The type, quality and quantity of oil, along with the state of your horse’s gastrointestinal health and body condition, should all be considered before adding oil to your horse’s feed.

However, if you feed your horse oil of any kind, there is another important consideration that is often overlooked:

How are you storing it?

Oil exposed to heat, light and air can rapidly oxidise (become rancid). And importantly, this process can happen long before we can smell or taste that something is ‘off’.

Why does this matter?

Rancid oil is not harmless.

As oil oxidises, it produces oxidation products that can contribute to oxidative stress and inflammatory processes in the body.

This is particularly important because many people feed oil with the intention of supporting their horse’s health and, in many cases, specifically to help reduce inflammation.

If that oil has been poorly stored and has oxidised, you may be inadvertently feeding something that works against the outcome you are trying to achieve, by potentially exacerbating inflammation.

So, if you feed oil, there are several simple things you can do to help preserve its quality:

• Store it in an opaque, light-proof container. No clear bottles, particularly if the oil is exposed to light.
• Always keep the lid well screwed on. Only take the lid off when pouring out oil for feed time.
• Don’t add oil to horse feeds ahead of time. Add it at the time of feeding.
• Store oil in a cool, dark place. Keep it out of direct sunlight and out of sheds or feed rooms that become hot.
• Use it as quickly as possible after opening. Don’t use oil that has been sitting open for months (even if it has been stored in accordance to all the previously mentioned factors).

It’s easy to overlook how we store oils, but if we are feeding them for their health benefits, we need to make sure we are looking after the oil properly too.

This however, can vary significantly, ranging from 320 days to 370 days.

Factors which influence gestation length include nutrition, breed, age of mare, breeding history of mare and her overall health.

There is some evidence to suggest that the gestation period of colts may be slightly longer than that of fillies.

The gut microbiota (the community of bacteria, fungi, viruses and other microorganisms living in the digestive tract) plays an important role in a foal’s development and health.

Increasingly, research is showing that what happens to this microbial community early in life may be associated with health and performance later on.

One factor that can significantly disrupt the developing gut microbiota is antibiotic use.

Antibiotics can be life-saving when they are genuinely needed, and responsible antibiotic use when treatment is indicated is important.

At the same time, antibiotics alter the developing microbial community, and those changes persist beyond the initial treatment period.

Interestingly, research has found that foals given antibiotics during their first month of life had a higher risk of respiratory disease later in life. They also went on to have poorer athletic performance compared with foals that had not received antibiotics.

This highlights just how important the early-life period may be, and how much we still have to learn about the relationship between the gut microbiota, disease and athletic performance.

When antibiotic treatment is necessary, considering what happens to the gut afterwards is incredibly important.

Supporting the gut and helping to optimise digestive health following antibiotic treatment is an area I work closely with as an equine naturopath and clinical nutritionist. Every horse is different, so the approach needs to be individualised rather than simply reaching for a generic “gut supplement”.

The decisions we make for a foal in those first few months of life may have consequences that extend much further than we realise.

When antibiotic intervention is necessary, supporting the horse through the recovery that follows is in the best interests of both its long-term health and performance.

Have you considered gut health when managing a foal after antibiotic treatment?

What can be even more challenging is when standard semen analysis appears ‘normal’.  Progressive motility is good, morphology is acceptable, sperm counts are adequate, and sperm viability is good- yet conception rates remain disappointingly low.

In these situations, it can be easy to attribute the issue to mares, timing, or management. However, when poor pregnancy rates persist despite careful mare selection, intensive reproductive management, and thorough veterinary oversight, it is generally indicative that the fertility issue lies with the stallion. These cases seem to have no clear answer, and the stallion is subsequently categorised as having ‘poor fertility’, which is deemed idiopathic.

Yet, there are answers. And for Thoroughbred stallions in particular, one factor which historically hasn’t been easy to identify is impaired acrosome exocytosis (IAE). This results in sperm failing to release necessary enzymes to properly fertilise a mare’s egg, despite sperm appearing normal on routine semen evaluation.

While this diagnosis can initially sound concerning, it also provides valuable direction for studs who are struggling with these stallions. There is much which can be done with judicious use of specific therapeutic nutrients, herbal medicines and dietary interventions to help these stallions and improve their fertility and conception rates.

Stallion fertility and breeding performance can be supported at any stage of the year. While the ideal time to investigate unexplained fertility concerns and proactively optimise reproductive health is several months before the breeding season, valuable improvements and practical support can still be achieved immediately prior to, or during the breeding season itself. If you are managing a stallion with suboptimal fertility, unexplained poor conception rates, or would like to explore integrative reproductive support strategies ahead of the season, please feel free to contact Optim Equine directly for a confidential discussion.

Magnesium is one of the most commonly used supplements in horses, which when used appropriately, can be significantly beneficial. Yet often little consideration is given to important specifics around the use of this mineral. These generally overlooked nuances can help to determine how effective the magnesium is and if it is actually helpful or harmful to give your horse.

