Sometribove
The recombinant cow growth hormone injected into dairy cows every two weeks to raise milk yield: what decades of trials found on milk, health and fertility, and why it does nothing for people
Sometribove is bovine growth hormone (bovine somatotropin) made by recombinant DNA, with one extra methionine at its start. As Posilac, a slow-release zinc suspension, it is injected under a dairy cow's skin every 14 days from about the ninth week after calving, and it raises milk yield by roughly 4 kg a day. Trials since the late 1980s, summarised in a 2014 meta-analysis of 26 studies, found more milk with little change in its composition and no overall effect on mastitis, lameness or culling. It is approved only for cows in the United States, and cow growth hormone does not act in humans.
No established human dose Details ↓
Recommended Dosing
No established human dose
No human dose exists for sometribove. It is approved only for lactating dairy cows, its US label says it is not for use in humans, and every study read here gave it to cows, calves, lambs or rats with amounts chosen for those animals.
What is it?
Growth hormone in a lactating cow does much of what it does in other mammals: it shifts nutrients away from body fat and toward productive tissue, and in a cow the most productive tissue is the udder. Recombinant DNA made it possible to produce bovine somatotropin in bacteria at scale. Sometribove is one such product: the cow's hormone with an extra methionine at its start, identical to the natural hormone at 190 of its 191 amino acids. Trials of it in dairy cows were published from the late 1980s, and in the United States it is approved as Posilac for healthy lactating dairy cows.
The product is a prolonged-release suspension of sometribove bound to zinc in an oil, so that one injection under the skin covers two weeks. The label calls for one syringe every 14 days, starting in the ninth or tenth week after calving and continuing to the end of lactation, for healthy lactating dairy cows. The early trials tested daily injections and two-weekly amounts below and above that level; milk yield rose with dose, and the label amount sat in the middle of the range tested in the 1991 dose titration.
The milk effect is the best-established finding. A 2014 meta-analysis of 26 studies that used the US product as labelled found about 4 kg a day more milk, with fat and protein yields up by about 0.14 kg a day and no change in their concentration. Individual trials in Holsteins, Jerseys, cows milked three times a day, and indigenous and crossbred cattle in Africa reported gains from about 7% to more than 30%. Cows ate more to support the extra milk, and over a treatment period their body condition fell slightly. Within each 14-day cycle, milk yield rose and fell as the injected hormone was released and used up.
Health was the controversy. Early trials, especially those that gave several times the label amount, saw more clinical mastitis, more digestive upsets and lameness, and delayed conception. Larger analyses, however, found no change in clinical mastitis in 15 full-lactation trials and 70 commercial herds, no effect on mastitis or culling in 1,213 cows on 28 US farms (though treated cows had slightly more foot problems), and no overall effect on mastitis, lameness, cystic ovaries or culling in the 2014 meta-analysis. That analysis found pregnancy rates slightly higher in the first two breeding cycles but slightly lower over the whole trial.
Concerns about milk for people were examined before approval. A 1990 review of the food-safety studies set out why regulators allowed milk and meat from treated cows with no withdrawal time: cow somatotropin is not active in humans, it is not absorbed intact when eaten, its residues in milk are in the parts-per-billion range and similar to the cow's own hormone, and the extra IGF-I in milk is small. A 1992 study of milk composition likewise found no change that would matter to dairy manufacturers or consumers. Outside the United States, the EMA medicines list holds no record of the drug.
Sometribove has also been tested in beef calves, finishing lambs and fish, where it made carcasses leaner and, in some studies, growth more efficient, but its approval covers only lactating dairy cows. It is a veterinary drug, the label says it is not for use in humans, and because it does not act on human growth hormone receptors it would not work as a growth hormone in a person even if injected. Human growth hormone treatment uses human somatropin.
Mechanism of Action
Sometribove acts as the cow's own growth hormone: it binds the growth hormone receptor, raises IGF-I, and redirects energy and nutrients toward milk synthesis rather than body fat, while appetite rises over the following weeks to cover the extra output.
