Pegbovigrastim
The PEGylated cow G-CSF injected around calving to raise neutrophils, what the large dairy trials found about mastitis and metritis, and why it is not a human medicine
Pegbovigrastim is bovine granulocyte colony-stimulating factor (G-CSF), the hormone that tells the bone marrow to make neutrophils, made by recombinant DNA and joined to polyethylene glycol so it lasts longer. Sold for cattle as Imrestor, it is injected under the skin of dairy cows about a week before calving and again on the day of calving, the weeks when their white cells work least well. It reliably multiplies blood neutrophils. Whether that prevents disease varied between trials: several large ones found less clinical mastitis, others found none, and some found more uterine infection. It is approved only for animals, and no study has given it to people.
No established human dose Details ↓
Recommended Dosing
No established human dose
No human dose exists for pegbovigrastim. It is approved only as a veterinary medicine for cattle, and every study read here was done in dairy cows, heifers or calves with amounts chosen for those animals.
What is it?
In the weeks around calving a dairy cow's immune system is at its weakest. Her neutrophils, the white cells that rush to infected tissue and kill bacteria, are fewer and less effective, at the very time the udder starts producing milk and the uterus is recovering from birth. That is when mastitis (infection of the udder) and metritis (infection of the uterus) are most common, and both cost farmers money and cows their health. Pegbovigrastim was developed to bridge that gap.
It is the cow's own granulocyte colony-stimulating factor, G-CSF, the signal that makes the bone marrow produce and release neutrophils, manufactured by recombinant DNA. On its own the protein is cleared within hours, so it is joined to a chain of polyethylene glycol (PEG) to make it last longer. The product, Imrestor, is approved for cattle in the United States and the European Union and is given as two injections under the skin: about a week before the expected calving date and again within a day after calving.
The blood effect is large and consistent. In a randomised trial in 34 Holstein cows, neutrophil counts roughly quadrupled within a day of the first injection, rose further after the second, and took about three weeks to return to baseline. Studies in New Zealand, Canada, Italy, Brazil and the United States all saw higher neutrophil, monocyte and lymphocyte counts, more myeloperoxidase release, and gene-expression changes in blood and uterine cells that point to cells primed to migrate and fight bacteria. A half or quarter dose, or a single injection, still raised counts, but with a different timing and duration.
Whether more neutrophils mean less disease is where the trials diverge. The US registration-type field study found 35% less clinical mastitis in the first 30 days of lactation; a 17-herd Mexican study of more than 10,000 cows found 25% less; and a four-farm New Zealand trial of 2,153 grazing cows found about a quarter fewer first cases of mastitis in the first month, an effect strongest in over-conditioned cows. But a Canadian trial of 1,607 cows found no effect on any recorded disease and slightly less milk early on, and a Florida trial of 840 cows found treated cows more likely to get at least one clinical disease. Several studies, including the Mexican one, reported more metritis in treated cows.
The mixed record has a partial explanation in the data. In New Zealand, the benefit on fertility and culling showed up only in cows with high fat-mobilisation markers before calving, the ones most likely to be immunosuppressed. Smaller studies have tried new uses: as an add-on treatment for severe mastitis, where survival over 30 days was 84% against 46% with saline; at drying-off, where a 20-cow pilot saw fewer udder infections; and in calves, where it raised white cell counts and phagocytosis but did not help calves infected with Mycoplasma bovis in one model. One small study found slower growth in calves born to treated cows.
Pegbovigrastim is a veterinary medicine. It is approved only for cattle, no study has given it to people, and the amounts in the cards below are amounts given to cows and calves. Human medicine uses its own recombinant human G-CSF products, filgrastim and pegfilgrastim, which are prescribed for low neutrophil counts after chemotherapy; a cow protein is not a substitute for them.
Mechanism of Action
Pegbovigrastim binds the G-CSF receptor on neutrophil precursors in the bone marrow and on mature neutrophils, so more neutrophils are made and released and those in circulation are more active; the PEG chain slows its clearance so two injections cover the weeks around calving.
More neutrophils from the marrow
Counts in cows rose four- to five-fold within a day of the first injection and stayed above controls for about three weeks after the second.
