Caring for a pregnant mare (UK): the HBLB codes, the EHV vaccine and the complications to know

By Sebastien Kister

Last reviewed 8 November 2026

A mare carries her foal for about eleven months, and for most of them she needs little more than she did before: the same forage, her exercise, her vaccines and her feet kept up. What changes is the last third, when the foal does most of its growing, and the foaling itself, where minutes count. In Britain two more things frame the year: the breeders' codes of practice, which set the tests a stud asks for and what happens after an abortion, and the foal's passport deadline. This page takes the pregnancy stage by stage, with what the veterinary sources say at each, then the complications worth knowing by their signs.

The pregnancy at a glance

The dates of each step, from the day she was bred, are on the foaling date calculator, which also gives the due date and the normal window around it. In outline:

Before she is covered: the HBLB codes

The Horserace Betting Levy Board publishes International Codes of Practice for breeders and revises them every year. They are voluntary recommendations, made for all breeds of horse and pony rather than for Thoroughbreds alone, and they are common to France, Germany, Ireland, Italy and the UK. A stallion stud working to them asks, for each mare it covers, for a laboratory certificate showing she is free of infection this season and a current mare certificate. The tests behind those certificates:

• Contagious equine metritis (CEM). A clitoral swab, taken at home or at the stud, and an endometrial swab taken from the uterus while she is in season, tested at a laboratory registered by BEVA for the purpose. A high-risk mare, which usually means one from outside the five countries, has more swabs, and her first before she arrives. CEM is notifiable across the UK: a laboratory finding of the organism must be reported to the Animal and Plant Health Agency under the Infectious Diseases of Horses Order 1987.
• Equine viral arteritis (EVA). The codes call it the safest option to blood test every mare, whether she is to be covered or inseminated, after 1 January and within 28 days before she is bred, and not to use her until the result is back. EVA is notifiable under the Equine Viral Arteritis Order 1995 when it is suspected in a stallion, or in a mare mated or inseminated in the previous 14 days.
• Equine infectious anaemia (EIA). There is no vaccine, so freedom is shown by a blood test, which can be taken from the same sample as the EVA test. Stallion studs may require it of every visiting mare, whether or not she has been anywhere EIA occurs, taken after 1 January and ideally within 28 days of mating. EIA is notifiable in Great Britain.

The codes ask mare owners to check the stud's own requirements well in advance of the date she travels. Equine herpesvirus is not notifiable: no law in the UK requires an EHV abortion to be reported, but the codes recommend telling your breeders' association all the same, the Thoroughbred Breeders' Association for Thoroughbreds and the breed society for others.

England's welfare code adds its own question before any of that: whether the mare is a suitable candidate for breeding, whether the stallion has been inspected and is free from heritable conditions, and whether you could buy or rehome a youngster instead. It reminds owners that a foal is expensive in money and time, that there is no guarantee it will turn into the horse you wanted, and that its future, at a time of too many horses in the UK, should be thought through before she is bred.

Feeding her through the pregnancy

For most of the pregnancy, a mare needs no more than she did before she was bred. The National Research Council's 2007 figures, as the Merck Veterinary Manual gives them, leave her energy needs unchanged until month five, then raise energy, protein and lysine by "approximately 3–4% over maintenance each month". For a 500 kg mare not in work, that is:

Protein rises faster at the end: 21%, 25% and 30% above maintenance in months nine, ten and eleven. That is when the foal grows: the Western College of Veterinary Medicine puts 65 to 70% of its growth in months eight to eleven, and Merck's chapter on the mare and foal expects her to gain 68 to 90 kg over the last three months. The same college adds that before month eight, a mare on good feed needs nothing extra, which the NRC's few per cent barely contradict.

How to give it matters as much as how much. England's welfare code names pregnant mares among the horses with special dietary requirements, asks you to consult your vet or an equine nutritionist if you have any concerns, and wants every change to the diet made gradually. The sources agree:

• Gradually. Merck asks for "a gradual, increasing plane of nutrition" in the last three months. The University of Kentucky's advice: raise her feed slowly, over seven to fourteen days, never by dramatic amounts.
• Denser, not just more. In the last two months the foal takes room, and Merck notes that she may eat less roughage. The ration's energy then has to come from a concentrate, Merck suggesting one of 12 to 14% protein, or, if she holds her condition on forage alone, from a ration balancer, as Kentucky advises.
• The same hay. Kentucky would keep her on the hay she knows; if it has to change, start the change at least a week to ten days before she foals.

