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Here’s a Round Up of My Premature and Dysmature Foal Research

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Here are abstracts, downloads and links for my research into the ongoing effects or premature or dysmature birth in horses.

These are the publicly available details of my thesis (full download) and published, peer-reviewed journal articles. The articles aren’t open access, but if you really want to read something, please contact me.

As always, huge thanks are due to the breeder owners who so very kindly allowed me to study their horses, and who provided such valuable images. Together, you’ve helped me to learn a lot and reach initial findings that I now hope to pass on.

 

Beyond the Miracle Foal: A Study into the Persistent Effects of Gestational Immaturity in Horses 

PhD Thesis, University of New England and CSIRO

Abstract

Breeding horses can be a financially and emotionally expensive undertaking, particularly when a foal is born prematurely, or full term but dysmature, showing signs normally associated with prematurity. In humans, a syndrome of gestational immaturity is now emerging, with associated long-term sequelae, including metabolic syndrome, growth abnormalities and behavioural problems.

If a similar syndrome exists in the equine and can be characterised, opportunities for early identification of at-risk individuals emerge, and early intervention strategies can be developed. This thesis explores the persistent effects of gestational immaturity manifest as adrenocortical, orthopaedic and behavioural adaptation in the horse.

Basal diurnal cortisol levels do not differ from healthy, term controls, but when subjected to a low dose ACTH challenge, gestationally immature horses presented a depressed or elevated salivary cortisol response, suggesting bilateral adaptation of the adrenocortical response. This may be reflected in behavioural reactivity, but the outcomes from a startle test were inconclusive.

A survey of horse owners indicated that gestationally immature horses tended to be more aggressive and active than controls, aggression being displayed mostly in families of Arabian horses. Case horses also tended to be more active, intolerant, and untrusting.

Gestationally immature horses have restricted growth distal to the carpal and tarsal joints, and this results in a more ‘rectangular’ conformation in adulthood compared to controls. They also often present with angular limb deformities that adversely affect lying behaviour and recumbent rest. This, however, can be mitigated using analgesic therapy, suggesting chronic discomfort.

Based on these findings, it is reasonable to postulate that a syndrome of gestational immaturity may persist, both clinically and sub-clinically, in affected adult horses. Further work is required to fully characterise this syndrome and validate the outcomes in larger populations, thereby providing a foundation for interventions applicable in the equine breeding industry.

Here is the downloadable doctoral thesis. This is a 236-page PDF.

Clothier, Jane  (author); Brown, Wendy  (supervisor); Small, Alison (supervisor); Hinch, Geoff  (supervisor)

 

Equine Gestational Length and Location: Is There More That The Research Could Be Telling Us?

Australian Veterinary Journal

Abstract

Clear definitions of ‘normal’ equine gestation length (GL) are elusive, with GL being subject to a considerable number of internal and external variables that have confounded interpretation and estimation of GL for over 50 years. Consequently, the mean GL of 340 days first established by Rossdale in 1967 for Thoroughbred horses in northern Europe continues to be the benchmark value referenced by veterinarians, breeders and researchers worldwide. Application of a 95% confidence limit to reported GL range values indicates a possible connection between geographic location and GL.

Improved knowledge of this variable may help in assessing the degree of the neonate’s prematurity and dysmaturity at or soon after birth, and identification of conditions such as incomplete ossification of the carpal and tarsal bones. Associated pathologies such as bone malformation and fracture, angular limb deformity and degenerative joint disease can cause chronic unsoundness, rendering horses unsuitable for athletic purpose and shortening ridden careers.

This review will examine both the factors contributing to GL variation and the published data to determine whether there is potential to refine our understanding of GL by establishing a more accurate and regionally relevant GL range based on a 95% confidence limit. This may benefit both equine industry economics and equine welfare by improving early identification of skeletally immature neonates, so that appropriate intervention may be considered.

The paper can be accessed here.

Clothier, J., Hinch, G., Brown, W. and Small, A. (2017), Equine gestational length and location: is there more that the research could be telling us?. Aust Vet J, 95: 454-461. https://doi.org/10.1111/avj.12653

Using Movement Sensors to Assess Lying Time in Horses With and Without Angular Limb Deformities 

Journal of Equine Veterinary Science

Abstract

Chronic musculoskeletal pathologies are common in horses, however, identifying related effects can be challenging. This study tested the hypothesis that movement sensors and analgesics could be used in combination to confirm the presence of restrictive pathologies by assessing lying time. Four horses presenting a range of angular limb deformities (ALDs) and four non-affected controls were used.

