The effect of Karoo browse and veldt feeding on long-chain and volatile fatty acid components in lamb

Abstract

A uniform group of typical Dorper lambs were obtained from a breeding farm in Upington in the Northern Cape Province of the Republic of South Africa. The sheep were randomly allocated into two groups; one herd was raised on Karoo browse veldt, and the other group grazed Karoo grass veldt. Both groups consisted of 5 ewes and 5 wethers. Lambs were allowed to graze for a period of ninety days at an initial live mass of approximately 27 kg in order to reach an average target live mass of 40 kg. Fat percentage and subcutaneous fat thickness of lambs did not differ significantly between those from Karoo browse veldt or Karoo grass veldt. Subcutaneous adipose tissue samples from lambs from Karoo grass veldt contained significantly higher molar concentrations of oleic acid (C18:1(n-9) cis) and significantly lower molar concentrations of myristic acid (C14:0) and linoleic acid (C18:2(n-6)) compared to subcutaneous fat tissue samples from those from Karoo browse veldt. The subcutaneous fat of lambs from Karoo browse veldt contained higher gravimetric concentrations of lauric acid (C12:0) compared to the subcutaneous fat of lambs reared on Karoo grass veldt. The subcutaneous fat from lambs from Karoo browse veldt displayed marginally higher saturated fatty acid to unsaturated fatty acid ratios compared to subcutaneous adipose tissue samples from those from Karoo grass veldt. Subcutaneous fat samples of lambs from Karoo browse veldt contained

significantly lower concentrations of monounsaturated fatty acids and significantly higher saturated fatty acid concentrations in comparison to the subcutaneous adipose tissue of lambs from Karoo grass veldt (P < 0.05). Subcutaneous fat of lambs from Karoo grass veldt displayed numerically higher cis fatty acid to trans fatty acid ratios. Interesting differences in longer-chain fatty acids (> C20) were discovered between dietary treatments. Gondoic acid (C20:1) was present at significantly higher gravimetric proportions in the fat of ewes from both Karoo browse veldt and Karoo grass veldt compared to wethers and was significantly higher in adipose tissue samples of animals reared on Karoo grass veldt (P < 0.05). The subcutaneous fat of lambs from Karoo grass veldt contained significantly higher molar proportions of behenic acid (C22:0) compared to the subcutaneous fat samples of lambs from Karoo browse veldt (P < 0.05). Erucic acid (C22:1(n-9)) was significantly higher in the oesophageal samples obtained from Karoo grass veldt compared to oesophageal samples from lambs that had grazed Karoo browse veldt (P < 0.05). Lignoceric acid (C24:0) was present in oesophageal samples, while it was absent in the samples from subcutaneous adipose tissue. The rate at which one fatty acid is deposited from the diet into subcutaneous adipose tissue compared to the rate at which a fatty acid is synthesized de novo can explain differences in fatty acid metabolism between different diets. The relation between dietary and tissue fatty acids displayed significant interactions between diet and sex for the ratio of C18:3(n-3)/ C16:0 (P < 0.05). Animal fatty acid metabolism did not differ significantly between Karoo browse veldt and Karoo grass veldt in this study (P < 0.05). The application of comprehensive gas chromatography time of flight mass spectrometry identified 3- methylthio-2-butanone as a potential marker for Karoo lamb in raw meat samples. Caryophyllene was present in three of the five Karoo grass-fed lamb samples. β-Caryophyllene may serve as a biomarker in meat to designate a grass diet (Priolo et al., 2004). Cymene was present in each of the Karoo browse and Karoo grass-fed lamb samples and may serve as a potential marker.