Cheryl Ashworth

Nutritional effects on oocyte and embryo development in mammals: implications for reproductive efficiency and environmental sustainability

The environment in which a breeding female lives prior to conception and during the early stages of her pregnancy has striking effects on oocytes developing in the ovarian follicle and on early embryos in the reproductive tract. Of the various environmental factors known to affect oocyte and embryo development, altered nutrition during this critical period has been particularly well studied. Alterations in the quantity of food consumed or the composition of the diet imposed solely during the pre-mating period affect oocyte maturity, blastocyst yield, prenatal survival and the number of offspring born alive. Importantly, nutrition at this time also affects the quality of embryos and resultant offspring, with increasing evidence from a variety of species showing that peri-conception nutrition can alter behaviour, cardiovascular function and reproductive function throughout post-natal life. In livestock species, it is important to devise nutritional strategies that improve reproductive efficiency and the quality of offspring but that do not add to the environmental footprint of the production system and which recognize likely changes in feedstuff availability arising from predicted changes in climate.

The influence of variation in embryo stage and maternal hormone profiles on embryo survival in farm animals

Abstract The physiological mechanisms that lead to the requirement for synchronous embryo transfer have been defined in some species, particularly the sheep. In mated animals, variation in hormone profile and embryo stage have been shown to be sufficient to cause some embryo loss, perhaps by generating an asynchronous relationship. During procedures of embryo transfer, there may be additional divergence between hormone profile and embryo stage. It may be beneficial to supply hormones to recipients and to transfer embryos at a particular stage of development at a precise interval after initiation of this treatment.

Micronutrients in fetal growth and development

The roles that the different vitamins and minerals play in fetal growth and development are reviewed, primarily with respect to growth and differentiation in humans; but, as appropriate, data provided from animal and cellular studies are also considered.

Effects of maternal vitamin A status on fetal heart and lung: changes in expression of key developmental genes

Vitamin A is required during pregnancy for fetal lung development. These experiments monitored fetal lung morphology in normal and vitamin A-deficient rats. The expression of elastin and the growth arrest-specific gene 6 ( gas6) in fetal and neonatal hearts and lungs was assessed by Northern blotting. In normal-fed rats, elastin and gas6 were expressed in the fetal lung and heart from day 19 of gestation up to day 2 postnatally. Maternal vitamin A deficiency altered fetal lung development. On day 20, the bronchial passageways were less developed and showed reduced staining for elastic fibers, and in the neonates, the relative air space and the size of the sacculi were reduced. In the fetal lung, the mRNAs for elastin and gas6 were reduced to 56 and 68% of the control values, respectively. In the fetal heart, the mRNA for elastin was reduced to 64% of the control value, whereas gas6 was increased twofold. In the neonate, there was no change in elastin expression in the lung or heart, but gas6 expression in the heart was increased twofold. These results suggest that, in the pregnant rat, vitamin A deficiency may retard fetal lung development or influence the differentiation of critical cell lines. The changes in elastin and gas6 expression may be used to identify the cell types affected.

Moderate maternal vitamin A deficiency affects perinatal organ growth and development in rats.

Vitamin A deficiency during pregnancy is associated with detrimental effects in the offspring. We have developed a rat model to examine specific effects of maternal vitamin A status on perinatal growth and development. A total of 54 female rats were fed a vitamin A-free (VAF), -marginal (VAM) or -sufficient (VAS) diet from weaning until mating (at 7 weeks) and throughout pregnancy. Half of the rats in each group were injected with a single large dose of vitamin A on day 10 of pregnancy. Fetal and neonatal samples were taken on day 20 of pregnancy and the day of birth respectively. Maternal plasma retinol concentrations on day 20 and at birth were 50% and 30% lower in the VAF and VAM when compared to the VAS group. Fetal weight and survival did not differ between groups although placental:fetal ratio was higher in the VAF group than in the VAS group (0.195 (SE 0.005) v. 0.175 (SE 0.004), P < 0.05). Rats fed the VAF diet gave birth at 23.5 d, an average of 1 d later than the other groups, and had lower number of live neonates at birth. Fetal liver, heart and lung weights relative to total body weight were lower in the VAF group and had altered growth trajectories. In neonates, only the relative lung weight was reduced. In addition, an increased protein:DNA ratio indicated hypertrophy in fetal kidneys. Vitamin A injection had no additional effect on length of gestation and fetal or neonatal number. However, injection increased relative fetal organ weights in the VAF group but did not alter the effects of vitamin A deficiency in the neonate. These data suggest that chronic vitamin A deficiency during pregnancy compromises liver, heart and kidney and impairs lung growth and development during the last few days of gestation and reduces number of live neonates at birth.

