Effect of dietary supplementation with Spirulina on the expressions of AANAT, ADRB3, BTG2 and FASN genes in the subcutaneous adipose and Longissimus dorsi muscle tissues of purebred and crossbred Australian sheep

<p><strong>Background:</strong> The demand for healthy, lean and consistent meat products containing low saturated fatty acid content and high quality polyunsaturated fatty acids (PUFA), especially long-chain (≥C₂₀) omega-3 PUFA, has increased in recent times. Fat deposition is altered by both the genetic background and dietary supplements, and this study aimed to assess the effect of dietary <i>Spirulina</i> supplementation levels on the mRNA expression patterns of genes controlling lipid metabolism in the subcutaneous adipose tissue (SAT) and <i>Longissimus dorsi</i> (<i>ld</i>) muscle of Australian crossbred sheep. </p> <p><strong>Methods:</strong> Twenty-four weaned lambs belonging to four breeds under the same management conditions were maintained on ryegrass pasture and fed three levels of <i>Spirulina</i> supplement (control, low and high). In terms of nutrient composition, <i>Spirulina</i> is a nutrient-rich supplement that contains all essential amino acids, vitamins and minerals. It also is a rich source of carotenoids and fatty acids, especially gamma-linolenic acid (GLA) that infer health benefits. After slaughter, subcutaneous adipose tissue (SAT) and <i>ld</i> samples were subjected to mRNA extraction and reverse transcription using quantitative polymerase chain reaction (RT-qPCR) to assess the mRNA expression levels of the <i>Aralkylamine N</i>-<i>acetyltransferase</i> (<i>AANAT</i>), <i>Adrenergic beta</i>-<i>3 receptor</i> (<i>ADRB3</i>), <i>B</i>-<i>cell translocation gene 2</i> (<i>BTG2</i>) and <i>Fatty acid synthase</i> (<i>FASN</i>) genes, which are associated with lipid metabolism. </p> <p> <strong>Results:</strong> Both low and high <i>Spirulina</i> supplementation levels strongly up-regulated the transcription of all the selected genes in both SAT and <i>ld</i> tissues (mostly in the subcutaneous adipose), but sheep breed and sex did not influence the gene expression patterns in these tissues. </p> <p><strong>Conclusions:</strong> The evidence indicates that high <i>Spirulina</i> supplementation level resulted in a decrease in intramuscular fat content in Australian purebred and crossbred sheep due to the enhanced production of melatonin in sheep muscle tissues and strong up-regulation of mRNA expression of <i>BTG2</i> in SAT which negatively affected fat deposition. In contrast, low <i>Spirulina</i> supplementation level strongly up-regulated the <i>ADRB3</i> and <i>FASN</i> genes responsible for fat production. These findings are consistent with the observed phenotypic data suggesting that low <i>Spirulina</i> supplementation level can increase lamb production, with higher long-chain PUFA content.</p>