Influence of feeding stearidonic acid (18:4n-3)-enriched soybean oil, as compared to conventional soybean oil, on tissue deposition of very long-chain omega-3 fatty acids in meat-type chickens

Abstract

In chickens, the desaturation of α-linolenic acid (ALA; 18:3n-3) to stearidonic acid (SDA; 18:4n-3) is considered to be rate-limiting for the hepatic conversion of ALA to very long-chain (VLC; i.e. >20 C) n-3 polyunsaturated fatty acids (PUFAs). Thus, we hypothesized that feeding broilers SDA plus ALA, as compared to ALA alone, would bypass this inefficient metabolic step and enrich meat with greater amounts of VLC n-3 PUFAs. Female Ross×Heritage broilers were fed mash diets containing 50g/kg of conventional soy oil (CON) from hatch until d 28. On d 29, they were divided into two groups and fed diets containing either 50g/kg CON or 50g/kg of SDA-enriched oil derived from the genetic modification of the soybean (SDASOY) until d 42. Final (42 d) body weights, as well as weight gains and feed conversion values from 29 to 35 d and 36 to 42 d, were not different (P>0.05) between treatments. Compared to the CON treatment, dietary SDASOY increased (P<0.01) total VLC n-3 PUFA contents of skinless and boneless breasts, tenders, and thighs by almost 3-fold. However, the SDASOY diet also contained more total n-3 fatty acids (ALA+SDA) than the CON diet (ALA only), and it was estimated that ALA and SDA were metabolized to VLC n-3 PUFAs and deposited into breast, tenders, and thigh meat with equal efficiency. Docosapentaenoic acid (DPA; 22:5n-3) was the predominant VLC n-3 PUFA in all three muscles, suggesting that another control point downstream of the initial hepatic Δ6-desaturase reaction was rate-limiting in the biosynthesis of DHA from ALA. Alternately, since broilers have the capability to convert ALA to DHA in the liver, it is likely that the capacity of the VLC n-3 PUFA biosynthetic pathway is simply not great enough to allow for the deposition of DHA into muscle at levels equal to those attained by direct dietary supplementation. It is also possible that, rather than undergoing elongation and desaturation, some of the ALA and SDA pool underwent β-oxidation in the liver, as suggested by others, while a large portion of each fatty acid was not metabolized and was transported out of the liver to other tissues, such as adipose. However, the relative hepatic expression of genes whose protein products are involved in fatty acid oxidation (as well as in desaturation and elongation or lipogenesis) were not significantly affected by dietary treatment or age.