Lab partners: oocytes, embryos and company. A personal view on aspects of oocyte maturation and the development of monozygotic twins

The present review addresses the oocyte and the preimplantation embryo, and is intended to highlight the underlying principle of the "nature versus/and nurture" question. Given the diversity in mammalian oocyte maturation, this review will not be comprehensive but instead will focus on the porcine oocyte. Historically, oogenesis was seen as the development of a passive cell nursed and determined by its somatic compartment. Currently, the advanced analysis of the cross-talk between the maternal environment and the oocyte shows a more balanced relationship: Granulosa cells nurse the oocyte, whereas the latter secretes diffusible factors that regulate proliferation and differentiation of the granulosa cells. Signal molecules of the granulosa cells either prevent the precocious initiation of meiotic maturation or enable oocyte maturation following hormonal stimulation. A similar question emerges in research on monozygotic twins or multiples: In Greek and medieval times, twins were not seen as the result of the common course of nature but were classified as faults. This seems still valid today for the rare and until now mainly unknown genesis of facultative monozygotic twins in mammals. Monozygotic twins are unique subjects for studies of the conceptus-maternal dialogue, the intra-pair similarity and dissimilarity, and the elucidation of the interplay between nature and nurture. In the course of in vivo collections of preimplantation sheep embryos and experiments on embryo splitting and other microsurgical interventions we recorded observations on double blastocysts within a single zona pellucida, double inner cell masses in zona-enclosed blastocysts and double germinal discs in elongating embryos. On the basis of these observations we add some pieces to the puzzle of the post-zygotic genesis of monozygotic twins and on maternal influences on the developing conceptus.

The degree of maternal nutrient restriction during late gestation influences the growth and endocrine profiles of offspring from beef cows

ContextCow–calf operations in Argentina are managed under extensive grazing condition and the quality of forages is often poor during the second half of gestation. The severity of nutrient restriction in bovine gestation, caused by seasonal pasture production, often results in poor production traits in progeny.AimsThe objective of the current study was to determine whether different levels of maternal nutrient intake in beef cows during late gestation affect fetal and postnatal growth, glucose metabolism, and insulin-like growth factor 1 (IGF1) concentrations in offspring of beef cattle.MethodsAt 180±4 days of gestation, multiparous Angus cows (n=56) were blocked by bodyweight (BW) and expected calving date, and assigned to pens (2 or 3 cows/pen). Pens (n=8 per treatment) were then randomly assigned to the following treatments: severely restricted (SR; 50% of net energy and 58% of CP requirements), moderately restricted (MR; 75% of net energy and 85% of CP requirements), or control (CON; 100% of net energy and 116% of CP requirements). Pen was the experimental unit and data were analysed by ANOVA or repeated measures analysis, as appropriate. After calving, all cows were managed in a single group until weaning.Key resultsCow BW and body condition score decreased as nutritional restriction increased (P<0.05). At parturition, birth weight of calves from SR dams and MR dams was lower than that of calves from CON dams (P=0.05; 4.9kg and 2.1kg respectively). Average daily gain of calves from birth to 24 days of age was higher (P=0.01) in calves from SR dams than in calves from CON and MR dams. Calves from MR dams were lighter (P=0.04) than were calves from SR and CON dams at weaning. Treatments did not affect milk production or composition (P>0.10) or glucose–insulin metabolism of offspring during lactation (P>0.10). Concentration of IGF1 tended to be lower in MR progeny than in SR and CON progeny during lactation (P=0.09).ConclusionsLate gestation maternal nutrient restriction, irrespective of the severity of the restriction, decreased birth weight of offspring; however, severe nutrient restriction induced early postnatal compensatory growth.ImplicationsThe severe nutritional restriction produced calves with weaning weights indistinguishable from the control cows due to early postnatal compensatory growth. However, the longer-term effects of nutritional restriction of the dam in the second half of pregnancy on metabolic and reproductive performance in replacement heifers or meat production/quality in steers is yet to be determined.

Age at First Gestation in Beef Heifers Affects Fetal and Postnatal Growth, Glucose Metabolism and IGF1 Concentration

Simple Summary

In cow-calf operations, replacement heifers are bred to calve at 2 years of age or older. However, as beef production has become more intensive during the last 20 years, an increasing number of farmers have lowered the age at first service. Numerous studies have focused on determining the optimum reproductive development of beef heifers to ensure a maximum pregnancy rate. Maternal age during gestation has been suggested to be an important influence on the nutritional environment for the embryo and fetal growth. No studies have been conducted to determine the possible effects of heifer age at first gestation on fetal and postnatal growth and development. This study aimed to determine the effects of age at first gestation on offspring growth performance, glucose metabolism and insulin-like growth factor 1 concentration from birth to weaning of calves from adult cows and heifers at 15 or 27 months of service. First-breed heifers produce lighter progeny at birth than mature cows, and calves from younger heifers were lighter at weaning than calves from older heifers. Milk production was similar between heifers and lower than that from adult cows. Age at first gestation may affect offspring postnatal growth performance, glucose metabolism and IGF1 concentration.