The study comprised two trials at separate paddock locations. Trial A consisted of a 3-day baseline phase and 2 × 3-day treatment phases, during which two analgesics were administered to two ALD horses and two controls in a standard crossover design. Trial B replicated trial A, except that as no difference between analgesics had been evident in trial A, only one analgesic was tested. Movement sensors were used to measure the horses’ lying time and lying bouts.

In trial A, ALD horses’ basal mean lying time was significantly less than controls (means ± SD for ALD horses 213 ± 1.4 minutes and for controls 408 ± 46.7 minutes, P = .007); with analgesic administration, the difference became nonsignificant. In trial B, ALD horses’ basal mean lying time was also significantly less than controls (ALD horses 179 ± 110.3 minutes; controls 422.5 ± 40.3 minutes, P < .001), again becoming nonsignificant with analgesic administration. Given the increases in ALD horses’ lying time with analgesic administration, it is possible that their shorter basal lying time is associated with musculoskeletal discomfort. Despite the small sample size, movement sensors effectively measured this behavior change, indicating that they could be a useful tool to indirectly assess the impact of chronic musculoskeletal pathologies in horses.

The paper can be accessed here.

Clothier J, Small A, Hinch G, Barwick J, Brown WY. Using Movement Sensors to Assess Lying Time in Horses With and Without Angular Limb Deformities. J Equine Vet Sci. 2019; 75:5559. doi: 10.1016/j.jevs.2019.01.011

 

Prematurity and Dysmaturity Are Associated With Reduced Height and Shorter Distal Limb Length in Horses 

Journal of Equine Veterinary Science

Abstract

The long-term effects of gestational immaturity in the premature (defined as < 320 days gestation) and dysmature (normal term but showing some signs of prematurity) foal have not been thoroughly investigated. Studies have reported that a high percentage of gestationally immature foals with related orthopedic issues such as incomplete ossification may fail to fulfill their intended athletic purpose, particularly in Thoroughbred racing. In humans, premature birth is associated with shorter stature at maturity and variations in anatomical ratios, linked to alterations in metabolism and timing of physeal closure in the long bones.

We hypothesized that gestational immaturity in horses might similarly be associated with reduced height and different anatomical ratios at maturity. In this preliminary study, the skeletal ratios of horses with a history of gestational immaturity, identified through veterinary and breeder records, were compared with those of unaffected, closely related horses (i.e., sire, dam, sibling).

External measurements were taken from conformation photographs of cases (n = 19) and related horses (n = 28), and these were then combined into indices to evaluate and compare metric properties of conformation. A principal component analysis showed that the first two principal components account for 43.8% of the total conformational variation of the horses’ external features, separating horses with a rectangular conformation (body length > height at the withers), from those that are more square (body length = height at the withers). Varimax rotation of PC1 and analysis of different gestational groups showed a significant effect of gestational immaturity (P = .001), with the premature group being more affected than the dysmature group (P = .009, P = .012). Mean values for the four dominant indices showed that these groups have significantly lower distal limb to body length relationships than controls. The observed differences suggest that gestational immaturity may affect anatomical ratios at maturity, which, in combination with orthopedic issues arising from incomplete ossification, may have a further impact on long-term athletic potential.

The paper can be accessed here.

Clothier J, Small A, Hinch G, Brown WY. Prematurity and Dysmaturity Are Associated With Reduced Height and Shorter Distal Limb Length in Horses. J Equine Vet Sci. 2020 Aug;91:103129. doi: 10.1016/j.jevs.2020.103129. Epub 2020 May 22. PMID: 32684267.

 

Perinatal Stress in Immature Foals May Lead to Subclinical Adrenocortical Dysregulation in Adult Horses: Pilot Study 

Journal of Equine Veterinary Science

Abstract

The persistent endocrinological effects of perinatal stress due to gestational immaturity in horses are unknown, although effects have been reported in other livestock species. This pilot study tested the hypothesis that persistent adrenocortical dysregulation is present in horses that were gestationally immature at birth by assessing the salivary cortisol response to exogenous ACTH.Case horses (n = 10) were recruited with histories of gestation length < 315 d or dysmaturity observable through neonatal signs. Positive controls (n = 7) and negative controls (n = 5) were recruited where possible from related horses at the same locations.

