Reducing the crude protein content in layer diet


The ever-increasing concern over the cost of feed and impact of intensive poultry farming on the environment through excretion of nitrogen have forced nutritionists to redefine the optimal level of dietary crude protein (CP) and other nutrients in poultry diets. This article highlights the literatures regarding the effect of low crude protein on productive performances and egg quality parameters in layer. Further reduction in CP level is possible with the balanced amino acid nutrition emphasising on the non-essential amino acids i.e. glycine and branched chain amino acids and with the addition of suitable feed additives. In this regard to enable nutritionists for successful integration of synthetic amino acid with the low protein levels in poultry industry proper knowledge on the nutrient requirements, their interactions, its impact on environment and the feasibility to optimise the feed cost, further research in this area is the requirement.


Protein is a vital nutrient in poultry nutrition since it has a great economic importance as well as its significant role in various functions e.g. growth, egg production and immunity etc. The efficiency of dietary CP utilization depends on the amount, composition, and the digestibility of the amino acids in the diet. Hence determination of optimum level of amino acids in feed formulations is fundamental not only from an economics point of view but also to reduce the nitrogen loss in poultry alleviating environmental pollution. After the ideal protein concept, it is common to include synthetic amino acids in diets which allows nutritionists to further decrease CP level while meeting the requirement more precisely for maintenance, egg production and tissue accretion. This review is a compilation of data on the recent studies conducted on the effect of reduced CP diet in laying hen and its impact on productive performances and egg quality parameters. The aim of this document is to have an idea about current knowledge on the of low CP diets in layers and to highlight the use of synthetic amino acids in low CP balanced diets can be a tool to optimize feed costs, maintain performance of birds, and simultaneously reducing the excretion of nitrogen.

Reduction of dietary CP in laying hens feed

Impact on productive performance

While formulating a ration with reduced CP level for laying hens, the primary objective is to obtain similar performance in terms of egg production, egg mass, egg weight and feed conversion ratio (FCR) with the reduction of feed cost and nitrogen emission. Recent research studies (2010-2020) conducted in laying hen on reduced CP level on productive performance of laying hen is given in Table 1. Most of the studies concluded no significant difference in production performance though numerical reduction is observed in low CP fed group due to the fact that the AAs requirement is met precisely through balanced nutrient supplementation. Though few studies showed statistically significant reduction in production due to lower crude protein level, the variation observed in suggested amino acid requirements (Waldroup et al., 1995) may be due to differing experimental conditions, including composition of the basal diet, strain of bird, types of feed ingredients, dietary energy content, feed intake (FI) level, and age of layers. These factors are known to influence the energy, protein, and amino acid requirements of layers (Baker et al., 2002). A large part of the differences in nutrient requirements may be attributed to differences in environmental temperature, strain, and age of the birds. Most requirement studies with layers have been conducted during a particular phase of production cycle. Experiments conducted for a short duration or for part of the egg production (EP) cycle may not truly represent the entire production cycle (Rama Rao et al., 2011). Since the ability of laying hens to store protein is limited, the protein concentration in the feed should be equated to achieve the desired egg production (Pesti, 1992).

