Estimating Adult Horse Bodyweight

September 1, 2019

Hi I’m Dr. Molly McCue. I’m an equine veterinarian here at the
University of Minnesota. Hi, my name is Krishona Martinson and
I’m the Equine Extension Specialist at the University of Minnesota, housed in
the Department of Animal Science. Hi, my name is Emily Glunk. I’m a PhD
student in equine nutrition working with Dr. Krishona Martinson here at the
University of Minnesota. So, this morning we’re going to talk
about estimation of weight in adult horses. This is an
important subject for horse owners to consider because one, we use weight to be able to
determine medications most commonly de-wormers is something that will be
administered by horse owners, but also because we use
weight to determine the appropriate amount of feed that should be given to horses and
also as an assessment overall physical health. So the most
accurate method to determine the weight of an adult horse is to use a livestock
scale. Unfortunately, livestock scales are not
available to the majority of horse owners, and so in lieu of that being
available there’s a couple of different ways that we can estimate weight. One would be by the use of weight tapes which
are usually based on a girth circumference, a
single measurement. A more accurate method, in lieu of a scale, would be to use a weight
equation, which are based on traditionally two, and sometimes three
measurements. So typically when we use a weight tape, which
are often supplied by feed companies, what we do is try to get
the horse to stand as square as possible. And then put the weight tape around the
horse’s girth, typically as close as we can to
the back of the elbow, once the horse is standing square. So these weight tapes are basically based
on a circumference of the girth measurement, but typically they’re
demarcated by an actual weight on the tape. And so
using the weight tape on Belle we have an estimation of her weight of
about 1,190 pounds so a little bit higher than her true
scale weight which is about 1125. So, weight estimation equations typically take
a minimum of two measurements and so we’re going to demonstrate the measurements
that are appropriate for the existing weight equation. So the first thing that we’re
going to do is determine the horse’s body length. And this is typically measured from
two landmarks. The first one is the point of the shoulder, which can be found
by kind of following the slope of the horse’s shoulder. And, at the point, you can actually palpate
a bony protruberance here. So this will be the beginning of the
body length measurement is here at the point of the shoulder. And we’ll measure to the point of the buttock,
which is actually demarcated by the ischial tuberosity.
So the measurement, then, is from the point of the shoulder, all the way to the ischial tuberosity,
which can typically be visualized by standing at the horse to the side and
looking for the most caudal, or the furthest point from the point of
the shoulder. Depending on the equation, it’s either exactly to that point or
actually wrapped around the back of the horse. So when we make
this measurement we can see that Belle’s body length would be recorded as 69.5 inches. So now we’ll
repeat a very similar girth measurement to what we did with the weight tape. So we’re
going to go around her heart girth, again trying to have the tape
right behind the point of her elbow on both sides. And so we can see that
from this measurement Belle is about 73 inches. Once we have the girth and length
measurements we can then put these
measurements into a standard body weight estimation equation. And so Emily’s going to make this
calculation: the first number is the girth squared, or in Belle’s instance, 73 x 73 and then this number times a body length, which is 69.5. Then, for
an adult horse, we divide it by 330, and we should have an estimation
of Belle’s weight. Emily: About 1122. Dr. McCue: So in this instance Belle’s
weight is estimated by this equation at 1122,
which is very close to her scale weight. But one thing that we recognize about
horses, especially when they start to gain weight and become obese, is that
they tend to gain weight in areas such as their
neck. And while they do gain some weight that can be picked up by heart girth circumference measurements,
there is weight gain and adiposity over their
entire body. And so just using the measurements of length and girth circumference are often not
as accurate for horses, particularly when they’re obese. So, to overcome this problem we did some
work where we wanted to develop a new equation that was perhaps one, more accurate in really estimating
scale weight in horses that were not of a normal body condition score and two, also to try to develop a way to
determine what a horse’s ideal weight would be if they were obese.
That way we can feed horses based on the weight that
they should be and also potentially administer medications based on the
weight that they should be. And perhaps, more importantly, give horse
owners a way to have some kind of estimate about their
horse’s body condition score particularly if they’re not trained in
this method. We did some research where we took
measurements of almost 700 horses and in addition to body length and heart