Cases and positive controls received an intramuscular, low-dose (0.1 ug/kg) of synthetic ACTH (Tetracosactrin 250 mg/mL, Synacthen); negative controls received no ACTH. Saliva samples were collected from all horses at baseline T = 0 and at 30 min intervals post injection from T = 30 to T = 150. These were assayed for salivary cortisol concentration (SCC) using a commercially available ELISA kit (Salimetrics).All baseline values (T = 0) were within normal published ranges. Peak and AUC values (corrected for baseline) for case horses were significantly different (ANOVA P < .001) to positive controls, with either higher (H-cases) or lower (L-cases) SCC values, outside the 95% Confidence Interval of the reference population.

There was no significant effect of breed, age, sex, test month, or location on results. The results suggest that gestational immaturity may lead to subclinical adrenocortical dysregulation, with affected horses presenting an elevated or blunted response to a low-dose ACTH stimulation, despite normal basal levels.

The paper can be accessed here.

Clothier J, Small A, Hinch G, Brown WY. Perinatal Stress in Immature Foals May Lead to Subclinical Adrenocortical Dysregulation in Adult Horses: Pilot Study. J Equine Vet Sci. 2022 Apr;111:103869. doi: 10.1016/j.jevs.2022.103869. Epub 2022 Jan 21. PMID: 35074402.

Cost of Survival: The Lifelong Problems of Premature and Dysmature Foals

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Were you around when your horse was born? If so, you’ll know about their neonatal health. If you weren’t, then understandably you don’t.

Your horse could have been a premature or dysmature foal and you might never, ever know.

Why is this a problem?

Well, anyone who’s been around me or reading my posts here over recent years will know that I’ve been researching the developmental issues experienced by premature and dysmature foals – or more specifically, the problems they carry forward into adulthood.

It’s an under-researched area, but I made some headway. Last year I was awarded my PhD for Beyond the Miracle Foal: A Study into the Persistent Effects of Gestational Immaturity In Horses.

In my thesis, I included studies that showed some of the lasting developmental effects in some (not all) horses with a history of prematurity or dysmaturity at birth. (Many twins are dysmature, by the way. Fascinatingly cute, but frequently devastatingly dysmature.)

You see, a lot of gestationally immature foals don’t just ‘get over it’, catch up and become exactly the same as they would have been had they not had problematic gestations. Some do, but many don’t.

Here’s the lowdown from my own research – which I’m convinced is the tip of the iceberg.

 © All text copyright of the author, Jane Clothier, https://thehorsesback.com. No reproduction of partial or entire text without permission. Sharing the link back to this page is fine. Please contact me for more information. Thank you!

Changes Linked to Prematurity and Dysmaturity

Conformation

Physically, they tend to have restricted distal limb growth and a more ‘rectangular’ conformation. I’ve published a paper on this in the peer reviewed journal, Journal of Equine Veterinary Science (JEVS).

Behavior

Owners indicated in a survey that affected horses tended to be more aggressive, active, intolerant and untrusting than closely related horses. This was more evident in the so-called ‘hotter’ breeds and in mares (no surprise on two counts there!).

Orthopedic issues

Angular limb deformities, a fairly common orthopaedic issue, can adversely affect these horses’ recumbent rest. This means that they find it harder to rest for the typical 20-30 minute bouts, a fact that could adversely affect valuable REM sleep. Again, I’ve published on this subject in JEVS.

Stress responses

When a low dose ACTH challenge was administered, these horses presented a lowered or heightened  salivary cortisol response. In other words, they have a different adrenocortical response to stress to closely related horses. As the adrenalin and cortisol ratios are affected, they may stay stressed for longer after a stress event. Different stress responses can affect health, learning, training, and quality of life.

Developmental Programming

There’s more – a lot more. This is part of what’s known as Developmental Programming, or the Developmental Origins of Health and Disease (DOHaD).

Previous researchers have established disorders including:

  • differences in hypothalamic-pituitary-adrenal axis function,
  • differences in pancreatic beta-cell function, and
  • glucose metabolism, plus
  • effects due to neonatal stress in pony foals (and clearly, weak or premature foals may experience neonatal stress, whether they are ill or not).

Don’t understand that? It doesn’t matter. All you need to know is that these studies already point towards pathologies such as kidney disease and Equine Metabolic Syndrome, plus a different physiological responses to stressors.

A Syndrome of Gestational Immaturity

In my view, there is definitely a Syndrome of Gestational Immaturity in horses.

By the way, gestation length on its own isn’t a good indicator of how badly a foal is affected, unless they’re extremely premature (here’s my paper on gestation length variability in the Australian Veterinary Journal).

