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Optimal tryptophan: lysine Ratio for 25-40 Kg Growing Pigs Fed Diets Containing 35 % Distillers Dried Grains with Solubles

Published on: 03/12/2021
Author/s : Author: J. Caroline González-Vega – Evonik Operations GmbH. John K. Htoo, n/a – Evonik Operations GmbH. Maryane S. Sespere Faria Oliveira, Postdoctoral Research Associate, University of Illinois. Hans H. Stein, Professor, Department of Animal Sciences, University of Illinois.

Distillers dried grains with solubles (DDGS) has a high concentration of Leu, and the Trp requirement for growing pigs may be increased if diets contain excess Leu. Therefore, the objective of this experiment was to determine the optimum standardized ileal digestible (SID) Trp:Lys ratio in growing pigs fed diets with excess Leu from DDGS. A diet based on corn, soybean-meal, and 35% DDGS was f...

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March 12, 2021
John Htoo,
Based on the summary presented, I would like to highlight as correct, the decision of the team of researchers responsible for the work, to have used a suboptimal level of lysine to determine the best tryptophan relationship with lysine. This decision-making is justified by the fact that animals require grams of amino acids per day or phase, not percentage. Thus it can be deduced that the percentage is established based on an expectation of consumption and is adopted because of its practicality. If in the study of the relationship between any essential amino acid with lysine, an optimum level of lysine is used, there is a risk that the animal's feed consumption will be above the estimated, which would result in excess lysine consumption, which would compromise the result, underestimating the relationship. And exactly because of this reality, I think there was a lack of treatment, that is, using lysine in the requirement of the animal with tryptophan at 15% of the lysine, which would be used to prove its deficiency in the test diets.
John Htoo John Htoo
Global Swine Expert at Evonik
Evonik Animal Nutrition Evonik Animal Nutrition
Rellinghauser, Hessen, Germany
April 13, 2021

Juarez Donzele
Dear Dr. Donzele,

Thank you for the comment. I can explain the logic for our trial design, setting Lys as suboptimal level in all diets (also for the diet at 15% Trp:Lys ratio), as follows.

The requirement of an amino acid (AA), e.g. Trp and Lys, can be estimated on the basis of grams per day. This factorial approach is used in growth model (e.g. NRC, 2021). Another approach, obviously, is empirical dose-response trials which is more frequently used to estimate AA requirement or ratio in pigs.
It is well known that for estimating the absolute requirement of an amino acid (e.g. Lys; % of diet), we have to make sure that all other amino acids (AA) should meet or preferably slightly above requirement in the basal diet to avoid potential their co-limitation and to make sure that the response is only due to graded levels of Lys.
For estimating the optimal ratio of an AA relative to Lys, theoretically it is also possible to provide dietary Lys level right at the requirement (as you are referring to) but the Lys level must not exceed requirement level to avoid the risk of underestimation of AA ratio relative to Lys. In practice, it is not so easy to know exactly Lys requirement for a group of pigs used in the trials.
In our experiment, estimation of optimal Trp:Lys ratio, to avoid underestimation of the determined Trp:Lys ratio, the level of Lys was balanced to be slightly below requirement throughout the experimental period. This means that Lys is second limiting AA while other AA (except Trp and Lys) were supplied at or above requirement.
This application of this methodological approach has been published, and commonly applied in today’s AA:Lys ratio trials. For example, Boisen (2000): Ideal Dietary Amino Acid Profiles for Pigs (Book Chapter 9) explained in detail about the need of setting Lys to be below requirement and gave a practical suggestion to target dietary Lys to be a 10% deficit and a 10% surplus of each of the other essential AA.
In poultry, Knowles and Southern (1998): The Lysine Requirement and Ratio of Total Sulfur Amino Acids to Lysine for Chicks Fed Adequate or Inadequate Lysine (Poultry Science 77:564–569) also validated that the optimal SAA:Lys ratio in broiler chicks was identical when chicks are fed at requirement (1.0% Lys) or slightly below their Lys requirement (0.82%).
I hope my response answers your question.

Best regards,
John Htoo

Zdzislaw Mroz Zdzislaw Mroz
Veterinary Doctor
April 5, 2021
Dear Hans,

As your old professional partner from ID-DLO Lelystad (Wageningen University in The Netherlands) I am happy to know that you are still very active in the nutritional research on pigs.
Your work I find very interesting and worthy to comment as follows:

Optimizing Trp:Lys ratios in diets for grower pigs (without or with DDG) has been subjected to many studies across the world. From my perspective, in your study, it would be also interesting to monitor changes in dietary L-Trp provision in relation to stress-related parameters such as serotonin, cortisol and intestinal integrity.
From our Dutch-American studies (see: Koopmans et al. in Journal of Animal Science, Volume 84, Issue 4, April 2006: 963–971) is known that supplemental dietary Trp (5 g/kg as fed basis) to piglets increased hypothalamic serotonergic activity, reduced the salivary cortisol response to mixing, improved intestinal morphology, and reduced physical activity 10 d after diet introduction. Consequently, diets containing high Trp levels improved neuroendocrine components of stress and increased gastrointestinal robustness.
Besides, adding DDG with solubles to weaner/grower diets presumably influence on the degree of satiety and behavioural/well-being criteria.
With friendly greetings.

Zdzislaw Mroz
April 9, 2021
Thank you Dr. Mroz. You likely know a lot more about Trp and stress than I do. But in some of our experiments with corn protein we demonstrated a close relationship between elevated concentration of Leu in the diet and reduced serotonin in the hypothalamus. This reduction can be partly overcome by adding more Trp to the diet. Because all corn proteins including DDGS have high concentrations of Leu we hypothesized that Trp requirements may be greater in pigs fed DDGS or other corn proteins. So that was the reason for conducting this research.
April 13, 2021
DR John Htoo, I think I was not clear enough in my considerations. My considerations were exactly highlighting the merit of the work for having used a suboptimal level of lysine. The suggestion that I made of using a reference treatment with lysine level in the animal's requirement, would be just to prove that the level of lysine in the test diets would be below the animal's requirement. I understand perfectly the correctness of maintaining the relationships of the other essential amino acids with the lysine just above that recommended in the ideal protein for the animal category, under study, thus guaranteeing lysine as the second limiting amino acid. I fully agree with the methodology used in this study, my intention was to highlight that detail.
John Htoo John Htoo
Global Swine Expert at Evonik
Evonik Animal Nutrition Evonik Animal Nutrition
Rellinghauser, Hessen, Germany
April 13, 2021
Dear Dr. Donzele,
Thank you for the feedback and additional explanation. Indeed, I fully agree the merit of adding an additional diet (we can call it as reference or positive control diet) containing Lys at adequate level. For example, we added such positive control diet which contained both Lys and Trp at adequate level in an experiment in Germany to check/make sure Lys was suboptimal in the Trp:Lys titration diets (published: M. Naatjes et al. / Livestock Science 163 (2014) 102–109). Sometimes, having not sufficient number of pens limited to have one more treatment but ideally, this positive control diet should be included in the AA:Lys ratio trials. Thanks for highlighting this.

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