November 4, 2019

Low Protein Diet in broilers --- How low can we go?

Tags: Poultry | Broiler | Amino Acids

Low Protein Diet in broilers --- How low can we go?

Hello everyone! Welcome to our Research Digest #12  --- another post written up in the air.

The paper that I wanted to share with you today was just published on the Poultry Science this month on October 11th. as Advanced Access, and is titled "Impacts of reduced-crude protein diets on key parameters in male broiler chickens offered maize-based diets".

This was a work from Dr. Sonia Liu’s lab at University of Sydney, Australia, collaborated with University of New England, Baiada poultry, and Evonik.


The application of Low-Protein Diets in swine and poultry has been a hot topic in certain countries the past few years, especially in China (not so much in the U.S. though at this point). One of the primary benefits of feeding low-protein diet is the reduced N excretion and therefore environmental pollution.

That would be nice, apparently. However, the question remains as to how low can we go without compromising the animal’s performance? And, at the low-protein levels, are there any strategies to help maintain that performance needed?

In this study, the authors tested a graded concentration of crude protein (CP) from 21% to 16.5%, and at the low level of 16.5%, tried 3 potential strategies ----

1). Increase Met level (because birds may be more sensitive to Met when on a low-CP diet);
2). Include pre-pellet whole corn (to enhance gizzard functionality because low-CP diet may contain less fiber);
3). Replace soybean meal by whey protein concentrate (because the latter is more rapidly digestible, and thus may help enhance FCR).

What was done?

The experiment design is shown below.

(Recreated based on Chrystal et al., 2019)

What was found?

The blue bars below represent the graded CP %, the 3 pink bars represent the 3 dietary modifications with the 16.5% CP diet.

1. Growth performance

  • CP reduction --- BW was not affected, FCR decreased from 21% to 18% CP, but further reduction to 16.5% CP did not yield good FCR. The best numeric performance was found in birds fed 18% CP diet.

(the authors thought that 16.5% CP diet didn’t work probably due to deficiency in certain non-essential AA, like glycine or serine)

  • Dietary modifications at 16.5% CP --- compared to birds fed 16.5% CP diet without any modifications (the light blue bar), the 3 modification strategies (the pink bars) didn't seem to help much; the inclusion of whole corn and whey protein concentrate even increased mortality from 4.8% to 12% (the authors were not sure why).

(Including pre-pellet whole corn also did not affect relative gizzard weights here).

(Recreated based on Chrystal et al., 2019)

2. Nutrient utilization

  • CP reduction --- With the reducing CP level, digestibility of amino acids and starch increased, so did energy utilization as shown by N-corrected AME. (I only showed Lys digestibility here, but most other amino acids followed the same trend). The enhanced energy utilization was likely due to the increased dietary starch level (with the reduced CP) along with the increased starch digestibility.
  • Dietary modifications at 16.5% CP --- All 3 strategies seemed to further improve AA, starch, and energy utilization numerically – the best AMEn was found in birds fed 16.5% CP with whey protein concentrate.
(Recreated based on Chrystal et al., 2019)

3. Other interesting findings

The authors calculated the ratio of ileal starch: protein disappearance rate (how much starch is disappearing vs. protein, g/bird/day), and found that this ratio would increase with reduction of CP. And interestingly, this ratio was related to FCR and fat-pad weights --- where the higher the ratio, the worse FCR & fat-pad weights were.

(Recreated based on Chrystal et al., 2019)

So there might be an optimal starch: protein digestive dynamics for broiler performance? Based on the regression, the lowest FCR was obtained at a ratio of 2.01.

In the discussion, the author referred to another paper (Sydenham et al., 2017) that talked about the the relevance of starch:protein disappearance rate ratios to broiler performance. This study was from the same research group. I took a look, and in this study, the authors found that "partial substitution of soybean meal by fishmeal promoted starch digestibility and energy utilisation and growth performance....Instructively, starch:protein disappearance rate ratios in the proximal jejunum were quadratically related to weight gain (r=0.849; P<0.001) and FCR (r=0.838; P<0.001)...These relationships emphasize the importance of digestive dynamics and in these examples there was an ideal balance between the bilateral bioavailabilities of starch and protein."

(Interesting...I would be interested to see how this information could be applied in practical formulation going forward)

Take-home message

Likely we can reduce crude protein from 21% to 18% for broiler (d14-35) without compromising growth.

Further reduction to 16.5% would negatively affect performance, and the 3 strategies tested here (Increase Met, include pre-pellet whole corn, and replace SBM by whey protein concentrate) failed to enhance bird performance.

P.S. Reading this paper reminded me of a review on Low-protein diets that I wrote a year ago, which was published on my Chinese blog and attracted 5000+ reads. When time allows, I will try to translate and post it here and I would be really interested to learn your thoughts on low-protein diets.

Full article access👇

Impacts of reduced-crude protein diets on key parameters in male broiler chickens offered maize-based diets


Chrystal, P.V., Moss, A.F., Khoddami, A., Naranjo, V.D., Selle, P.H. and Liu, S.Y., 2019. Impacts of reduced-crude protein diets on key parameters in male broiler chickens offered maize-based diets. Poultry science.

Sydenham C.J., Truong H. H., Moss A. F., Selle P. H., Liu S. Y.. 2017. Fishmeal and maize starch inclusions in sorghum-soybean meal diets generate different responses in growth performance, nutrient utilisation, starch and protein digestive dynamics of broiler chickens. Anim. Feed Sci. Technol. 227:32–41.

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