Her condition

Not too thin, not too fat, and the sources do not quite agree on the number. Merck's nutrition chapter keeps broodmares at a body condition score of 5 to 6 out of 9, 6 being ideal, and Kentucky aims for 5 to 6 in late pregnancy. Merck's chapter on the mare and foal puts the ideal at foaling higher, at 6.5 to 7.5. On why it matters they agree: a mare that is too fat runs more risk of metabolic trouble, laminitis and a difficult foaling; one too thin milks poorly and is harder to get back in foal, and, as Extension Horses notes, condition is very hard to put on once she is feeding a foal. All of those figures are on the nine-point scale. The chart in England's welfare code has six bands, from emaciated to obese, so write the scale beside the number; the UK feeding guide explains why that matters. The weight calculator tracks her from a tape measure.

Minerals: more is not safer

• Iodine. Merck reports iodine poisoning in pregnant mares eating as little as 40 mg a day, and goitre in mares and their foals, several cases from kelp supplements.
• Selenium. The margin between too little and too much is narrow, and some forages carry enough to poison. Too little in the mare's diet, and her foal can be born with nutritional myodegeneration, the muscle disease also called white muscle disease. Whether her ration needs selenium depends on where it was grown: ask your vet before adding any.
• Copper. Studies disagree on whether extra copper for the mare protects her foal's joints: one trial found fewer lesions, two later ones found no effect.

Exercise and riding

Merck asks for "adequate daily exercise in a paddock or pasture" right through the pregnancy. Riding is less settled. Two small studies found no harm from moderate work: mares exercised for 45 minutes six days a week from day 16 to day 80 of pregnancy all went on to deliver healthy foals, and in six pregnant Standardbreds put through short graded treadmill tests at about nine months, the foal's heart rate did not change. No veterinary body we found sets a date by which riding must stop, so how long to keep her in work is a question for your vet, and the answer may depend on her and on the work.

Where she lives, and with whom

Most adult horses probably carry EHV without showing it, and can shed it again under stress, which is why the HBLB's code on the virus spends as much time on how pregnant mares are kept as on vaccines. Its recommendations:

• Apart from other stock. Pregnant mares are kept separate from young stock (weaned foals, yearlings, horses out of training) and from non-pregnant horses and ponies of every kind. England's welfare code gives the same reason in one line: EHV is common in young horses, so pregnant mares should be separated from them.
• Small groups, similar dates, outdoors. Groups as small as possible, of mares due at about the same time, formed early in the pregnancy and kept together without re-mixing until they foal, out at pasture rather than stabled, and above all not in barns that share one air space. Stabling a mare suddenly after she has lived out can bring on an EHV abortion, even in a vaccinated herd.
• Foaling at home, if possible. The code would have a mare foal at home and go to the stallion with a healthy foal at foot. If she has to foal away, she should arrive at the stud at least 28 days before she is due, spend two weeks in quarantine, then join a small group of healthy mares at a similar stage.
• Travelling and new arrivals. A pregnant mare should not travel with other horses, mares that have recently aborted least of all. One arriving from a sale or from abroad counts as high risk, and every new arrival, or horse returning from elsewhere, is quarantined away from the residents.

Late in the pregnancy, England's code adds that a mare heavily in foal may need to be kept apart from other horses, and that a communal barn may not suit her; Scotland's code says that in a communal barn she should be. A mare with a young foal can be very protective of it, and the code asks that she be kept away from other horses and from the public if she is.

Vaccines and worming

EHV. The one EHV vaccine the HBLB's 2026 codes list as available in the UK is Zoetis's Equip EHV-1,4, and its authorisation from the Veterinary Medicines Directorate sets the schedule for pregnancy itself: a single dose during the fifth, seventh and ninth months, to reduce abortion caused by EHV-1. It is a prescription medicine, so it comes through your vet. On a stud farm the codes ask for more: every resident horse fully vaccinated, with boosters every six months, and the pregnant mares given their doses at five, seven and nine months on top. Vaccination will not stop an individual mare aborting, the codes say, but abortion storms are much less likely in properly vaccinated mares. Some vets add a dose at three months (the AAEP's guidelines).