Magnesium plays many vital roles in the body. It is needed for over 300 enzymatic processes. From helping ‘wired’, reactive or anxious horses to reducing inflammation, supporting fertility, promoting bone health, metabolic function, and insulin regulation, magnesium has a wide range of applications.

Because magnesium is a naturally occurring nutrient, it is frequently assumed to be completely safe and free from side effects. Yet in reality, it isn’t quite this simple. Like many other supplements and nutrients, there are many factors which determine the safety and effectiveness of magnesium: how and what it is used for, the quantity of magnesium a horse is given, the duration of supplementation, the form of magnesium used, a horse’s overall diet and intake of other specific nutrients, exercise and activity levels, breed, sweat rate, any health conditions a horse may have, the state of its gastrointestinal health and any medications a horse is on. 

If you’re already supplementing or considering using magnesium for your horse, here are some key things worth considering.

Not all magnesiums are created equal

Magnesium comes in a variety of forms, depending on what it’s bound to. This refers to the chemical structure of the magnesium, not just whether it is in liquid or powdered form. The most commonly used forms of magnesium (which also tend to be the cheapest forms of magnesium) in equine supplements include:

• Magnesium oxide
• Magnesium chloride
• Magnesium sulphate

Each of these forms differs in terms of absorption, bioavailability, and how they interact with the digestive system. Yet they are generally not the most clinically effective forms of magnesium to use.

This matters more than many people realise.

Magnesium can irritate the gut

Some forms of magnesium, particularly at higher doses can irritate the digestive tract.

Clinically, this may present in our horses as:

• loose and/or more frequent manure
• gassiness/excessive passing of wind
• changes in gut comfort and/or signs of mild colic
• worsening of existing digestive sensitivity

This is often dismissed or overlooked, especially if magnesium is being used for behavioural reasons.

Over-supplementation can disrupt the gut microbiome

High doses, poorly absorbed forms of magnesium or long-term over-supplementation may contribute to gut dysbiosis (an imbalance in gut bacteria). This can have wider consequences, including:

Magnesium can help to promote a healthy gut microbiome and reduce gastrointestinal-associated inflammation, but more is not always better.

• negative impacts on immune function
• altered nervous system function
• changes in neurotransmitter production and function

Our horses’ digestive systems can play a significant role in their behaviour, anxiety levels and learning capacity, thanks to the role of the gut-brain axis. Ironically, this means that excessive magnesium use may actually make some horses more reactive or sensitive, not less.

Magnesium can interfere with other essential nutrients, causing relative nutrient deficiencies

Magnesium doesn’t work in isolation. It interacts closely with other minerals including:

• calcium
• phosphorus
• zinc

Excess magnesium can interfere with the absorption and utilisation of these nutrients, which are critical for:

• bone strength and development
• proper neuromuscular function
• healthy immune function
• healthy nervous system function
• reducing oxidation and inflammation 
• muscle, tendon and ligament health

Calcium and zinc in particular, play key roles in the synthesis and function of neurotransmitters such as:

• Dopamine
• Serotonin
• GABA

Imbalances in these neurotransmitters can directly influence behaviour, sensitivity, pain perception, reactivity, learning ability and response to training.

Magnesium and behaviour: not always a simple fix

Magnesium is often used to help calm or relax our horses, and in some cases, when used appropriately it can be most beneficial. When magnesium doesn’t help to address the underlying cause(s) of anxious or excitable behaviour however, the effects of supplementation will be minimal.

The effectiveness of magnesium supplementation will also be minimal and may compound behavioural issues if the delicate balances of other minerals are disrupted, magnesium is overused, poorly bioavailable forms of magnesium are employed, or the gut microbiome is negatively impacted. In these cases behavioural issues may actually worsen rather than improve.

It is important to remember that many things can contribute to adverse behaviour in our horses, and in the vast majority of cases, there are multiple causes at any one time, not just one single factor. Whilst diet, nutrient deficiencies and gut microbiome all play an important part, it would be remiss to overlooked issues such as pain, learned conditioning, side effects of other medications used (if applicable) and other underlying health issues. Supplemental magnesium will be of very limited benefit if the issues causing a horse’s poor behaviour are not properly addressed.

This is why a blanket approach to supplement with magnesium doesn’t always deliver consistent results.

Where magnesium can be highly beneficial

When used appropriately, magnesium can be valuable, particularly in horses with:

Metabolic Challenges

Magnesium plays a role in regulating blood glucose and insulin levels. It can be especially supportive in horses with:

• insulin resistance (IR) or insulin dysregulation (ID)
• equine metabolic syndrome (EMS)
• laminitis or at risk of laminitis

Increased Physical Demand

Horses lose magnesium through sweat, and in the case of broodmares, through their milk. Requirements may increase in:

• horses in intense workloads
• hot and/or humid climates
• lactating mares
• during travel

In these cases, intake may increase in the range of 1.5 to 2 times maintenance levels.