More active neutrophils
Treated cows' neutrophils released more myeloperoxidase and, in several studies, showed more phagocytosis and oxidative burst; genes for adhesion, pathogen recognition and killing were expressed at higher levels.
Longer-lasting through PEGylation
Joining G-CSF to polyethylene glycol slows its removal, which is why a short course of two injections covers the transition period.
Not always less disease
More circulating neutrophils did not translate into fewer infections in every herd; the benefit was clearest in cows with high fat mobilisation before calving.
Published Research
These studies of pegbovigrastim were read from their PubMed abstracts on October 30, 2026. Every one was done in dairy cows, heifers or calves; none was carried out in people, and the amounts in the cards are veterinary amounts given to cattle, not human doses. They include the large field trials on disease, fertility and economics, the blood and gene-expression studies, and the newer trials of other timings and uses.
US multicentre field study: 35% less clinical mastitis
In cows and heifers on US commercial dairies treated about a week before and within a day of calving, neutrophil numbers rose four- to five-fold within 24 hours and stayed up for at least a week after the second dose. Clinical mastitis in the first 30 days fell by 35% against saline, failure to show heat by 80 days fell by 52%, and milk composition, pregnancy length and calf viability did not differ.
More than 10,000 cows in 17 Mexican herds
Treated cows had 25% less clinical mastitis in the first 30 days and needed fewer mastitis treatments, but metritis was 17% more frequent. Retained placenta did not differ, the odds of insemination in the first 100 days rose slightly, and treated multiparous cows that did get sick gave more milk than sick controls. Controls received no placebo.
2,153 grazing cows in New Zealand: fewer mastitis cases, no effect on metritis
Across four farms, treatment cut first cases of clinical mastitis in the first 30 days by 24.6% and reduced cases over the full lactation, though the protection faded as lactation went on. In over-conditioned cows the cut was 49.5%. Retained placenta and metritis were unchanged.
1,607 Canadian cows: no effect on disease
In a double-blind, placebo-controlled trial on six farms, given as the label directs, there was no effect on retained placenta, metritis, displaced abomasum, clinical or subclinical mastitis, vaginal discharge or endometritis, nor on culling or fertility. Treated cows had slightly lower blood glucose and gave about 1 kg a day less milk over the first three test days.
840 Florida Holsteins: more clinical disease
Treatment tripled to quadrupled circulating neutrophils, lymphocytes and monocytes, yet did not reduce mastitis, retained membranes or metritis. Treated cows had higher odds of one or more clinical diseases (odds ratio 1.39), and the authors concluded it was detrimental to health in this herd; first-calf heifers gave more milk.
270 cows: more clinical metritis
Milk yield and composition were unaffected and too few mastitis cases occurred to compare. Treated cows were 2.46 times more likely to develop clinical metritis, while puerperal metritis did not differ.
Embryo-recipient Jersey cows induced to calve
In 60 cows carrying transferred embryos, metritis tended to be more common after treatment (25% against 8.8%), with no effect on mastitis, culling or early-lactation fertility.
Fertility and culling depend on pre-calving fat mobilisation
In the New Zealand trial cows, treatment helped only those with high non-esterified fatty acids before calving: they were inseminated sooner (hazard ratio 1.15) and culled less (0.79), and those with mastitis or uterine disease got pregnant sooner. Cows with low fatty acids showed no effect.
The New Zealand trial's economics
Over a full lactation, partial net return was higher in treated cows by about 210 US dollars per cow per year, mostly through lower mastitis-treatment costs and a non-significant drop in culling costs.
Antibiotic use in four UK herds
Of 1,865 cows, 11.6% of treated and 13.2% of untreated cows received an antibiotic in the first 30 days of lactation (odds ratio 0.51), but the effect varied by farm: on one of the four, untreated cows were treated less often.
How far and how long neutrophils rise
In 34 Holsteins, neutrophils rose from about 4.3 to 18.2 × 10⁹ per litre the day after the first injection and from 16.4 to 32.8 the day after the second, then fell back to baseline over about three weeks. Controls stayed flat.
