Bovine Somatotropin: Physiology and What Research Reports

What bovine somatotropin is

Bovine somatotropin (bST) is the species-specific form of growth hormone produced by cattle. Like other somatotropins, it is a single-chain polypeptide of roughly 190 amino acids stabilised by two intramolecular disulfide bonds, secreted in pulses by somatotroph cells of the anterior pituitary gland. "Somatotropin" and "growth hormone" describe the same molecule; the prefix simply identifies the species of origin. Bovine somatotropin is sometimes called bovine growth hormone (BGH), and the laboratory-produced version made in bacteria is written rbST (recombinant bovine somatotropin).

The bovine sequence is closely related to, but not identical with, human growth hormone, and bST is not a human therapeutic product. It appears in the scientific record almost entirely as a veterinary and animal-science tool — used in dairy cattle, beef cattle and sheep studies — and as a model protein in protein-stability chemistry.

Where it is produced and what it does in the body

Pituitary release of somatotropin is governed by hypothalamic growth hormone-releasing hormone (stimulatory) and somatostatin (inhibitory), with feedback from insulin-like growth factor 1 (IGF-1). Once in circulation, somatotropin binds the growth hormone receptor, a class I cytokine receptor that signals through JAK2 and STAT5. Two broad categories of action follow:

• Indirect (IGF-1-mediated) actions. Hepatic and local IGF-1 production increases, supporting cell proliferation, skeletal growth and — in ruminants — ovarian and mammary tissue responses.
• Direct metabolic actions. Somatotropin shifts nutrient partitioning: lipolysis in adipose tissue rises, glucose use by peripheral tissues falls, and nutrients are redirected toward the mammary gland or growing tissue. In lactation biology this coordinated shift is described as homeorhesis.

Because of that nutrient-partitioning role, most bST research sits at the intersection of lactation, energy metabolism and reproduction rather than in "growth" alone.

How it is measured and studied

Circulating somatotropin and IGF-1 are typically quantified by immunoassay in serum or plasma, while downstream endpoints are measured directly in the tissue of interest — milk yield and milk component analysis, ultrasound-based follicular counts, follicular fluid steroid concentrations, immunohistochemical markers of cell proliferation and apoptosis, and pregnancy diagnosis after insemination. Studies of the protein itself use chromatography and mass spectrometry to track degradation products.

One such chemistry study examined solid-state photodegradation of bovine somatotropin and reported evidence for tryptophan-mediated photooxidation of its disulfide bonds (PMID 12884256), an illustration of why light exposure and formulation state matter for any protein handled in a laboratory.

What the literature reports

Lactation, milk composition and mammary tissue

A multidose longitudinal study of recombinant bovine somatotropin analysed bovine milk composition and the milk fatty acidome, and researchers reported dose-related changes in milk constituents and fatty-acid profiles (PMID 36360090). At the tissue level, a dairy-science study of continuous milking with bovine somatotropin supplementation examined mammary epithelial cell turnover — proliferation versus loss — as the mechanism behind sustained secretory capacity (PMID 17183085). In crossbred Holstein × Gyr (3/4 and 7/8) cows, researchers evaluated how recombinant bovine somatotropin was best applied under tropical dairy conditions and reported production and physiological responses that differed with genetic composition (PMID 36735164).

Endocrine and metabolic responses

A study in lactating dairy cows tested somatotropin under both ad libitum and restricted feed intake and reported effects on thyroid hormones and circulating cytokines, linking the hormone's metabolic actions to broader endocrine and immune mediators (PMID 11768084). In late-pregnant Holstein heifers, researchers injected bovine somatotropin and reported changes in metabolic parameters alongside the steroidogenic potential of the first postpartum dominant follicle (PMID 28863349).

Ovarian function and reproduction

Reproductive physiology accounts for a large share of the bST literature. In non-lactating dairy cows, a study of recombinant bovine somatotropin treatment reported effects on follicular population and follicular development (PMID 32368271), while an earlier dairy-science report in nonlactating cows described ovarian, conceptus and insulin-like growth factor system responses during pregnancy (PMID 15377605). In beef cattle bred by fixed-time artificial insemination, researchers reported that bovine somatotropin increased the pregnancy rate (PMID 38894646). Pre- and post-weaning injections of bovine somatotropin were studied in Bos indicus beef heifers with puberty achievement as the endpoint (PMID 32704815).

