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Animals : an Open Access Journal from MDPI logoLink to Animals : an Open Access Journal from MDPI
. 2022 May 27;12(11):1371. doi: 10.3390/ani12111371

Dynamics of Growth and Egg Traits in Three Dietary Balanced Protein Scenarios Applied for Laying Hens

Ingryd Palloma Teodósio da Nóbrega 1, Matheus de Paula Reis 1, Freddy Alexander Horna Morillo 1, Luis Filipe Villas-Bôas de Freitas 1, Letícia Cardoso Bittencourt 2, João Batista Kochenborger Fernandes 1, Nilva Kazue Sakomura 1,*
Editors: Vincenzo Tufarelli, Fulvia Bovera
PMCID: PMC9179259  PMID: 35681839

Abstract

Simple Summary

This study aimed to investigate the impact of three dietary balanced protein levels on laying hens, during the rearing and laying phases. The performance and body composition were monitored at 7, 11, 15, and 18 weeks old, while for the laying phase the responses were monitored every 28 days, from 19–102 weeks of age. The dietary protein applied in this study did not affect the responses evaluated in the rearing phase, but it clearly affected the long-term egg production. Overall, the egg production of hens consuming a high protein diet was superior compared to hens in the lower protein group and similar results were observed for body weight and body composition. The benefits of this study were to demonstrate the dynamic traits of laying hens in the long-term egg production cycle in three dietary balanced protein scenarios as similar data could not be found elsewhere.

Abstract

The objective of this study was to evaluate laying hens from 8 to 102 weeks old, regarding their changes in performance, body composition, and egg components produced in three scenarios of nutrition. Three treatments designed to contain different levels of balanced protein (BP) were randomly assigned to the experimental units, performing ten replicates per treatment with 20 birds each. A standard feed was formulated to meet hen requirements and the ideal ratio between essential amino acids. Then, two experimental feeds were formulated to contain 20% above or below the dietary BP used in the standard feed. The responses evaluated were cumulated feed intake (g), daily feed intake (g/day), body weight (g), body composition (g of protein, fat, and ash), hen-housed egg production (%/hen-housed), egg production (%), egg weight (g), egg mass (g), and egg components (percentages of yolk, albumen, and eggshell). The dietary BP influenced the body composition, egg production, egg weight, and egg mass of white laying hens. The increase in dietary BP was related to an increase in body contents and egg weight, whereas hens consuming the low dietary balanced protein presented a lower body weight, leaner, and produced smaller eggs.

Keywords: essential amino acid, body components, egg, poultry

1. Introduction

Currently, there is a concept to keep hens for extended periods in production, aiming to increase profitability and sustainability. Despite the benefits of doing so, controlling the excess body fat and eggshell quality in old laying hens is reported to be the main concern on poultry farms [1,2]. The body fat and egg components are influenced by the feed offered [3] and eggshell quality reduces as egg weight increases, which may be partially controlled with nutritional strategies [4,5]. In addition, the feed offered to hens during the rearing phase may affect the development of reproductive organs [6], influencing the long-term laying cycle.

The ability of laying hens to overcome a nutritional deficiency or an imbalanced diet is not completely elucidated. Some effort was made to investigate the effects of a previous feed on the laying cycle phase [7,8,9] but little or no knowledge is available in the literature describing how a modern hen may deal with a deficient diet during the growth and its impact in a long-term laying cycle. This information is convenient for poultry nutritionists because they often change the feed formula to improve the economic return and sustainability of egg production farms. In this sense, protein is frequently investigated in poultry nutrition given its importance for growth [10,11], egg production [12,13], economic return [14,15], and sustainability of the farm [16,17]. Because amino acids are the basic constituents of proteins and that essential amino acids should be offered in the feed in a proper ratio with lysine [18], it seems reasonable to investigate the effects of balanced protein in a long-term egg production cycle.

