Effect of the feeding system on the fatty acid composition, expression of the Delta9-desaturase, Peroxisome Proliferator-Activated Receptor Alpha, Gamma, and Sterol Regulatory Element Binding Protein 1 genes in the semitendinous muscle of light lambs of the Rasa Aragonesa breed

Abstract

Background: Conjugated linoleic acids (CLAs) are receiving increasing attention because of their beneficial effects on human health, with milk and meat products derived from ruminants as important sources of CLA in the human diet. SCD gene is responsible for some of the variation in CLA concentration in adipose tissues, and PPARgamma, PPARalpha and SREBP1 genes are regulator of SCD gene. The aim of this work was to evaluate the effect of the feeding system on fatty acid composition, CLA content and relative gene expression of Delta9-desaturase (SCD), Peroxisome Proliferator-Activated Receptor Gamma (PPARgamma), Peroxisome Proliferator-Activated Receptor Alpha, (PPARalpha) and Sterol Regulatory Element Binding Protein (SREBP1) in Rasa Aragonesa light lambs in semitendinous muscle. Forty-four single-born male lambs were used to evaluate the effect of the feeding system, varying on an intensity gradient according to the use of concentrates: 1. grazing alfalfa, 2. grazing alfalfa with a supplement for lambs, 3. indoor lambs with grazing ewes and 4. drylot.

Results: Both grazing systems resulted in a higher concentration of vaccenic acid (VA), CLA, CLA/VA acid ratio, and a lower oleic content, oleic acid (C18:1)/stearic acid (C18:0) ratio, PUFA n-6/n-3 ratio and SCD expression compared to other diets. In addition feeding system affected the fatty acid composition and SCD expression, possibly due to CLA concentration or the PUFA n-6/n-3 ratio. Both expression of the SCD gene and the feeding system were important factors affecting CLA concentration in the animal's semitendinous muscle. PPARgamma, PPARalpha and SREBP1 expression seemed to be unaffected by the feeding system. Although no significant results were found, PPARgamma, PPARalpha and SREBP1 showed similar expression pattern as SCD. Moreover, the correlation results between SCD expression and PPARgamma (p < 0.01), as well as SREBP1 (p < 0.01) expression, may suggest that these genes were affecting SCD expression in a different way.

Conclusions: The data indicated that the feeding system is the main factor affecting the fatty acid composition and SCD gene expression, which is also affected by CLA and possibly by n-6/n-3 PUFAs.

Figure 1

Total intramuscular fat content (%) according to feeding system. ALF: Grazing Alfalfa; ALF+S: Grazing alfalfa with supplement for lambs; IND-GRE: Indoor lambs with grazing ewes; and IND: Indoors. Different subscripts differ with at least P < 0.05.

Figure 2

Mean fatty acid composition of the semitendinous muscle in Rasa Aragonesa lambs for each feeding system. A: Mean values of total satured (SFA), monounsatured (MUFA) and polyunsatured (PUFA) fatty acids, and n-3 and n-6 PUFA composition (expressed as the percentage of total fatty acids). B: Fatty acid ratios. ALF: Grazing Alfalfa; ALF+S: Grazing alfalfa with supplement for lambs; IND-GRE: Indoor lambs with grazing ewes; and IND: Indoors. Different subscripts differ with at least P < 0.05. The ratio of PUFA/SFA was calculated as (C18:2+C18:3+C20:4+C20:5+C22:4+C22:5+C22:6)/(C10:0+ C12:0+C14:0+C16:0+C18:0+ C20:0). The ratio of n-6/n-3 was calculated as (C18:2 n-6+C20:4 n-6+C22:4 n-6)/(C18:3 n-3+ C20:5 n-3+ C22:5 n-3+ C22:6 n-3.

Figure 3

Effect of feeding system on mRNA expression of SCD, PPARγ, SREBF1 and PPARα genes of Rasa Aragonesa lambs. ALF: Grazing Alfalfa; ALF+S: Grazing alfalfa with supplement for lambs; IND-GRE: Indoor lambs with grazing ewes; and IND: Indoors. Different subscripts differ with at least P < 0.05.