Diet still matters: natural sources of magnesium

Like many minerals, magnesium naturally occurs in feeds commonly given to our horses. Lucerne (alfalfa) hay is a useful natural source of magnesium. Fortified concentrate and balancer feeds have varying levels of magnesium.

However, it is not always quite as simple as relying on feed alone (or even, relying on nutritional information on a feed bag or product label).

Feeds or supplements which contain high levels of calcium (such as lucerne/alfalfa) can inhibit magnesium absorption to some degree. This highlights the importance of looking at the whole diet, not just individual nutrients or feed components, nor relying on feed programs or calculators alone.

Medications can change magnesium requirements

Many commonly used medications in horses can alter magnesium absorption, metabolism, or excretion, meaning their requirements may shift.

These include:

• corticosteroids
• proton pump inhibitors (the include the most commonly used ulcer medications which contain omeprazole)
• antibiotics
• non-steroidal anti-inflammatory drugs (NSAIDs)
• antihistamines
• clenbuterol  (β2-agonists, which are often sold under names such as Claire Gel, Broncopulmin, Airway Gel, Ventipulmin, Equipulmin, etc).

If your horse is on medication, magnesium supplementation should always be considered more carefully. Dose, form, timing and duration of magnesium supplementation is crucial to take into account.

In summary: use magnesium strategically, not automatically

Magnesium is a powerful and valuable tool in equine nutrition and medicine, but it’s not without its limitations.

Used well, it can support:

• metabolic health
• muscle function
• nervous system balance and in turn, behaviour 
• skeletal health
• fertility
• gastrointestinal (‘gut’) health

Used poorly, it can:

• disrupt gut health
• create mineral imbalances and relative nutrient deficiencies
• contribute to ongoing behavioural issues
• interfere with normal bone development and health

The key is not just whether your horse is supplemented with magnesium, but what their actual requirements for it are. The form of magnesium used to supplement, the reasons to supplement it, the duration of supplementation, factors which increase requirements or interfere with magnesium absorption and metabolism should all be taken into consideration.

Take home message

Good equine nutrition is never about using a single supplement in isolation. Assessing the unique needs of the individual horse in front of you is crucial.

Before supplementing magnesium, it’s always worth asking:

• does my horse actually need it? And if so, how much?
• is the diet balanced overall? And what role would supplemental magnesium potentially play in this?
• could there be deeper underlying causes contributing to the reasons which are prompting me to supplement magnesium?

The safest, most effective and sustainable results come from a thoughtful, tailored approach.

Equine asthma is a condition that can affect horses of all abilities, but is most frequently diagnosed in performance horses and racehorses, and is a common cause of poor performance. The term ‘equine asthma’ covers a broad range of inflammatory conditions of the lower airways, which can vary in their presentation and severity. Conditions that were previously referred to as ‘recurrent airway obstruction’, ‘heaves’, ‘inflammatory airway disease’, ‘chronic obstructive pulmonary disease’, and ‘summer pasture associated asthma’ are now all known as ‘equine asthma’.

When a horse has been diagnosed with, or is suspected of suffering from asthma, it is natural for us to want to provide them with relief. From a pharmaceutical standpoint, that can often mean the use of corticosteroids and, in many cases, clenbuterol (often sold under names such as Claire Gel, Broncopulmin, Airway Gel, Ventipulmin, Equipulmin, etc). While use of these medications may help relieve some clinical signs of asthma, they do not address the underlying causes of the condition and may also come with unintended health consequences. Unfortunately, these side effects are often overlooked, or simply not discussed.

Whilst clenbuterol may provide some initial relief in equine asthma, the use of this drug can contribute to a vicious cycle, potentially perpetuating the condition.

Clenbuterol has been demonstrated to deplete the amino acid taurine. Taurine plays a significant protective role in lung health by exerting powerful anti-inflammatory, antioxidant, and membrane-stabilising effects. It also helps to inhibit allergic responses, which can play a role in many cases of equine asthma. Reduced taurine levels may increase the severity of equine asthma and the likelihood of lung tissue damage as a result of ongoing airway changes. Taurine is also needed to promote healthy gut integrity and microflora: gut health is increasingly recognised as an important factor in respiratory conditions such as asthma.

Clenbuterol decreases levels of potassium and magnesium in the body—two key nutrients known to support respiratory health and reduce the severity of asthma. Potassium is essential for controlling airway smooth muscle tone and supporting respiratory muscle function.  Low potassium can increase airway reactivity and hamper breathing, further exacerbating clinical signs of asthma. Depleted potassium levels can also lead to cramping in susceptible horses. Magnesium acts as a bronchodilator (helping the airways relax) and helps reduce airway hyperactivity, spasms, and inflammation.