More milk, same composition
Milk yield rises in proportion to dose up to the label amount and beyond; fat, protein and lactose concentrations barely change, so component yields rise with volume.
Fat mobilised, intake rises
Treated cows lost body fat (28 against 46 kg in one body-composition study) and later ate more, so energy balance over a full treatment period was similar to controls.
A two-week release cycle
The zinc-oil formulation releases the hormone over about 14 days; milk yield and composition follow a cyclic pattern within each interval, and circulating bST and IGF-I stay raised between injections.
Species-specific
Its sequence differs enough from human growth hormone that it does not bind human receptors, and as a protein it is digested when eaten.
Published Research
These studies of sometribove were read from their PubMed abstracts on October 30, 2026. They are trials in dairy cows, a few in beef calves, lambs and rats, and the review of food-safety studies behind its approval. None was carried out in people, and the amounts in the cards are veterinary amounts, not human doses.
Meta-analysis of 26 studies of the US product used as labelled
Milk, fat-corrected milk, fat and protein yields rose by about 4.0, 4.0, 0.14 and 0.14 kg a day, without changing component concentrations. Pregnancy in the first two breeding cycles was 5.4% higher but over the whole trial 5.5% lower; body condition fell slightly. Somatic cells, days to pregnancy, fetal loss, twins, cystic ovaries, lameness, mastitis and culling were unaffected.
1,213 cows in 28 commercial US herds
Cows treated every 14 days from the ninth or tenth week of lactation gave 932 kg more milk over 305 days. Mastitis, pregnancy rate, days open, twinning, cystic ovaries, abortion and culling were unaffected; treated cows used more medication for other conditions, mainly foot and hock problems, and had slightly more foot disorders.
Mastitis across 15 full-lactation trials and 70 herds
In 914 cows in full-lactation trials in Europe and the US and 2,697 cows in short-term studies, clinical mastitis was similar in treated and control cows. Mastitis rose with peak milk yield, and treatment did not change that relationship.
Lameness after at least two lactations of treatment
In a matched case-control study across eight herds, 43% of cows were lame, but long-term treatment was not associated with lameness. Two of 21 limb-lesion types were more common in treated cows and two less common.
Dose titration in 241 Holsteins
Two-weekly doses below, at and above the later label amount raised fat-corrected milk by 10% to 27% in a dose-dependent way over 252 days, with no change in fat, protein, lactose or somatic cells. Cows ate more, so body weight gain and energy balance matched controls.
First long-term test of the prolonged-release formulation
In 80 Holsteins treated every 14 days for 36 weeks, fat-corrected milk rose 11.4% in first-calf and older cows alike. Protein and phosphorus in milk rose slightly; milk yield followed a cyclic pattern within each injection interval.
Jersey cows over a full lactation
In 46 Jerseys, fat-corrected milk rose 5.3 kg a day (31%) and energy intake 23%. Treated cows had more mastitis and some injection-site reactions; 85% of treated and 100% of control cows calved again successfully, and the next lactation was unaffected.
Up to six times the label amount over two lactations: production
Eighty-two Holsteins received one, three or five unit doses every two weeks. Milk rose by 7 to 9 kg a day in year one; in year two the highest dose caused more mastitis and less saleable milk. Milk composition did not change, hormone levels in milk serum were very low, and no toxic effects were seen.
The same high-dose study: health and reproduction
Ketosis, milk fever and pneumonia were unaffected. Digestive upsets rose in year one, lameness and mastitis mainly at the highest dose, and conception was delayed with more abortions; eight treated cows and no controls died or became moribund over two years. The authors found no treatment-specific toxic changes.
Which cows respond
In 78 Holsteins, first-calf cows responded less than older cows, while pretreatment yield and genetic merit did not change the response significantly. Treated cows ran slightly warmer in hot weather without losing their milk response.
