Why Some IVF Calves Grow Too Big: New Multi-Omics Study Offers Clues

Calves born after in vitro embryo production, the laboratory technique in which cattle oocytes are matured, fertilized and cultured outside the body before being transferred to a surrogate dam, frequently weigh more at birth than calves conceived by artificial insemination. That extra bulk is not a benign curiosity. Heavier fetuses stretch gestation, raise the odds that a recipient cow will need calving assistance, and can jeopardize the health of both dam and calf. Yet the molecular machinery driving this fetal overgrowth has remained largely unexplored. A new study published in BMC Genomics by Leiyu Qu of Yanbian University, Zhengyu Hang and Yachun Wang of China Agricultural University, and colleagues, now maps the physiological, hormonal, transcriptomic and metabolomic signatures that accompany elevated birth weight in Holstein calves produced in vitro, offering the first integrated picture of what is happening inside these oversized offspring.

The research team compared two carefully matched groups of nine calves each: one group of IVP calves with increased birth weight, and a control group of nine IVP calves with normal birth weight. Rather than relying on a single measurement, the investigators layered multiple analytical approaches on top of one another. They recorded physiological and biochemical blood parameters, profiled circulating hormones, sequenced the whole transcriptome to capture messenger RNAs, long non-coding RNAs, microRNAs and circular RNAs, and ran untargeted metabolomics to inventory the small molecules coursing through the calves’ systems. This multi-omics design matters because fetal overgrowth is unlikely to be governed by any single gene or metabolite; it is a systems-level phenomenon in which regulatory RNAs, protein-coding genes and metabolic pathways reinforce one another.

The first striking finding concerned gestation itself. Increased birth weight in the IVP calves was accompanied by prolonged gestation length in the recipient dams, meaning the oversized fetuses were not simply growing faster at a fixed endpoint but were also staying in utero longer. Alongside this, multiple physiological, biochemical and hormonal parameters shifted significantly between the two groups. The study tracked markers familiar to livestock physiologists, including albumin, alanine aminotransferase, creatinine, total cholesterol, triglycerides, high- and low-density lipoprotein cholesterol, non-esterified fatty acids and beta-hydroxybutyrate, as well as antioxidant measures such as catalase, glutathione peroxidase, superoxide dismutase and total antioxidant capacity. Hormonal profiling encompassed growth hormone and insulin-like growth factor 1, two central regulators of fetal growth, along with immune markers including immunoglobulins A and G and interleukins. The pattern that emerges is one of systemic metabolic and endocrine reprogramming, not merely a mechanical consequence of a large fetus occupying the uterus.

On the metabolomics side, the untargeted screen was remarkably deep. The platform detected 3,259 metabolites in total, from which the researchers distilled 132 differential metabolites that separated the heavy calves from the normal-weight controls. Of these, 82 were significantly up-regulated and 50 were significantly down-regulated. Among the metabolite classes represented were phosphatidylcholines, lysophosphatidylcholines, diacylglycerols and linoleic acid species, pointing toward perturbed lipid metabolism, a theme that resonates with the altered cholesterol, triglyceride and fatty acid measures in the blood biochemistry. Lipids are not only fuel; they are signaling molecules and structural components of every cell membrane, and their dysregulation during development can have lasting consequences for organ growth and function.

The transcriptomic analysis went beyond protein-coding genes to interrogate the non-coding RNA landscape, an area increasingly recognized as central to developmental programming. Using weighted gene co-expression network analysis, the team identified gene modules whose expression patterns correlated with birth weight, and they constructed a competing endogenous RNA, or ceRNA, network to map how circular RNAs might sponge microRNAs and thereby modulate messenger RNA targets. Two candidate axes stood out. The first links the circular RNA circ36279 to the microRNA bta-miR-431, with predicted target genes including SPON2, TNN, INSIG1 and AEN. The second connects circ35151 to bta-miR-154b, with predicted targets SHD, TBX2 and IL20RA. Each of these targets tells a plausible story: INSIG1 sits at the heart of cholesterol and lipid metabolism regulation, TBX2 is a transcription factor implicated in developmental patterning, IL20RA participates in inflammatory signaling, and SPON2 and TNN relate to extracellular matrix biology, the scaffolding that tissues remodel as they grow.