Long-term use of clenbuterol may also have negative impacts on immune function, further contributing to a self-perpetuating cycle of equine asthma.

An often overlooked side effect of clenbuterol is the influence it may have on temperament and behaviour in our horses. Clenbuterol belongs to a class of drugs known as beta-2 adrenoceptor agonists, which work by mimicking the effects of epinephrine (adrenaline) in the body. This results in a stimulating effect, which may lead to changes in behaviour, including increased excitability, reactivity or nervousness in some horses.

Helping a horse at risk of, or diagnosed with asthma, starts with good management practices. Identifying and appropriately addressing the factors that contribute to the underlying pathophysiology of equine asthma, meeting the individual horse’s nutritional requirements (which often differ from basic nutrient requirements due to medication use), and the judicious use of suitable herbal medicines can significantly support respiratory health, allowing a horse to remain healthy and perform at its best. There is much that can be done for the horse diagnosed with asthma, using approaches that not only support airway health and performance, but also promote overall wellbeing. If your horse has been diagnosed with asthma, or you suspect respiratory issues may be affecting performance or comfort, a tailored approach can make a significant difference. Get in touch with Optim Equine to discuss a personalised plan to your support your horse’s health and performance.

At Optim Equine, we regularly work with horses affected by respiratory conditions…

Depending on the herb (or combination of herbs used) and their application, they can help to:

• reduce inflammation
• modulate immune function
• aid healing and tissue repair
• assist recovery from infections
• prevent and/or manage equine asthma
• soothe the gut lining and promote healing of both gastric and colonic ulcers
• reduce colic 
• support digestion
• assist fertility
• help regulate hormone levels
• calm nervous horses
• provide gentle pain relief
• promote healthy hoof growth and integrity
• help to reduce the severity of osteoarthritis and maintain joint health
• Aid in blood glucose control and assist in the treatment of insulin resistance, equine metabolic syndrome and laminitis

Whilst herbal medicines are incredibly versatile, they’re not magic. And they can’t replace a poorly balanced diet….

One of the biggest misconceptions I see is that herbs can fully meet a horse’s nutritional needs or correct nutritional deficiencies on their own. 

This is simply not true. 

The vast majority of herbs (with few exceptions) do not provide sufficient quantities of key minerals and vitamins our horses need for optimal health and functioning.

Take the calcium rich herb nettle (Urtica diocia) for example….

100 g dried nettle leaf (~4–5 cups) provides approximately 300–500 mg calcium.

For a 500 kg (1100 pound) horse, calcium requirements typically fall in the range of 20–40 g/day (depending on life stage, workload, and physiological status).

This means:

• 100 g nettle provides roughly 0.3–0.5 g calcium
• This equates to approximately 1/40 to 1/133 of daily calcium requirements

To meet calcium needs via nettle alone would require:

• 4–5 cups × 40–133 = ~160–665 cups per day

This is neither practical nor appropriate.

Whilst strategically employed herbal medicines can help to restore optimal gastrointestinal health and function in our horses (including digestion, absorption and metabolism)- which in turn, can aid in better nutritional status, herbs in and of themselves don’t provide enough levels of nutrients our horses needs to meet daily nutrient requirements.

It seems almost impossible to read news reports and social media posts these days without coming across someone telling you how important it is to look after your microbiome. From managing our mood and our weight, to reducing the risks of any number of diseases, someone, somewhere, will make a link to the billions of bacteria living in you, or on you.

But a recent study, published in the open-access journal Nature Scientific Reports, made a new and extraordinary connection: a foal’s internal hitchhikers may affect how fast he runs. And not just that – they can predispose to, or protect from, a range of conditions that might even prevent him from racing at all.

The paper followed 52 foals, born between February and May 2018, from five Thoroughbred stud farms in the UK. These foals were followed as they entered training (dispersed between 29 different training yards) and through to the end of their 3-year-old season.

In the earliest part of the study, faecal samples were obtained from each individual on day 2 postpartum and at regular intervals up until one year of age. These samples were then analysed and the number, variability, and different types of bacteria in the samples were assessed and recorded. The study was prompted by increasing evidence that not only are there a range of non-communicable diseases in humans affected by the bacteria within the intestines, but also that babies with differing birth and early-life circumstances may be predisposed to certain conditions, because of differences in their microbiome. 

The clinical and racing histories of the foals were then compared to the results of the microbiological evaluations. 

The results were striking: the gut bacterial community in the first months of life could predict the risks of specific diseases and athletic performance in later life. Foals with lower diversity (i.e. fewer different species of bacteria in their samples) at one-month-old had a significantly increased risk of respiratory disease in later life. A higher diversity was associated with a decreased risk of orthopaedic disease. And, when athletic performance was assessed — judged by comparing official ratings, number of starts/wins/places, and prize money earned — positive effects were again seen in foals with a greater diversity of bacteria at one-month-old and could even be linked to the relative abundance of specific bacterial families.