Lower dose rates and a single injection
In grazing cows, half and quarter dose rates still raised neutrophils, band cells, lymphocytes and monocytes and myeloperoxidase activity in a dose-dependent way. One injection a week before calving had no lasting effect after calving; one on the day of calving gave a delayed response. Milk yield was unaffected.
White cells in first-calf and older cows
In 541 grazing cows the rise in white cells, neutrophils, lymphocytes and monocytes at about six days in milk did not depend on parity or body condition, and treatment reversed the drop in neutrophils seen in untreated cows with high fatty acids before calving.
Underfeeding before calving does not blunt the response
In 99 pasture cows, restricting feed to about 85% of energy needs before calving did not change how much treatment raised white cells or increased neutrophil myeloperoxidase release.
Neutrophil and uterine gene expression
Treatment increased expression of genes for migration, pathogen recognition and inflammation in blood neutrophils, and shifted uterine cells towards an antimicrobial profile typical of neutrophils that have reached tissue; milk cells changed in the same direction, less strongly.
Immune gene networks in Holstein and Simmental cows
Three days after calving, whole-blood leukocytes of treated cows of both breeds expressed more genes for pathogen recognition (including TLR2 and TLR4), adhesion, antimicrobial proteins and the inflammatory cascade than saline controls.
Blood counts in Simmental cows
White cells and neutrophils stayed higher than in controls for about three weeks after calving and monocytes for three days; treated cows had fewer red cells and a wider red-cell distribution width later in the month.
Add-on treatment for severe clinical mastitis
In a double-blind trial of 77 cows with severe mastitis, mostly from Klebsiella or E. coli, adding one injection to standard antibiotic and anti-inflammatory therapy raised 30-day survival to 84% from 46% with saline. Bacteriological cure and milk yield did not differ.
Pilot of injections at drying-off
Twenty late-lactation cows were injected a week before and at drying-off. Udder quarters of saline controls had five times the rate of intramammary infection; somatic cell count and milk yield showed treatment-by-period interactions. The authors call for larger studies.
No change in the vaginal microbiome
Sequencing vaginal samples from 195 cows at calving and at 7 and 35 days found that treatment did not alter the microbiome, while cows that developed metritis or vaginal discharge had distinct bacterial profiles.
Nonspecific immunity in healthy calves
In 11 five-week-old calves given two injections a week apart, total leukocytes and every subset measured rose, phagocytic activity increased, and cytokines shifted in an anti-inflammatory direction compared with saline.
Calves infected with Mycoplasma bovis
In an infection model, enrofloxacin alone worked best; adding flunixin meglumine and pegbovigrastim gave no benefit, and the combination appeared ineffective.
Calves born to treated cows grew more slowly
Eight Simmental calves from cows injected a week before calving weighed less from four weeks to two months of age, drank less milk replacer around three to four weeks, and showed lower retinol and tocopherol and higher oxidative markers than nine calves of untreated cows.
Cows with chronic Staphylococcus aureus mastitis
Four of eight chronically infected mid-lactation cows were given two injections a week apart. Blood neutrophils and lymphocytes rose, and neutrophils and macrophages in milk carried more surface myeloperoxidase, while blood neutrophils changed other surface markers.
No Established Human Dose
No human dose exists for pegbovigrastim. It is approved only as a veterinary medicine for cattle, and every study read here was done in dairy cows, heifers or calves with amounts chosen for those animals. No study giving it to people was found, so the veterinary amounts are not shown as doses and none applies to a person. People who need G-CSF are treated with the human products filgrastim or pegfilgrastim.
What this rests on: PMID 28601453, PMID 34099297, PMID 38050892.
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
Unknown: no product of Pegbovigrastim is approved for people, and we hold no copy of a veterinary label or a published test that says what forms it is sold in (its approvals are under Legal status below). A vial's own label is a seller's claim, not a source.
Mixing a vial: a worked example
Unknown: no human dose of Pegbovigrastim 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
Unknown: no label or published stability study on file says how to store Pegbovigrastim, before or after mixing. The mixing guide sets out the general rules, with their sources: keep a mixed vial in the fridge, and use it promptly, as the bacteriostatic water label says of any drug dissolved in it. The 28 days often quoted is the limit for an opened multiple-dose vial from a manufacturer, an outer limit set for sterility, not a time a mixed solution has been shown to keep. Nobody has published how long Pegbovigrastim stays intact once mixed.
