Diet analysis software may not sufficiently discriminate between breeds or the disciplines they are involved in.

Diet analysis and feeding errors

Knowing what’s good dietary advice and what isn’t is vital for your horse’s wellbeing. DR JENNIFER STEWART dives deep into the detail.

Cresty neck is a sign your horse needs to lose weight.

We are becoming increasingly aware of the strong association between nutrition, diet and health – for ourselves and for our horses. As well as the part they play in health, welfare and behaviour, diet and nutrition can help prevent as well as support recovery from several common veterinary conditions.

Nutrition is involved in the pathogenesis (the development of disease), management, treatment and prevention of a wide range of equine performance, behavioural and clinical conditions. In addition to disease prevention, correct nutrition is a necessary adjunct when a combination of dietary and medical/surgical management is recommended.

There is an ever-expanding body of research, recommendations and anecdotes around feeding our horses. Much is accurate and applicable, some is not. Some must be interpreted or combined with other information for it to be useable, while certain anecdotes and recommendations have been proven to be false, or are true only under certain circumstances. Nevertheless, they are often repeated by those who are unaware of findings to the contrary.

Currently available diet analysis programs are primarily based on the minimum feeding standards for horses developed by the National Research Council (NRC). The NRC used several sources for their calculations, including the results of feeding experiments and estimations derived from studies of other species, and this is what nutritionists use to provide diet and feeding advice.

But there are limitations within the NRC standards. They were established for a population of horses of a given age, weight, reproductive and performance status and are ‘averages’ – hence they meet the needs of only 50% of horses. Factors not covered include breed, age, discipline, weather, climate or the requirements of an individual horse that may vary considerably from group averages. Second, they were established for healthy horses and minimum requirements are just that – calculated according to the amount required to prevent clinical signs of deficiencies and excess.

However, equine clinical nutrition goes beyond minimum recommended intakes. Examples of horses who benefit from dietary analysis, evaluation, feeding management and nutritional support include: pregnant mares; growing horses; those at risk for or affected by conditions such as arthritis; behavioural issues; body composition concerns; convalescence; Cushings disease; dental conditions; diarrhoea; endocrine problems; EPSM; PSSM; injuries; insulin resistance; lack of muscle and topline; laminitis; orphan foals; poor hoof quality; performance problems; post-surgery; ulcers and skin conditions.

Identifying problems

In dealing with these health issues, diet analysis can indicate the approp- riateness of the current diet and reveal any feeding errors. Common problems and errors discovered during diet analysis include:

The calcium:phosphorus ratio: Often borderline or significantly unbalanced, reasons for this include reliance on pasture, meadow/cereal hay and chaff. Most grasses provide plenty of phosphorus, but little calcium. Antacid ulcer medications are also a risk factor as they reduce stomach acid to levels below the ideal for calcium absorption. Oxalates in high-oxalate grasses also prevent absorption of calcium, so that even though on paper intake may meet requirements, the diet is calcium deficient.

Diets low in available calcium, or with an unbalanced calcium:phosphorus ratio, lead to osteoporosis or nutritional secondary hyperparathyroidism, commonly known as ‘big head’. However, only 5% to 15% of horses develop big head, and there are many other symptoms indicating a horse has reduced bone density and osteoporosis.

Overlap: Common when a combination of manufactured feeds and supplements are fed, which often leads to excesses and imbalances. This is especially important when feeding hoof products containing high levels of zinc. Although toxicity is rare in horses, the gut flora is extremely sensitive to zinc. When hoof supplements are combined with manufactured feeds, many diets analysed have close to the maximum legal limits set in EU countries, while others exceed them. Although the effects on the horse may be negligible, the impact on the gut environment is significant, with a decrease in the abundance, richness and diversity of beneficial microbiota.

Growing horses benefit from dietary analysis and evaluation.

Other potential overlaps are with iodine and selenium. Horses have a narrow range of tolerance to both, and when several supplements are used, especially with kelp products, excess iodine intake can occur. As with selenium, clinical signs of excess are similar to those of deficiency and they are often subtle and difficult to detect other than by diet analysis.

Excess iron: High in iron, blood builders to increase blood counts, improve performance and increase oxygen carrying capacity sound like a good idea. But iron deficiency in horses has only been reported after blood loss and haemorrhage. However, deficiencies of the many vitamins and minerals involved in red cell production can mimic iron deficiency. A lack of B12 and folate could cause anaemia and horses on long term acid-suppression ulcer medications, or with gut disturbances or reduced appetite, may benefit from supplementation. Deficiencies in copper and vitamin B6, and lead poisoning reduce production of haemoglobin, but providing extra iron won’t help anaemia caused in this way.

Iron never leaves the body, and an overload may occur. This can be identified through diet analysis, or diagnosed based on blood tests. Your vet may test for serum iron, transferrin and ferritin levels. Iron is toxic to the liver and levels in the spleen and liver can be very high in older horses. Horses particularly sensitive to iron are those with raised blood insulin (the most common cause of laminitis in horses with metabolic disorders, Cushings and other insulin-resistance syndromes). Excessive oral and injectable iron can damage red cells and cause low red blood cell counts in high performance horses. Other than in the event of haemorrhage and blood loss, normal diet sources – soil, grass, hays and sugar beet are all high in iron – should be enough.

Other factors

To avoid feeding errors, other areas to consider are:

Pasture: The major factor in the development of obesity, pasture must be restricted or eliminated to achieve weight loss. Recommendations for horses needing to lose weight, those with insulin dysregulation, and those either at risk of or with laminitis, include a diet of low sugar or soaked hay only, plus a low calorie, protein, vitamin and mineral balancer. Hay is low in essential minerals, vitamins and amino acids, especially as nutrients as well as sugar are stripped out when it is soaked.

