Elsevier

Theriogenology

Volume 78, Issue 3, August 2012, Pages 632-645
Theriogenology

Research article
Oocyte and embryo production and quality after OPU-IVF in dairy heifers given diets varying in their n-6/n-3 fatty acid ratio

https://doi.org/10.1016/j.theriogenology.2012.03.009Get rights and content

Abstract

Dietary fat supplementation can improve oocyte quality in ruminants. The influence of the type of dietary fat on the number and quality of oocytes collected by ovum pick-up and on the production of embryos in vitro was investigated in Holstein heifers. Heifers were given hay plus one of two dietary supplements for 42 days. The supplements were linseed (L, rich in linolenic acid, C18:3n-3, n = 9) or soya bean (S, rich in linoleic acid, C18:2n-6, n = 9). Oocytes were collected by ovum pick-up (OPU) for 6 wks (2 sessions/wk) and morphologic quality assessed. Half the oocytes were frozen and the other half was used to produce embryos. Blood samples were analyzed for: insulin, insulin-like growth factor-1, glucose, non-esterified fatty acids, β-hydroxy butyrate and urea and the proportions of fatty acids. Neither growth rate nor plasma hormone and metabolite concentrations were affected by dietary supplement. However, L significantly increased the proportion of plasma C18:3n-3 while S significantly increased the proportion of C18:2n-6(P < 0.001). Neither oocyte characteristics (number, their quality and number fertilized and cleaved per heifer per session) nor embryo characteristics (number and quality per heifer per session) and embryo development stages were affected by dietary treatment. Real-time RT-PCR was performed on immature and mature cumulus-oocyte complexes (COC). Prostaglandin E synthase-1 expression increased in L compared to S heifers. In conclusion, the type of fatty acid did not modify the numbers of oocytes and embryos produced by OPU-IVF and their quality in dairy heifers. Upregulation of prostaglandin E synthase-1 may ensure sufficient PGE2 production for oocyte maturation even when its precursor is low.

Introduction

Ovarian follicle growth can be influenced by nutritional and metabolic status [1], [2], [3], [4]. This effect is mediated by changes in plasma metabolites and metabolic hormones, such as insulin and insulin-like growth factor-1 (IGF-1) [5], [6] and/or hormones and growth factors in follicular fluid [7]. Diet can also affect oocyte morphology [8], oocyte developmental capacity and embryo production. Many studies have illustrated the harmful effects of negative energy balance on these parameters in postpartum dairy cows [9]. While in non-lactating animals overfeeding has also been shown to be detrimental [10], [11], [12], [13] whereas dietary restriction especially in previously overfed animals could have a positive effect [5], [14], [15], [16], [17] on oocyte quality and embryo development.

In addition to an effect of feeding level, the composition of the diet can also modify oocyte and embryo production. For example, Sinclair, et al. [18] showed that in heifers, excessive levels of protein in the diet negatively affect the subsequent development of oocytes in vitro. Recently lipid supplementation in diets of dairy cattle has been used to boost energy intake [19]. Lipids contain 2 to 3 times more net energy than starch for the dairy cow [20] and limited quantities do not adversely modify rumen fermentation. Dietary fat supplementation influences reproduction through effects on follicle growth [21] and steroid production [22]. The choice of the type of lipid supplement is probably not anodyne since the component fatty acids can affect physiological processes either directly or indirectly. For example, linolenic acid (C18:3n-3) is the precursor for the series 3 prostaglandins and linoleic acid (C18:2n-6) for the series 2 prostaglandins and long chain polyunsaturated fatty acids (LCPUFA) can affect important cellular processes, such as membrane stability, gene expression cell adhesion and proliferation and intra- and intercellular transport [23].

During the periovulation period, prostaglandin E2 (PGE2) and progesterone are thought to be required for successful terminal differentiation of the cumulus-oocyte complex (COC) [24], [25], [26]. We have previously reported the coordinated induction of prostaglandin-endoperoxide synthase 2 (PTGS2) and prostaglandin E synthase 1 (PTGES1) expression in bovine COCs to promote PGE2 production during the maturation process [27], [28]. We have also reported the expression patterns of CYP11A1 and STAR (encoding cholesterol side chain cleavage cytochrome P450 and StAR protein, respectively), which are steroidogenesis-related enzymes, as well as the rising level of progesterone production in periconceptional COCs.

Therefore, the objective of the present study was to examine the effect of a short-term (42 days) dietary fat supplement (C18:2n-6 vs. C18:3n-3) given to dairy heifers on oocyte quality, oocyte developmental capacity, evaluated by in vitro embryo production and to investigate whether this is related to differences in relative abundance of transcripts coding for the enzymes involved in PGE2 and progesterone biosynthesis pathways.

Section snippets

Animals and housing

All experimental work was performed in an experimental farm of the French Union Nationale des Coopératives d'Elevage et d'Insémination Animale (UNCEIA), in Isère, in the southeast of France. Eighteen Holstein dairy heifers, 16 to 20 months old, average live weight (LW) 367 ± 8.2 kg and body condition score (BCS, on a scale from 0 = thin to 5 = fat [29]) 2.3 ± 0.1 were used for the study. Heifers were confirmed to be cyclic by rectal palpation before being introduced into the experimental farm

Growth rate and BCS

LW and BCS were not significantly different between the groups at the start of the experiment (LW, S, 382 ± 11.6 kg vs. L, 354 ± 11.6 kg, P > 0.05 and BCS, S, 2.3 ± 0.12 vs. L, 2.2 ± 0.12, P > 0.05). Growth rate during the experimental period was unaffected by diet (S, 0.93 ± 0.21 kg/day vs. L, 0.90 ± 0.21 kg/day, P > 0.05). Average BCS was also unaffected by dietary treatment (S, 2.7 ± 0.11 vs. L, 2.6 ± 0.11, P > 0.05) but increased with time from the beginning of the experiment to the end

Discussion

Although previous experiments have compared dietary supplements of marine oils (rich in docosahexaenoic and eicospentaenoic acids) with plant oils (variable FA profile), to our knowledge, the effect of specifically modifying the linoleic/linolenic acid ratio in the diets of dairy heifers, on oocyte and embryo production after OPU-IVF and gene expression of the enzymes involved in PGE2 and progesterone production have not been reported previously. Linoleic and linolenic acid are of particular

Acknowledgments

This work was supported by the National Research Agency (Réseau GENANIMAL, contract GA11) and by Apis - Gene. The authors wish to thank J. Arnault, K. Guélou, G. Valy, S. Ponchon, C. Gonzalez and C. Ficheux for their expert technical assistance throughout the experiment.

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