Abstract

This study aimed to determine the effects of age at first gestation on offspring growth performance, glucose metabolism, and IGF1 concentration. Heifers impregnated by AI from a single bull at 15 months of age (15 M, n = 20), or 27 months of age (27 M, n = 20), and multiparous cows (adult, n = 20) were used. Dams from all groups were managed in a single group during gestation and lactation. Gestational length was longer in the 15 M and 27 M than in adult dams (p = 0.009). Bodyweight at birth, at weaning and ADG during lactation were higher in calves from adult dams than in those from 27 M dams, and higher in calves from the latter than in 15 M calves (p < 0.001). Calves from 15 M dams had an increased head circumference/BW ratio compared to calves from 27 M dams, while calves from this latter group had an increased ratio compared to calves from adults (p = 0.005). Body mass index was greater in calves from adults than in those from 15 M and 27 M dams (p = 0.002). Milk production from 15 M and 27 M dams was similar but lower than that from adults (p = 0.03). Calves born from adult dams had greater blood glucose concentrations than those from 15 M and 27 M dams (p < 0.05). Serum IGF1 concentrations were higher in calves from adults than in calves from 15 M and 27 M dams (p = 0.01). This study showed that age at first gestation affects offspring postnatal growth performance, glucose metabolism and IGF1 concentration.

Genome-wide association analyses identify genotype-by-environment interactions of growth traits in Simmental cattle

Understanding genotype-by-environment interactions (G × E) is crucial to understand environmental adaptation in mammals and improve the sustainability of agricultural production. Here, we present an extensive study investigating the interaction of genome-wide SNP markers with a vast assortment of environmental variables and searching for SNPs controlling phenotypic variance (vQTL) using a large beef cattle dataset. We showed that G × E contribute 10.1%, 3.8%, and 2.8% of the phenotypic variance of birth weight, weaning weight, and yearling weight, respectively. G × E genome-wide association analysis (GWAA) detected a large number of G × E loci affecting growth traits, which the traditional GWAA did not detect, showing that functional loci may have non-additive genetic effects regardless of differences in genotypic means. Further, variance-heterogeneity GWAA detected loci enriched with G × E effects without requiring prior knowledge of the interacting environmental factors. Functional annotation and pathway analysis of G × E genes revealed biological mechanisms by which cattle respond to changes in their environment, such as neurotransmitter activity, hypoxia-induced processes, keratinization, hormone, thermogenic and immune pathways. We unraveled the relevance and complexity of the genetic basis of G × E underlying growth traits, providing new insights into how different environmental conditions interact with specific genes influencing adaptation and productivity in beef cattle and potentially across mammals.

Effects of inorganic selenium injection on the performance of beef cows and their subsequent calves

Sixty-seven pregnant Angus cows and their subsequent calves were used in a randomized design to evaluate the effect of inorganic Se injection from 80 d of gestation until weaning on cow reproductive parameters, BW and BCS evolution, milk yield and quality, calf growth and calf hematology parameters. The treatments were as follows: 1) Se+: cows were administered Se as sodium selenite at doses of 0.05 mg/Kg of BW at 80, 140, 200, 260 d of gestation and 30, 90, 150 and 240 d of lactation. Calves from Se + cows were Se as sodium selenite subcutaneously injected with a dose of 0.05 mg/Kg of BW at 70, 104, 144 d of age; 2) Control: cows and calves were administered sterile NaCl solution (9 g/l) at the same volume and intervals as Se + treatment. At the start of the experiment, forage Se concentration was 58.6 ppb ± 7.6 ppb, and cow whole blood Se concentration was similar (P > 0.10) between treatments (Se+, 29.3 ± 0.3 ppb; Control, 28.1 ± 0.5 ppb). After Se injection, cow whole blood Se concentration was increased (P < 0.01) in Se + cows in relation to control cows until the end of the experiment. Calf whole blood Se concentration was increased (P < 0.01) at birth and 30 d of age in calves from Se + cows compared to calves from Control cows. However, calf whole blood Se concentration was not different (P > 0.10) between treatments at d 70 after birth. After the first Se injection (70 d of age), calf whole blood Se concentration was increased (P < 0.01) at 104 and 144 d of age in calves from Se + cows compared to calves from Control cows. Cow BW and BCS did not differ (P > 0.10) between treatments throughout the experiment. Ovarian follicle diameter measured by ultrasound 47 d postpartum was greater (P = 0.03) in Se + cows compared to Control cows. Pregnancy rate to fixed time artificial insemination (FTAI), overall pregnancy rate (P > 0.10) and pregnancy loss (P = 0.19) did not differ between groups. Selenium injection did not affect (P > 0.10) milk yield and composition. Calf morphometric parameters, BW at birth and growth rate during lactation were not affected (P > 0.10) by treatments. No significant effect (P > 0.10) was observed between treatments on hematological results of blood samples from calves at weaning. Results of this study shown that inorganic Se injection was an efficient tool to improve Se-status in cow-calf operation under extensive management. Selenium injection increased follicle diameter in postpartum beef cow, however, did not affect the rest of the variables studied.