Flu and tetanus before she foals. The codes' guidelines on equine influenza advise a flu booster about four to six weeks before her predicted foaling date, given with her tetanus booster as a combined vaccine, so that her colostrum carries the antibodies to the foal. The UK vaccination guide has the flu rules if she also competes or races. Early in pregnancy, the sources hold off: the University of Minnesota gives no vaccine in the first 60 days, and Merck's chapter on the mare and foal says vaccination is avoided in the first 90.

Worming is safer than many owners think. Merck says "most anthelmintics are safe for use throughout pregnancy", provided the warnings on the label are followed. The label is where the exceptions are: fenbendazole was tested in mares at every stage of pregnancy with no effect on reproduction, but its five-day, 10 mg/kg larvicidal (large strongyle) course "has not been evaluated" in pregnant mares. In a study of ivermectin with praziquantel, twenty mares dosed at three times the dose every two weeks until they foaled, and their foals, showed no ill effect.

Around the foaling, the sources disagree outright. Merck advises ivermectin or a benzimidazole one to three days before foaling, against the threadworm Strongyloides westeri, which reaches the foal through the milk. The AAEP's parasite guidelines say there is "no basis" for that practice at present, and the University of Kentucky's parasitologist Martin Nielsen advises treating pregnant mares like any other adult, having found no rise in their egg counts around foaling. Others worm the mare after the foaling instead, from within 48 hours (another Merck chapter) to about a week (Colorado State). Which your vet or prescriber follows is their call; a faecal egg count says whether she needs a wormer at all.

In Great Britain a wormer sold as a POM-VPS medicine can be prescribed and supplied by a vet, a pharmacist or a suitably qualified person (SQP), and the prescriber does not have to examine the horse. Tell them she is in foal, and when she is due: the label's exceptions are the ones that matter for her. The UK worming guide covers egg counts and the supply rules.

Feet, teeth and the Caslick

We found no guidance that changes a pregnant mare's routine care: Merck's intervals, a trim about every six weeks and teeth checked at least once a year, still apply (the farrier and dental guides have the detail). If work on her needs a sedative, that is your vet's decision: the studies of sedatives in pregnant mares are small.

A mare stitched with a Caslick (a vulvoplasty, which closes the top of the vulva against infection) must be opened before she foals, or the foal will tear her. Merck says about two weeks before, Nebraska Extension at least 30 days. EquiDiary's pregnancy plan offers it as a step of its own.

Getting ready to foal

The place. England's and Scotland's welfare codes say only that boxes for foaling, and for mares with a foal at foot, need more space than an ordinary stable, for which they quote the British Horse Society's minimum of 3.65 × 3.65 m (12 × 12 ft) for a horse. Penn State Extension, Nebraska Extension and Merck put a foaling box at 4.3 × 4.3 m (14 × 14 ft) at least, and Merck finds a double box of 3.7 × 6.1 m (12 × 20 ft) better still. A small grass paddock works too; Penn State prefers it to a dry lot, and Merck notes that mares do well foaling outdoors on turf, weather permitting. Wherever it is, it is where she should already be living: the calculator dates the move.

The bedding. Straw, deep and clean. Penn State advises against shavings, whose dust raises the risk of respiratory infection, and Merck because they get into the newborn foal's nostrils and mouth.

The kit. The AAEP's foaling checklist names a clean tail bandage, an umbilical disinfectant, towels, warm water with a mild soap, scissors, gloves and a Brix refractometer, which tells you in seconds whether her colostrum is good enough. Colorado State's longer list adds a thermometer, milk-calcium test strips and foal IgG tests; Penn State's puts the vet's number at the top, with a torch, a head collar and a lead rope. When labour starts, wrap her tail and wash her vulva and udder (Nebraska, Penn State).

The signs. How the udder fills, waxing, and the milk tests that predict the night are on the foaling calculator.

The foaling, and its time limits

A mare's labour has three stages, and the second is short: a foal held up in it, or with its cord squeezed, runs short of oxygen (the Western College of Veterinary Medicine).

