Slide 1
Hi. I am Hans H. Stein, and I am a professor at the University of 
Illinois in the Department of Animal Sciences. I would like to talk to 
you today about different methodologies that are used to value the 
quality of feed ingredients fed to pigs.

Slide 2
This is the second presentation in this series. In the first 
presentation, we talked about the first area of nutrition, which 
includes what we feed to the animals. And that is related to the 
nutrient composition of ingredients.

Slide 3
In this second part of the presentations, I will talk about what happens 
in the gastrointestinal tract of the pigs after we have fed the 
ingredient. And what happens here includes digestion of the feed, 
absorption of the nutrients, and excretion of excesses. So we will take 
a look at each of these three different areas, and talk about what 
happens when we feed our ingredients to the pigs.

Slide 4
When we talk about determining digestibility values of nutrients fed to 
pigs, we have a general equation that we can use. And this equation can 
be used to calculate the digestibility value on a percentage basis of 
nutrients or energy that are included in ingredients we feed to the 
pigs. This is a pretty simple equation. We simply subtract the output of 
that nutrient from the intake, and then we divide by the intake and 
multiply by 100 to get it on a percentage basis. So as an example, if we 
feed 10 grams of a nutrient and we collect 2 grams of that nutrient in 
the fecal output, then the digestibility of the nutrient in this 
ingredient would be (10-2)/10, multiplied by 100, and that would give 
you 80%. We call this the digestibility value of 80%, or if we don't 
multiply by 100, then we call it a digestibility coefficient, and that 
would be 0.80.

Slide 5
And we use this equation to calculate digestiblity of nutrients and 
energy in all ingredients. However, when we collect the output of the 
nutrient or energy from these ingredients that we fed to the pigs, we 
have to realize that the output contains the undigested feed nutrients 
and also some nutrients that were of endogenous origin. And these 
endogenous nutrients, they are nutrients that were absorbed from the 
intestinal tract by the animal, but then they are incorporated into 
enzymes or other compounds that are secreted back into the intestinal 
tract of the animal. That mean that when we collect the output in the 
feces or other places, then the nutrients we find in the feces contain a 
combination of the endogenous nutrients and the undigested feed 
nutrients. And this will influence the digestibility values that we 
calculate.

Slide 6
As an example here, we can see that if we feed different levels of a 
nutrient to pigs, then we get different digestibility values. In this 
example, we are feeding 3, 5.3, 7.7, or 9.7% of lipids in diets fed to 
pigs. And the lipids in this case are coming from corn oil and we can 
see that the more corn oil we include in the diet, the greater is the 
digestibility that we calculate. And this is because in this case, we 
calculate the digestibility the same way as I showed in the equation to 
begin with, where we subtract the output from the input, and then we get 
what we call apparent total tract digestibility of lipids. And the 
reason the apparent total tract digestibility of these lipids increase 
the more of the lipids we include in the diet is that the output we 
collect -- in this case the feces -- contains more endogenous lipids if 
we have a low inclusion rate than if we have a higher inclusion rate of 
lipids. So, at the lower inclusion rate, we get a greater proportion of 
the total output as endogenous lipids, and that results in a calculated 
value for the apparent total tract digestibility that is relatively low. 
However, as we increase the inclusion rate of lipids in the diets, we 
get a relatively smaller contribution of the endogenous output to the 
total output, and therefore our digestibility values that we calculate 
increase.

Slide 7
We can correct for the endogenous losses if we can find a way of 
determining the total endogenous losses. And in this case, we have 
determined the total endogenous losses and subtracted those endogenous 
losses out of the equation, and then we calculate what's called the true 
total tract digestibility of the lipids. And we can see here that now we 
don't have an influence of the inclusion rate on total tract 
digestibility values. So, by correcting for the endogenous output of the 
nutrients, we can get a better estimate of the digestibility of that 
nutrient. And in particular, we don't get this increase in the 
digestibility as we increase the inclusion rate of the nutrient, and 
therefore these values for true total tract digestibility are more 
accurate than values for the apparent total tract digestibility. We can 
also sometimes determine what we call basal endogenous losses and 
correct the digestiblity values for these basal endogenous losses. And 
if that's the case, then we do not determine true digestibility of 
lipids, we only determine the standardized digestibility of the lipids 
or other nutrients.

