Carbohydrates and energy. Important for growth, important for gain, important for lack. We need to understand how some of those requirements and the content of the feed is calculated so that we can better understand how to formulate the right ration for the right set of animals. We'll get into into that today on diving in today diets. I'm Brad White. Joined today by doctor. Philip Lancaster and nutrition here. It's Beef Cattle Institute. Good morning, Philip. Keep going,
Brad. So happy to have you with us, and this is a a great time to Kinda get into the details, almost said diving into the details. Excited about our title here, but get into the details of, things like carbohydrates and energy and understanding both how cattle use them and how some of those requirements and contents are calculated, And I may have you start out by just giving us some background on the basics of, what do we use carbohydrates for? What are cattle use carbohydrates for?
So the the main thing and really the only this energy. So carbs provide the bulk of the energy in beef cattle diet. So there... There's lots of different forms of carbs that beef cattle used, but that's what they didn't and they provide energy. Not only for the animal, but they provide energy for the microbes in the room. And so that's that's the main thing that we're concerned about with carbs.
So when we think about making sure that they have enough, that energy requirement, varies quite a bit by both stage of production and age. Right? When when are some of the maybe high need times versus low need times? So the energy requirement varies through the production cycle of a cow, where when she is in early lac, those first... 3 to 4 months after calvin. That's her highest energy demand, our highest energy requirement of the whole production system.
The lowest energy time is after she leans that calf. She's in mid gestation for the next 2 to 3 months. And the fe is hasn't really ramped up its growth, a whole lot yet, and so that's her lowest energy. Environment of the production cycle. And then as she gets into late gestation, and that would be kind of the the in between where that fetal growth is ramping up and so her energy requirements are increasing, but they're not as high as they are
during early lac plantation. Given those changes, when we think about how we're measuring energy, which is really what we're talking about. 1 of the most common ways that that's described is through the net energy system. So what maybe define the net energy system and tell me how that net energy is calculated. So the net energy system was designed to to take us all the way down from... The gross energy in a feed or the to the energy in a feed that is
goes to different functions in the animal. So let's let's walk through it and let's break it down. So we start with the gross energy and the feed. That's the total amount of energy in a feed, but it tells us nothing about how much energy the animal is going to get out of the that feed. And so the next step or the first step really is to go from gross, energy in the feed to that digestible
energy from the feed. And so what we lose there is the fecal energy, So if you take gross energy minus the energy that's in the feces, you get the digestible energy that is provided by that you feed. And digestible energy is the biggest part of the energy that an animal gets out of that feeds. So fecal energy is generally the largest loss of energy from a feed stuff. And so why does it go through to the feces why doesn't
why don't they digest more of it? Is it something functional about that type of energy? No, it's it's... It's something functional about the type of carbohydrates that are in that feed stuff. So let's take for instance, forage, We talk about a Td in value or a digest ability of forge being somewhere around 60 percent. Well, that means 40 percent is coming out in the feces. So that's a really big energy loss as a proportion of the total. Things like corn grain.
They have a digestive... It has a digest ability of around 88 percent, and so then that means only 12 percent is coming out in the feces. And so we... Put a lot of emphasis on digestible energy because it's the biggest energy loss or or right there. And so another term that you probably are more familiar with is Td in or total digestible nutrients. And, that is roughly equivalent to digestible energy. And so lots of times when we're formulating diets for beef cows. We are...
Talking about Td, not digestible energy. So you... You're... The 3 terms that we're using Td, digestible energy and net energy are close to synonyms or they are synonyms. No. So digestible energy and Td in are close to synonyms. Net energy is no... Not a s for digestible energy. So the next step... From digestible energy is the animal has to do something with those carbs
that it digested and absorbed. And so We go from digestible energy to what we call the the amount of energy that's metabolized. So metabolized energy of a feed. And the difference between those is the amount of energy that is lost to methane. Which is a little bit weird is how they use it because really that's lost during the digestion process, but that's where that calculation comes in. And then the amount that is lost in urine. So it was... That energy was... So those carbs.