To bridge the gene-level and metabolite-level data, the researchers compared the KEGG pathways enriched independently among differentially expressed genes and among differential metabolites, and identified five overlapping pathways enriched on both sides of the omics divide. Within these shared pathways, Pearson correlation analysis of selected differentially expressed genes and differential metabolites revealed concrete cross-omics associations, pairs of genes and metabolites whose abundance moved together across the two groups of calves. The pathway that the authors single out as the strongest recommendation for further investigation is arginine and proline metabolism. This choice is biologically compelling: arginine is a precursor for nitric oxide, polyamines and creatine, all of which influence vascular tone, cell proliferation and energy metabolism in the developing fetus, while proline is central to collagen synthesis and thus to the growth of connective tissue and skeleton.

What makes this study notable in the broader context of assisted reproduction is its framing of fetal overgrowth as a molecular phenotype rather than a breeding-management nuisance. The phenomenon echoes large offspring syndrome, a well-documented complication of in vitro embryo technologies in ruminants, in which calves and lambs derived from cultured embryos show excessive birth weight, elongated gestation and metabolic abnormalities. By working exclusively within IVP calves, comparing heavy versus normal birth weight offspring produced under the same laboratory pipeline, the authors isolated the molecular correlates of overgrowth from the confounding effects of comparing IVP calves with artificially inseminated ones. That design choice strengthens the inference that the observed transcriptomic and metabolomic differences are genuinely tied to the overgrowth phenotype itself.

The clinical stakes for the dairy industry are tangible. Recipient dams carrying oversized IVP calves face higher rates of dystocia, and calving assistance carries costs in veterinary intervention, lost milk days, calf mortality and compromised welfare. If the ceRNA axes and metabolic pathways identified here can be validated as biomarkers, embryo production programs could potentially screen or select embryos, or manage recipient dams differently, to reduce the incidence of heavy births. More fundamentally, the identification of circ36279-bta-miR-431 and circ35151-bta-miR-154b as candidate regulatory circuits provides mechanistic entry points for experimental follow-up: manipulating these RNAs in embryo culture systems could test whether they causally influence growth trajectories rather than merely correlating with them.

The study also illustrates how far livestock genomics has moved in a decade. Whole-transcriptome sequencing that captures circular RNAs, once a niche pursuit in human biomedicine, is now being deployed on farm animals to solve practical production problems, and untargeted metabolomics capable of cataloguing more than three thousand compounds provides the chemical context in which genes act. The integration of these layers, anchored by physiological and hormonal measurements, reflects a maturing multi-omics paradigm in animal science. The authors, who also include Yao Chang, Lei Wang, Ruina Ma, Shanjiang Zhao, Qingshan Gao and Qing Xu, acknowledge support from the China National Modern Agricultural Industry Technology System, and the work was approved by the Animal Ethics Committee of China Agricultural University.

For now, the findings are associative, and the authors are appropriately measured in their conclusions, presenting the two ceRNA axes and the arginine and proline metabolism pathway as candidates for further examination rather than proven drivers of overgrowth. But the roadmap they provide is clear. Follow-up studies can validate the expression of SPON2, TNN, INSIG1, AEN, TBX2 and IL20RA, quantify the metabolites in the overlapping KEGG pathways, and test whether interventions in arginine availability during embryo culture or gestation moderate fetal growth. If those experiments succeed, the oversized IVP calf, long a stubborn side effect of a technology the dairy world increasingly depends upon, may finally become a problem that can be predicted, and perhaps prevented, at the molecular level.

Subject of Research: Molecular mechanisms of fetal overgrowth in Holstein calves produced by in vitro embryo production

Article Title: Exploring the transcriptomic and metabolomic associations with fetal overgrowth in Holstein cattle derived from in vitro embryo production

Article References: Qu, L., Hang, Z., Chang, Y., Wang, L., Ma, R., Zhao, S., Gao, Q., Xu, Q., & Wang, Y. (2026). Exploring the transcriptomic and metabolomic associations with fetal overgrowth in Holstein cattle derived from in vitro embryo production. BMC Genomics. https://doi.org/10.1186/s12864-026-13408-0

Image Credits: AI Generated

DOI: 10.1186/s12864-026-13408-0

Keywords: in vitro embryo production, Holstein cattle, fetal overgrowth, large offspring syndrome, transcriptomics, metabolomics, ceRNA network, circular RNA, microRNA, arginine and proline metabolism, lipid metabolism, multi-omics