What normal looks like. A white, glistening membrane (the amnion) first, then two front feet, soles down, one a hand's width ahead of the other (Merck puts it at about 15 cm), then the nose lying on them, "a diving position", as Penn State puts it. Anything else is a call to the vet straight away: one foot only, soles pointing up, a nose without feet, a tail, or a red membrane instead of the white one, which is the emergency called a red bag, below.

The placenta. Never pull it, and never cut it away. Tie it up so that she cannot tread on it, and keep it for the vet, who checks that it came away whole (the AAEP, Penn State, Colorado State): a piece left inside can make her very ill. Handle it with gloves. A normal one weighs about a tenth of the foal (Merck).

The first hours: the 1-2-3 rule

The AAEP's foaling sheet gives it as: the foal stands within one hour, nurses within two, and within three passes its first droppings (the meconium), while the mare passes the placenta. Colorado State's version is the same without the meconium. Merck is a little more patient: in nine foalings out of ten, the foal lies on its chest within an hour, stands within two and nurses within three. A foal behind those times needs the vet.

A foal takes its first antibodies from the colostrum, and can absorb them only in the first 18 to 24 hours (Merck, Cornell). That is why the vet's check of the newborn is usually made at 12 to 24 hours (Colorado State, Penn State, Cornell), with a blood test for IgG, the antibodies the colostrum passed on. Below 400 mg/dL at 24 hours the transfer has failed, and 400 to 800 is partial (Merck); below 800, Merck's chapter on the mare and foal has the vet give plasma. The Brix refractometer in the kit reads the colostrum before the foal does: above 30% is excellent, below 20% not enough (Cornell).

Merck has the navel dipped in 0.5% chlorhexidine or 1% povidone-iodine. Most foals pass the meconium within a few hours, some not for nine to twelve (Penn State); a foal straining without result, or none passed by 24 hours, needs the vet.

After the foaling

A reddish-brown discharge in the first week is normal; a white one may be an infection and needs the vet (Nebraska Extension). Colic after foaling needs more care: mild cramps are common, but in an older mare, colic with pale gums is the sign of the bleeding described below. Her foal heat comes 5 to 11 days after foaling in most mares (Merck). Mares bred after day 10 conceive more often, and Merck advises against breeding on it at all after a difficult foaling or a retained placenta. In a study of over 3,000 cycles on one Kentucky Thoroughbred farm, mares bred before day 22 were less likely to conceive and those bred before day 13 more likely to lose the pregnancy. If she is to be covered again, the HBLB codes add one test for a mare whose foaling was difficult enough to need a vet and antibiotics: an extra clitoral swab after the foaling, taken more than seven days after the treatment ended, besides the usual endometrial swab.

Registering the foal

Every foal born in Great Britain needs a passport from a passport issuing organisation and a microchip, which only a vet may implant (in England, a member of the Royal College of Veterinary Surgeons). Every equine living in the UK has to be on the Central Equine Database, and the issuing organisation records the foal there. The deadline depends on the nation the foal lives in:

Until then the foal may move with its dam or a foster mare. Trading Standards' guidance for England adds that it may be sold without a passport if it stays with its dam, and that one to be sold before the deadline otherwise needs its microchip and passport sooner. The UK passport guide has the rest, the food-chain page included.

Complications, and the signs an owner sees

Most pregnancies run their course with none of what follows. Each is here for the signs an owner can see, because in most of them what decides the outcome is how soon the vet is called.

Twins

A mare's uterus cannot carry two: the placenta that two foals share is too small, and Colorado State puts the chance that a twin pregnancy ends with two live, healthy foals at under 10%. Left alone, twins are usually aborted at seven to nine months (Colorado State; eight to nine, says Merck), sometimes after the udder has filled early. This is what the first scan at days 14 to 16 is for: the vet can see both embryos and pinch one out while they still move around the uterus, before they settle at about day 16. Thoroughbreds, warmbloods and draught breeds have twins most often (Colorado State), and twins were the cause of about 6% of the losses that diagnostic laboratories investigated in Kentucky and in the UK.

Early pregnancy loss

In 2,246 Thoroughbred pregnancies on 29 UK studs, 6.4% were lost between day 15 and day 42, and 1.6% more by day 65; another study put the loss from day 15 to day 65 at 7.9%, the odds rising with each year of the mare's age. There is nothing to see: the mare may simply come back into season. Only a scan finds it, which is what the later checks in the calendar are for.