Body condition status at mating affects gestation length, offspring yield and return rate in ewes

Abstract. The present study was planned to determine the effect of ewe body condition score (BCS) and parities on fertility, return rate, gestation length, fecundity, litter size and lamb birth weight. Data were collected from 284 heads of ewes with first to fifth parity and raised at a state farm for three consecutive (2002–2004) years. Teaser rams were used to monitor estrus twice daily in the morning and in the evening from September to October. BCSs and body weights (BWs) were recorded at mating and postpartum. The ewes, at mating time in breeding season and within first 6 h after the expulsion of fetal membranes, were divided into four groups on the basis of their BCS: thin (BCS = ≤ 2.0; n=70; 38), medium (BCS = 2.5–3.0; n=122; 142), fat (BCS = 3.5–4.0; n=72; 59) and very fat (BCS = ≥ 4.5; n= 20;17). BCSs and BWs of ewes at postpartum were highly correlated with lamb birth weight (R=0.486, P < 0.01, and R=0.130, P < 0.05, respectively). BCSs and BWs of ewes at postpartum had positive effects on lamb birth weight (Y=3.43 ± 0.10 + 0.130 + 0.047 ewe body condition score (EBCS), P < 0.01; Y= 2.92 ± 0.42 + 0.018 ± 0.009 ewe body weight (EBW), P < 0.05 kg of lamb birth weight per BCS and kilogram of ewe live weight, respectively). The fertility rate, litter size and fecundity were higher in the medium and fat groups than thin and very fat groups (χ2= 10.607, P < 0.01). The BW and BCS at postpartum affected gestation length positively (P < 0.05). Return rate or number of coitus for conception were higher (P < 0.05) in thin and very fat groups than medium and fat groups. The data revealed that the ewes with medium and fat body condition (BCS = 2.5–4.0) scores were profitable.

Timing of exogenous progesterone administration is critical for embryo development and uterine gene expression in an ovine model of maternal constraint

Progesterone (P4) administration in early pregnancy enhances embryo growth in sheep but is associated with decreased embryo survival. This study examined the effects of exogenous P4 administered during specific time periods between pregnancy Day 0 and Day 6 to determine the critical time point for advancement of embryo growth without pregnancy loss and to examine Day 6 and Day 19 endometrial gene expression. Suffolk (S) embryos were transferred into Cheviot (C) ewes that received exogenous P4 (CP4) on Days 0–3 (CP40–3), Days 0–6 (CP40–6), Days 2–4 (CP42–4) or Days 3–6 (CP43–6). Additionally, S embryos were transferred to C and S ewes that did not receive P4 (CnP4 and SnP4). Day 19 embryos from CP4 ewes were longer (P < 0.05) than those from CnP4 ewes. CP42–4 ewes had embryos of similar size to those of CP40–3 and CP40–6 ewes but had higher pregnancy rates. There was altered expression of genes associated with embryo implantation and histotroph production: diacylglycerol-O-acyltransferase (DGAT2), hepatocyte growth factor (HGF) and prostaglandin endoperoxide synthase 2 (PTSG2) on Day 6 and endometrial galectin 15 (LGALS15) and mucin glycoprotein 1 (MUC1) on Day 19. This suggests that specific timing of P4 administration is critical to the enhanced embryo growth and survival observed. These findings provide a platform for further investigation aimed at advancing embryo development and survival.

Effect of exogenous progesterone on embryo size and ewe uterine gene expression in an ovine 'dam size' model of maternal constraint

Progesterone (P4), acting via its receptor, regulates uterine function and histotroph production, which are crucial to embryo growth. This study aimed to examine exogenous P4 effects on embryo size and differential endometrial gene expression at Day 19 of gestation using a 'dam size' sheep model of maternal constraint. Purebred Suffolk (S, genotypically large) embryos were transferred into recipient groups of Cheviot (C, genotypically small) or Suffolk ewes that had, or had not, been pre-treated with P4 from Days 0 to 6 of pregnancy. At Day 19S embryos were collected from four experimental groups: P4 pretreated S ewes (SP4; n=5), untreated S ewes (SnP4; n=15), P4 pretreated C ewes (CP4; n=7) and untreated C ewes (CnP4; n=21). Day-19 embryos from CP4 ewes were larger (P<0.05) than those from CnP4 ewes and similar in size (P>0.05) to embryos from SnP4 and SP4 ewes. Expression of mucin 1 (MUC1) and prostaglandin-endoperoxide synthase 2 (PTGS2) was upregulated in uterine horns ipsilateral to the corpus luteum from CP4 ewes. Prostaglandin receptor (PGR), MUC1 and PTGS2 expression was upregulated, whilst cathepsin L (CTSL) and radical S-adenosyl methionine domain-containing 2 (RSAD2) expression was downregulated in the ipsilateral horn of SP4 ewes. This suggests that pretreating ewes with exogenous P4 may alleviate early pregnancy maternal constraint via mechanisms that alter uterine function. However, further research is required to investigate the timing of P4 administration and its impact on conception rates.

