Hi, everyone. My name is Woongbi Kwon from the Stein Monogastric Nutrition Laboratory at
the University of Illinois. Today, I’m glad to share with you some data related to
branched-chain amino acid nutrition for growing pigs. And this is also part of my Ph. D.
dissertation work.  

Leucine, isoleucine, and valine: they are indispensable amino acids for swine. And they’re
categorized as the branched-chain amino acids because of the structural similarity of
their side chain. For this reason, they have the interaction in their metabolism—for
example, the antagonistic effects of excess leucine. 

Previous literature indicated that if pigs consume excess leucine diets, they surprisingly
can detect branched-chain amino acid imbalance within one hour of ingestion. And most
studies indicated that excess leucine reduced their growth performance, especially average
daily feed intake. And they concluded that the troublemaker in excess leucine diet was
KIC. KIC is α-keto isocaproate, which is the metabolite of leucine. This compound can
stimulate the enzymatic degradation of all three branched-chain amino acids, which means
excess leucine can create the antagonism among the branched-chain amino acids.

So previous research has been conducted to investigate excess leucine effects, and we
concluded that excess leucine reduced growth performance and nitrogen retention. And we
also confirmed excess leucine increased catabolism of all three branched-chain amino
acids. Interestingly, we found one more thing: excess leucine reduced serotonin
concentrations in the brain. Based on these serotonin results, we could explain why
average daily feed intake was affected by excess leucine, because serotonin is the
neurotransmitter that is involved in feed intake regulation. Since tryptophan is the
precursor of serotonin in the brain, we were thinking there must be something in between
leucine and tryptophan. So, we’ve conducted a second study with leucine and tryptophan and
concluded leucine had the negative effect on tryptophan uptake in the brain. And adding
more tryptophan increased serotonin concentration in the brain and it also increased
average daily feed intake and average daily gain, but it couldn’t fully overcome the
negative effect of excess leucine. In addition to the negative effects on tryptophan
utilization, if excess leucine reduces the efficiency of utilization of isoleucine and
valine, which are the other two branched-chain amino acids, how do we handle this problem?

Therefore, in this study we tested the hypothesis that adding more valine and isoleucine
will overcome detrimental effects of excess leucine on nitrogen balance and branched-chain
amino acid metabolism of growing pigs.

So, we utilized 144 growing barrows with initial body weight of 28.5 kg and they were
housed in metabolic crates and were assigned to 18 dietary treatments.

We formulated the basal diet using less amount of corn and soybean meal and greater amount
of wheat and barley, because this is the only way we could get the diet containing SID
leucine level at the requirement. Otherwise, we will always over-formulate diets above the
SID leucine requirement. In order to investigate the effect of increasing level of dietary
leucine, isoleucine and valine, we used crystalline L-leucine, L-isoleucine and L-valine.
Finally, we had two levels of leucine and three levels of isoleucine and valine,
respectively. One thing I want to point out—the dietary concentration that I put here with
orange colors, they are the requirement of each branched-chain amino acid from NRC (2012).
So, three levels of each isoleucine and valine represent below the requirement, at the
requirement, and above the requirement. Therefore, we had 18 dietary treatments with
different SID branched-chain amino acid levels.

After five days of adaptation period, total amount of urine and feces were collected for
five days according to the marker-to-marker procedure. For sample collection, all pigs
were euthanized on day 13. Blood samples were collected on both day 0 and day 13, and
tissue samples of liver and muscle were collected right after euthanization.   

Before we jump in to the results, since we couldn’t find any three-way interaction for all
response criteria from this 2x3x3 factorial treatment arrangement, I would like to show
you the data based on two-way interactions and main effects. Let’s see the nitrogen
balance data first. For nitrogen retention, we only found a leucine effect. As we added
more leucine, nitrogen retention was decreased. For biological value of protein, we had
exactly the same trend here. As we added more leucine, biological value of protein was
decreased, indicating that excess leucine has negative effects on nitrogen balance in
growing pigs.

How about plasma urea nitrogen? There was a similar trend as we saw in the nitrogen
balance data, but we also found a valine effect. As we added more leucine, plasma urea
nitrogen was increased. However, as we added more valine, plasma urea nitrogen was
decreased. Therefore, adding more valine is beneficial in terms of efficiency of amino
acid utilization.

And this is the data of branched-chain amino acid concentrations in skeletal muscle. For
all three branched-chain amino acids, we only found leucine effects. As we added more
leucine, concentrations of all 3 branched-chain amino acids in skeletal muscle were
decreased.

How about branched-chain amino acid concentration in the liver? We found only leucine
effects here as well. However, unlike skeletal muscle, as we added more leucine,
concentrations of all three branched-chain amino acids in the liver were increased. Based
on the data from these two different tissues, we can conclude that excess leucine could
change the branched-chain amino acid composition and their metabolism in the body.

Now let’s see the plasma free branched-chain amino acid data. For isoleucine, we found the
interaction between leucine and isoleucine, leucine effect, and isoleucine effect. As we
added more leucine, plasma free isoleucine decreased; however, as we added more
isoleucine, plasma free isoleucine increased. According to the interaction, the increase
is greater if we have lower leucine in the diets.

How about valine? Exactly the same trend here as well. We found the interaction between
leucine and valine, leucine effect, and valine effect. Like I mentioned before, these
plasma free isoleucine and valine data indicate that excess leucine has clear negative
effects on availability of isoleucine and valine for protein synthesis.

For leucine, it’s pretty obvious we found only leucine effects. The more leucine we have
in the diets, the more leucine in the plasma.

Now let’s see the branched-chain α-keto acid data. We analyzed three different
branched-chain α-keto acids from the metabolism of branched-chain amino acid in the
plasma. For KMV, which is the metabolite of isoleucine, we found interaction between
leucine and isoleucine, leucine effect, and isoleucine effect. As we added more leucine,
plasma KMV decreased; however, as we added more isoleucine, plasma KMV increased. The
increase is greater if we have lower leucine in the diet.

For KIV, which is the metabolite of valine, we had similar data here as well. As we added
more leucine, plasma KIV decreased; however, as we added more valine, plasma KIV
increased. According to the interaction, the increase is greater if we have lower leucine
in the diet. Notice that these results for KMV and KIV have a similar trend to what we saw
in the plasma free isoleucine and valine.

However, for KIC, which is the metabolite of leucine, we couldn’t find any interaction,
but we found leucine effects and valine effects at the same time. It was surprising
because we were only expecting increased KIC concentration in excess leucine, but we
didn’t expect the valine effect. As we added more valine, plasma KIC was clearly
decreased. This indicates that adding more valine could inhibit the stimulating effects of
KIC on branched-chain amino acid catabolizing enzymes by reducing KIC concentration in the
blood.

In conclusion, we confirmed the negative effects of excess dietary leucine in growing pigs
in terms of nitrogen retention, efficiency of amino acid utilization, and availability of
the other two branched-chain amino acids for protein synthesis. However, valine
supplementation can partly overcome the negative effects of excess leucine in terms of
efficiency of amino acid utilization, and it might reduce the catabolism of branched-chain
amino acids by reducing KIC concentration in plasma.

I would like to thank the sponsor, Ajinomoto, for financial support, and I want to
acknowledge all the members in the Stein Monogastric Lab. If you want to learn more about
our research, please visit our website. Thanks for your attention.