Sheep studies extend the same theme across species: inseminated hair sheep treated with bovine somatotropin were assessed for lambing rate and prolificacy (PMID 26951204), and ewes given two doses of bovine somatotropin were compared for superovulatory response and embryo development (PMID 25459075).

Study snapshot

Adverse Events and Tolerability: What Studies Report

The verified studies summarised here were designed around production and reproductive endpoints rather than formal safety surveillance, so they describe physiological responses rather than a catalogue of adverse events. Several report changes that are relevant to tolerability in animals: the feed-intake study reported shifts in thyroid hormones and cytokines with somatotropin treatment (PMID 11768084), and the late-pregnancy heifer study reported altered metabolic parameters after injection (PMID 28863349). Changes to milk constituents and the fatty acidome were also reported as dose-dependent (PMID 36360090). Broader veterinary safety questions — including mastitis and reproductive performance at herd level — are addressed in regulatory reviews that fall outside the papers cited on this page.

Why the term matters to readers of peptide literature

Bovine somatotropin is frequently encountered by people reading about growth hormone biology, IGF-1 or "peptide hormones" generally, and it is easy to confuse with human growth hormone or with GH-secretagogue peptides. Three distinctions are worth keeping clear:

1. bST is a full-length protein hormone of animal origin, not a short synthetic peptide.
2. Its research record is an animal-agriculture and veterinary record — dairy cows, beef cattle and sheep — not a human clinical one.
3. Regulatory status is jurisdiction-specific: recombinant bST has been approved for use in dairy cattle in some countries and not permitted in others, including within the European Union and Canada. This paragraph is a description of regulatory context, not legal advice.

This page is for educational purposes only and is not medical advice; consult a licensed physician or qualified veterinarian for questions about any hormone, medication or animal-health product. Nothing here describes human use, and the doses and treatment schedules in the cited papers belong to those specific animal study designs.

References

• How to use recombinant bovine somatotropin in crossbred Holstein × Gyr (3/4 and 7/8) cows? (Tropical Animal Health and Production, 2023)
• Lambing rate and prolificacy in inseminated hair sheep treated with bovine somatotropin (Tropical Animal Health and Production, 2016)
• Effect of bovine somatotropin injection in late pregnant Holstein heifers on metabolic parameters and steroidogenic potential of the first postpartum dominant follicle (Theriogenology, 2017)
• Impact of Recombinant Bovine Somatotropin on Bovine Milk Composition and Fatty Acidome: A Multidose Longitudinal Study (Foods, 2022)
• Effect of continuous milking and bovine somatotropin supplementation on mammary epithelial cell turnover (Journal of Dairy Science, 2007)
• Superovulatory response and embryo development in ewes treated with two doses of bovine somatotropin (Animal Reproduction Science, 2014)
• Effect of recombinant bovine somatotropin (rbST) treatment on follicular population and development in non-lactating dairy cows (Animal Reproduction, 2019)
• Solid-state photodegradation of bovine somatotropin (bovine growth hormone): evidence for tryptophan-mediated photooxidation of disulfide bonds (Journal of Pharmaceutical Sciences, 2003)
• Effect of somatotropin on thyroid hormones and cytokines in lactating dairy cows during ad libitum and restricted feed intake (Journal of Dairy Science, 2001)
• Bovine somatotropin increases the pregnancy rate in fixed-time artificial insemination in beef cattle (Reproduction in Domestic Animals, 2024)
• Pre- and post-weaning injections of bovine somatotropin to optimize puberty achievement of Bos indicus beef heifers (Translational Animal Science, 2019)
• Pregnancy and bovine somatotropin in nonlactating dairy cows: I. Ovarian, conceptus, and insulin-like growth factor system responses (Journal of Dairy Science, 2004)