There’s a wide range of possible problems – some horses have some of them, other horses have others, and some have none at all. They’re individuals, while everything else in their experience and care makes a difference too.

That’s how it is with syndromes. And right now, it’s all flying completely under the radar.

These are silent problems that are only recognized when they rear their proverbial ugly heads further down the line – if they are recognized at all. My heart aches for these horses and ponies, for many do not find life easy.

(c) Jane Clothier, The Horse’s Back.

All About Crooked Legs: Angular Limb Deformities in Horses and Foals

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Angular Limb Deformities: it’s the technical term for crooked leg problems. The term sounds alarming, but how bad are they and exactly how common?                                                    

We’ve all seen shocking pictures of crooked foal legs in groups and forums, but thankfully they stand out exactly because they’re not so common.

However, many horses have mild or moderate versions of these. And what is normal is that many tend to slip under the radar, undetected by owners and breeders. And that’s not a good thing.

Image (c) Nådhammar on Flickr

The problem is that moderate angular limb deformities (ALDs, as we’ll now call them) can create bigger problems as the horse grows older, with increased risk of lameness, instability, and joint degeneration. 

They can cause complications when the horse is injured elsewhere in the body and needs to compensate, but can’t, because the non-straight limbs are already under pressure.

To repeat: many ALDs aren’t an issue. In fact, many are so mild that they’re never a problem.

The thing is, you need to know the difference. And that means knowing what to look for.

Some are obvious, others need veterinary radiographs to be sure. For all of them, the earlier you catch them in foals, the better. Always talk to your vet first.

So without further ado, here are ten ALDs you really ought to know about.

 

© All text copyright of the author, Jane Clothier, https://thehorsesback.com. No reproduction of partial or entire text without permission. Sharing the link back to this page is fine. Please contact me for more information. Thank you!

1. Carpal Valgus

‘Knock Knees’

Carpal valgus (c) vetstream.com. Additional markup: THB.

This is the most commonly seen ALD in foals and horses. Technically it is an outward deviation of the lower leg from the mid line. Most of us see the other effect – the knees coming closer together.

In foals, the hoof often points outward. In older horses, the hoof may turn inwards – this is compensation to bring weight bearing back in.

There may have been a fetlock valgus (see #3) lower down, which has then caused the carpal valgus higher up.

This can be congenital. It can also be acquired, as a result of physitis of the radial growth plate immediately above the knee at a few months of age.

Incomplete ossification, when the carpal bones are underdeveloped at birth due to dysmaturity or prematurity, can contribute to this problem.

Key points: ALD of forelegs; knock-kneed appearance; lower leg angled outwards; affects one or both forelegs.

 

2. Tarsal Valgus

‘Cow Hocks’ (mistaken for)

Tarsal valgus in a foal (c) Redden, RF [1]
This is an ALD that very often gets mixed up with the conformational trait of cow hocks. To further confuse matters, mature horses with back issues may also stand unusually behind.

In these limbs, the point of hock angles inwards, while the lower limb angles outwards. Often, the pasterns are also angled outwards, giving a splay-footed look. In walk, the foot will swing in and then land wide.

The entire leg may be rotated out from the midline, as in this image.

In older horses, the medial heel may be crushed or under run.

Key points: ALD of hind legs; lower limb or whole limb angled out; affected hinds land wide; affects one or both limbs; one limb often worse.

 

3. Fetlock Valgus

‘Toe Out’

Fetlock valgus. (c) unknown. Additional mark-up: THB.

It’s extremely hard to find a picture that shows a fetlock valgus with no other visible limb deformity. Even the mild ones tend to be associated with rotation at knee level (see #10).

This is when the pastern and therefore hoof are angled away from the midline, below the level of the fetlock.

The valgus in this photo is reasonably clear, although there’s some rotation in the knee. Note that the foal is weighting this limb less and an upright foot is already starting to develop.

Key points: usually ALD of forelegs; sometimes with tarsal valgus in hind legs; one or both feet angled outwards; one often worse.

 

4. Fetlock Varus

‘Toe In, Pigeon-toed’

Fetlock varus (c) Stephen O’Grady [3]. Additional mark-up: THB
A fetlock varus is also often confused for conformation or a horse ‘just being like that’. 

With this problem, the foot is angled towards the midline below the level of the fetlock,

This problem is often combined with offset canons or rotated carpals (see # 9,10), as the foal is compensating in an effort to bring the weight bearing line back beneath the shoulder joint.

