Single Nucleotide Polymorphisms of the Ovine ADRB3 Gene in Crossbred Australian Sheep Supplemented with Spirulina (Arthrospira platensis) Cyanobacterial Microalgae

Abstract

The adrenergic-receptor beta3 (ADRB3) gene is an obesity gene that is involved in the regulation of energy balance and a variety of physiological functions by increasing lipolysis and thermogenesis. Spirulina (Arthrospira platensis) is a blue-green cyanobacterial alga containing 60-70% protein with an extensive history of human consumption, and more recently, inclusion in animal feeds. We had earlier demonstrated that low level oral supplementation by drenching prime lambs with 100 mL/head/day of 1g of Spirulina powder dissolved in 10 mL of water (10%wt:vol) increased live weight and body conformation measurements in Black Suffolk (BS) x Merino crossbred sheep. The hypothesis that genetics-nutrition interactions between sheep breeds with fewer mutations at the ADRB3 locus and an optimal Spirulina supplementation level will increase lean meat production was tested in the current study. Forty-eight crossbred Australian prime lambs sired by four rams of diverse breeds under the same pasture-based management conditions were subjected to a nine-week feeding trial with Spirulina, followed by genomic DNA extraction and single nucleotide polymorphism (SNP) analysis. Eleven SNPs in both the coding and noncoding regions of the ovine ADRB3 gene were detected. Nine of the SNPs were in exon I and two in the intron. Variations in SNP frequencies were highly significant (P <0.0001) between all sheep breeds. The maximum and minimum number of SNPs were found in purebred Merinos (4.83) and Black Suffolk x Merino (BS) crossbreds (1.67). In total, one indel and six transverse mutations were detected that resulted in six amino acid substitutions. BS crossbreds had the lowest frequency of mutation and amino acid substitutions in their population in agreement with our hypothesis. In conclusion, BS sheep genetics matched with low level (100 mL/head/day) of Spirulina supplementation can lead to higher meat production with less fat content in a typical pasture-based sheep production system.