That those, actually, it's part of the proteins go into energy 2. And so the amount of nitrogen that is treated in urine. It's not completely ox or metabolized, so that's a loss of energy from the total amount of gross energy that was in that feed. So that's how we go down to tab. And then from energy, then we go to net energy. And so the difference between metabolized energy and net energy is the the amount of heat that's produced during metabolism of those carbs.
And so net energy then has several different functions. So if I take if I think about a feed stuff, a feed stuff has 1 gross energy value. It has 1 digestible energy value. For an animal or a for a a beef or a cat rum. It has 1 metabolized energy value but it may have multiple net energy values because it may have a net energy for maintenance value, and net energy for gain value a net energy for lac location value.
And so it will have several net energy values depending on how that energy is being used by the animal. So however, that metabolize energy is being used, that trans formation from metabolized energy to net energy is different. So maintenance and lac plantation, use net energy or use the metabolized energy more efficiently.
So a feed stuff will have a higher net energy for maintenance value or a higher net energy for lifetime value, then it will a net energy for growth value because that transformation of energy to net energy for growth, basically the growth of muscle and fat, is lower that that efficiency is lower than it is if I... If the animal is using that metabolism energy for maintenance or lac relaxation. Okay. So now now you've let me to several questions. Yeah. Let me make sure I'm
on the right track here. So my... Total energy in the diet, I really don't care about. The Td is what I do care about or the metabolized energy. Mh. But then after that step, there are some more losses before I get to what the animal can use, and that's where the net energy calculation comes into play. Yes. Right. And so my net energy, if I just think of it simply as, if I have... Let's say I have a growing calf, and we'll leave lac plantation out for a second. I've got a growing calf.
He has to fulfill his net energy for maintenance requirement every day to maintain his body weight. Anything above and beyond that is net energy for gain. Right? Yes. So my feed will have both M, net energy maintenance and G, net energy gain listed on it. But the G number as you're saying is often smaller, even though it's the same feed stuff. So I'm struggling to understand. Yeah. Why wouldn't it just be the same energy because it's really about how the animal is using the metabolism
energy. So the conversion from energy to net energy for maintenance has an efficiency of around 0.7. Alright? So only 30 percent of it goes to heat production and 70 percent of it is used to to maintain the animal. The conversion from metabolized energy to body tissues, so muscle and fat has a efficiency of about 0.4. And so that means that when I take metabolized energy times 0.4. I get a much lower number than when I take metabolized energy times point set... It. So why why is it that
much so sufficient for gain? What's the basis behind that? Because of what what we think and we understand is because of the process, a coupled different things. The process of s sizing new molecules, alright, to grow tissue requires more Atp and so you get more heat production because you're s synthesized new molecules. And so proteins in the body are constantly turning over, even muscle proteins.
And so you've got some proteins that are being broken down, and then they gotta be rebuilt, so there's an inefficiency there because proteins that were already built have be rebuilt as as that protein turnover happens. And so there's an there's a... That decreases the efficiency then of metabolize energy being used for, muscle and fat growth. K? So, I have to understand the differences between those, and there's also the net energy for lac relaxation, which obviously
applies to lac cows. Which similar to growth as less efficiency because we're making new stuff, basically what you're studying. But but yes, it does, but not nearly as much. Which because there's no there's there's no turnover of stuff in milk. It's made once, and it leads. And so the efficiency of metabolize energy lac relaxation is is very close to the efficiency for maintenance. So it's... In fact, the dairy industry just uses 1 number. They they use 1 number for net energy because those 2
users. So close that it doesn't make that big a difference when it comes to formulating die. K. So when I'm using those for making a irrational, and I'm gonna make a ration for growing calves, I have... And and just for example, Let's say I've got a pound of feed, and it has a net energy value of something, and then it has a net energy gain of something. So would that be, like, 1 and 0.4 0.9 and 0.4 or something like that? Yeah. So let's... So depends we're gonna we're gonna focus on,
mega cows per pound. Alright? And so you're you're gonna be somewhere... Your energy for maintenance is gonna be somewhere around, you know, 0.7 to 1, somewhere in that ballpark, and your net for gain is gonna be somewhere in around 0.3 to 0.6. Okay. So so let's say I've got that feed, and it's 0.7 and 0.3, for example. Then... Do do I get both of those out of that same pound of feed? So can I use a pound to feed and and I can say, okay, I'm getting 0.7 from?