In older horses, the lateral heel may be crushed or wear down quicker. Depending on severity, there may be a tendency to ringbone in later life.

Key points: usually ALD of forelimb; affects one or both legs; often accompanied by a carpal ALD.

 

 

 

5. Carpal Varus

‘Bow Legs’

In a carpal varus deformity, the lower leg is angled inwards, towards the midline. Our eye tends to see it as the joint being angled outwards.

Advanced carpal varus (c) unknown

You don’t often hear about bow legs in horses, do you? That’s because it’s rare.

It’s usually seen in older horses, when the problems have layered up. Arthritis may already be present in the joints, while tendons and ligaments may have lesions.

Some may have had lax ligaments at birth, or have ruptured the common digital extensor tendon at a young age, causing misalignment of the carpal bones.

Key points: rare ALD of foreleg; bow-legged look; foot dishes inward; arthritis and lameness likely.

 

6. Flexural Deformity

‘Contracted Tendons’ (so-called)

This is a common deformity in newborn foals (call your vet).

Sometimes it affects the carpal (knee) joints only and the foal is still able to use the lower leg quite effectively. Or, it affects both the carpal joints and the fetlocks, leading to a more serious situation where they can’t walk on the hoof.

Severe congenital flexural deformity (c) J. Clothier

This can also be an acquired deformity related to incorrect nutrition during the first weeks and months of life. In these cases, nutritional measures, remedial hoofcare and even surgery may be required .

The hind legs can also be affected, although this is less serious as the direction of joint flexion encourages correction.

Mild cases in foals can often come right on their own in the first days of life with a little help. However, it is always important to involve a vet at an early stage for monitoring.

Key points: ALD mostly affecting forelegs; either knees only or knees and fetlocks.

 

7. Hyperextension

‘Lax Tendons’

Again, this is super-common in newborn foals and it can often resolve all on its own in the first few days of life with a mix of confinement and limited exercise.

Hyperextension in the hindlimbs

Occasionally, in the case of dysmature and premature foals, the problem can be more complex. Combined with incomplete ossification and lax ligaments, hyperextension can lead to another level of ALD, as the cuboid bones of the carpals and tarsals become misshapen.

Once more, give the foal a couple of days to straighten up and then talk to your vet if it persists.

Key points: affects forelegs and hindlegs often together; usually resolves with conservative exercise; support for limbs and hooves may be required.

 

8. ‘Windswept’

This startling looking deviation is often seen in foals that are  post-mature – they have had a long gestation and have been restricted within the uterus.

What we’re looking at is a combination of ALDs: carpal valgus and varus in front, and/or a tarsal valgus and varus behind.

The problem will general resolve within a few days, sometimes with a bit of hoofcare and bodywork to assist.

However, if the foal appears weak despite being ‘over-cooked’, with hyperextension (#7) as well, be sure to monitor it especially carefully during the early weeks and months. This is because incomplete ossification may also be present.

Key points: affects forelimbs and/or hindlimbs; hyperextension may also be present; often resolves in days. 

9. Offset Cannons

Offset cannon (c) horsesidevetguide.com Additional markup: THB

Strictly speaking, this is a conformational trait, as it often visible in the sire or dam. However, it is still classified as an ALDs on account of the structural weaknesses involved. 

In the offset cannon, the cannon bone is positioned wider than the midline of the leg, although it still faces forwards. The hoof is also forward facing.

In one leg, this ALD may have no negative effect on athletic performance. Yet if present in both forelegs, the horse may be less stable in some situations, such as going downhill.

It increases the chances of two things: developing a splint (medial leg) and a tendency for the foot to turn inwards, which could then lead to an acquired fetlock varus (see #4).

In racehorses, it can increase the chance of injury in the medial carpals, while other sports horses may be prone to osteoarthritis in the joint.

Key points: cannon appears shifted sideways; cannon, hoof and knee face forwards; usually inherited conformation; medial splints more likely.

 

10. Carpal Rotation

‘Bench Knees’

Rotated carpals with associated fetlock valgus. (c) unknown. Additional markup by THB.

In this ALD, the cannon bones are rotated slightly outwards, as are the lower knee bones and the feet. This sets the horse up for a fetlock valgus (‘toe out’), as can be seen in the left foreleg in this image.

Also a conformational trait, this kind of leg is frequently seen in Quarter Horses. A wide chest and narrow lower limbs can also contribute to a postural rotation of the foreleg.