Foals are born without a functioning microbiome and must acquire all of their gut bacteria from their dam and their environment. This early phase of development, where foals are born with an immune system that is yet to encounter external challenges, is sometimes referred to as a ‘critical window’ — essentially a period when the gut microbial community imprints immunity and future health outcomes onto a blank canvas. There is now a great deal of interest in humans as to how this might be contributing to a variety of diseases: from obesity, diabetes and allergies, to diseases of the circulatory system, bones and neurodevelopment disorders such as autism. 

This particular study did not examine the gut microbial profile of the mares delivering and rearing the foals. But the authors point out that the gut bacterial profile of human mothers is known to be a primary driver of gut colonisation in human infants. Indeed, in human medicine, there is increasing engagement of methods to optimise this ‘handover period’ in neonates. There is limited evidence for how feeding mares may influence foals in this early phase. But a recent study, that fed two groups of mares on the same stud farm separate and distinct rations, demonstrated a stark difference in failure of passive transfer — assessed by levels of IgG in the foals’ blood within twenty-four hours of birth — between the two sets. Other researchers have confirmed that the microbial population of foals varies between stud farms, most likely due to differences in management styles. Numerous studies in other species have demonstrated links between maternal nutrition and various measures of colostrum quality, and there is evidence that a pro-inflammatory profile is seen in colostrum produced by obese mares, along with reduced medium-chain saturated fatty acid levels (important as an energy source and in the development of gut microbiota and immunity).

So, what if the balance could be tipped back in favour of the newborn foal, simply by adjusting how the mare is fed? And what if this could also affect the vigour of our young athletes? The developmental origin of health and disease (DOHaD) — first advocated by David Barker in the early 1990s — seeks to understand how exposure to environmental factors during periods of high plasticity in the early stages of life (including the gestational period) influences the program for development and disease risk in the progeny, that extends well into adult life.

Before the middle of the twentieth century, the foetus was believed to be immune from the effects of the maternal environment. It is now understood that in laboratory animals and humans, which is where of course almost all of this research has been done, numerous external factors influence the health and development of the foetus before birth. Historically, the focus has been on those causing adverse effects, such as polycyclic aromatic hydrocarbons — found in vehicle exhaust fumes and cigarette smoke — alcohol, and certain notorious pharmaceuticals. Epidemiogical studies began to link certain aspects of development, some not immediately obvious at birth, with environmental factors that had not been appreciated earlier and may be influenced by microbiome effects. For example, having “furry pets” at home impacts meconium bacterial diversity, and children reared with domestic animals from infancy have reduced prevalence of allergic-related diseases; maternal consumption of artificial sweeteners produces profound metabolic changes and microbiome changes in mouse pups (with profiles similar to those seen in human obesity). ‘Barker’s theory’ on the foetal origins of adult disease considered three characteristics: latency, where the effects may not be apparent until much later in life; persistency, in which conditions affecting the foetus continue; and genetic programming, where specific genes are switched on due to the prenatal environment. Brief windows at the very start of development, when a small number of cells are dividing rapidly and vulnerable to a range of influences, drive the development program of the entire individual, all the way through to adulthood.

Much of the work on the transferability of a healthy microbial population from one individual to another was prompted by early observations, reported in 1958, that patients affected by a particularly unpleasant and intractable cause of severe diarrhoea showed drastic improvements following a novel treatment. Clostridioides difficile is an anaerobic bacteria (it thrives in low-oxygen environments), commonly found in the intestinal tract of normal people. It doesn’t cause any issues until it proliferates uncontrollably, and the commonest reason for this is when the other bacteria in the intestine ecosystem are knocked out, usually by the patient receiving antibiotics for another problem. ‘C. diff’ is the commonest cause of antibiotic-associated diarrhoea, and it is notoriously difficult to treat in some cases — it only responds to a select group of antibiotics, many cases remain refractory, and it has a fatality rate of up to 40%. Back in the 1950s, the doctors were utilising a therapy that had been written about in the fourth century: transplanting gut bacteria from a healthy individual into the affected patient. And they did so by taking faeces from those healthy volunteers and delivering it via an enema (the very earliest records describe it being given as a ‘soup’).

Faecal microbiota transplantation (FMT) is now used in cases of C. diff that do not respond to first-line treatments and is well established for this, with impressive success rates of 80-90%. It works because it restores the normal balance of gut microbes, which prevents the Clostridia from maintaining a hold on the intestinal environment and, basically, out-competes them for the resources available. But as well as this, restoring the regular bacteria found in a healthy gut revitalises the relationship between the host —  us, or the animal — and the trillions of single cell organisms we live with.