High producers milked three times a day
In 104 Holsteins given daily injections for 12 weeks, milk rose 18.8% (6.1 kg a day) and milk protein slightly; fat, lactose, somatic cells and body weight were unaffected, body condition was a little lower, and mastitis, foot rot, displaced abomasum and lameness did not differ.
No practical change in milk composition
In 79 Holsteins, treatment increased milk and every component's yield, with nearly identical concentrations of fat, lactose, casein and true protein and the same proportions of the major milk proteins; total protein and non-protein nitrogen were slightly higher.
Seven field studies in Africa
In N'Dama cattle in Gambia a lower two-weekly amount raised milk by about 22%; in Zimbabwean crossbreds milk rose from 8 to 10 kg a day; in Kenyan crossbreds the lower amount raised milk by 2.5 kg a day and the label amount added nothing more. Delaying the start to 120 or 150 days in Holsteins gave similar gains.
Grazing cows in the southeastern US
In 32 mid-lactation cows on pasture, treatment raised fat-corrected milk (17.7 against 15.8 kg a day) and IGF-I and helped cows hold body weight, but they grazed longer and ran higher body temperatures; the authors saw limited gains in pasture systems.
Body composition of treated cows
Eight weeks of daily injections in mid-lactation raised milk from 30.2 to 34.3 kg a day and cut total body fat from 45.7 to 28.3 kg, with more gut tissue and contents, showing the extra milk came partly from body fat.
Rumen function unchanged
In six fistulated Holsteins, daily treatment raised milk by 4.0 kg a day and feed efficiency, while rumen fermentation, digesta passage, digestibility and dry-matter intake were unaffected over six weeks.
Treatment in the dry period does not carry over
In 135 commercial Holsteins injected daily for two weeks before calving, the following lactation's milk yield did not rise once previous yield was accounted for, and calving difficulty and udder oedema did not differ.
LH secretion during the breeding period
In 16 cycling Holsteins, daily treatment raised milk by 7% but did not change basal LH, the LH response to a GnRH challenge, or luteal progesterone.
Ovarian follicles
In lactating cows, treatment raised the number of medium-sized follicles to the level seen in non-lactating cows and enlarged the second-largest follicle, without changing the size of the largest.
Pituitary function after four lactations of treatment
In six cows treated through four consecutive lactations, baseline somatotropin and ACTH were higher than in controls, the somatotropin response to TRH was lost, cortisol responded less to ACTH and progesterone more to GnRH; thyroid, prolactin and gonadotropin release were unaffected.
Immune cells in the dry period
In small groups of cows, treatment during the dry period did not change how blood or udder mononuclear cells proliferated, but raised interleukin-2 secretion in cows also treated during the previous lactation.
The food-safety case for zero withdrawal time
The review behind regulators' decision explains that cow somatotropin is not active in humans because of sequence differences, is not active by mouth (rats fed very large amounts for 90 days did not grow faster), leaves residues in milk and meat comparable to the cow's own hormone, and raises IGF-I in milk only marginally; IGF-I fed to rats was also inactive.
Leaner carcasses in dairy bull calves
Ten Holstein calves injected daily for six weeks grew no faster but had 5% more carcass protein and 36% less carcass fat; packed cell volume fell about 7%, with no effect on health measures.
Long-term Posilac in bull calves, with or without an implant
In 56 Holstein-Friesian bull calves over about 238 days, two-weekly injections raised daily gain by 9% and feed efficiency by 10% and cut large carcass fat depots by 34%; an oestrogenic implant added nothing.
Finishing lambs
A slow-release formulation given every one or two weeks for six weeks improved feed conversion by 9% to 19% and cut fat thickness by 17% to 42% with rising dose, with metabolic changes like those of daily injections.
No Established Human Dose
No human dose exists for sometribove. It is approved only for lactating dairy cows, its US label says it is not for use in humans, and every study read here gave it to cows, calves, lambs or rats with amounts chosen for those animals. Cow somatotropin also does not act on human growth hormone receptors and is digested when eaten, so the veterinary amounts are not shown as doses and none applies to a person.