Similar rotation in the lower forelimb can also be an acquired ALD, if a young horse has to change its weight bearing for a long time, due to (say) an injury in the diagonally opposite hind limb.

From certain angles, this rotation can look like a carpal valgus. Always check from different angles to be sure.

Key point: face of cannon and knee appear rotated outwards; pastern and toe often angled outwards, medial splints more likely; medial hoof wears faster.

 

 

Other resources

[1] Redden, RF. How to Evaluate Foot Flight and Leg Alignment
AAEP PROCEEDINGS, Vol. 57, 2011, p.407

[2] https://www.rossdales.com/assets/files/Angular-limb-deformities-in-foals.pdf

[3] O’Grady, SE, Routine Trimming and Therapeutic Farriery in Foals, Th Veterinary Clinics of North America, Equine Practice, 2017

Is Your Mare Having a First or a Third World Pregnancy?

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Pregnancy Header When foals are born prematurely, many people tend to think it’s just one of those things. Causes such as placentitis (inflammation of the uterus) are fairly well-known, although the causes behind many premature births remain a mystery.

What’s less recognised is that the mare’s general health is often a factor in prematurity, and that how we feed the mare can have a strong influence on this.

It’s easier to think that an underlying infection just happened anyway, or that some other external factor caused the premature birth.

Something toxic that was accidentally eaten by the mare, a traumatic event or an uncontrollable infection are far easier reasons to latch on to, rather than acknowledging that our own approach to feeding the mare may have contributed.

How Can Horses Have a First or Third World Pregnancy?

In horses as in humans, the diet of expectant mothers can have a huge effect on the outcome of the birth and the infant’s development. In humans, there are differences between the problems that occur in developed and under-developed countries.

Exmoor mare on her natural terrain (c) paul h - Fotolia.com
Exmoor mare on her natural terrain  (c) paul h – Fotolia.com

In poorer nations, bad nutrition due to lack of food is an issue, whereas in wealthier nations, the problems are often linked to obesity and eating too much of the wrong type of food.

It’s the same with horses. However, a mare experiencing a First World pregnancy can be in the same country, region or town as a mare experiencing a Third World pregnancy, because it all comes down to how the owner manages that horse. They could even be in neighbouring paddocks.

That’s not to say that regional issues such as drought or over-abundant rich grass don’t make a difference – of course they do. And it’s not being over dramatic to compare drought affected areas with famine zones.

Yet it’s how we respond to those challenges that marks out how they affect the mare. But can a mare’s feed affect the chances of a foal being born prematurely? Sometimes, but not always – but that’s no reason to overlook it. If we can tilt the odds towards a healthy outcome for a pregnant horse, then it’s up to us to do so.

And the great thing is that if we feed the mare properly and a foal is born after a full-term gestation, good nutrition will improve its chances of being born in great health and with a good start in life..

© All text copyright of the author, Jane Clothier, https://thehorsesback.com. No reproduction of partial or entire text without permission. Sharing the link back to this page is fine. Thank you!

Nutrition, Placentitis and Premature Foals

Through good nutrition, we can influence the chances of our mares experiencing one of the biggest causes of equine prematurity – placentitis.

Placentitis accounts for around 1/3 of late abortions, premature births, and births of full-term but weakened (dysmature) foals. It can also lead to the foal’s death in the first day or two of life, as the foal can be infected in the uterus with the same bacteria that caused the problem.

The most common form is ascending placentitis, where the mare’s uterus is infected by bacteria (commonly a streptococcus species) via the reproductive tract. I won’t try to describe the process here – there are lots of descriptions online that do the job perfectly well and far better than I can.

The premature birth occurs because the tissues in the reproductive tract become inflamed and the mucus layers that protect the uterus become compromised. Once the placenta itself is affected and damaged, the foetus can’t be supported. Without veterinary intervention, a premature birth can easily follow.

Why an Underweight Mare May Have a Premature Foal

Placentitis is a greater risk for underweight and undernourished mares.

Dry areas create different dietary requirements. © cratervalley - Fotolia.com
Dry areas create different dietary requirements. © cratervalley – Fotolia.com

First, they are likely to have a compromised immune system, as they haven’t received the correct nutrition for function of their organs. Second, in these mares, the anus can also become sunken and swollen, causing the vulva’s opening to widen, making it easier for faecal bacteria to enter. It’s then easier for the bacterial infection to break down the cervical mucus barriers and invade the uterus.