Beneficial effects of a high fibre diet on oocyte maturity and embryo survival in gilts

The present study examined the effects of feeding gilts a high fibre diet from the third post-pubertal oestrus until either day 19 of the same cycle or insemination at the following oestrus on oocyte maturity, embryo survival and associated changes in reproductive hormone concentrations. Gilts fed with the high fibre diet had lower circulating oestradiol concentrations on days 17, 18 and 19 of the cycle and increased LH pulse frequency on day 18. More oocytes recovered on day 19 from gilts receiving the high fibre diet were at metaphase II after 46-h culture in medium containing 10% of their own follicular fluid, despite fewer large (>7 mm) follicles in these gilts when compared with control animals. There was no effect of diet on ovulation rate, corpora lutea size or progesterone concentrations on days 10-12 after insemination, but embryo survival on days 27-29 after insemination was higher in gilts that received the high fibre diet. This study demonstrates that a high fibre diet that increases embryo survival also improves oocyte maturity and provides information on endocrine correlates that may shed light on underlying mechanisms.

A genome-wide linkage analysis for reproductive traits in F2 Large White × Meishan cross gilts

Female reproductive performance traits in pigs have low heritabilities thus limiting improvement through traditional selective breeding programmes. However, there is substantial genetic variation found between pig breeds with the Chinese Meishan being one of the most prolific pig breeds known. In this study, three cohorts of Large White × Meishan F2 cross-bred pigs were analysed to identify quantitative trait loci (QTL) with effects on reproductive traits, including ovulation rate, teat number, litter size, total born alive and prenatal survival. A total of 307 individuals were genotyped for 174 genetic markers across the genome. The genome-wide analysis of the trait-recorded F2 gilts in their first parity/litter revealed one QTL for teat number significant at the genome level and a total of 12 QTL, which are significant at the chromosome-wide level, for: litter size (three QTL), total born alive (two QTL), ovulation rate (four QTL), prenatal survival (one QTL) and teat number (two QTL). Further support for eight of these QTL is provided by results from other studies. Four of these 12 QTL were mapped for the first time in this study: on SSC15 for ovulation rate and on SSC18 for teat number, ovulation rate and litter size.

Effects of cobalt/vitamin B12 status in ewes on ovum development and lamb viability at birth

Scottish Blackface ewes from cobalt-deficient farmland were fed a diet containing 0.06 mg cobalt per kg dry matter from approximately 30 days before embryo recovery/transfer until lambing. Ewes remained untreated (-Co; n = 82) or were given an intraruminal cobalt-containing bolus to compensate for the dietary deficit (+Co; n = 82). Ewes used as embryo donors (-Co, n = 17; +Co, n = 16) were artificially inseminated with semen from a single Suffolk sire. Day 6 embryos obtained from -Co and +Co donors were transferred in singleton to -Co and +Co recipients in a 2 x 2 factorial-designed experiment to determine the effects of cobalt/vitamin B12 status during the periconception period (factor 1) and pregnancy (factor 2) on lamb viability at birth. Mean (+/- s.e.m.) circulating concentrations of vitamin B12 in -Co and +Co donors at ovum recovery were 182 +/- 10 and 1288 +/- 64 pmol L(-1), respectively (P < 0.001), and the number of corpora lutea per ewe ovulating was 9.9 +/- 1.6 and 14.4 +/- 1.3, respectively (P < 0.05). Treatment did not affect the proportion of recovered ova that contained >32 cells (viable) or the median stage of development (late morula), but viable ova recovered from -Co v. +Co ewes had a better morphological grade (2.0 +/- 0.1 v. 2.20 +/- 0.04, respectively; P < 0.01). There was no effect of treatment on the proportion of recipient ewes that became pregnant. Circulating concentrations of vitamin B12 were lower in -Co than +Co ewes during pregnancy (P < 0.001) and at birth in lambs born to -Co ewes compared with those born to +Co ewes (P < 0.001). There was no effect of donor or recipient cobalt/vitamin B12 status on lamb birthweight, neonatal vigour or neonatal rectal temperatures, but lambs derived from +Co v. -Co embryo donors were more active in the first 3 days after birth (P < 0.05). Results show that sub-clinical cobalt/vitamin B12 deficiency reduces ovulatory response in superovulated ewes and that periconception nutrition can affect neonatal lamb behaviour.