The addition of a correctly formulated supplement is critical for horses that have had laminitis. The suffix ‘itis’ indicates a disease characterised by inflammation, and in laminitis this causes massive damage to the laminae attaching the pedal bone to the inside of the hoof wall as well as disruption to blood vessels. Healing requires many nutrients that are not found in hay. Unless these are supplied with the addition of an appropriate supplement, healing will be delayed, prolonged or impossible. Talk to your vet for reliable information regarding laminitis.

Feed labels: Extremely important for determining if a feedstuff will meet recommended levels of intake. Some nutrients such as vitamin C are not usually needed as horses synthesize their own. In some circumstances such as stress, no access to fresh grass, or illness, supplementary vitamin C, generally between 10-20gms daily, is required. There are no benefits if fed below these amounts.

Other nutrients such as biotin can be helpful to some horses, but again the correct amount (20-30mg/day) must be provided, and the label is the best way to determine whether the feed will meet requirements. Amounts of iodine in seaweed products can vary by a factor of 10, but a guaranteed analysis on the label can help determine whether the amounts will be excessive.

Ingredients: Listed on websites, these can reveal more information about a feedstuff. Some ‘grain-free’ feeds contain bran, pollard, millrun and/or millmix, which are all grain by-products high in sugar and starch.

Poor quality protein: This is quite common and affects body composition and the power-to-weight ratio (the amount of muscle and fat in the body). On paper, a feed might have an appropriate percentage of protein, but if it doesn’t provide essential amino acids, it will be unusable. So look for a breakdown to determine whether it will provide the essential amino acids, particularly lysine, methionine and threonine. Other impediments to the amount of useable protein – and a major reason why a horse may not be thriving even though it appears all the requirements are being met – are anti-nutritional factors (ANF).

Feeding blood builders to improve performance can result in damaging levels of iron.

ANFs interfere with the horse’s digestive processes and include lectins, which reduce nutrient absorption, digestive enzyme inhibitors, compounds causing gas production, and others that disrupt the absorption processes of the small intestine. The major pulse groups (chickpea, faba/broad bean, field pea, lentil, lupin and mung bean) contain significant ANF levels, and, depending on the content, can have negative impacts on the utilisation of nutrients in the diet due to reduced digestibility – especially if they are fed raw or unprocessed.

Regulations: The Australian Pesticides and Veterinary Medicines Authority has very strict feed labelling requirements. These regulations particularly focus on health claims. Any product that mentions a specific disease or condition, or refers to the prevention, reduction, treatment, alleviation or cure of any disease or condition, is considered a veterinary product and requires registration. This includes wording related to:

gastrointestinal disease, diarrhoea, constipation, colitis, inflammatory bowel disease or the like
heart or cardiac disease or conditions
urogenital disease or conditions including renal disease or insufficiency, or struvite uroliths
gum disease or conditions such as gingivitis or periodontal disease
immune system dysfunction
diabetes
primary behavioural disorders or aggression
neoplasia, cancer or tumours
musculoskeletal disease or conditions
pruritus (itchiness), allergic conditions or food allergies
allergy or intolerance
fungal disease, bacterial disease or any other infectious disease.

Unfortunately the regulations don’t apply to product brochures, marketing material and website information, which often contain misleading material or report benefits found in humans, rodents and other species, and are therefore unreliable.

Calcium and oxalate plants: All plants contain oxalates but some, including sub-tropical grasses such as Buffel, Signal and Guinea, have more than others. There are two types of oxalates, and both are detrimental: soluble oxalates dissolve in the gut allowing the freed oxalate to attach to calcium preventing its absorption; and insoluble calcium oxalate doesn’t dissolve at all so the calcium is not available to the horse. When on oxalate pastures, there are five considerations to address:

meeting daily calcium requirements
providing extra calcium to remineralise the bones – for horses on oxalate pasture, or with a low calcium intake for 2-3 months, this can take up to 12 months
mopping up oxalates in the gut before they are absorbed into the blood and lead to kidney failure
inactivating the free soluble oxalates
balancing the calcium:oxalate ratio by increasing calcium and reducing oxalate intake.

Complex requirements

Although many diet errors are unlikely to cause acute clinical disease, they will impact on overall health, bone strength, muscle mass, performance, recovery and risk of veterinary clinical conditions. The NRC feeding standards are a useful guide for nutritionists to estimate requirements, but they lack precision and do not include more recent veterinary and scientific studies.

Mathematical calculations alone don’t reflect the complexity of requirements for a wide range of veterinary clinical conditions and many nutritional recommendations change as new research expands our knowledge.

Estimates can be found in textbooks, spreadsheets and feeding guides, but diet advice based on generic, computer-based diet analysis programs have several disadvantages, the main being the one-size-fits-all approach and use of average values for the average horse – making the results applicable to less than 50% of horses. Other issues include an erroneous emphasis on nutritional requirements in terms of absolute values, especially for micronutrients, when in reality an optimum range exists; no provision for the suitability of the energy source (carbohydrate, fibre and oil) which is critical for many horses in terms of clinical health, growth or performance; and insufficient discrimination between breeds, or the type of exercise. In addition, care is required in interpreting the software’s output.

For peace of mind, a professional analysis of your horse’s diet combined with a veterinary interpretation of the result is always the best option.

Dr Jennifer Stewart BVSc BSc PhD is an equine veterinarian, a member of the Australian Veterinary Association and Equine Veterinarians Australia, CEO of Jenquine and a consultant nutritionist in Equine Clinical Nutrition.

All content provided in this article is for general use and information only and does not constitute advice or a veterinary opinion. It is not intended as specific medical advice or opinion and should not be relied on in place of consultation with your equine veterinarian.