The effect of dietary omega-3 and -6 polyunsaturated fatty acids on ovine ovarian function and the pre-implantation embryo

Hughes, Jaime (2011) The effect of dietary omega-3 and -6 polyunsaturated fatty acids on ovine ovarian function and the pre-implantation embryo. PhD thesis, University of Nottingham.

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Abstract

There is considerable interest in the beneficial role of dietary polyunsaturated fatty acids (PUFA) on reproduction in ruminants. Detailed information regarding the mechanisms behind this beneficial effect is limited. The main objective of this thesis was to test the effects of dietary supplementation with omega-3 (n-3) or -6 (n-6) PUFA on gene expression, fatty acid (FA) composition and steroidogenesis in granulosa and theca cells and pre-implantation embryo development.

A previous study in our laboratory reported increased follicular-fluid progesterone concentrations in ewes fed an n-3 compared to an n-6 PUFA-enriched diet, but detected no differential effect of n-3 and n-6 PUFA enriched high-density lipoproteins (HDL) on granulosa cell steroidogenesis in vitro. Also, n-6 PUFA enriched HDL reduced early embryo development, but in the absence of a net uptake of FA. In view of these observations it was hypothesised that (i) effects of n-3 PUFA on ovarian steroidogenesis are mediated by theca rather than granulosa cells and (ii) during embryo culture lipids are acquired solely from the albumin fraction of serum, so that albumin delivered n- 3 and n-6 PUFA would exert a greater differential effect on embryo development than either LDL or HDL delivered PUFA.

Initial investigations into granulosa cell gene expression profiles using an ovine gonad-targeted cDNA macroarray were unsuccessful, highlighted by subsequent qRTPCR analysis. A thorough investigation confirmed that inconsistencies were due to poor array hybridisation. In vitro data confirmed that n-3 PUFA, via delivery by HDL, increase progesterone production solely in theca cells and that this is associated with an increase in STAR transcript expression. We also demonstrate that albumin is the only serum fraction that leads to a net uptake of FA during embryo culture. PUFA enriched serum and albumin accelerated the development of embryos and increased the yield of morphologically poorer quality blastocysts with increased transcript expression for the antioxidant enzyme SOD1. Important differential effects of n-3 and n-6 PUFA on ovarian steroidogenesis acting solely on theca cells are identified, but differentially effects of PUFA on embryo development are less apparent.

Item Type:Thesis (PhD)
Supervisors:Lea, Richard
Sinclair, Kevin
Uncontrolled Keywords:polyunsaturated fatty acids, PUFA, cattle reproduction, steroidogenesis
Faculties/Schools:UK Campuses > Faculty of Medicine and Health Sciences > School of Veterinary Medicine and Science
ID Code:1800
Deposited By:Dr Jaime Hughes
Deposited On:18 Jan 2012 08:57
Last Modified:18 Jan 2012 08:57

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