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Dietary stimulation of insulin in post partum dairy cows has been found to enhance ovarian follicle development but to impair oocyte developmental competence. The objective of this study was to test the hypothesis that pregnancy rate would be improved by feeding a diet to stimulate higher insulin (H) until cows resumed ovarian cyclic activity after parturition, and then feeding a diet to lower insulin (L) during the mating period. Each diet was fed to 30 post partum dairy cows until their first rise in milk progesterone, when 15 cows in each group were transferred to the other diet (treatments HL and LH) and 15 cows in each group remained on their original diet (treatments HH and LL) until 120 days post partum. Treatments did not affect dry matter intake, milk yield and metabolisable energy balance. Plasma insulin concentration was elevated in cows fed on H compared with cows fed on L. Treatment did not affect days to first progesterone rise, first oestrus or first insemination. At 120 days post partum, 27% of cows on each of treatments HH, LL and LH were pregnant, but 60% of cows on treatment HL were pregnant (P=0.021). These findings support the concept that physiological relationships between insulin and the reproductive system vary according to stage of the reproductive cycle, and suggest that pregnancy rate can be enhanced by a two-diet strategy tailored to optimise responses before and after the first post partum ovulation.

Maternal B-vitamin status at conception can affect fertility and the health of offspring. This study details transcript expression for genes encoding key enzymes in the linked methionine/folate cycles in the bovine oocyte, somatic cells of the ovarian follicle and pre-implantation embryo. Transcripts for all 12 enzymes that were studied and for the two folate receptors (FOLR1 and FOLR2) and reduced folate carrier (SLC19A1) were expressed in liver cells, but transcripts for betaine-homocysteine methyltransferase and methionine adenosyl transferase 1A were absent in all ovarian cells, and transcripts for FOLR2 were absent in embryonic cells. Transcripts for glycine methyltransferase were also absent/weak in cumulus and granulosa cells. The absence of these enzymes could have a profound effect on single-carbon metabolism within the ovary and pre-implantation embryo. Immunocytochemical analysis revealed SLC19A1 protein expression on the plasma and basal-lateral membranes of the pre-implantation embryo. The folate antagonist methotrexate (MTX) enters the cell via SLC19A1, and in the current study, MTX inclusion in bovine/ovine culture media at either 1 or 10 μM from the 1-cell stage inhibited embryo development beyond the 8-cell stage. Hypoxanthine and thymidine (100 μM) increased the proportion of embryos that developed to blastocysts, but the cell number was reduced by 20%. The reduced uptake of [³⁵S] methionine into intra-cellular S-adenosylmethionine and S-adenosylhomocysteine pools, together with reduced uptake of glutamate and tryptophan, was consistent with depleted intra-cellular pools of reduced folates. These data provide an insight into the importance of maternal dietary folate/B-vitamin status during the peri-conceptional period.

This study assessed the interactive effects of carbohydrate type (fibre vs starch) and fatty acid (FA) supplementation (0% vs 6% calcium soaps of palm oil FA) on the post-fertilisation development of oocytes recovered from low and moderate body condition score (BCS) heifers. A secondary objective was to compare the FA composition of plasma to that of granulosa cells (GCs) and cumulus–oocyte complexes (COCs) from these animals, and to relate these findings to the developmental potential of oocytes. Plasma, GCs and COCs were recovered from 32 heifers on day 5 of a synchronised oestrous cycle for FA analyses. Oocytes were also recovered on days 10 and 15 of the same cycle after short-term ovarian stimulation (FSH + GnRH), and matured, fertilised and cultured to the blastocyst stage in vitro. High levels of dietary starch increased (P < 0.01) plasma insulin but, together with dietary FA, reduced (P < 0.05) blastocyst yields in low, but not in moderate, BCS heifers. Diet-induced alterations to the FA content of plasma were less apparent in GCs and COCs. In summary, although dietary lipids increased the FA content of COCs, the selective uptake of saturated FAs at the expense of mainly polyunsaturated FAs within the follicular compartment ensured that the FA composition of COCs was largely unaffected by diet. However, the concentration of saturated FAs within COCs was inherently high, and so further increases in FA content may have impaired post-fertilisation development. The data establish a robust nutritional framework for more detailed studies into the mechanistic effects of dietary composition on the post-fertilisation developmental potential of oocytes.