Abortion, and what to do if it happens

Later in pregnancy a mare can lose her foal to an infection — of the placenta, below, or EHV, equine viral arteritis or leptospirosis — or to something else: twins, a twisted umbilical cord, a high fever or a severe illness (the AAEP's guidelines on infectious abortion). Often there is no warning at all. The HBLB's code asks for a sudden, unexpected abortion to be treated with suspicion until EHV is ruled out, and its steps are the ones to follow:

• Call the vet straight away, and put the mare in strict isolation.
• Keep the foetus and the whole placenta, double-wrapped in strong, leak-proof bags or containers, for your vet to send to a laboratory that can examine them for EHV, kept cool in a cool box with ice packs (the AAEP) but never frozen (Merck). Only a laboratory can say why, and the answer decides what the other mares need: even two large Kentucky series of aborted foetuses, stillborn and newborn foals found no cause in about one case in six. For members of the Thoroughbred Breeders' Association, the codes say a contribution may be available towards the laboratory's costs for an aborted foetus or a foal that dies within 14 days of birth.
• Close off the place it happened, so that no pregnant mare, including those that were with her, can reach it, and disinfect it once everything is removed. Do not spray or hose the foetus and membranes, which can put the virus in the air (the AAEP's abortion guidelines). Whoever handles the foetus should have no contact with other horses, pregnant mares above all.
• Stop horses leaving the premises, and let no pregnant mare in, until EHV is ruled out; destroy the contaminated bedding and disinfect the boxes, equipment and lorries, as your vet directs (the HBLB codes).

EHV-1 abortion

The equine herpesvirus aborts mares from about the seventh month, most often in the last third of the pregnancy, from two weeks to several months after the infection, and the mare shows nothing beforehand (Merck, the AAEP); the HBLB's code puts most of them from the eighth month on, and some as early as the fourth. The foetus is often born still inside its membranes. A foal infected late may instead be born alive but weak, jaundiced or struggling to breathe, and usually dies, or has to be put down, within three days (the HBLB codes). It spreads among pregnant mares, and although single cases are now the rule, outbreaks of several abortions still happen (Kentucky). If a laboratory confirms EHV, the codes keep isolation, movement restrictions and the hygiene measures in place for at least 28 days after the last EHV abortion, stillbirth or newborn foal death; the pregnant mares on the premises stay there until each has foaled a healthy foal, and the mare that aborted is kept from pregnant mares for the rest of the season. The vaccine in the fifth, seventh and ninth months, small groups, and keeping pregnant mares away from young and travelling horses are the prevention, though a vaccinated mare can still abort.

Placentitis

An infection of the placenta, usually climbing in through the cervix, and one of the main causes of late abortion, of foals born early and of foals that die in their first day (Merck): the University of Kentucky puts it behind nearly a third of late abortions and of deaths in a foal's first day. The signs: an udder that fills, or milk that runs, weeks or months before she is due — an udder should develop in the last couple of weeks, Colorado State says, not months — and a discharge from the vulva. Call the vet promptly: treatment works best when it starts early, and does not always work (Kentucky). A Caslick for a mare whose vulva does not close well, and clean breeding, are the prevention (Merck).

Milk before foaling

Milk that runs before the foal is born, whatever the cause (placentitis, twins, an abortion on its way), is colostrum the foal will not get, and Merck lists it among the reasons a foal fails to receive its antibodies. Call the vet, who may have it milked and frozen for the foal (Extension Horses), and make sure the foal's IgG is tested after the birth. The Brix refractometer grades the colostrum she has left: under 15% poor, 15 to 20% borderline, 20 to 30% adequate, over 30% good (the AAEP).

Hydrops

Too much fluid around the foal, usually the allantoic fluid (hydrallantois), building up over days to weeks in the last third of the pregnancy. The belly grows suddenly — in one reported case of hydramnios, from 230 to 320 cm around in six days — with a painful swelling underneath, reluctance to walk, laboured breathing, colic or a mare off her feed. It is rare and an emergency, because the weight can tear the body wall. In a Kentucky hospital series of 30 mares over ten years, 27 of 30 mares survived, and 95% (20 of 21) of those bred again had a foal.