Estimates of the numbers of bacteria within the body vary, but it’s safe to say it’s in the tens of trillions. It’s also safe to say that in most people the bacteria outnumber the human cells, in some cases by an order of magnitude. Whether the same is true of horses isn’t known, but considering the horse has evolved to rely almost entirely on bacterial activity within the intestine for its existence, it’s almost certain that the numbers involved are even more impressive. But the bacteria (and other microorganisms such as viruses and fungi) don’t just provide the necessary enzymes to digest food — they have evolved with the host and are absolutely vital for the development and maintenance of other functions, particularly the immune and nervous systems. Even within the intestine, it isn’t just a matter of dissolving the food as it passes through for the animal to absorb: the microbes are fundamental to those pathways developing adequately and operating effectively, from the earliest stages of life to the very last day of it.

The most striking examples of the absolutely cardinal role of bacteria in health and development can be seen in laboratory animals. Mice can be born and reared in sterile conditions, so that they develop without any (or very few) microbes in their environment and without the normal gut colonies they would usually possess. These so-called germ-free, gnotobiotic, or axenic mice do not develop normally. They can be fed the optimum diet and housed comfortably but they do not thrive: their immune and digestive systems are stunted, they do not gain weight normally, and they are vulnerable to a wide range of diseases. Even if introduced to ‘healthy’ microbial populations found in conventionally-reared animals they do not recover, most likely because they have missed the aforementioned, once-in-a-lifetime, critical window. Interestingly, germ-free mice can live longer than their colonised compatriots (if reared very carefully), which has recently raised important questions over the role of the microbiome in ageing and its implications for humans. 

Mammals need microbes. So where does a new-born mouse, human, or foal get these essential organisms from and, knowing what we know about the dangers that some types of bacteria present, how do they get the right ones?

It is now established that babies born via caesarian rather than vaginal delivery are more at risk from a number of conditions, including inflammatory and neurodevelopment disorders, and diseases of the bowel, lungs and joints, so much so that the technique of ‘vaginal seeding’ has become a much-discussed technique. Much of the impact of surgical delivery has been attributed to alterations in the microbial community that the infant is exposed to in the very earliest stages of neonatal life. While caesarian delivery is a very much rarer event in horses, the effect of early exposure to the ‘correct’ microbiome (sometimes referred to as ‘pioneer colonisers’) has been demonstrated in other species. The hygiene hypothesis is a term used to describe the way that early exposure to particular microorganisms is protective, and that a lack of such exposure leads to poor immune tolerance. Unfortunately, this term has sometimes been misunderstood: it doesn’t mean hygiene is a bad thing — we all need protection from pathogens — and it certainly doesn’t imply that having more infections during early life is advantageous. But a broad exposure to a variety of certain microbes is an essential part of development.  

But this exposure may begin even earlier. For many years, it was considered incontrovertible that the foetal environment in utero was sterile and that exposure to bacteria and other organisms only began at birth. However, recent work has challenged this ‘sterile womb paradigm’ and a number of studies have demonstrated the presence of microbial material within placental and foetal tissues. The debate is still ongoing, not least around whether the presence of bacterial DNA actually represents viable bacteria or simply fragments of long-deceased organisms; even the ability to breed axenic animals (as mentioned above) suggests foetal microbial colonisation is unlikely. 

What is emerging is a general consensus that the products of bacterial life in the mother may well be influencing foetal development, and could be crucial to it. Maternal microbiota produce bioactive metabolites that can enter the maternal circulation and may be actively or passively transferred through the placenta.

We know that elements of the microbiome that affect offspring are transferable: for example, bacteria taken from the gut contents of obese mice and transferred to pregnant, normal-weight mice, lead to overweight offspring with altered inflammatory responses. Maternal obesity causes changes in microbiota correlated with altered foetal brain development, while maternal undernutrition in humans affects infant immunity by attenuating responses to vaccines in early childhood (among many other effects). There is a huge volume of data concerning nutrition, and its effects on offspring, across many species, and it’s beyond the scope of this article to go into direct nutrient effects. Nonetheless, work has shown that foals born to obese mares are more likely to be affected by osteochondrosis, and supports the hypothesis that maternal relative hyperinsulinaemia may be a contributory factor through its role in cartilage differentiation. Foals born to overweight dams also have evidence of systemic inflammation (higher levels of plasma SAA) which may also affect development through inhibitory effects on bone growth. Crucially, the impact on progeny may be different depending on the alignment of the disturbance: i.e. whether the mares were obese at conception or overfed during the early or later stages of gestation. Maternal undernutrition is much less likely to be a problem in commercial breeding operations, but when it is, mares may develop a syndrome close to gestational diabetes in humans, a condition widely recognised to have potentially very serious consequences to the neonate, and even beyond. Again, timing is crucial: studies of epidemics, famine, and war show that mothers and their children have different outcomes depending on at which stage, from preconception to early childhood, the crisis occurred. 