Understanding the dynamics of body and egg components represents a step towards an effective way to improve long-term egg production given feeds should be formulated based on physiological needs and the response of laying hens. In a conventional poultry house, the feed offered is the only source of energy and nutrients for a laying hen. Therefore, a change in voluntary feed intake is the only mechanism that a hen can use to consume a proper amount of all nutrients. If they fail to do so, body and egg components are expected to change [6,19] along with the egg production [20]. This highlights the importance to elucidate the dynamics of body and egg composition over different sets of nutrition scenarios.

The effects of dietary balanced protein for hens in the rearing phase and its cumulated influence in the long-term laying cycle have not been investigated so far. In the context aforementioned, we hypothesized that balanced protein levels affect the body and egg components leading to a shift in the long-term laying cycle; thus, the aim of the present research was to describe how laying hens respond to three levels of dietary balanced protein from 8 to 102 weeks old.

2. Materials and Methods

2.1. Ethics Approval

All procedures described were approved by the Ethical Committee on the Use of Animals of the School of Agrarian and Veterinary Sciences, São Paulo State University (UNESP), Jaboticabal, São Paulo, Brazil (Process 012598/2018; approved on 14 February 2019).

2.2. Bird Husbandry

A total of 600 Lohmann LITE LSL-NA were obtained from a breeding company (Planalto Postura LTDA. Uberlândia, MG. Brazil). The hatchlings were raised in conventional cages from 1 to 7 weeks before being moved to wire rearing cages (375 cm2 per pullet) from 8 to 18 weeks. At 19 weeks, hens were transferred to wire-laying cages (563 cm2 per hen). All cages were equipped with trough feeders and nipple drinkers. Hens received a corn-soybean meal-based diet to meet or exceed breeding company recommendations from 1 to 7 weeks old. A feed program with three feeds was offered from 8 to 18 weeks, for grower (8–11 weeks), developer (12–15 weeks), and pre-laying phases (16–18 weeks). At the laying phase, a feed program with five feeds was formulated according to the breeding company recommendations: layer one (19–26 w-old), layer two (27–46 w-old), layer three (47–66 w-old), layer four (67–82 w-old), and layer five (83–102 w-old). Birds had free access to feed and fresh water throughout the trial. The lighting program adopted was 24 L in the first week, reduced gradually to 12L:12D up to 10-w-old, which was maintained until the pullets achieved 5% of egg production (20-w-old). After the onset of egg production, the lighting program was gradually increased from 12–16 h of light by adding one hour per week and was then kept constant up to 102 weeks of age. In the period of 0–7, 8–18, and 19–102 w-old, the maximum temperatures recorded were 31, 26, and 27 °C, while the minimum were 24, 17, and 19 °C, respectively. The maximum relative humidity of the air was 77, 79, and 84% while the minimum records were 51, 57, and 50%, respectively for the same phases. One laying cycle was considered as 28 consecutive days.

2.3. Experimental Design and Feeds

Three treatments were randomly assigned to 30 experimental units of 20 pullets each, totalling ten replicates per treatment, performing a completed randomized design. Treatments consisted of three dietary levels of balanced protein (BP): 1—standard feed (S), formulated to meet or exceed breeding company recommendations; 2—reduction of 20% in dietary balanced protein (L), in reference to the S feed; 3—increase of 20% in dietary balanced protein (H), in reference to the S feed. Dietary balanced protein was defined as a constant ratio of essential amino acids with lysine [21] and the ratio was the same proposed by the breeding company [22]. Standardized ileal digestible lysine (SID-Lys) was the reference to produce the three levels of dietary balanced protein (Table 1).

Table 1.

Composition and nutritional content of experimental feeds in the rearing phase.