Body wall tear and prepubic tendon rupture

Late in pregnancy, mostly in older mares and after hydrops, the wall of the belly, or the tendon that anchors it to the pelvis, can give way under the weight. The signs: a sudden swelling along the underside, often with a lot of oedema, a mare unwilling to walk, and the udder pushed forward. Call the vet now. A mare with a torn wall cannot push the foal out herself, so the foaling is assisted or a caesarean (the Western College of Veterinary Medicine). In a series of 13 mares, foals did better when the birth was not induced.

Uterine torsion, and colic in a pregnant mare

The uterus can twist on itself in the second half of the pregnancy or at foaling, cutting the foal's blood supply. What you see is colic, severe or subtle, easily taken for gut pain or for the start of labour. It usually needs surgery; in one series, 97% of mares and 72% of foals survived when it happened before day 320, against 65% and 32% after. Any colic in a pregnant mare needs the vet: of the pregnant mares one referral hospital treated for colic, 70% went home, and a fifth of the pregnancies then ended badly.

A difficult birth (dystocia)

Most difficult births are a foal in the wrong position, rarely one too big to pass (Merck), and for the foal, minutes count. In a study of over a thousand births, a second stage longer than 40 minutes significantly raised the foal's risk of dying, and only 37% of foals survived once a dystocia had to be resolved at a hospital. Call the vet if there is no progress 15 to 20 minutes after the waters break, or for one foot only, more than two, feet upside down, a nose without feet, feet without a nose, or a foal coming backwards (Extension Horses, the American College of Veterinary Surgeons). While you wait, walk her, so that she does not lie down and strain, and do not pull on the foal unless the vet tells you to (Penn State).

Red bag

The membrane that appears first should be white. If a red, velvety one appears instead, the placenta has come away from the uterus before the foal is out and the foal is losing its oxygen: Merck calls it the most acute cause of a foal's asphyxia. Call the vet, and do not wait for them: Merck, Colorado State and Penn State all say to cut or tear the red membrane open and deliver the foal, carefully, so as not to cut it, which is why scissors are in the kit. Colorado State links it to placental infection and to stress.

Retained placenta

A placenta not passed within three hours is retained (Merck, the AAEP, Penn State and most others), which happens in 2 to 10.6% of mares, Friesians more than most (Merck). In a mare it is serious: it can bring an infection of the uterus, endotoxaemia and laminitis (Merck). Do not pull it; tie it up and call the vet.

Bleeding after the foaling

An artery to the uterus can tear, most often in older mares: in Kentucky's post-mortem records, 78% of the 513 mares that died of it were 15 or older. Younger mares are not spared: in 73 cases referred to a hospital, the median mare was 14 and had had eight foals, the youngest was 5, and the authors found it can happen at any age and after any number of foals; 86% of those mares bled after the foaling rather than before. The signs are those of colic — pawing, sweating, rolling — then of shock, with pale gums and a racing heart; or sudden death. A mild case can pass for the cramps that often follow a foaling, which is why a mare that seems uncomfortable afterwards should be seen. Call the vet now.

Hyperlipaemia in ponies, miniatures and donkeys

A pony, a miniature horse or a donkey that stops eating can flood her blood with fat until her liver and kidneys fail, and late pregnancy is the classic time (Merck): in a UK series, 9 of the 14 mares affected were in foal, and 12 of the 18 animals were fat. The signs are dullness, not eating, weakness, and later a swelling under the belly, colic and trembling. Call the vet the same day: two in three animals in that series died. England's welfare code warns that obesity in donkeys can bring on a disorder that can be fatal, and asks for extra care that they do not become overweight.

Tears in the birth canal

Most happen at a first foaling, with a large or badly placed foal or a forceful assisted delivery. They are graded from first degree to third, which runs through the anal sphincter; a foot pushed up through the roof of the vagina leaves a hole into the rectum, a rectovaginal fistula. Check her for tears after the foaling (Penn State); the repair usually waits four to six weeks.

