4) related genes, and the transcription factor PPARA mRNA levels.

In contrast to SAT, only a slight breed effect was obtained for muscle, with the expression levels of PPARG and CPT1B showing a tendency to be higher in Barrosã bulls. However, the low silage diet, relative to the high silage diet, increased the levels of FABP4 and ACACA mRNA and tended to decrease LPL expression in the muscle.

Taken together, the results herein presented show that lipid metabolism in SAT is more sensitive to breed than muscle, whereas lipid metabolism in the latter tissue appears to be mostly diet-dependent.

The differential gene expression patterns in SAT and muscle are likely responsible for the fatty acid partitioning between both tissues, thus reinforcing the prevailing role of SAT over intramuscular fat in the de novo fatty acid synthesis.

These findings provide evidence for breed- and tissue-specific variations in fatty acid content and composition of beef cattle, which can be explained, at least in part, by the expression of key adipogenic and lipogenic genes involved in lipid metabolism.

This insight into the molecular mechanisms underlying fat deposition in bovine SAT and muscle in different breed may contribute to the development of diet-based strategies to improve competitiveness of beef industry in order to satisfy consumers’ expectations.