I began my analysis by calculating two numbers and choosing a category to use for the formulas I'll be selecting for different requirements as I go through the book. As a reminder, they are:
Nimo's weight: 680 kg
Nimo's work load: Very Heavy
Nimo's food amount/day: 8.73 kg DM (dry matter)
After making the calculations above, the next step is to look at energy requirements.
When we think of energy requirements for people, we typically think in terms of calories. The calories we see on food labels are actually kilocalories (see http://recipes.howstuffworks.com/question670.htm), but kilocalories are probably too small a measurement to be practical for horses. Instead, megacalories (Mcal) is the measurement used. A Mcal is 1,000 kilocalories.
But, there is another layer to figuring out a horse's energy requirements, and that layer is a concept called "digestible energy" (DE). Technically,
The apparent digestible energy (DE) content of a ration is calculated by subtracting the gross energy in the feces from the gross energy (intake energy) consumed by an animal. The term "apparent" is used because some of the material excreted in the feces does not originate from the feed but from cells sloughed from the gastrointestinal tract and digestive secretions. The true DE of a feed may be calculated if fecal endogenous losses are known. Endogenous fecal energy losses are not routinely determined in studies with horses and thus most DE values represent apparent DE, not true DE. (see Nutrient Requirements of Horses: Sixth Revised Edition, p. 3)Clear as mud, right? And determining DE can be complicated by the chemical composition of a particular feed as well the digestibility of what is in the feed. Plus, calculating the DE of a feed can only determined with real accuracy through a feeding trial for horses (different species will get different levels of DE from the same feed!). Nutrient Requirements does offer some formulas that can be used to estimate the DE of a particular feed on p. 4, and I may be coming back to those at a later date because the feeds that I use do not provide DE on the feed label.
To start with, though, I just want to figure out how many Mcal Nimo needs each day, with the understanding that a Mcal is not just a Mcal, every horse is different, horses heavier than 600 kg may need a different formula for estimating energy requirements, the environment the horse lives and works in may change caloric needs, and the degree of difficulty of exercise each day may vary depending on footing, intensity of work, weight of the rider and tack, and temperature, so the calories needed will vary too. For the sake of developing a baseline, I will be using this formula for horses in Very Heavy work from p. 26:
DE (Mcal/d) = (0.0363 x BW(kg)) x 1.9
Essentially, this formula calculates how many Mcal Nimo needs each day, based on his body weight in kilograms and given that he is working at the Very Heavy level.
The result is: DE = 0.0363 x 680 x 1.9 = 46.9 Mcal
Now you might think that if Nimo is getting 46.9 Mcal every day, he should be in good shape. As it turns out, not so much. Certain things like the ratio of calcium to phosphorus can cause problems like weight loss if it isn't appropriate, no matter how many calories Nimo is eating. In fact, deficiencies in protein or any number of vitamins and minerals can lead to serious physical symptoms no matter how much Nimo eats.
Of course, the simplest way to figure out if Nimo is getting enough to eat is to look at him. Nutrient Requirements doesn't go into body condition in this section of the book, but I think the vast majority of horse owners are aware of body condition scoring, where a horse is scored from 1 (emaciated and death is imminent) to 10 (put this horse on a diet now!!!). Endurance horses typically score in the 3-5 range (at least based on what I've seen), and my preference is for Nimo to be at a 5.
Earlier this year, a vet scored Nimo as a 4 at the Cheshire CTR in May. That kind of bothered me, not because the vet was necessarily wrong, but because I really do want to make sure Nimo is getting enough to eat and Friesians are not known for their super model slimness. At the time, I was suspicious that Nimo was not getting enough to eat, not because the barn wasn't providing enough food but because the grass in his field was nonexistent due to overstocking and Nimo just didn't seem to want hay when he kept seeing grass growing on the other side of the fence. The barn has since changed its management of the fields, and Nimo does have decent access to grass now, which made a nearly instant change in his weight and attitude.
Here is how he looked last night:
|The lighting isn't that great, but hopefully you can see that he's in pretty good shape:)|
Even though I like the way he looks, I still want to make sure I'm looking at more than just the amount he's eating and the way he looks. So, the next thing to do is to figure out how much Nimo needs of different nutrients and then analyze what he is eating to see if his diet is even in the ballpark.
Before we get to vitamins and minerals, though, I want to spend the next three posts going through the main sources of energy: carbohydrates, fat, and protein. Horses need a combination of these sources, but it can be hard to know what the optimum combination is, and that is what I'll be trying to figure out during those posts:)