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Preparation of Broodmares for Breeding Season - Part 2: Condition & Nutrition

written by: Agata Zagrajczuk (PhD in Animal Reproduction)

Part 2: Overall physical condition and Nutrition

There are a few things, that the breeder can assess as a starting point on the way to successful reproduction:

Overall Physical Condition

Fatness and ‘musculature’ are physical indicators of the horse’s health. Obesity is often related not only to wrong nutrition, but it can also indicate metabolic disorders, e.g. equine ‘Cushing Syndrome’ or insulin resistance known as Equine Metabolic Syndrome. Regardless of the initial reason, it may cause hormonal disorders.

On the other hand, an emaciated (i.e. very thin and weak) mare is more prone to develop an Early Embryonic Death, premature labour or birth a weak foal.

The optimal Body Condition Score is ‘3’ on a scale of 0 to 5. But even a perfect body condition does not guarantee, that your horse does not suffer from nutritional deficiency: Periods of drought or floods, long-lasting feed storage, or geological conditions in some regions affect plants and bioavailability of critical nutrients, vitamins and trace minerals.


The most crucial vitamins for a successful reproduction are vitamins A and E. However, depending on negative environmental conditions (drought, floods, long-term storage), these vitamins are first lost in forage/hay. Among minerals, a sufficient availability of calcium, iodine and selenium are considered key elements for ensuring an efficient reproduction process. It’s worth mentioning that in some regions of Australia (identified in Central Queensland, and along the coast of the Cape York Peninsula) a selenium toxicity can occur. Iron, in which Australian pastures are rich, is an antagonist of iodine. It may negatively affect thyroid gland functions, and thus fertility. Vitamins A/E are lost in hay during periods of long storage. Thus, hay has low levels of vitamins in late winter and early spring.

The protein or amino acid requirements for a horse is dependent upon the activity level and/or physiological requirement (e.g. work level, gestation, lactation). The majority of amino acids can be synthesized in the hindgut through providing a good quality hay. However, when lesser quality hay or pasture are fed with additional activity levels or physiological requirements the horse may encounter protein and/or amino acid limitations or deficiencies. There is a group of 10 essential amino acids, that must be delivered daily through the feed. If these amino acids are absent or insufficient quantities are available to the horse’s metabolism, the horse will be unable to build protein tissues (e.g. used for muscles development), produce hormones or synthesize enzymes. Three amino acids assumed critical for body condition and milk production include: leucine, lysine and methionine.

Equine nutritional research has not identified an ‘ideal protein’ or specific amino acid quantity/ratio for physiological demands of growth, work, pregnancy or lactation. However, the one amino acid requirement that has been identified (i.e. high requirement or low in natural feedstuffs) and well researched is lysine. Horses do benefit from amino acids supplementation, yet exacting quantities and/or ratio is unknown. Mineral and vitamin deficiency decreasing fertility rates in the mare as well as potentiates health problems in a new born foal (e.g. malformations, premature delivery, white muscle disease).

Protein and amino acid research in other species (e.g. human, swine, poultry & cattle), observes that deficiency influences foetal and neonatal development as well as limits mares milk yields.

To further analyse the horse’s nutritional requirement, a hay nutrient analysis is very helpful when securing large quantities of hay from single versus multiple sources. The nutrient analysis can significantly vary for hay from various sources and seasonal harvest.

Relative Feed Value RFV, is the most commonly used indicator of hay quality (e.g. desirable range 100 to 160%). The RFV is calculated from digestible dry matter and theoretical dry matter intake.

Critical hay analysis may include the following nutrients and/or calculated values: Crude Protein CP, Acid Detergent Fibre ADF, Neutral Detergent Fibre NDF, Crude Fat CF, Non-Fibrous Carbohydrates NFC , Non-Structural Carbohydrates NFC, Water-Soluble Carbohydrates WSC, Starch, major minerals (e.g. calcium Ca, phosphorus P, potassium K, magnesium Mg, sulphur S) and energy (DE MJ/kg or Mcal/lb).

The trace mineral content is more elusive to interpret from a feed analysis. The absence of a trace mineral indicates that it is not available. Whereas, the presence of a specific trace mineral does not ensure its bioavailability to the animal. This relates to trace mineral antagonistic interactions and/or imbalances created with individual trace mineral excesses competing for absorption site (e.g. copper, manganese, zinc) or blocked absorption. Selenium (Se) is a trace mineral that is potentially toxic, and owners should be aware of its content in primary feed sources versus the quantity supplemented.

Diagnostic blood serum tests are of some value in assessing minerals and vitamins availability within the horse. However, the animal’s metabolism will strive to maintain minimal blood serum values through tissue mobilization to satisfy present homeostasis. It must also be recognized that animals in altered physiological states (e.g. oestrus, pregnancy, stressful work), may present altered mineral values in their blood serum.

The breeder should be aware, that the average time period required to nutritionally compensate for tissue deficiencies is approximately 2-3 months. It’s particularly important to consider this proactive husbandry practice well before the start of the breeding season.

The most simplistic method to ensure your horses mineral and vitamin nutrient requirements are satisfied is through daily supplementation.

Vitamin/mineral supplements that tend to be of greater nutritional value contain chelated trace minerals. Chelated trace minerals are bound to an amino acid (e.g. zinc + methionine) which have been found to be more bioavailable or better utilized than inorganic sources in livestock. The reason is related to a high rate of absorption (i.e. small intestines, amino acid transport) and metabolism into tissues.


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