ReferenceAge (wk)StrainCP%AA%Egg prod %Egg mass (g. h/d)Egg wt (g)Feed intake (g)FCRE level (ME/Kg)Nitrogen Excretion g/d
Nassiri, MH et al., 201270-76Hy-line W3614.3Met+ Lys76.852.368.1126.552.952756 
Bouyeh & Gevorgian, 201152-56Hy-line W3613 68.75b 59.7799.27b2.542863 
   14 72.75a 60.37111.95a2.652860 
Rama Rao et al., 201121-72Babcock15Met 0.08+Lys HCl 0.3488.71 51.99102.12.372350 
   16.5Met 0.10+Lys HCl 0.2984.31 52.61103.62.352350 
   18Met 0.12+Lys HCl 0.2384.01 52.48103.32.352350 
Rama Rao et al., 201121-72Babcock15Met 0.08+Lys HCl 0.1986.68 52.45102.92.272600 
   16.5Met 0.10+Lys HCl 0.0985.94 52.58101.82.262600 
   18DL-Met 0.1284.98 52.61101.62.282600 
Latshaw and Zhao, 201129-57 13g/dSynthetic AAs meeting NRC (1994)88.452.159.198.7   
   15g/dSynthetic AAs meeting NRC (1994)89.652.458.592.2   
   17g/dSynthetic AAs meeting NRC (1994)91.152.858.093.6   
Mousavi et al., 201325-33Hy- line W36 & Lohman LSL15.5DL-Met- 0.14%92.3249.93c55.92b104.14a1.908a2900 
   16.5DL-Met- 0.16%+ L- Lys-0.07 + L- Thr-0.01393.2250.91bc56.76a100.91b1.853b2900 
   17.5DL-Met- 0.18%+ L- Lys-0.14 + L- Thr-0.0593.6351.70b56.73a102.20b1.835b2900 
   18.5DL-Met- 0.20%+ L- Lys-0.20 + L- Thr-0.0892.6453.08a57.07a101.90b1.836b2900 
Burley et al.,201318-51Lohmann LSL21.88 96.6856.8460.49 1.922864 
   20.35 96.6856.2860.43 1.912864 
   19.90 96.9456.1360.03 1.922864 
Torki et al., 201452-60Lohmann LSL16.5DL-Met-0.0479.1a50.6a64 2.032720 
   15DL- Met- 0.0778.7a50.1a64.3 2.012720 
   13.5DL- Met- 0.11+ L-Try-0.0179.0a50.3a63.7 1.962720 
   12DL- Met- 0.14 +Lys- HCl-0.06 +L-Try-0.0376.0ab47.1ab61.9 2.022720 
   10.5DL- Met- 0.17 +Lys- HCl- 0.16 +L-Thr- 0.05+L-Try-0.0470.0b43.1b61.5 2.102720 
Rojas et al.,201530-42Hy-line W3615.5 8651.059.3101.41.992894 
   13Trp+Ile+ Thr87.752.459.8101.613.22894 
Alagawany et al., 201620-42Lohmann Brown16Lys HCl+DL-Met72.5040.23b54.55b100.652.50a28001.57b
   18Lys HCl+DL-Met76.4545.10a58.65a102.852.28b28001.95a
Kumari et al .,201625-44WLH13.38Lys HCl 2.15+ DL- Met- 1.4589.48 53.37 2.27270039.09%
   15.58Lys HCl 2.30+ DL- Met- 1.2988.90 54.97 2.38270045.83%
   17.00Lys HCl 1.45+ DL- Met- 1.8092.19 53.92 2.34270048.03%
Azzam et al., 201628-40 16 94.55a60.21a63.67117.661.96abc2842 
   14Dig Thr-0.4389.58b5613b62.69113.862.03a2849 
   14Dig Thr-0.4994.39a59.65a63.19117.111.96abc2849 
   14Dig Thr-0.5795.66a60.54a63.28116.561.93bc2849 
   14Dig Thr-0.6696.07a61.39a63.90116.521.90c2849 
   14Dig Thr-0.7494.28a59.14a62.73118.972.01ab2849 
Alagawany et al.,202018-34Lohmann Brown16DL- Met+Lys- HCl73.30 55.02b 2.50a2800 
   18DL- Met+Lys- HCl76.48 58.15a 2.27b2800 
Table 1 Recent studies conducted on effect of reduced CP level on productive performance of laying hen