Net energy maintenance and I'm getting 0.3 from gain or do I have to use them sequentially. I gotta do maintenance before I can do gain. We... Technically, the animals using everything all at the same time. Right. But mathematically and for our brains to to handle it, we do it sequentially. So what we do is we we calculate the net energy for maintenance requirement. Of an animal. And then we use that 0.7 number to figure out how many pounds of feet is gonna require or to meet that net
energy for maintenance requirement. And then we've got... Well, then we've got... So let's say, the animal is eating 20 pounds of feet. Okay? And so let's say it took 8 pounds of feed to meet the maintenance requirement. That means I've got 12 pounds of feed left suit that can be used for gain. And so then I take that 12 pounds since times the net energy for gain number, the 0.3, that tells me how many mega calories of energy are available for gain on it per day.
And then I can use some other equations to estimate what the rate of gain would be for that animal based on having 12 mega cows of net energy for gain available. Because I can't I can't get the gain unless I do maintenance first. And and, yes, they're using them both at the same time. The analogy that I've used before and you can tell me if this... Makes sense or not. Is it it if you had a pitcher, like a drinking pitcher and you put a small glass inside of it,
until you... If that glass represents maintenance until I fill up the glass, I I don't have any water in my pitcher, which is gained. And I always have to fill up the glass first. Is that is that a reasonable analogy So you you gotta you you pour the water into the glass Yep. And then when the glass starts to overflow, then you have some water that starts to fill up the rest of the
picture. And, yes. That's of that's a pretty good analogy that we gotta fill up the maintenance glass first before we can have anything flow over into the game to get your. And it doesn't matter if your feed says it's got a high E g value. You never use it unless you fill up that maintenance glass. First. Yep. Exactly. So I
think that that helps me make sense. The the problem is I I have a grasp on that Net energy system But then if I send feed to the lab, when I get it back, it has things like India, Td d in. Ad d f, may even have other... It's a alphabet soup of... You may... I mean, you may also have AANDF0DF, So I appreciate that the nutrition are working with other professionals on really up in their acronym game. Right? Really going making everything in acronyms, so nobody can understand it. We're almost
as good as the government. Yeah. Almost as good. So help me sort this out, Td. Let's start with Td d, Ad f and Nd, What are they? And what do they mean relative, and and especially, relating back to Net energy for me. Okay. So Td, we talked about a little bit about, Td is total digestible nutrient. So it's the amount of carbs plus protein plus fat that are digested. I'm okay. So you add them all So if I got, you know,
part... My feet is 70 percent carbs and those carbs are 60 percent digested, and then I take that number, and I've got feed that's 15 percent protein that is 70 percent digested and I... So that's how I get that total digestible nutrients. And that is, like I said, roughly equal to digestible energy in the net energy system. In the f is neutral detergent fiber, and this is a number that's I say relatively unique to rum in the fact that, the old feed analysis system used to use crude fiber.
And that value was very to rum nutrition because it doesn't tell you much of anything about how much actual fiber is in there. It works for mono gas, but not very well for room it's. And so the neutral detergent fiber is an estimate of the total fiber in a feed stuff. So it's the cellulose, the hem cellulose and the l. And and gives me an idea of everything all the fiber or plant cell wall that's there. The Ad
is the acid detergent fiber. And the acid detergent fiber is a a little bit different analysis, it breaks down the hem cellulose. So what I'm left with is the cellulose and the Malignant. And the difference between those 2 numbers is the Nd mdf number tells me the total amount of fiber and it tells me kinda how bulky that feed is gonna be. It's gonna... It's it's somewhat related to intake. How especially on forage.