Gestation-related gene expression and protein localization in endometrial tissue of Suffolk and Cheviot ewes at gestation Day 19, after transfer of Suffolk or Cheviot embryos

The objective of this study was to investigate the gene expression of progesterone and estrogen receptor α (PR, ERα), insulin-like growth factor (IGF) 1, IGF-2, their receptor (IGFR1), IGF-binding proteins (BP) 1 to 6, insulin receptor, adiponectin receptors (AdipoR1/2), cyclooxygenase 2 (PTGS2), mucin 1 and to localize PR, ERα, IGF-1, IGFR1, PTGS2, and proliferating cellular nuclear antigen (PCNA) in the endometrium of pregnant (Day 19) Suffolk and Cheviot ewes carrying Suffolk and Cheviot embryos transferred within and reciprocally between breeds. Gene expression was determined by real-time quantitative polymerase chain reaction (RT-qPCR), and antigen determination was measured by immunohistochemistry in the luminal epithelium (LE), superficial and deep glands (SG, DG, respectively) and superficial and deep stroma. Gene expression of PR, IGF-1, IGFBP2, and IGFBP5 was higher in Suffolk than that in Cheviot ewes (P < 0.05). Greater abundance of IGF-2 and IGBP3 expression was found in Cheviot ewes carrying Cheviot embryos than Cheviot ewes carrying Suffolk embryos (P < 0.05). No staining for PR and ERα was observed in the LE, very scarce staining in SG and DG, whereas positive staining was observed in both superficial and deep stroma. No differences were found for PR staining, but Cheviot ewes had higher ERα staining intensity than Suffolk ewes (P < 0.05). Positive staining for IGF-1 was observed in all cell types except DG, and staining of IGFR1 was observed in all cell types. No differences among groups in staining were found for IGF-1 or IGFR1 in any cell type. Positive staining of PTGS2 was observed in LE and SG in all groups. An interaction between ewe and embryo breed affected PTGS2 staining (P < 0.05), whereby Cheviot ewes carrying Suffolk embryos had a lower PTGS2 staining than Suffolk ewes carrying Suffolk embryos. Positive staining of PCNA was found in LE and SG. Suffolk ewes carrying Suffolk embryos showed lower PCNA immunostaining than Cheviot ewes carrying Suffolk embryos (P < 0.05), whereas no differences were observed in ewes carrying Cheviot embryos. This study showed that gestation-related protein expression in the endometrium of Suffolk and Cheviot ewes is affected by both ewe and embryo breed at Day 19 of pregnancy.

Maternal insulin sensitivity in midpregnancy does not determine birth weight after embryo transfer between large and small breed sheep

Embryo transfer of large sheep breed embryos (Suffolk) into small breed ewes (Cheviot) constrains birth size, but the maternal factors influencing fetal growth restriction are unknown. We hypothesized that reciprocal embryo transfer crosses between breeds of divergent size would affect pregnancy-related development of maternal insulin resistance in midgestation, thereby influencing fetal growth. Following superovulation, embryos were surgically collected 6 d postmating and transferred to recipients on the same day. Between- and within-breed transfers were performed. Between 60 and 70 d of pregnancy overnight-fasted ewes underwent hyperinsulinemic-euglycemic clamps for assessment of insulin sensitivity. Maternal insulin sensitivity did not vary with transferred lamb breed. Overall, Cheviot ewes tended to have higher fasting glucose (P = 0.068), fasting insulin (P = 0.052), and steady-state glucose (P = 0.065) concentrations than Suffolk ewes at the stage of pregnancy studied. As expected, transferred between-breed Suffolk lambs were born lighter (P = 0.014), and transferred between-breed Cheviot lambs tended to be heavier at birth (P = 0.056) than respective lambs transferred within breed. Midgestation insulin sensitivity does not appear to be a major factor constraining growth of large breed sheep fetus transferred into smaller breed or a factor in releasing constraint in growth of a small breed fetus within a larger breed ewe. However, as embryo size is already different between transferred groups by 19 d, factors other than maternal gestational insulin resistance may determine fetal growth in this embryo transfer paradigm.