Slide 8
So, if we look at different procedures we have to measure the 
digestibility of nutrients, we basically work with two different 
procedures. We either have the total tract digestibility procedure or we 
have the ileal digestibility procedure.

Slide 9
And the total tract digestibility procedure involves placing a pig in a 
metabolism cage, and this metabolism cage will allow us to collect all 
the fecal material that is excreted from the pig, because we have the 
screen under the slatted floor in the cage.

Slide 10
We also have a urine pan sitting under the screen, so we can collect all 
the urine that is excreted from these pigs. And that means we know what 
the pig is eating, and we know what the pig is excreting in the feces, 
and by subtracting the amount of nutrients excreted in the feces, we can 
calculate the total tract digestibility value of these ingredients. If 
we're working with energy, we will subtract both what's excreted in the 
feces and what's excreted in the urine from the intake of energy of the 
pig, and that allows us to calculate what we call the metabolizable 
energy value of energy.

Slide 11
The second procedure we have is what we call the ileal digestibility 
the distal ileum of thse pigs, and that allows us to determine how great 
a proportion of the ingested nutrients were absorbed in the small 
intestine. And we use this procedure for nutrients where there is a 
significant fermentation or degradation or synthesis of nutrients in the 
hindgut of the pig. And in this case, the fecal or total tract 
digestibility will not give us a good measure of the digestibility of 
this nutrient, but if we can get access to the ileal fluids, then we can 
determine the ileal digestibility, which for some nutrients is more 
accurate than the total tract digestibility.

Slide 12
To gain access to the ileal fluids, we have to surgically insert a 
T-cannula into the distal ileum. And on the picture to the left here, we 
are showing a pretty commonly used T-cannula that we use for growing 
pigs, and you can see the dimensions here. And the cannula is produced 
from stainless steel, and we then put on a plastic washer to keep it in 
place towards the body wall of the pig, and we have a cap we can put on 
when we don't collect digesta. When we collect the digesta, we simply 
remove the cap and then we can put a little bag on the cannula, and that 
allows us to collect the ileal fluids. And we use different sizes of 
cannulas depending on the size of the pig, so we can actually cannulate 
pigs that are only 10-15 days old, we can cannulate growing pigs, and we 
can cannulate sows. It only depends on how big a cannula we are using.

Slide 13
And, you can see the cannula is sticking out of the side of the pig, and 
by opening the cap of this cannula, we can directly collect the ileal 
fluids of the pig. That means we can calculate the ileal digestibility 
of nutrients. And we use this technique to calculate digestibility of 
different nutrients, and in particular of amino acids. And for amino 
acids, we have shown many times that the most accurate way of 
determining digestibility of amino acids in pigs is to determine the 
standardized ileal digestibility of amino acids. So that means we need 
to have access to the ileal output of the amino acids, and we also need 
to determine the basal endogenous losses of amino acids. Then we can 
calculate the apparent ileal digestibility of amino acids, correct these 
values for the basal endogenous losses, and by doing that, we calcuate 
the standardized ileal digestibility of amino acids. It's very well 
documented that this procedure is the most accurate procedure to 
determine the digestibility of amino acids in different feed 
ingredients, and for that reason, we usually measure the standardized 
ileal digestibility of amino acids in any feed ingredient that we use in 
diets fed to pigs.

Slide 14
If we look at other nutrients, we first start with phosphorus.

