Looks can be deceptive!

How much can looks can be deceptive?

How much can looks can be deceptive?

21 August 2017

Calculating weight estimates in horses

Being able to accurately assess the weight of an animal is important for many reasons, particularly for calculating medication quantities such as wormers and in aiding dietary management. But unless you have ready access to a weighbridge this is sometimes easier said than done especially as research shows weight estimates by eye can vary as much as 30%.

To test the theory we ran a fun competition on our Westgate Labs Facebook Page using our 6 year old Highland Pony Bertie who stands at 14hh. He was weighed by Horse Logic Ltd. and condition scored at 3.5 using the Blue Cross scale minutes before this picture was taken.

436 people responded to our call to action and the results were fascinating. Fewer than 5% correctly estimated Bertie’s weight within the 3 kg tolerance that we set for the target. The average (mean) guess was 472kg but there was significant variance, the highest estimate being 666kg and the lowest 310kg – more than 350kg difference.

So what is the answer? Bertie is a solid wee chap currently tipping the scales at 525kg. Weighing him in by eye underestimated his size by an average of 11%.

What does Bertie weigh?

As we don’t have ready access to a weigh bridge we took the opportunity to put a weight tape around him at the same time to see how this correlated. It was reassuring to see the tape reading come in only slightly under at 518kg.

The tape uses a defined formula to correlate equine girth size into estimated mass. Weight tapes are generally a useful tool to use regularly for weight guidance but as they only take in one measurement they don’t work for all horses. The biggest inequalities happen where fat distribution is uneven, so they may be slim on the girth but perhaps carry the weight on their crest or bottom.

It’s worthwhile getting your horse weighed and using a tape at the same time to see how the results correlate.

Results from our Facebook experiment prove that Bertie would have been under dosed if we had calculated his wormer quantity gauging weight by eye.  One of the golden rules of worming is to give enough chemical for the weight of the animal. Not doing so gives insufficient amounts of the active ingredient to kill the worms effectively while still exposing them to the drug and is one of the fastest ways to increase resistance.

Wormers are very safe drugs and so to overcome the challenges of estimating weight and giving sufficient dose, veterinary advice is to add 10% to a weight tape estimate when calculating wormer quantity.

Many thanks to everyone who took part in our online quiz, it just goes to show how looks can be deceptive!

The five lucky winners of a horse weight tape are: Gill Langridge, Caitlin 'Kdy' Kretzschmar, Suzanne Poulton, Jacqui Harrison, Hannah Fleetwood - please contact us with your address so we can send your prize.

> Weight tapes are available to purchase in our online shop