If the mare has a depleted immune system, she is more vulnerable to infections anyway. This is just one of many double whammys that accompany malnutrition.

Even if placentitis isn’t involved, plain old lack of food can still lead to prematurity. Research shows that if a pregnant mare is severely undernourished, the placenta compensates by becoming thicker. So while the foal may be smaller due to lack of nutrition, it also has less space within which to survive.

This again can make a premature birth more likely, with a greater chance of an underdeveloped foal that needs veterinary attention.

Another risk of an enlarged placenta is dystocia, or incorrect foetal positioning due to a restricted growth space in the uterus. This often leads to premature birth as well.

On top of that, when the mare is undernourished, her colostrum and milk production may be poor – even more so if the birth is also premature – reducing the foal’s chances of a healthy start even further. It’s another double or even triple whammy.

Why an Overweight Mare May Have a Premature Foal

Remember that a round and shiny mare is not necessarily a healthy round and shiny mare.

Aside: did you know that overweight pregnant women on a high sugar, high carbohydrate diet have a greater chance of having a premature birth than women with a healthy diet? (Cnattingius S, Villamor E, Johansson S, et al. Maternal Obesity and Risk of Preterm Delivery. JAMA. 2013;309(22):2362-2370. doi:10.1001/jama.2013.6295.)

If a mare is overweight with abundant grazing and low exercise levels, her obesity may be linked to sub-clinical laminitis – ie, the signs are not yet noticeable, as the hooves aren’t visibly showing the effects, although her metabolism is affected.

Condition score doesn't tell you if the nutrition is correct - or not. © cratervalley - Fotolia.com
Condition score doesn’t tell you whether the nutrition is correct. © cratervalley – Fotolia.com

Many so-called good-doers or easy-keepers are affected by Equine Metabolic Syndrome, previously known as insulin resistance, which also results in obesity and laminitic outbreaks. A mare that is already insulin resistant can abort or have a premature foal.

Here’s how. High insulin can cause inflammation in the reproductive tract, just as in the hooves. The inflammation leads to changes in the mucus production, and this can allow chronic uterine infections to happen. And here we are, back to risk of ascending placentitis.

On top of this, insulin levels normally rise during pregnancy, meaning that a mare with pre-existing high insulin levels may have serious issues that cause her to founder before foaling. (If she suffers a retained placenta, then the chances of toxic laminitis are even higher, with foundering happening quicker if the hooves are already compromised.)

Incidentally, over-feeding can lead to difficult births, with obese mares lacking the muscle tone for effective contractions. Links have also been established to over-long pregnancies that produce dysmature (under-developed although full-term) foals. Dysmature foals can have similar musculoskeletal issues to premature foals.

Remember that horses can be overweight without having Equine Metabolic Syndrome, simply because they’re being overfed and are getting too many calories. Good care does not equate to giving over-large feeds. There are kinder ways to show your horse that you love her.

Feeding to Reduce the Risk of a Premature Foal

Clearly, you can’t tell whether a mare has a healthy diet simply by looking at her, even though a condition score will indicate whether she’s too thin or too weight.

So play safe. Get her nutritional needs even half right and you’ll dramatically improve your mare’s chances of a problem-free pregnancy, and the newborn foal’s chances of healthy development in its first months of life.

If you can reduce the chances of a premature foal, it's worth doing
If you can reduce the chances of a premature foal, it’s worth doing

There are as many approaches to nutrition out there as there are approaches to other areas of horse care, but most agree on the general principles of feeding a pregnant mare. Look at the commercial feed companies’ advice pages and you’ll see the same points coming up again and again.

To repeat, there are many causes of prematurity. However, it makes sense to influence those that we can influence, even when it’s something as simple and easy as feeding the right stuff. This means avoiding those First and Third World pregnancy problems by feeding the mare for good nutritional health – for herself and the unborn foal.

I’ve listed the key points in this single page PDF: Feeding the Pregnant Mare

 

1. Energy intake

Most of the embryo’s growth occurs during the last stages, the so-called third trimester, of pregnancy. For this reason a mare in the last 3 to 4 months of pregnancy needs a higher energy intake, but without the calories. What she needs is more protein. What she doesn’t need is more carbohydrates.

Protein is used in the unborn foal’s development. 22 amino acids make up protein, but lysine is critical for development. If it is too low or missing, it will prevent the protein being utilised effectively in the foal’s growth in the uterus.