Maternal stress during early pregnancy has been shown to reduce faecal bacterial diversity and alter taxa composition in pregnant mice and has been replicated in human studies. Conversely, severe maternal stress in the last trimester was associated with increased bacterial diversity in newborn babies. Maternal depression may alter the ratio of certain bacterial families in neonates, specifically by reducing numbers of Proteobacteria, a pioneer taxon which creates the environment for later anaerobic colonisation. 

A number of studies have identified known risk factors for infant severe respiratory tract infections, the leading cause of child mortality globally, including a carbohydrate-rich, fruit-/fibre-/vegetable-poor maternal diet, and/or never breastfeeding. In a 2023 study, researchers demonstrated that mice fed high-fibre diets produced a milk microbiota that increased infant gut propionate levels, leading in turn to increased production of specific cells in the bone marrow that confer protection against respiratory infections. Indeed, therapy with specific propionate-producing bacteria, and even propionate supplementation, were shown to act in a similar way. Fermentable dietary fibre favourably influences the gut microbiome resulting in the production of metabolites that modulate the immune system (particularly short-chain fatty acids — SFAs). It is widely accepted that SFAs play an important part in regulating intestinal barrier integrity, and there is now evidence that they have a role in placental structure and vascularisation. Breastmilk also contains regulatory cytokines, growth factors and oligosaccharides, all of which influence the developing infant. Metabolic disorders, such as gestational diabetes, affect the levels of SCFAs and other metabolically significant metabolites causing changes in the maternal immune system with knock-on effects for the developing foetus. The authors of this study suggested that the “manipulation of the maternal diet during pregnancy and during the pre-weaning period, or through the provision of defined tailor-made prebiotics and/or probiotics directly to infants, may present novel opportunities for enhancing resistance to inflammation-mediated diseases.” Other researchers have described the transport of even more molecules across the placenta, including lipopolysaccharides and other bacterial cell fragments. Preconception infections with some intestinal parasites can lead to maternal imprinting in mouse offspring, thereby suggesting that the transfer of immunity is not solely dependent on the passive transfer of antibodies. 

These metabolites may also exert an effect on the genetic material within cells. Epigenetics is the set of factors and molecules that modify gene expression while not changing the genome sequence itself. Only around 2% of mammalian DNA is associated with protein-encoding genes; the rest (non-coding DNA — what used to be referred to as ‘junk DNA’) modifies the links on the chain to switch genes on and off at crucial junctures. These modifications are commonly associated with environmental cues — good and bad — that can result in significantly different outcomes (phenotypic plasticity) for two genetically identical individuals. In one Danish study, children who exhibited allergic rhinitis at the age of six were found to have a distinct DNA methylation pattern (an epigenetic signature) in their nasal mucosal cells associated with reduced microbial diversity at one week of life. It was folate’s role in countering the development of neural tube defects that first pointed to the foetal nutritional programming hypothesis through epigenetic programming. And as the stage most susceptible to environmental stressors is embryogenesis, where DNA methylation is closely associated with optimal differentiation and growth, consideration of preconception dietary factors is fundamental (folate supplements are recommended when pregnancy planning, but gut bacteria produce significant amounts of folate in humans with a healthy microbiome).

While epigenetic changes do not change the base-pair sequences within the genome, they are heritable, meaning that future generations may inherit far more than just the A–T and G–C building blocks. It seems certain that different epigenetic mechanisms may partly explain why dietary factors at critical developmental stages might affect the susceptibility to diseases in adulthood. 

With microbes contributing 99% of all genetic information present in the body, maternal microbial transmission should be viewed as an additional and important mechanism of genetic and functional change in evolution. Horses are selected for characteristics such as temperament, strength, speed, and endurance. Although genetic selection tools have been developed to assist breeders in the choice of sires and dams, there is also a growing body of research reporting that the maternal environment modulates the genetic potential of the offspring. Under natural conditions, microbes that promote host fitness, especially in females, will simultaneously increase their odds of being transferred to the next generation. Under controlled breeding programmes, efforts to assist this beneficial effect should be encouraged: the trajectory of the young foal’s colonisation process has lifelong clinical implications. And being aware of its influence may not only improve the outlook for your foal, but your foal’s foals as well. 

Why Broodmare Body Condition Matters

It’s common practice to maintain broodmares in what is considered “good condition.” In reality, this often means mares are kept overweight, based on the belief that heavier mares are more fertile.

But research and field experience suggest otherwise. Excess body fat in broodmares is associated with an increased risk of developmental orthopaedic disease (DOD) in their offspring, including:

• Osteochondrosis (OC)
• Osteochondritis dissecans (OCD)
• Angular limb deformities
• Flexural limb deformities

These conditions can significantly impact sale value, veterinary expenses, training timelines, and long-term soundness and performance outcomes.