What this rests on: PMID 2080839, PMID 25148097, PMID 11384036.
Educational information, not medical advice. The doses on this page come from approved labels, published studies and, where no study exists, amounts reported by users. None is a recommendation for you. An unapproved compound has no established safe or effective human dose, and products sold for “research use only” are not made or tested for people. Talk to a doctor before acting on anything on this site, including before you start, stop or change any medicine or dose. Full medical disclaimer.
What a Buyer Needs to Know
What is sold, how it is mixed, stored and taken, and what is known about its safety, quality and legal status. Each part names its source. Where we have none, it says unknown.
What is sold
No product is approved for people. The approved veterinary product, as its US veterinary label describes it:
- Posilac (sometribove suspension) (veterinary): Single-dose syringes in 25 or 100 count boxes.
Source: Posilac (sometribove suspension) veterinary label, How Supplied (DailyMed version 6, effective March 19, 2025).
Mixing a vial: a worked example
Unknown: no human dose of Sometribove has been established (see No Established Human Dose below), so there is no amount to work out. The reconstitution calculator does the arithmetic for any vial, water and dose.
Storage before and after mixing
No product of Sometribove is approved for people. The US veterinary label of the approved animal product says how it is stored:
Posilac (sometribove suspension) (veterinary): “Store under refrigeration (2° to 8° C; 36° to 46° F).” “DO NOT FREEZE.” “Allow syringes to warm to room temperature (15° to 30° C; 59° to 86° F) before use.”
These describe the veterinary product in its own container, not a vial sold for people. The mixing guide sets out the general rules for a mixed vial, with their sources.
Source: Posilac (sometribove suspension) veterinary label, storage section (DailyMed version 6, effective March 19, 2025).
How it is taken
Unknown: with no established human dose, there is no established way of taking Sometribove. What the human studies gave and how is set out under No Established Human Dose.
What to expect, and when
Unknown: no cited half-life and no label or trial duration on this page says how long Sometribove lasts or how long it was given. Results reported in the studies are under Published Research.
Side effects, and when to stop or get help
From the Side Effects section: More mastitis in some single-herd trials and at several times the label amount, but no overall effect across 15 full-lactation trials, 28 commercial herds or the 2014 meta-analysis (PMIDs 1474209, 1757623, 7962847, 11384036, 25148097); Slightly more foot and hock problems in commercial herds (PMID 11384036); Digestive upsets, lameness, delayed conception and more abortions at high doses (PMID 1541726); Lower body condition during treatment and lower pregnancy rates over a whole trial (PMID 25148097); Local reactions at the injection site (PMID 1474209); The Posilac label warns people handling it that frequent skin contact with a protein may cause an allergic reaction (veterinary label). Full list and cautions ↓
When to stop or get help: unknown; no label or trial on file sets rules for stopping Sometribove. Treat a severe or unexpected reaction as a reason to stop and see a doctor.
Source: the Side Effects section below (“Reported in cattle; no human safety data exist”).
Interactions
Unknown: a PubMed search for human interaction studies of Sometribove (reviewed 2026-10-28) found none. Unknown is not the same as safe to combine.
Every peptide's record, with its source: the interaction matrix.
Checking what you bought
Unknown: no published independent test of Sometribove products is in our lab-results database yet, so how products sold under this name measure up is not known.
To read a certificate of analysis, paste it into the COA decoder. Trust & Verification explains what independent testing can and cannot show.
Legal status
US: Veterinary Only (Approved only for animals). Sport: Prohibited at all times (S2.2.3).
Country by country ↓ · Regulatory tracker
Source: this entry's approval status and the WADA Prohibited List, as in Legal Status below.
Side Effects & Contraindications
Reported Side Effects
Reported in cattle; no human safety data exist.
Contraindications & Cautions
For people, the point is simpler:
Legal Status
Sometribove is a veterinary drug approved in the United States for dairy cows. No human approval was found.
Frequently Asked Questions
?What is sometribove?
