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Effects of Dietary Soy Inclusion on Broiler Chick Performance and Metabolisable Energy

23 February 2014

Iowa State University Extension

High concentrations of soy products did not affect growth of young broilers but feed intake was reduced in this study at Iowa State University. Soy might limit feed intake, possibly due to anti-nutrient or non-digestible components, according to researchers, Matie N. Hanson and Michael E. Persia.

Soybean protein is the major source of protein and amino acids in poultry diets, although soy contains several indigestible and anti-nutritional components that might negatively affect broiler chick performance.

Two experimental diets were formulated to contain:

  • high-soy - a  combination of toasted full fat soybeans and soybean meal 48, and
  • low-soy - soy protein reduced and replaced with dried distillers grains with solubles (DDGS), canola meal, meat and bone meal and synthetic lysine.

From these two diets, three concentrations of dietary soy inclusion were generated including low (20 per cent soy products), middle (28 per cent soy products), and high (35 per cent soy products) by using either 100 per cent or a 50/50 mixture of the two diets.

Experimental diets were fed to broilers from day 10 to 21.

Nitrogen corrected Apparent Metabolizable Energy (AMEn), feed intake, feed conversion ratio (FCR) and bodyweight gain data were collected.

High-soy inclusion significantly reduced feed intake in comparison to the both low and middle soy inclusions. Bodyweight gain, FCR and AMEn were not negatively affected.


The objective of this research was to determine the effect of dietary soy inclusion on broiler performance parameters and metabolisable energy.

Traditionally, soybean products have been vastly utilised in poultry and other monogastric diets within the United States. Nutritionally, soy is a good source of protein and when utilised with corn protein, it can provide a well-balanced amino-acid profile.

A concern with feeding soy to poultry is the indigestible and anti-nutritional components and their effects on performance and digestibility. Some of the anti-nutrients in soy include non-starch polysaccharides, phytates, raffinose, stachiose and β-mannans.

Materials and Methods

Male Ross 708 broiler chicks were fed a corn-soybean meal based starter diet (including five per cent toasted full-fat soy) for 10 days prior to feeding of experimental diets.

Birds were weighed into groups to help minimise differences between final cage weights once all birds were assigned to cages.

In total, 576 birds were selected and grouped into an experimental unit (EU) consisting of eight birds. Each of the three treatments was replicated 24 times in Petersime battery cages.

Experimental chamber temperature was maintained at 85°F, at the start of chick housing, and was decreased 5°F each week until reaching a final temperature of 70°F. Supplemental heat was offered at one end of the battery cages, allowing chicks to select a thermoneutral temperature. Light was provided continuously and birds were monitored twice daily with mortality recorded and removed as it occurred.

Three experimental diets were provided containing three different inclusion levels of full-fat soybean meal and toasted soy. Inclusions of soy products were 20, 28 and 35 per cent (Table 1).

Table 1. Dietary formulations for corn-soybean meal based starter diet
and three experimental treatments with varying inclusions of soy products
at 20, 28 and 35%
Corn 51.83 50.52 51.18 51.85
DDGS 10.00 9.95 12.48 15.00
Meat & bone meal 4.13 0.00 1.45 2.90
Rapseed solv. Extr. 2.39 0.00 2.73 5.47
Soybean meal 48 23.38 25.00 22.50 20.00
Soybeans full-fat 5.00 10.00 5.00 0.00
Soy oil 0.50 0.50 1.16 1.82
Salt 0.31 0.39 0.35 0.30
DL-methionine 0.29 0.22 0.21 0.20
Threonine 0.05 0.02 0.01 0.00
Bio-Lys 0.47 0.21 0.30 0.40
Limestone 0.92 1.11 0.97 0.84
Dicalcium phosphate 0.00 0.86 0.43 0.00
Choline chloride 60 0.10 0.10 0.10 0.10
Vitamin premix 0.63 0.63 0.63 0.63
TiO2 0.00 0.50 0.50 0.50
Crude protein % 23.45 22.75 22.25 21.75
Poultry ME kcal/kg 2960 2960 2960 2960
Calcium % 0.89 0.74 0.74 0.74
Phosphorus % 0.63 0.60 0.59 0.58
Avaiable P % 0.35 0.30 0.30 0.30
Fat % 5.07 5.49 5.64 5.78
Fibre % 3.38 3.31 3.49 3.68
Methionine % 0.66 0.58 0.57 0.56
Cystine % 0.38 0.38 0.38 0.37
Methionine + Cystine % 1.04 0.96 0.94 0.93
Lysine % 1.40 1.27 1.24 1.21

Both experimental diets and water were provided ad libitum throughout the experimental period (days 10 to 21). All birds were individually weighed at the start and completion of the experimental period and the difference was used to calculate bodyweight gain. Bodyweight gain was reported for the 10- 21 day period.

Feed intake was determined for each cage by calculating the difference between the amount of feed offered and the amount of feed refused and reported for the 10 to 21 day period.

Feed conversion ratio (FCR) was calculated from days 10 to 21 using the ratio of bodyweight gain and feed intake.

Clean excreta samples were collected from pans below each cage for AMEn determination after a two-day collection period. All samples were immediately transported to the laboratory and frozen at -20?C until analysis. Excreta and feed samples were oven dried. After drying, excreta samples were ground through a Whiley 1.0-mm screen and feed samples were ground through a 0.5-mm screen.

Titanium dioxide concentration was determined for feed and excreta samples. Gross energy (GE) for excreta and feed samples was determined using an adiabatic oxygen bomb calorimeter. Nitrogen content of excreta and feed samples was established using LECO Trumac N.

Dietary AMEn values for each diet were calculated as follows:

AMEn = dietary GE - [excreta GE × dietary Ti/excreta Ti - 8.22 × (dietary N -excreta N × dietary Ti/excreta Ti)]

Data were analysed using ANOVA and students T-test to separate means if significance was detected, with significance determined at (P≤0.05)

Results and Discussions

In the current experiment, dietary soy inclusion rate was varied from a high concentration of soy (35 per cent of the diet from soy products) to low (20 per cent of the diet from soy products) with an intermediate diet (28 per cent of the diet from soy products).

After feeding from 10 to 21 d, body weight gain and FCR were not different (Table 2).

Table 2. Statistical analysis of chick nitrogen-corrected apparent
metabolisable energy (AMEn), bodyweight gain (BWG), feed intake (FI),
feed efficiency (FE) and feed conversion ratio (FCR)
Soy inclusionAMEn
Feed intake
Feed efficiency
Low (20%) 3131 462 721 a 755 1.358
Middle (28%) 3119 477 709 ab 784 1.296
High (35%) 3155 462 684 b 785 1.294
Pooled SEM 17.8 7.5 10.3 21.9 0.038
P-value 0.35 0.24 0.05 0.54 0.40

However, feed intake was significantly reduced in birds fed the high-soy (35 per cent) treatment in comparison to middle- and low-soy diets.

These data may indicate birds fed high-soy diets reduced feed consumption with the high concentrations of soy.

This might partially be explained due to the high concentration of indigestible or anti-nutrients found in soy causing the birds to reduce feed consumption.

In this case, there were no negative effects on bird AMEn values generated from these diets, suggesting energy utilization is not affected or is accounted for with current formulation values.

In conclusion, high concentrations of soy did not affect growth or energy utilisation of growing broilers but did reduce feed intake suggesting soy might limit feed intake, possibly due to anti-nutrient or non-digestible components of soy.

Further Reading

You can view more studies from the Iowa State University Animal Industry Report 2014 by clicking here.

February 2014

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