Slide 15
For phosphorus, we have a situation that's a little bit different than 
for amino acids, because for phosphorus, there is no difference between 
the apparent ileal digestibility and apparent total tract digestibility. 
And in this case, we have the apparent ileal digestibility values in the 
red bars, and we have total tract digestibility values in blue bars. And 
we have three different ingredients here: corn, low-phytate corn, and 
soybean meal, and we can see for each of these three ingredients there 
is absolutely no difference between the ileal digestibilty and total 
tract digestibility. And therefore, we usually determine the apparent 
total tract digestibility because then we don't have to insert the 
cannulas into the pigs. So for phosphorus, we don't usually determine 
ileal digestibility; we usually determine total tract digestibility.

Slide 16
We saw before with lipids that the values we determined for the apparent 
digestibility was influenced by the level of lipids in the diet. We can 
look at the same thing for phosphorus. In this case, we have three 
different types of whey powders that we fed to pigs. One source was a 
conventional whey powder that contained 95.8% dry matter and 0.63% 
phosphorus. We also looked at whey permeate, containing 97.7% dry matter 
and 0.57% phosphorus. And finally, we had a low-ash permeate that 
contained 98.4% dry matter and 0.10% phosphorus.

Slide 17
We determined the apparent total tract digestibility of phosphorus in 
these three ingredients. And we can see here that the whey powder and 
the conventional permatte had the same digestibility but the low-ash 
permeate had a much lower digestibility of phosphorus.

Slide 18
However, these were the apparent total tract digestibility values. And 
as we've seen before, if we correct these values for the basal 
endogenous losses, then we can calculate values for the standardized 
total tract digestibility. So we did that in this example.

Slide 19
So what we have on this slide is not only the apparent total tract 
digestibility values in orange, as we saw before. In this case, we also 
have the standardized total tract digestibility values. And remember, 
the standardized total tract digestibility values are calculated from 
the apparent total tract digestibility values by correcting the apparent 
total tract digestibility values for the basal endogenous losses. And we 
see here that while there was a difference in the apparent total tract 
digestibility among the three ingredients, when we correct for 
endogenous losses, there is no longer a difference among the three 
ingredients -- we have just about 90% digestibility of phosphorus in all 
three ingredients. So what this tells us is that the reason for the low 
apparent total tract digestibility in the low-ash permeate simply was 
that there was so little phosphorus in this ingredient that the 
endogenous losses contributed a larger proportion of the total output, 
and therefore we calculated a low value for apparent total tract 
digestibility. And this clearly shows us that values for the 
standardized total tract digestibility are more accurate than values for 
the apparent total tract digestibility of phosphorus.

Slide 20
So the conclusion on phosphorus is that diets fed to pigs should be 
formulated based on values for the standardized total tract 
digestibility of phosphorus, and not based on values for the apparent 
total tract digestibility of phosphorus because, as we just saw in the 
previous slide, values for the standardized total tract digestibility of 
phosphorus are much more accurate than values for the apparent total 
tract digestibility.

Slide 21
Let's talk a little bit more about lipids.

Slide 22
As was the case with phosphorus, the first thing we have to decide is 
whether to use values for apparent ileal digestibility or values for 
apparent total tract digestibility of lipids. So here are data from an 
experiment in which we used two different sources of lipids. One, we had 
diets that were fortified with extracted lipids, which is simply liquid 
corn oil that we added to the diet. And we had another set of diets 
where we used intact corn oil, which means these lipids were not 
extracted; they were simply included in corn germ then we added more and 
more corn germ to get more and more lipids into the diets. And if we 
look at the digestibility of these two different sources of lipids, we 
can clearly see that the extracted lipid sources, they have a greater 
digestibility than the intact lipid sources. So that is the first 
conclusion here. We can also see that for the extracted lipid sources, 
there are no differences between ileal digestibility and total tract 
digestibility, and ileal digestibility is illustrated here in the red 
bars, and total tract digestibility in the yellow bars. So for extracted 
fat, there is no difference beteen ileal and total tract digestibility. 
However, when we look at intact fat, we can see that the values for 
apparent total tract digestibility are less than the values for apparent 
ileal digestibility. We believe that the reason for this reduced 
digestibility is that when we added the intact lipids to the diet, we 
added increasing levels of corn germ. And the more corn germ we add, the 
more fiber we also add, and fiber serves as a source of nutrients for 
the microbes in the hindgut, and the microbes can then synthesize fat. 
So, we actually got microbial fat excreted into the feces of these pigs. 
So when we calculated the total tract digestibility of fat, we had not 
only the undigested feed lipids that were present in the feces, we also 
had lipids that were synthesized by the microbes. And that is the reason 
we got a reduced digestibility when we looked at the apparent total 
tract digestibility compared with the apparent ileal digestibility.