How much is that Animal gonna be able to eat because that feed is gonna be really bulky and how much room is gonna take up in her in the room. The Ad f value is gonna be somewhat related to the Td. Alright? Because I took out the most digestible part of the fiber, which is the hem cellulose, and the ad, is the cellulose and ligand, which are the 2 least digestible parts of the fiber. So when we talk about forage an Ad f value that's higher means lower
digest ability. And so most labs use that Ad value to estimate the Td. There are some equations that have been developed to relate those 2 things. There are some other equations that use Ad f, plus Nd, plus crude protein, but most labs use equation that is just based on Ad f. Because lab don't The only way to truly get Td in is to feed the feed to an animal, and that's not practical.
From a wet lab perspective. And so we have these equations then that can convert Ad to Td d in And the question from a from a practical standpoint is knowing what equation they're using and how well that equation works for your type of forage because there are some based on alfalfa, there are some based on grasses and and they're different and they they don't necessarily cross over well. So how do I relate any or all 3 of those to my net energy? Okay.
So good question. So that we said the Td in is pretty much equivalent to the digestible energy. So then I can take there's in the in the beef cattle Rc nrc, there are... Couple of equations where I can take Td in and I can convert that to net energy. And then lots of times, a feed lab will do that for you, and they'll report a Td end and net energy values
on the feed report. Sometimes they don't. But you can get those equations for from the Nrc, and you can convert that to, NEM and E g. To a couple... And that helps because that's what we've talked about as far as formulating my ration a couple other things that we talked about may show up were a India. And o m Nd f. What it what do those mean? So those are adjustments that we've made over the years to the Nd procedure.
So the original Nd procedure just had the neutral buffer in there to break down the cell si, and then what you're left with was the plant cell wall. Well, different feed stuff that have some things that can hinder that process. So feeds that have a lot of starch, starch tends to clog up the filter, that we use to filter out the cell valuables. And so then what you end up with as an inflated number of plant cell wall because, not all the cell soluble will
go through the filter. So the a in a and d f means that they have added alpha amy to the procedure, to break down the starch and let it filter through, and then you can get a more accurate estimate of the Nd mdf. The... O m, part of Nd f is stands for organic matter. So now what we're doing is we're we're adjusting Nd mdf as a proportion of the organic matter not of the total feed. So we take the ash out.
And now we look at Nd mdf as a proportion of the total organic matter instead of as a proportion of the total diet. And so when you got some feeds that have a high ash content, that can make a pretty big difference. Excellent. So this... If I send a sample to the lab, I'm gonna get these type of values back. If I'm purchasing a feed and I look at the feed tag, what... Which value should I look at to figure out what my net energy is.
None. Nothing and that is the that is the biggest limitation of manufactured feeds is a feed tag does not require any kind of energy value to be reported there. So you have no way of estimating the energy value of a commercial fee. Yeah. But but there's there's no there's no Td in. There's there's no nothing reported on the tag. It was it's not required as... Part of law, and so you that you just don't have anything. So the only thing you can... 2
options. You can call the feed sure, and they may have something from their formulation that they might be willing to share, or you have to send in a sample of that feed to a lad where they will do a nut nutrient analysis and give you an estimate of Td in that you can then work with. Which which there may be times that it depends on how much of that feed I'm feeding and why I'm feeding it, but there may be times that
that's important. There may be times that's not as important because I'm feeding it for another reason. Yeah. So Yeah. Feed tags labeling laws were designed to, protect the consumer from fraudulent, Feed manufacturing, not designed for nutritionists to be able to form to be ration with those feeds. Yeah. Absolutely. Great information on energy today, Philip up. I appreciate you sharing with us. We walk through the net energy system. We talked about what we would do with our feed analysis.
Appreciate you sharing that info. Thanks, Philip. Yep. Thank you.