Impact on egg quality parameters

The present era consumers focus on the product quality in addition to production traits which is emphasized in the current studies conducted. Egg quality is comprised of those characteristics of an egg that affect its acceptability to the consumer. In table 2 some recent studies on the effect of reduced CP level is examined on the egg quality parameters like albumin, yolk quality, Haugh Unit (HU), and also shell quality i.e. shell thickness and shell strength. The HU is a measure of egg protein quality based on the height of its egg white. Specific gravity also indicates egg shell quality as well as its freshness. Egg shell quality is an important parameter as it prevents shell damage and ultimately affects its acceptance in the market. In the studies highlighted in table 2, the reduced level of CP did not affect significantly the egg and shell quality mostly because all the nutrient requirement for laying hens were taken in to consideration. Sulfur containing amino acids play a vital role in maintaining shell strength as they increase the calcium binding ability (Novak, 2006). As the incidence of shell quality problems and the proportion of broken eggs increase with age in laying hen, so in spite of preferences for large eggs by consumers, a very large increase in egg size in old hens might not be of benefit (Abdallah et al., 1995). As hens grow older, the nutrient requirements decrease with corresponding decreases in egg production. According to Mizumoto et al. (2008), nutrition as well as the breeding system has an influence on egg quality. Some studies have shown that calcium absorption decreases with ages in layers (Keshavarz & Nakajima, 1993). Absolute daily retention of Ca (Keshavarz, 2003) and shell weight (Roland et al., 1975) remain constant as hens age. The reason for reduced shell quality is increase in egg size, which distribute a constant amount of shell over a larger egg surface. Consequently, limiting egg size should also prevent loss of shell thickness (Keshavarz, 2003). Increase in egg size has resulted in reduction in eggshell thickness and eggshell weight (as a percentage of egg weight) (Roland, 1988). Thus, researchers have been interested in reducing egg size during the late stages of the egg production cycle by dietary manipulation of nutrients for increasing eggshell quality.

ReferencesAge (wk)StrainCPAAAlbumin %Yolk%Shell%HUShell Breaking strengthShell thickness mmSp. Gravity %
Latshaw and Zhao 201129-57 CP 13g/d 64.725.010.386.1   
   CP 15g/d 64.824.910.385.7   
    CP 17g/d 64.625.110.484.8   
Nassiri, MH et al., 201270-76Hy-line W3614.3Met+ Lys     0.3801.062
   12.87Met+Lys     0.3811.063
Mousavi et al 201325-33Hy- line W36 & Lohman LSL15.5DL-Met- 0.14%62.0927.8110.1079.393.790.319a1.080
   16.5DL-Met- 0.16%+ L- Lys-0.07 + L- Thr-0.01363.1327.179.6981.673.520.312a1.079
   17.5DL-Met- 0.18%+ L- Lys-0.14 + L- Thr-0.0563.0626.999.9580.683.670.312a1.080
   18.5DL-Met- 0.20%+ L- Lys-0.20 + L- Thr-0.0863.0227.319.6780.293.570.304b1.079
Burley et al.,201318-51Lohmann LSL21.88    93.574284.91g force at failure0.36 
   20.35%    94.154321.91g force at failure0.37 
   19.90    94.074370.26g force at failure0.37 
Torki et al. 201452-60150 Lohmann LSL16.5DL-Met-0.04 40.12** 80.41 0.3741.087
   15DL- Met- 0.07 42.07** 79.78 0.3701.088
   13.5DL- Met- 0.11+ L-Try-0.01 39.44** 82.09 0.3641.086
   12DL- Met- 0.14 +Lys- HCl-0.06 +L-Try-0.03 40.08** 76.76 0.3691.090
   10.5DL- Met- 0.17 +Lys- HCl- 0.16 +L-Thr- 0.05+L-Try-0.04 44.20** 76.35 0.3551.090
Azzam et al 201628-40 16    71.7543.24*0.36 
   14Dig Thr-0.43   73.1541.48*0.35 
   14Dig Thr-0.49   72.8939.03*0.37 
   14Dig Thr-0.57   75.8138.24*0.35 
   14Dig Thr-0.66   73.0741.18*0.36 
   14Dig Thr-0.74   75.7342.07*0.36 
Alagawany et al 202018-34Lohmann Brown16DL- Met+Lys- HCl62.4025.0212.5988.02 0.407 
   18DL- Met+Lys- HCl63.1623.9712.8286.07 0.383 
Table 2 Recent studies conducted on effect of reduced CP level on egg quality parameters in laying hen

*Shell strength in Newton units; **Yolk index in %age


            A better understanding of the CP and individual amino acids requirements in layers fed different concentrations of ME may increase the possibility of reducing the dietary CP with optimal levels of amino acids, which in turn will reduce the excretion of nitrogen from intensive poultry farming without affecting laying performance. The availability of individual feed grade synthetic amino acids (i.e. L-Tryptophan, L-Valine, L-Arginine, L-Isoleucine) in the market increase further scope of reduction in crude protein level.

References available on request