Slide 23
This problem is clearly illustrated on the next slide, where we have 
calculated the endogenous losses of fat both at the end of the ileum and 
over the total tract. The ileal endogenous losses here are illustrated 
in the blue bars, whereas the total tract endogenous losses are 
illustrated in the orange bars. And we can see that for the extracted 
fat, there is no difference between the ileal and the total tract 
endogenous losses. And that is the reason, as we saw in the previous 
slide, that there is no difference between the apparent ileal 
digestibility and the apparent total tract digestibility of fat. 
However, when we look at the intact fat, we can see that the ileal 
endogenous loss is greater for the intact fat compared with the 
extracted fat. We can also see that the total tract endogenous loss is 
much greater than the ileal endogenous loss. And that means that we get 
a lower value for apparent digestibility calculated -- which is exactly 
what we saw on the previous slide. So, the reason for that lower 
digestibility over the total tract compared with at the end of the ileum 
is simply that we have an increased endogenous loss over the total 
tract.

Slide 24
To avoid the contaminating factors of these microbial lipids that are 
synthesized in the hindgut of the pig and therefore increase the 
endogenous loss, it is more accurate to calculate the digestibility of 
lipids at the end of the ileum than over the total tract. And for that 
reason, we should determine lipid digestibility as either true ileal 
digestibility or standardized ileal digestibility of the lipids. And we 
therefore need to have cannulated pigs exactly the same way as we had 
cannulated pigs when we worked with amino acid digestibility.

Slide 25
The last group of nutrients I want to talk aobut today is the 
carbohydrates.

Slide 26
And we have different types of carbohydrates in our diets. The entire 
fraction of carbohydrates consists of monosaccharides, disaccharides, 
oligosaccharides, and polysaccharides, and the polysaccharides can be 
divided into starch and into non-starch polysaccharides, which is also 
called NSP and lignin. And we can see three of the groups of 
carbohydrates here are highlighted in light blue, and the reason for 
that is that these nutrients are absorbed mainly in the small intestine 
of the pig. So to get an accurate estimate of the digestibility of these 
nutrients, we need to use the ileal digestibility of the nutrients 
rather than the total tract digestibility of these nutrients. So again, 
we have to work with cannulated pigs and determine the output of the 
nutrients at the end of the ileum.

Slide 27
And the reason for that is illustrated on this slide, where we have 
measured starch digestibility in field peas. In this case we had four 
different types of field peas. The red bars illustrate the raw field 
peas that had not been heat treated. We had some field peas that had 
been extruded at a temperature of 75 degrees Celsius, they are in the 
yellow bars. We have another group of field peas that have been extruded 
at 115 degrees Celsius, they are in blue bars. And finally the last 
batch of field peas were extruded at 155 degrees Celsius, those are the 
green bars. And we measured both the ileal digestibility and the total 
tract digestibility. And we can see here that the ileal digestibility 
was less than 90% for the raw field peas, but as we heated the field 
peas, we increased the ileal digestibility up to about 95%. So there was 
a linear increase in digestibility as we heat treated the field peas, 
and there were differences among the four groups. However, when we 
looked at total tract digestibility, we can see that there is no 
difference among the four batches of field peas. They are all digested 
by about 99% which means that if we determine the total tract 
digestibility, we are not able to pick up the differences that exist 
among these ingredients. So, this illustrates that if we want an 
accurate estimate of starch digestibility in field peas, we need to 
determine the ileal digestibility rather than the total tract 
digestibility.

