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Knowing your horse’s body weight is important to determine their nutritional requirements, administer certain medications and monitor their health status. However, not all horse owners have an easy way to measure their horse’s body weight.
Mature adult horses can weigh anywhere between 300 – 1,000 kg (650 – 2,200 lb) and require special weighbridges or scales to assess weight. On-farm scales are rare, and unless your horse travels to a local animal hospital, you may never get an accurate body weight measurement.
Fortunately, several methods are available to estimate your horse’s weight. This includes using a weight tape or calculating their approximate weight from girth and body length measurements.
It’s also important to know your horse’s body condition score and ideal body weight based on their breed and size. Reference ranges for various breeds exist so you can track whether your horse is overweight or underweight.
Why Do I Need to Know my Horse’s Body Weight?
Accurately determining your horse’s body weight is important for many reasons, including establishing nutrition requirements and formulating a balanced diet.
It’s also important to track weight changes over time so you can determine how well your horse’s feeding plan is meeting their energy requirements and make appropriate adjustments.
Nutrient Requirements
In the National Research Council’s Nutrient Requirements of Horses, the daily requirements for various macronutrients and micronutrients are based on the horse’s body weight and physiological status. [1]
If you work with an equine nutritionist to formulate a feeding program, one of the first questions they will want to know is how much your horse weighs.
For horses at maintenance, daily requirements are solely based on body weight (BW) in kilograms. Example calculations in the NRC include: [1]
- Dry matter intake: 0.02 kg of intake per kg of body weight (0.02 x BW)
- Digestible energy: 0.033 mcal per kg of body weight (0.033 x BW)
- Crude protein: 1.26 grams per kg of body weight (1.26 x BW)
- Calcium: 0.04 grams per kg of body weight (0.04 x BW)
- Phosphorus: 0.028 grams per kg of body weight (0.028 x BW)
- Magnesium: 0.015 grams per kg of body weight (0.015 x BW)
- Sodium: 0.02 grams per kg of body weight (0.02 x BW)
Calculations for exercising horses also take into account estimated sweat losses based on exercise level. Growing horses, lactating and gestating mares and stallions will also have different requirements than maintenance horses.
Many commercial feed tags list their recommended feeding levels on the basis of body weight. Under- or over-estimating your horse’s weight can lead to feeding inappropriate amounts.
Evaluating Weight Changes
Along with measuring body weight, you can assess whether your horse needs to gain or lose weight by evaluating their body condition. On the Henneke 9-point scale, an ideal body condition is 5 out of 9.
Surveys in Australia and the United Kingdom show that horse owners often underestimate their horse’s body condition. [2][3] This can lead to over-feeding to support weight gain in horses that are already at optimal weight or overweight.
Combining accurate assessment of body condition and your horse’s body weight can help properly assess whether your horse needs to gain or lose weight.
Weight Gain
Underweight horses may be affected by dental issues or gut health concerns such as gastric ulcers or internal parasites that make it harder to gain weight. These horses are often referred to as hard keepers. Hard keepers also includes horses with a naturally high metabolic rate, like thoroughbreds, or horses that have locomotive stereotypies and constantly weave or pace.
Before adjusting their diet to support weight gain, consult with your veterinarian to identify underlying causes that may be contributing to poor body condition.
To support weight gain from a body condition score of 4 towards 5, the NRC recommends feeding 1.8 – 6.7 mcal of digestible energy per day above maintenance requirements. The amount depends on how quickly you would like to achieve weight gain. [1]
Horses that are beginning with a body condition of 1 – 3 need to be carefully managed to avoid metabolic concerns related to weight gain, such as refeeding syndrome.
Weight Loss
To promote weight loss, your horse’s digestible energy intake should be restricted to 64 – 94% of maintenance requirements. This is roughly equivalent to restricting their hay to 1.25 – 1.5% of their body weight. [4]
Horses that are resistant to weight loss may require further restriction. However, this needs to be balanced against the risk of gut health and behavioural issues if forage intake is too low.
Adding straw or choosing mature hay are options that allow higher forage intake while supporting weight loss. Soaking hay is another option to reduce calories in forage by reducing sugar content. This can allow higher hay intake in a weight loss program. [4]
It is recommended to target a rate of weight loss between 0.5% – 1% of body weight per week. Aiming for faster weight loss can put your horse at risk of hypertriglyceridemia – a potentially life-threatening metabolic state for ponies, minis and donkeys. [4]
Medication Dosages
The amount of medication that your horse needs is dependent on their weight. For example, the recommended dose of omeprazole used to treat gastric ulcers is 4 mg / kg of bodyweight.
An incorrect weight estimate could lead to your horse getting a dosage that is lower or higher than what they need. In a survey of 17 horse owners, 23.5% were giving an incorrect dose of prescribed medications. This can impact efficacy, side effects and cost. [5]
Providing a lower dosage could cause the medication to be less effective, while a high dosage could increase the risk of adverse reactions. In addition, it’s important to follow the medication dosing schedule to avoid drug resistance, a growing concern regarding dewormers and antibiotics in particular.
Calculating Carrying Capacity
The general recommendation is that horses should not carry more than 20% of their body weight, which includes both tack and rider. Heavier loads can contribute to a higher degree of muscle soreness and tightness. [6]
A small study in Warmbloods found issues with gait symmetry and lameness when carrying more than 15% of their body weight. [7]
Knowing your horse’s body weight can help you determine the maximum amount they should carry, especially if they are unconditioned or entering work.
How to Determine Your Horse’s Bodyweight
Here are several ways to determine your horse’s body weight, ranked from the most accurate to the least accurate.
1) Using a Scale
This is the most precise and reliable way to determine your horse’s body weight. Since large animal weigh scales are expensive, they are not accessible to the typical horse owner or small farms.
However, some feed representatives or veterinary practices may have portable scales that can be used. You can also ask to use scales at veterinary schools, feed companies, flour mills or weigh stations on highways.
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2) Girth and Body Length Measurement
If a scale is not available, you can estimate your horse’s body weight using length and girth measurements. This is considered the most accurate way to estimate weight. [8][9]
To obtain your horse’s body length and girth length:
- Ensure your horse is standing square
- Measure their girth: place a measuring tape or string around your horse’s girth, directly behind their elbow
- Measure body length: place a measuring tape or string at the point of the shoulder and measure to the point of the buttock. You will want another person to hold one end of the tape or string for an accurate measurement.
- For both measurements, ensure the tape is snug but not tight. Check for twists in the tape and measure after the horse has exhaled.
Input these values into the calculator below to estimate your horse’s body weight.
The following nomogram can also be used to estimate equine body weight by drawing a straight line from the girth (cm) to the length (cm). The weight measurement can be read where the line crosses the centre axis. [13]