How it is taken
Unknown: with no established human dose, there is no established way of taking Pegbovigrastim. 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 Pegbovigrastim 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 metritis in several herds: 17% more in Mexican herds, 2.46 times the odds in a 270-cow trial, and a trend in embryo-recipient cows (PMIDs 28161183, 32135413, 36974221); Higher odds of at least one clinical disease in an 840-cow Florida trial (PMID 30316593); Slightly lower early milk yield and blood glucose in a 1,607-cow Canadian trial (PMID 34099297); Fewer red blood cells later in the first month in Simmental cows (PMID 31640199); Slower growth in calves born to treated cows, in one small study (PMID 37012186). Full list and cautions ↓
When to stop or get help: unknown; no label or trial on file sets rules for stopping Pegbovigrastim. 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 Pegbovigrastim (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 Pegbovigrastim 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 (S0 catch-all).
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
Pegbovigrastim is a veterinary medicine. No human approval was found.
Frequently Asked Questions
?What is pegbovigrastim?
Recombinant cow G-CSF, the hormone that drives neutrophil production, joined to polyethylene glycol so it lasts longer. It is sold for cattle as Imrestor.
?What is it used for?
To support the immune system of dairy cows around calving, when neutrophil function dips and mastitis and uterine infections are common. It is injected about a week before calving and again on the day of calving.
?Does it prevent mastitis?
In several large trials it reduced clinical mastitis in early lactation by about a quarter to a third; in others it made no difference. The effect seemed largest in cows mobilising a lot of body fat before calving.
?Does it have downsides in cows?
Several studies found more metritis in treated cows, and one large trial found more clinical disease overall. One small study found slower growth in calves of treated cows.
?Is it related to filgrastim or pegfilgrastim?
It is the cattle version of the same idea. Filgrastim and pegfilgrastim are human G-CSF products prescribed to people; pegbovigrastim is the bovine protein, approved only for cattle.
?Can a person use it?
No. It has never been studied in people and is approved only for animals.
References
- [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 141-392, Imrestor, active ingredient pegbovigrastim. https://animaldrugsatfda.fda.gov/adafda/views/#/search
- [other] European Medicines Agency, medicines list (JSON report, downloaded October 28, 2026): Imrestor (pegbovigrastim): category veterinary, authorised.
- [other] US FDA, Drugs@FDA (openFDA): no application for pegbovigrastim. Read October 28, 2026.
- [pubmed] Canning P, et al. "Efficacy and clinical safety of pegbovigrastim for preventing naturally occurring clinical mastitis in periparturient primiparous and multiparous cows on US commercial dairies." J Dairy Sci, 2017;100(8):6504-6515. PMID: 28601453.
- [pubmed] Ruiz R, et al. "Investigation of the effect of pegbovigrastim on some periparturient immune disorders and performance in Mexican dairy herds." J Dairy Sci, 2017;100(4):3305-3317. PMID: 28161183.
- [pubmed] Barca J, et al. "Effect of pegbovigrastim on clinical mastitis and uterine disease during a full lactation in grazing dairy cows." PLoS One, 2021;16(5):e0252418. PMID: 34043727.
- [pubmed] Van Schyndel SJ, et al. "The effect of pegbovigrastim on early-lactation disease, production, and reproduction in dairy cows." J Dairy Sci, 2021;104(9):10100-10110. PMID: 34099297.
- [pubmed] Zinicola M, et al. "Effects of pegbovigrastim administration on periparturient diseases, milk production, and reproductive performance of Holstein cows." J Dairy Sci, 2018;101(12):11199-11217. PMID: 30316593.
- [pubmed] Oliveira MXS, et al. "Evaluation of production parameters and health of dairy cows treated with pegbovigrastim in the transition period." Prev Vet Med, 2020;176:104931. PMID: 32135413.
- [pubmed] Cortes D, et al. "Pegbovigrastim use in periparturient embryo-recipient cows: Effects on health and reproduction." JDS Commun, 2023;4(2):116-120. PMID: 36974221.