Effect of inclusion of serum and granulocyte–macrophage colony stimulating factor on secretion of interferon-τ during the in vitro culture of ovine embryos

In each of three experiments, in vitro-matured and -fertilised zygotes were cultured to Day 7 post insemination in synthetic oviductal fluid (SOF). In Experiment 1, zygotes were cultured in groups in either SOF plus albumin (SOFA) or serum (SOFS) and then blastocysts were cultured individually for a further 24 h without a change of media. In Experiment 2, zygotes were cultured in groups using a 2 x 2 factorial design in SOFA or SOFS, with or without recombinant ovine granulocyte-macrophage colony stimulating factor (GM-CSF; 5 ng mL(-1)). Blastocysts were then cultured individually using a split-plot design in SOFA or SOFS with or without GM-CSF. In Experiment 3, zygotes were cultured in SOFA in which GM-CSF was absent (A) or present (P) during Days 1-3, Days 3-5 or Days 5-7 of IVC in six combinations as follows: AAA, AAP, APP, PPP, PPA and PAA. Serum or GM-CSF increased secretion of interferon (IFN)-tau in Experiments 1 and 2 both between Days 5 and 7 of group culture and during individual culture. Secretion of IFN-tau during individual culture was determined by the medium in which embryos were group cultured and the effects of GM-CSF and serum were not additive. In Experiment 3, the presence of GM-CSF between Days 1 and 3 of culture was responsible for stimulation of secretion of IFN-tau between Days 5 and 7; IFN-tau secretion was detected as early as Day 3 post insemination.

Pre-natal social stress and post-natal pain affect the developing pig reproductive axis

This study assessed the effect of pre-natal social stress and post-natal pain on the reproductive development of young (approximately day 40) pigs. Male pigs carried by sows that were stressed by mixing with unfamiliar older sows for two 1-week periods during mid-pregnancy had lower plasma testosterone (0.54 vs 0.86 ng/ml, S.E.D.=0.11; P=0.014) and oestradiol (E(2); 22.9 vs 38.7 pg/ml, S.E.D.=7.80; P=0.021) concentrations compared with males carried by unstressed control sows. Although there was no effect of pre-natal stress on female E(2) concentrations, female pigs carried by stressed sows had fewer primordial ovarian follicles (log -4.32/μm(2) vs -4.00/μm(2), s.e.d.=0.136; P=0.027). Tail amputation on day 3 after birth reduced E(2) concentrations in female (4.78 vs 6.84 pg/ml, s.e.d.=0.86; P=0.03) and in male (25.6 vs 34.9 pg/ml, S.E.D.=3.56; P=0.021) pigs and reduced both testis weight (0.09% of body weight vs 0.10% of body weight, S.E.D.=0.003; P=0.01) and the percentage of proliferating Leydig cells (1.97 vs 2.12, S.E.D.=0.114; P=0.036) compared with sham-amputated littermate controls. There was a significant (P=0.036) interaction between the effects of pre-natal stress and post-natal pain on testicular expression of the steroidogenic enzyme 17α-hydroxylase, such that amputation increased expression in pigs born to control sows, but reduced expression in animals born to stressed sows. This study shows that stressful procedures associated with routine animal husbandry can disrupt the developing reproductive axis.