Slide 28
When it comes to the non-starch polysaccharides and oligosaccharides, 
this is the fraction that we also call fiber. And those fibers are not 
digested by enzymes in the small intestine the same way as the starch 
was. These fibers are fermented in the large intestine by the microbes 
and then the pigs can absorb volatile fatty acids that can contribute 
energy to the animal. To illustrate that, we have determined the 
digestibility of fiber in distillers dried grains with solubles, also 
called DDGS. And in this case, we had total dietary fiber, which are the 
blue bars, we had the soluble dietary fiber, which are the yellow bars, 
and we had insoluble dietary fiber, which are the red bars. And we 
determined both the ileal and the total tract fermentation of these 
fibers. And we can see that the ileal disappearance or fermentation of 
fiber is relatively low, but the total tract fermentation is much 
greater, which illustrates that the microbes are mainly present in the 
hindgut of the pig, and therefore we get more fermentation in the 
hindgut. In this case, we can also see that the soluble dietary fibers 
are very well fermented by pigs, whereas the insoluble dietary fibers 
are poorly digested by less than 40% overall. So, for this particular 
ingredient, we can see that the overall digestibility of the total 
dietary fiber is less than 50% because DDGS contains more insoluble 
dietary fiber than soluble dietary fiber. But these data also illustrate 
that if we can increase the solubility of our fibers, then our pigs can 
increase the utilizaiton of the fibers because they can ferment soluble 
dietary fiber much better than insoluble dietary fiber.

Slide 29
And the difference between digesting carbohydrates in the small 
intestine and fermenting carbohydrates in the large intestine is mainly 
caused by different energy values that the pig can get from absorbing 
glucose in the small intestine and volatile fatty acids in the large 
intestine. And we can see that for glucose, a pig can utilize about 1.46 
kcal/g of glucose that is absorbed. Whereas for volatile fatty acids, 
the pigs can utilize only 1.02 kcal/g. So what this illustrates is that 
the pig is more efficient in utilizing energy that is absorbed in the 
form of glucose compared with utilizing energy that is absorbed in the 
form of volatile fatty acids. So we would prefer to have as much as 
possible digested in the small intestine and absorbed in the form of 
glucose compared with absorption of volatile fatty acids in the hindgut.

Slide 30
So to conclude on the energy from fiber, what we need to do is to 
determine the concentration of total dietary fiber in the feed 
ingredient. It has to be in percent or in g/kg. We then measure the 
apparent total tract digestibility of total dietary fiber on a 
percentage basis, and then we can multiply those two values and 
calculate the quantities of digested total dietary fiber in g/kg. And 
from there, we can calculate the total amount of kcal that the pig can 
utilize from fiber by multiplying the total grams of digested dietary 
fiber by 1.02 kcal/g. That will tell us the total amount of energy that 
the pig can utilize from digesting and fermenting fiber.

Slide 31
So in summary on carbohydrates, we have seen that sugars are absorbed in 
the small intestine, and they are assumed to be 100% digestible. We 
usually don't determine digestibility of sugars because they are so 
easily absorbed. Starch digestibility needs to be measured as ileal 
digestibility. So in this case, we need to work with cannulated pigs as 
we have seen, and fiber is determined as apparent total tract 
digestibility of fiber, and we can calcuate the energy value of fiber as 
1.02 kcal/g. So these are the different procedures that we use to 
determine the digestibility of carbohydrates, and therefore we also 
determine the energy value of carbohydrates in our feed ingredients.

Slide 32
So this concludes this part of the presentation. We've talked about the 
digestibility of amino acids, of phosphorus, of lipids, and 
carbohydrates. And I would like to thank you for your attention, and if 
you are interested in more information about feed ingredients, you can 
visit our website that is found at nutrition.ansci.illinois.edu. Thank 
you very much.