- [pubmed] Barca J, et al. "Effect of pegbovigrastim on fertility and culling in grazing dairy cows and its association with prepartum nonesterified fatty acids." J Dairy Sci, 2022;105(1):710-725. PMID: 34763910.
- [pubmed] Barca J, et al. "Pegbovigrastim treatment resulted in an economic benefit in a large randomized clinical trial in grazing dairy cows." J Dairy Sci, 2023;106(2):1233-1245. PMID: 36460504.
- [pubmed] Cook JG. "Effect of pegbovigrastim treatment on the incidence of post-calving antimicrobial treatments in four UK dairy herds." Vet J, 2020;259-260:105479. PMID: 32553236.
- [pubmed] Van Schyndel SJ, et al. "The effect of pegbovigrastim on circulating neutrophil count in dairy cattle: A randomized controlled trial." PLoS One, 2018;13(6):e0198701. PMID: 29953439.
- [pubmed] Crookenden MA, et al. "Effect of dose rate and timing of administration of pegbovigrastim on white blood cell responses in grazing dairy cows." J Dairy Sci, 2021;104(11):11955-11972. PMID: 34419282.
- [pubmed] Barca J, et al. "Increase in white blood cell counts by pegbovigrastim in primiparous and multiparous grazing dairy cows and the interaction with prepartum body condition score and non-esterified fatty acids concentration." PLoS One, 2021;16(1):e0245149. PMID: 33411851.
- [pubmed] McDougall S, et al. "Effect of prepartum energy balance on neutrophil function following pegbovigrastim treatment in periparturient cows." J Dairy Sci, 2017;100(9):7478-7492. PMID: 28647326.
- [pubmed] Heiser A, et al. "Pegbovigrastim treatment affects gene expression in neutrophils of pasture-fed, periparturient cows." J Dairy Sci, 2018;101(9):8194-8207. PMID: 29960779.
- [pubmed] Lopreiato V, et al. "Pegbovigrastim Treatment around Parturition Enhances Postpartum Immune Response Gene Network Expression of whole Blood Leukocytes in Holstein and Simmental Cows." Animals (Basel), 2020;10(4). PMID: 32260288.
- [pubmed] Trimboli F, et al. "Effect of Pegbovigrastim on Hematological Profile of Simmental Dairy Cows during the Transition Period." Animals (Basel), 2019;9(10). PMID: 31640199.
- [pubmed] Denis-Robichaud J, et al. "Randomized controlled trial of pegbovigrastim as an adjunct therapy for naturally occurring severe clinical mastitis cases in dairy cows." JDS Commun, 2021;2(6):398-402. PMID: 36337107.
- [pubmed] de Campos JL, et al. "Cows enrolled in a pilot randomized clinical trial evaluating pegbovigrastim administered to dairy cows at dry-off had reduced incidence of intramammary infection." Am J Vet Res, 2022;84(1). PMID: 36346698.
- [pubmed] Galvão KN, et al. "Effect of pegbovigrastim administration on the microbiome found in the vagina of cows postpartum." J Dairy Sci, 2019;102(4):3439-3451. PMID: 30799104.
- [pubmed] Dudek K, et al. "The effect of pegbovigrastim administration on the nonspecific immunity of calves." J Vet Intern Med, 2024;38(1):505-513. PMID: 38050892.
- [pubmed] Dudek K, et al. "Preliminary study on the effects of enrofloxacin, flunixin meglumine and pegbovigrastim on Mycoplasma bovis pneumonia." BMC Vet Res, 2019;15(1):371. PMID: 31655595.
- [pubmed] Lopreiato V, et al. "Maternal treatment with pegbovigrastim influences growth performance and immune-metabolic status of calves during the pre-weaning period." Res Vet Sci, 2023;158:151-163. PMID: 37012186.
- [pubmed] Putz EJ, et al. "Differential phenotype of immune cells in blood and milk following pegylated granulocyte colony-stimulating factor therapy during a chronic Staphylococcus aureus infection in lactating Holsteins." J Dairy Sci, 2019;102(10):9268-9284. PMID: 31400902.
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 and the EMA medicines list, read October 28, 2026; a PubMed search for pegbovigrastim or Imrestor returned 32 records, all in cattle. 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.