Recombinant bovine growth hormone (bovine somatotropin) with one extra methionine at its start, sold for dairy cows as Posilac. It is often called rbST or rbGH.
?What does it do in cows?
Injected every two weeks from about the ninth week after calving, it raises milk yield by roughly 4 kg a day on average, with little change in milk composition.
?Is it bad for cows' health?
Early and high-dose trials saw more mastitis, lameness and fertility problems. Large analyses of the product used as labelled found no overall effect on mastitis, lameness or culling, slightly more foot problems in commercial herds, and lower body condition during treatment.
?Is milk from treated cows safe to drink?
Regulators allowed it with no withdrawal time because cow somatotropin is not active in humans, is digested when eaten, and leaves residues similar to the cow's own hormone; trials found no practical change in milk composition.
?Would it work as growth hormone in a person?
No. Its sequence differs from human growth hormone enough that it does not act on human receptors, and it is labelled not for use in humans.
?Where is it approved?
In the United States, for lactating dairy cows only. The EMA list holds no record of it.
References
- [fda-pi] Posilac (sometribove zinc), US FDA-approved veterinary label (description, use and dosage; DailyMed set 1d3664b8, version 6, effective March 19, 2025; read October 28, 2026).
- [other] US FDA Center for Veterinary Medicine, Approved Animal Drug Products (Green Book), Section 2 active-ingredient list downloaded from Animal Drugs @ FDA, read October 28, 2026: NADA 140-872, Posilac, active ingredient bovine somatotropin (sometribove zinc). https://animaldrugsatfda.fda.gov/adafda/views/#/search
- [other] US FDA, Drugs@FDA (openFDA): no application for sometribove. Read October 28, 2026.
- [pubmed] St-Pierre NR, et al. "Meta-analysis of the effects of sometribove zinc suspension on the production and health of lactating dairy cows." J Am Vet Med Assoc, 2014;245(5):550-64. PMID: 25148097.
- [pubmed] Collier RJ, et al. "Effects of sustained release bovine somatotropin (sometribove) on animal health in commercial dairy herds." J Dairy Sci, 2001;84(5):1098-108. PMID: 11384036.
- [pubmed] White TC, et al. "Clinical mastitis in cows treated with sometribove (recombinant bovine somatotropin) and its relationship to milk yield." J Dairy Sci, 1994;77(8):2249-60. PMID: 7962847.
- [pubmed] Wells SJ, et al. "Effect of long-term administration of a prolonged release formulation of bovine somatotropin (sometribove) on clinical lameness in dairy cows." Am J Vet Res, 1995;56(8):992-6. PMID: 8533990.
- [pubmed] Hartnell GF, et al. "Evaluation of sometribove in a prolonged-release system in lactating dairy cows--production responses." J Dairy Sci, 1991;74(8):2645-63. PMID: 1918539.
- [pubmed] Bauman DE, et al. "Long-term evaluation of a prolonged-release formulation of N-methionyl bovine somatotropin in lactating dairy cows." J Dairy Sci, 1989;72(3):642-51. PMID: 2715460.
- [pubmed] Pell AN, et al. "Effects of a prolonged-release formulation of sometribove (n-methionyl bovine somatotropin) on Jersey cows." J Dairy Sci, 1992;75(12):3416-31. PMID: 1474209.
- [pubmed] Eppard PJ, et al. "Response of dairy cows to high doses of a sustained-release bovine somatotropin administered during two lactations. 1. Production response." J Dairy Sci, 1991;74(11):3807-21. PMID: 1757623.
- [pubmed] Cole WJ, et al. "Response of dairy cows to high doses of a sustained-release bovine somatotropin administered during two lactations. 2. Health and reproduction." J Dairy Sci, 1992;75(1):111-23. PMID: 1541726.
- [pubmed] Sullivan JL, et al. "Factors affecting response of cows to biweekly injections of sometribove." J Dairy Sci, 1992;75(3):756-63. PMID: 1569267.