The Hidden Problem: “Good Doers” & Nutritional Imbalance

When it comes to health and nutrition of broodmares, some of the most common issues I see in practice are:

• Misjudged body condition
• Underestimated nutrient requirements
• Over-reliance on pasture alone as a sole or primary feed source
• Haphazard or uninformed supplement use
• Feeding based solely on body weight and condition, not nutrient requirements

This is especially true for “good doing” mares. In an effort to control weight, many broodmares are not feed sufficient quantities of a suitably fortified feed or mineral balancer, meaning they:

• Lack key minerals needed for fertility, immune function and foetal growth and development (e.g. copper, zinc, calcium, magnesium, selenium, iodine)
• Receive inadequate micronutrient support
• May not consume sufficient amounts of essential amino acids such as lysine
• Still consume excess energy

This results is a mare that is overweight but undernourished. The implications of these don’t just impact her immediate health, but reproductive outcomes.

At the same time, supplemental feed, vitamin or minerals are often added without a clear understanding of:

• What the mare actually requires
• How her nutrient needs change from preconception, during the different stages of pregnancy, through to lactation
• Correct dosages
• How nutrients interact
• How any medications the mare may be receiving impact nutrient requirements 
• What is already being supplied through pasture and current diet

This can lead to:

• Nutrient imbalances
• Shortfalls in key nutrients required for optimal reproductive health and sound orthopaedic development of the mare’s offspring
• Excesses of nutrients that interfere with absorption of other minerals
• A false sense of “covering all bases”

More supplements generally don’t equate to better nutrition: precision matters. And when it comes to the healthy development of young horses, this is an area which you cannot afford to overlook.

Nutrition & Orthopaedic Development Are Linked

When managing DOD risk in young horses, nutrition and body condition cannot be separated.

All of the following may increase DOD risk:

• Overfeeding energy
• Poor gut microbial health (in both the mare and/or foal)
• Underfeeding essential nutrients
• Feeding certain minerals in excess
• Mineral imbalances
• Inconsistent feeding practices
• Sudden changes in feed
• Feeding in ways that promote high insulin levels

A foal’s orthopaedic health doesn’t start at birth: it starts with how the mare is managed before conception and throughout pregnancy.

The Real Cost of Getting It Wrong

Many developmental issues don’t appear immediately. Instead, they show up later as:

• Swelling, stiffness, lameness (sometimes only subtly)
• Radiograph (x-ray) findings
• Inconsistent performance
• Reduced athletic potential

By that point, the financial and reputational costs are significantly higher.

How to Get It Right

Optimising broodmare nutrition isn’t about feeding less or more, it’s about feeding in a way that promotes health and fertility in the broodmare and sound orthopaedic development in her offspring.

That means:

• Maintaining an appropriate body condition score (not overweight)
• Providing balanced minerals and trace elements in forms which the mare can readily digest, absorb and metabolise
• Adjusting feeding based on pasture, environmental conditions, and reproductive stage
• Ensuring energy (calorie) intake is appropriate given the mare’s unique requirements
• Taking a mare’s reproductive history into account and addressing specific nutrient requirements in relation to this
• Monitoring condition consistently and objectively
• Assessing and addressing the nutritional and metabolic impact of any medications a mare may be receiving 
• Feeding to promote optimal gastrointestinal health

Need Help Assessing Your Broodmare Program?

If you’re unsure:

• Where your mare’s body condition currently sits
• Whether her diet is properly balanced
• Specific nutritional requirements of your broodmare
• How to reduce DOD risk in your youngstock
• Why you mare may struggle with fertility or reproductive challenges, despite extensive veterinary intervention

Now is the time to address it, before small issues become expensive problems.

I work with breeders to optimise broodmare nutrition and management, supporting both fertility and the long-term soundness of their youngstock.

If you’d like a clearer understanding of where your mares currently sit and how to improve outcomes heading into the breeding season, feel free to get in touch.

However, the use of intra-articular steroids come with risks to our horses and ponies. Particularly those with insulin dysregulation, insulin resistance, equine metabolic syndrome (EMS), pituitary pars intermedia dysfunction (PPID) or those who are at risk of, or have previously had laminitis.

Intra-articular corticosteroids have been shown to increase blood glucose and insulin levels and increase the risk of laminitis, particularly in susceptible horses. The risk may be further increased in horses receiving high-grain or high-starch diets.

When giving our horses any medication or supplement, whether natural or pharmaceutical, both the potential risks and benefits should be taken into account.

For the horse with osteoarthritis or any other degenerative joint disease, diet, exercise (load) management, weight and body composition should all be taken into account. Overweight horses or those with insulin resistance may be at an increased likelihood of developing osteoarthritis due to higher levels of systemic inflammation associated with excess body fat. This highlights the need to be particularly mindful of the risk in these horses and ponies if the use of corticosteroid injections are being considered.

Many nutraceutical and herbal medicine supplements can safely and significantly help horses with osteoarthritis, when selected and used appropriately.