girth we also got two more measurements. One is height, and the other is neck circumference.
So now I’m gonna have Krishona come and just demonstrate how we did these
measurements because they’re slightly different
from the measurements we’ve demonstrated before. So the first measurement is height
and what we want to do again is have the horse standing as square as possible and
Belle’s doing a pretty good job for us here. And then we want to measure at the
height at the third thoracic vertebrae. So this is easy to find if you’re a
veterinarian or are used to palpating thoracic vertebrae but difficult if you’re not familiar and so a fairly
good landmark is actually the end of the mane hairs. For most horses
their mane ends about at that third thoracic
vertebrae. So you can use a height measurement stick like we have here or actually any
measuring tape. The most important thing is to make
sure that you have the tape all the way to the ground and that you’re looking level with their third thoracic
vertebrae. And so when we do this measurement with
Belle we get her to be about 59 inches tall. So the next measurements
that we take for our new weight equation, the girth measurement is the same that we’ve
already calculated on Belle and recall that that was 73 inches. The next
one that we want to take is a neck measurement and so this measurement is
actually made at the middle portion of their neck. The first thing we need to do is figure
out where we want to measure and so we do that by looking at the horse’s length from her poll to basically the
third thoracic vertebrae again on the withers. And so we see with Belle
it’s at about 38 inches. And so we’re going to measure her
circumference here at about 19 inches. So we’re going to look at her
neck circumference and we’re going to see that she’s about 38
inches in neck circumference. So the length
measurement that we do for our weight equation is fairly similar
to the measurement that we showed you before. The landmarks in the front are
going to be the same. So remember we’re going to follow the slope of the shoulder and
find the point of the shoulder. Okay, so this is the bony point and we’re
going to put the beginning of our tape on the bony
point. So when we’re looking at the most distal measurement, we’re doing something a little bit differently and part of this
is because many horse owners had difficulty really determining where the point of the buttocks is. So to simplify this measurement, and hopefully make our weight equation more accurate, instead of wrapping the tape around the
back side of the horse what we want to do is stand
perpendicular to the back of the horse and look at the most distal, or the
longest point, which is basically the point of the buttocks. And you can see that Krishona here is just
using some kind of flat object or straight edge to kind of come
out to this measurement. And with this measurement we see that
Belle is about 65.5 inches. So based on the four measurements that
we’ve just described in nearly 700 horses, we worked to develop an
equation that we thought would be more accurate and have shown to be more accurate in
estimating body weight. So one of the problems with this equation
is that mathematically it’s actually pretty complicated and so being able to
do the measurements and plug in the numbers and make the estimation takes a
little more sophistication than the previous body weight equation.
So to overcome this problem, what we did was design an app for iPads, iPhones and soon Android
devices where horse owners can actually put in
the measurements and then the app will return estimated body
weight. So Krishona has entered Belle’s measurements and we see that her
estimated body weight is 1128 pounds, so within three
pounds of her actual weight. The other thing that was advantageous
for the app as I mentioned earlier we really were trying to look at also calculating a horse’s ideal body
weight based on measures that wouldn’t be
overly affected by them being obese or having excess adipose tissue. So doing so we also have an equation in the app that will estimate a horse’s ideal body weight. And so we see that the estimated ideal
body weight for Belle is 1135 pounds. So really close to
the weight that she is and we mentioned earlier that she really is in an ideal body
condition score of 5 range. The final thing that the app
does, and probably the thing that will be most useful for horses and managing the health of their horse is that we
used the numbers from nearly 700 horses to give you an idea of what the horse’s
percentile is. And so we see for Belle that she’s in the
78th percentile and what we know is that horses that are
between the 48th and 83rd percentile are a normal body weight, or most likely
to be a normal body weight. So with Belle we would know that we
probably don’t need to be concerned about her either being under weight or obese. If your horse comes
back with a score that’s higher than 83 percent or lower than
48 percent then we would suggest that you actually
get the assistant of an equine professional, either a veterinarian or
somebody else who’s familiar body condition scoring to help give you
direction about how to manage your horse.

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