The evidence that omega-3 (n-3) and -6 (n-6) polyunsaturated fatty acids (PUFAs) have differential effects on ovarian function, oocytes and embryo quality is inconsistent. We report on the effects of n-3 versus n-6 PUFA-enriched diets fed to 36 ewes over a 6-week period, prior to ovarian stimulation and follicular aspiration, on ovarian steroidogenic parameters and embryo quality. Follicle number and size were unaltered by diet, but follicular-fluid progesterone concentrations were greater in n-3 PUFA-fed ewes than in n-6 PUFA-fed ewes. The percentage of saturated FAs (mostly stearic acid) was greater in oocytes than in either granulosa cells or plasma, indicating selective uptake and/or de novo synthesis of saturated FAs at the expense of PUFAs by oocytes. High-density lipoproteins (HDLs) fractionated from sera of these ewes increased granulosa cell proliferation and steroidogenesis relative to the FA-free BSA control during culture, but there was no differential effect of n-3 and n-6 PUFAs on either oestradiol or progesterone production. HDL was ineffective in delivering FAs to embryos during culture, although n-6 PUFA HDL reduced embryo development. All blastocysts, irrespective of the treatment, contained high levels of unsaturated FAs, in particular linoleic acid. Transcripts for HDL and low-density lipoprotein (LDL) receptors (SCARB1 and LDLR) and stearoyl-CoA desaturase (SCD) are reported in sheep embryos. HDL reduced the expression of transcripts for LDLR and SCD relative to the BSA control. The data support a differential effect of n-3 and n-6 PUFAs on ovarian steroidogenesis and pre-implantation development, the latter in the absence of a net uptake of FAs.

Abstract

Reproductive management in cattle requires the synchrony of follicle development and oestrus before insemination. However, ovulation of follicles that have not undergone normal physiological maturation can lead to suboptimal luteal function. Here, we investigated the expression of a targeted set of 47 genes in (a) a first-wave vs final-wave dominant follicle (DF; the latter destined to ovulate spontaneously) and (b) 6-day-old corpora lutea (CLs) following either spontaneous ovulation or induced ovulation of a first-wave DF to ascertain their functional significance for competent CL development. Both the mass and progesterone-synthesising capacity of a CL formed following induced ovulation of a first-wave DF were impaired. These impaired CLs had reduced expression of steroidogenic enzymes (e.g. STAR and HSD3B1), luteotrophic receptors (LHCGR) and angiogenic regulators (e.g. VEGFA) and increased expression of BMP2 (linked to luteolysis). Relative to final-wave DFs, characteristic features of first-wave DFs included reduced oestradiol concentrations and a reduced oestradiol:progesterone ratio in the face of increased expression of key steroidogenic enzymes (i.e. CYP11A1, HSD3B1 and CYP19A1) in granulosa cells and reduced expression of the HDL receptor SCARB1 in thecal cells. Transcripts for further components of the TGF and IGF systems (e.g. INHA, INHBA, IGF2R and IGFBP2) varied between the first- and final-wave DFs. These results highlight the importance of hormones such as progesterone interacting with local components of both the TGF and IGF systems to affect the maturation of the ovulatory follicle and functional competency of the subsequent CL.

The effects of in vitro culture systems for sheep zygotes on subsequent fetal growth and development to day 61 and day 125 of gestation were studied. Zygotes recovered from superovulated Scottish Blackface ewes approximately 36 h after intrauterine insemination using semen from a single Suffolk sire were cultured for 5 days in (a) a granulosa cell co-culture system (co-culture); (b) synthetic oviductal fluid medium without serum (SOF−); and (c) synthetic oviductal fluid medium supplemented with human serum (SOF+). Control embryos were recovered from superovulated donor ewes at day 6 after oestrus. Embryos were transferred at day 6 to synchronous Scottish Blackface recipient ewes. In total, 146 gravid uteri were recovered, comprising 97 at day 61 (20 co-culture, 27 SOF−, 25 SOF+ and 25 control) and 49 at day 125 (13 co-culture, 8 SOF−, 6 SOF+ and 22 control) of gestation. Fetuses derived from co-cultured embryos were 14% heavier (P < 0.01) by day 61 of gestation than those derived from control embryos. Growth coefficients derived from the linear allometric equation log _e y = log _e a + b log _e x (where y = organ mass; x = fetal mass) were significantly greater (P < 0.05) for liver, heart, kidneys and plantaris muscle in fetuses derived from co-cultured embryos, and for liver in fetuses derived from SOF+ embryos than those for control fetuses. Fetuses derived from co-cultured embryos were 34% heavier (P < 0.001) and fetuses derived from SOF+ embryos were 18% heavier (P < 0.01) by day 125 of gestation than those derived from control embryos. Growth coefficients for liver and heart for fetuses derived from co-culture and SOF+ embryos were also significantly greater (P < 0.05) at this stage of gestation than those for control group fetuses. In contrast, allometric coefficients for these organs in fetuses derived from embryos cultured in SOF without serum supplementation were not different from those for controls. Excessive volumes of amniotic fluid (polyhydramnios) were observed in 23% of conceptuses derived from co-cultured embryos. In vitro embryo culture can significantly influence fetal growth and this study provides quantitative evidence of major shifts in the patterns of organ and tissue development.