Table of Contents:
An accurate knowledge of the weight of a horse is obviously important for the consideration of the quantity of feed that should be given. However, this is not the only concern relating to body weight. It is essential to have an, as accurate as possible, estimation of a horse's weight for many reasons including:
The most accurate method of weighing your horse is through the use of an equine
specific weighbridge which will give an accurate and quick (within five seconds)
reading of bodyweight. These scales would however, be required to be calibrated
to ensure their level of accuracy. Equine weigh scales are expensive to buy,
approximately £2000 (in the United Kingdom in 1999), but are worth the investment
especially for larger establishments. Public weighbridges are often available
for use although it is likely that you will have to be prepared to travel to
them. These tend to be calibrated and accurate only for larger weights. One
suggestion would be to drive your lorry onto the weighbridge (with the horse
on board) and make a note of the weight. Then remove the horse and re-weigh
the lorry. Subtract the second result from the first to give you the weight
of the horse. Equine calibrated weighbridges are presently the only reliable
method for determining the weight of pregnant mares and youngstock.
Other available methods of estimating weight are through the use of a weigh
tape or by the use of ordinary tape measurements being placed into a formula.
Weigh tapes are readily available through most saddler's for under £10 (in
the United Kingdom in 1999). Weigh tapes are easy to use and if they are used
in a consistant manner by the same operator they can be used effectively for
monitoring purposes. They give an estimation of the weight of the horse, but
depending upon a number of factors including breed, conformation, fitness etc,
their accuracy can vary. Different formula may help to improve the accuracy
for some animals.
When the horse is standing square, the weigh tape should be dropped over the horses belly from the base of his withers and brought underneath him just behind his elbow and foreleg. The reading should be taken where the tape joins the tape (or in some cases from the point of arrow) and will either represent his weight in kgs or lbs. If the angle where the tape to tape joins forms a vertical line, your tape has been brought too far back producing an inaccurate reading. You want to aim for a slightly back slash angled line (/).
As mentioned earlier, weigh tapes are an unsuitable method of accurate weight estimation in pregnant mares. Using a weighbridge in these circumstances may be the only suitable method to take full account of the foetus and foetal fluids. In the same way, estimating the weight of a horse with unusual conformation or one that is very fit / unfit may be extremely difficult. Weigh tapes tend to be more accurate when used on a horse of average (ideal / good) condtion score. If the horse has either a lower or higher condition score then it is likely that the weigh tape will reflect this either by an under or over estimation. A high fibre diet, especially if it is of a poor nutritional quality, can result in an increase in the hind gut and a ‘hay belly’ which can lead to an increase in bodyweight, which may not be fully allowed for when using this method of weight estimation.
Using a weight formula can be even more accurate when compared to the weigh
tape method. As with the weigh tape you must make sure that your horse is standing
square and then using an ordinary measuring tape measure the girth as described.
Note this reading in cms. For the formula used here the next step is to measure
from the point of shoulder to the point of buttock. The tape should either follow
the contours of the horses body for this measurement or simply be held taut
and in place from one point to the next.
Our suggestion would be to ensure that whichever method you choose, remain regular and consistent each time you measure or as recommended by a particular tape and weighing formula. By following a set procedure you will be able to monitor change which, as mentioned earlier, can be used as an indicator or good or ill health. So, having decided upon your methodology, note this measurement (in cm) and insert your readings into the calculations below:
Another method of estimating weight is through the use of a bodyweight calculator (similar to a weigh tape) such as a Nomogram. For these purposes this is a scale that relates total diameter of heart girth to the length of the horse. In the above example this is measured from the point of shoulder to point of hip* (all measurements taken in centimetres).
To use the Nomogram, firstly measure the horse, from the point of shoulder to the point of hip, recording the measurement in centimetres (again ensuring that you will be consistent in the method you use e.g. tape taut or following contours of the body). Then measure the depth of girth as described earlier (again in cms) when the horse has breathed out. Finally, draw a line on the nomogram between the two measuring points (depth of girth and length) to provide an estimation of the horses weight in kilograms.
*NB this uses a different measuring point for length than the weighing formula.
All of these methods (other than a calibrated weigh-bridge) will only give you a guide to the weight of your horse. However, if used in a consistent manner they can give a very good estimate of any change in weight. These methods are not appropriate for foals or young growing horses as the relative body proportions change with age.
So, now you know how to estimate a horses’ weight. Try it yourself and keep a record that you can refer back to. Look at how much feed you are giving and see if this relates to his condition (whether you think he is looking a little too thin or too fat, see condition score for further information on how to asses a horse’s condition). One important point to remember is to ensure that whether you actually weigh the horse or estimate the weight that it is done at the same time on each occasion and on the same type of day (with respect to prior exercise/feeding etc. where possible). This will take into account any food that may have been eaten or work that has been done, providing a more reliable and consistent estimation. For example, outside the box on a concrete base, first thing in the morning, before exercise and being fed hard food or hay will aim to keep the parameters for each weighing consistent.
Carroll
C.L. and Huntingdon P.J., (1988) Body Condition Scoring and Weight Estimation
of Horses. Equine Veterinary Journal 20 (1), 41-45
Ellis J. M. and Hollands T., (1998) Accuracy of Different Methods of Estimating
the Weight of Horses. The Veterinary Record 143, 335-336
Milner J. and Hewitt D., (1969) Weights of Horses: Improved Estimates Based
on Girth and Length. Canadian Veterinary Journal 10 (12), 314-316