Related guides

• Foaling date calculator — the due date, the normal window and every step dated from one day
• Horse vaccination schedule (UK) — flu boosters, tetanus, and the rules by discipline
• Horse worming schedule (UK) — worm egg counts, tapeworm tests and winter redworm
• Horse passports and microchipping in the UK — the food-chain page, imports and changes of owner
• Horse feeding plan (UK) — what the Defra code asks for, and the condition scale it prints

Sources

• Horserace Betting Levy Board — International Codes of Practice, 2026, and the full 2026 codes: the introduction (voluntary, all breeds, five countries), the codes for CEM, EVA, EHV (management of pregnant mares, vaccination, what to do after an abortion, notification) and EIA, the guidelines on equine influenza (boosters before foaling) and appendix 8 (vaccines available in the UK, November 2025)
• Veterinary Medicines Directorate — Equip EHV1,4, summary of product characteristics (Vm 60021/3009, approved October 2025): the fifth, seventh and ninth months
• Defra — Code of practice for the welfare of horses, ponies, donkeys and their hybrids (England; PDF), paras. 1.15, 1.16, 2.13, 2.14, 4.6, 5.9, 5.15 and 5.16; Scottish Government — Welfare of equidae: code of practice (stable sizes, and mares in communal barns)
• The Equine Identification (England) Regulations 2018, regs. 6 (the application deadline) and 13 (microchips by a vet); Business Companion (Trading Standards) — Horse passports, England (May 2026) and Wales (June 2026); Scottish Government — Horse passports: application and identification deadlines (2019); British Equestrian — Introduction to passports (the Central Equine Database)
• GOV.UK — Retail of veterinary medicines (POM-VPS, SQPs, no clinical assessment)
• Merck Veterinary Manual — Nutritional requirements of horses (2026: the NRC's needs by month, condition, minerals) and its table of energy needs in pregnancy; Perinatal mare and foal care (feeding, condition at foaling, exercise, vaccines, the foal's first hours); Parasite control during pregnancy; Parturition (stages, the Caslick, red bag); Dystocia; The early postpartum period (foal heat); Failure of transfer of passive immunity; Abortion in horses and its reproductive-system chapter (twins, EHV, placentitis); Retained fetal membranes; Neonatal encephalopathy (red bag); Hyperlipemia; Nutritional myopathies (selenium); Dental, coat and hoof care
• AAEP — Foaling monitor sheet (2025: the kit, the time limits, the 1-2-3 rule, colostrum grades); Equine infectious abortion field diagnostic guidelines (2026); EHV-1 and EHV-4 guidelines; Equine alphaherpesvirus vaccination guidelines (2025: the extra dose at three months); Internal parasite control guidelines (worming at foaling)
• University of Kentucky — Broodmares' nutritional needs during late gestation (2012); Sustainable equine parasite control (2012); Placentitis research (2009); Manifestations of equine herpesvirus-1
• Colorado State University Equine Reproduction Laboratory — Twin management (2022); Red bag in horses (2025); Placentitis in mares (2025); Foaling out: easy as 1-2-3 and Foaling kit checklist (2024); CSU Veterinary Health, Foaling guide (2022)
• Penn State Extension — Foaling season: tips for delivery (2025); When to call the equine vet (2025)
• Nebraska Extension G1874 — The foaling mare (2008); Extension Horses — Nutritional considerations for broodmares and Horse foaling management guidelines (2020); University of Minnesota Extension — Caring for your mare (no vaccines in the first 60 days); Western College of Veterinary Medicine — The foaling mare; Cornell — Foal speed ahead (2023); American College of Veterinary Surgeons — Dystocia in horses
• Label: fenbendazole for horses (DailyMed, US National Library of Medicine)
• Studies — exercise: days 16 to 80, 2014, treadmill at nine months, 2009; worming: ivermectin and praziquantel, 2003; copper: 1998, 2005, 2007; early loss: UK studs, 2018, 2019; causes of abortion: Kentucky, 1993, a second Kentucky series, 1993, UK, 2003; hydrops: Kentucky, 2022, 2021; body wall: 2008; uterine torsion: 2007; colic: 2021; dystocia: 2012, 2024; bleeding: 2008, Kentucky post-mortems, 2012; hyperlipaemia: 1992; rebreeding: 2012; tears: 2025

The HBLB revises its codes every year and guidance on pregnant mares changes as studies come in; the sources above disagree in places, which this page says where they do. Your vet sets your mare's programme.

Next: the foaling date calculator — the due date, the window, and the calendar of the pregnancy.

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