So while you’re upping the fiber available and mixing up extra feeds during these last months, it’s important not to rely on high levels of grains and mixed feeds containing molasses. Instead, if your grass is depleted or poor quality, you should focus on good quality hay, fed little and often (there won’t be space for large feeds in her gut due to the growing foal).

 

2. Roughage

Constant access to low-carb roughage will help to maintain the mare’s digestive functions. Why should you limit carbohydrate intake? Undigested carbohydrates add to the risks for horses with Equine Metabolic Syndrome, as mentioned earlier. In any horse, an overload can upset the gut’s microbial population, increasing colic risk.

Both conditions can cause pregnancy issues and premature birth. Colic can create unacceptable uterine conditions, leading to premature birth, while elevated insulin due to high carbohydrate levels can open the way for secondary uterine infections (as mentioned earlier).

 

3. Minerals – General Points

Angular limb deformities in foals are often linked to poor mineral intake © http://eswt.net
Angular limb deformities in foals are often linked to poor mineral intake © http://eswt.net

Ensuring an appropriate mineral intake is really important. It’s vital for the mare’s immune system, meaning she is at reduced risk of infections, including the bacterial infections that lead to ascending placentitis.

It’s reasonably well-known that macro minerals (including calcium and phosphorus) and trace minerals (including copper and zinc) are essential for the unborn foal’s health bone and joint growth. If you want to minimise the risk of angular limb deformities of any growing foal, be sure to get these right when you’re feeding the mare.

There’s something even more important. The mare’s milk is low on mineral content, so the unborn foal stores essential trace minerals (zinc, copper, selenium and manganese) in its liver for use during the first 3 months of its life. It’s not going to get them anywhere else once it’s born.

 

4. The Most Important Minerals

So, when it comes to minerals, if you deprive the mare, you’re also depriving the newborn foal.

Calcium is vital for the structure, mineralization and strengthening of the developing foal’s bones. It’s also crucial for milk production. Calcium deficiency has also been associated with dystocia (incorrect positioning of the foetus, leading to birth complications).

Flexural deformities can lead to premature birth and related complications © www.horseadvice.com
Flexural deformities can lead to premature birth and related complications © www.horseadvice.com

In combination with phosphorous, calcium also plays a role in brain and nerve function. Phosphorous must be present in the right proportion for calcium to be absorbed – most commonly quoted is 2 parts calcium to 1 part phosphorous (ie, 2:1 ratio).

Foals not receiving enough copper have more early osteopathic problems, including physitis and angular limb deformities (particularly flexural deformity – think club feet). You don’t want any of these problems in your foal, which needn’t be premature to have them.

Horses can’t get nutritional iron deficiency, despite the fact that foals do need more than adult horses. It’s not widely known, but excess iron can actually lead to a relative deficiency in copper and zinc, leading to joint issues.

Selenium is hugely important. With too little, there’s a greatly heightened risk of a retained placenta, which, if not treated urgently, leads to toxicity and a critical laminitis episode in the mare. This could kill her.

It’s also true is that selenium is vital for functional immune and antioxidant systems, and therefore lower risk of infection. Low selenium can also lead to poor quality colostrum – this is a major issue for any foal, but massively so for a weakened premature foal. It’s another triple or even quadruple whammy.

Be careful. Many commercial supplements are high in iron, but low in selenium. You need to get the dosage right, as too much selenium can be fatal too. You can read more here.

Iodine requirements are also complicated. Either too little or too low can lead to a foal with incomplete development of the joints. Adding indiscriminate amounts of kelp to the mare’s feed isn’t a good idea.  

 

Think About Prematurity Before It Happens

The best time to start thinking about pregnancy issues in your mare is before you need to.

Rather than keep worrying about horror stories in social media, take a short while to get informed on the basics of feeding the pregnant mare.

It needn’t be complicated or expensive – if you get the above factors right, yet it could make a huge difference.

Nobody wants the trauma of a premature or under-developed foal, so it’s wise to do what you can to minimise the causes of that happening.

With good nutrition, you can aim for the best of a First World pregnancy by reducing the chances of problems, even though nobody can eliminate them all.

 

I intentionally haven’t gone into quantities or amounts in this article, with the exception of the calcium-phosphorous ratio. I recommend getting a hay or pasture test done before organising your mare’s feed, so that you know exactly what’s already going into her system already. Many major feed companies as well as government agriculture departments offer this service. In Australia, I recommend this service from Carol Layton of Balanced Equine: Why Test Your Pasture or Hay?

 

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