- [pubmed] Jordan DC, et al. "Effects of recombinant methionyl bovine somatotropin (sometribove) in high producing cows milked three times daily." J Dairy Sci, 1991;74(1):220-6. PMID: 2030169.
- [pubmed] Barbano DM, et al. "Effect of a prolonged-release formation of N-methionyl bovine somatotropin (sometribove) on milk composition." J Dairy Sci, 1992;75(7):1775-93. PMID: 1500574.
- [pubmed] Phipps RH, et al. "Use of bovine somatotropin in the tropics: the effect of sometribove on milk production in western, eastern, and southern Africa." J Dairy Sci, 1997;80(3):504-10. PMID: 9098800.
- [pubmed] Fike JH, et al. "Southeastern pasture-based dairy systems: housing, posilac, and supplemental silage effects on cow performance." J Dairy Sci, 2002;85(4):866-78. PMID: 12018432.
- [pubmed] Brown DL, et al. "Influence of sometribove, USAN (recombinant methionyl bovine somatotropin) on the body composition of lactating cattle." J Nutr, 1989;119(4):633-8. PMID: 2539448.
- [pubmed] Winsryg MD, et al. "Effect of sometribove on rumen fermentation, rate of passage, digestibility, and milk production responses in dairy cows." J Dairy Sci, 1991;74(10):3518-23. PMID: 1744279.
- [pubmed] Bachman KC, et al. "Milk yields and hormone concentrations of Holstein cows in response to sometribove (somatotropin) treatment during the dry period." J Dairy Sci, 1992;75(7):1883-90. PMID: 1500585.
- [pubmed] Dalton JC, et al. "Effect of sometribove administration on LH concentration in dairy cattle." Theriogenology, 1994;41(2):437-45. PMID: 16727401.
- [pubmed] De la Sota RL, et al. "Effects of recombinant bovine somatotropin (sometribove) on ovarian function in lactating and nonlactating dairy cows." J Dairy Sci, 1993;76(4):1002-13. PMID: 8486832.
- [pubmed] Adriaens FA, et al. "Pituitary response to thyrotropin, corticotropin, and gonadotropin-releasing hormones in lactating cows treated with sometribove for a fourth consecutive lactation." Domest Anim Endocrinol, 1995;12(4):301-16. PMID: 8575163.
- [pubmed] Torre PM, et al. "Influence of recombinant bovine somatotropin (sometribove) on mononuclear cells during the nonlactating period." J Dairy Sci, 1993;76(4):983-91. PMID: 8486850.
- [pubmed] Hammond BG, et al. "Food safety and pharmacokinetic studies which support a zero (0) meat and milk withdrawal time for use of sometribove in dairy cows." Ann Rech Vet, 1990;21 Suppl 1:107S-120S. PMID: 2080839.
- [pubmed] Neathery MW, et al. "Effects of sometribove on performance, carcass composition, and chemical blood characteristics of dairy calves." J Dairy Sci, 1991;74(11):3933-9. PMID: 1757630.
- [pubmed] Holzer Z, et al. "The effects of long-term administration of recombinant bovine somatotropin (Posilac) and Synovex on performance, plasma hormone and amino acid concentration, and muscle and subcutaneous fat fatty acid composition in Holstein-Friesian bull calves." J Anim Sci, 1999;77(6):1422-30. PMID: 10375220.
- [pubmed] McLaughlin CL, et al. "Performance, clinical chemistry, and carcass responses of finishing lambs to formulated sometribove (methionyl bovine somatotropin)." J Anim Sci, 1994;72(10):2544-51. PMID: 7883610.
Sources & Citations
Every study on this page was read from its PubMed record on October 30, 2026. Approval status comes from the FDA Green Book, the DailyMed veterinary label and the EMA medicines list, read October 28, 2026; a PubMed search for sometribove or Posilac returned 104 records, none a study in people. Grey Peptides sells nothing and links to no vendor.
Medical Disclaimer: This content is for educational and informational purposes only. It is not medical advice, and nothing here is an instruction to obtain or use any compound. Talk to a licensed clinician about your own situation.