Composition (%) Grower (8–11 Weeks) Developer (12–15 Weeks) Pre-Layer (16–18 Weeks)
Standard Low High Standard Low High Standard Low High
Corn (8.8%) 62.2 68.0 56.3 58.2 63.0 53.4 55.5 61.0 49.9
Soybean meal (45%) 23.3 15.0 31.6 16.9 10.0 23.8 17.1 10.0 24.2
Wheat bran 10.1 13.0 7.10 17.5 20.0 15.0 17.0 20.0 14.0
Potassium carbonate 0.120 0.240 - 0.105 0.210 - 0.143 0.280 0.005
Corn gluten (60%) - - - 1.50 1.50 1.50 1.00 - 2.00
Meat and Bone Meal 48% - - - 2.66 2.66 2.66 3.42 2.97 3.87
Soybean oil 0.825 0.150 1.50 0.935 0.370 1.50 1.05 0.685 1.42
Dicalcium phosphate 1.18 1.17 1.20 0.150 0.140 0.161 0.105 0.210 -
Limestone 1.39 1.46 1.32 1.32 1.38 1.26 3.87 3.98 3.75
Salt 0.353 0.287 0.420 0.260 0.215 0.306 0.236 0.215 0.256
Sodium Bicarbonate 0.100 0.200 - 0.133 0.200 0.065 0.154 0.198 0.110
Vitamin and Mineral Premix 1 0.200 0.200 0.200 0.200 0.200 0.200 0.200 0.200 0.200
DL-Methionine (99%) 0.108 0.055 0.161 0.057 - 0.114 0.078 0.045 0.111
L-Lysine HCl (78%) 0.062 0.100 0.024 0.019 0.038 - 0.061 0.095 0.027
L-Threonine (98.5%) 0.015 - 0.031 - - - - - -
Choline chloride (60%) 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100
Total 100 100 100 100 100 100 100 100 100
---------- Calculated nutritional content (%) ----------
Met. energy (kcal/kg) 2 2881 2883 2880 2860 2860 2860 2778 2778 2778
Crude protein 3 17.1 14.3 20.0 17.1 14.7 19.5 17.0 13.9 20.2
Crude fibre 3 3.22 3.28 3.30 4.32 4.15 3.75 4.42 3.96 4.33
Starch 3 45.9 46.8 43.0 40.2 43.1 41.5 38.9 43.3 37.8
Digestible Lysine 0.803 0.645 0.960 0.700 0.560 0.840 0.742 0.593 0.890
Digestible Methionine + cysteine 0.592 0.476 0.709 0.544 0.434 0.653 0.552 0.442 0.662
Digestible Threonine 0.589 0.475 0.703 0.553 0.471 0.635 0.546 0.441 0.652
Digestible Tryptophan 0.187 0.148 0.226 0.171 0.139 0.203 0.169 0.133 0.206
Digestible Isoleucine 0.628 0.496 0.760 0.589 0.480 0.698 0.581 0.444 0.719
Digestible Valine 0.698 0.568 0.827 0.680 0.573 0.787 0.672 0.532 0.812
total Calcium 1.04 1.04 1.04 1.05 1.05 1.05 2.08 2.08 2.08
Available Phosphorus 0.460 0.460 0.460 0.430 0.430 0.430 0.457 0.457 0.457
Sodium 0.180 0.180 0.180 0.170 0.170 0.170 0.170 0.170 0.170
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1 Content/kg of feed: Vit. A 9700 IU, Vit. D3 2700 UI, Vit. E 17 UI, Vit. K3 2.79 mg, Vit. B1 2.00 mg, Vit. B2 5.50 mg, Pantothenic acid 10.6 mg, Vit. B6 3.05 mg, Vit. B12 15.0 mcg, Niacin 0.039 g, Folic acid 1.00 mg, Biotin 0.0083 mg, Choline chloride 0.150 g, Iron 0.044 g, Copper 9.00 mg, Manganese 0.050 g, Zinc 0.050 g, iodine 1.00 mg, selenium 0.250 mg, Phytase 600 FYT. 2 Nitrogen-corrected apparent metabolizable energy. 3 Values represent the mean analysed composition by near-infrared spectroscopy (NIR).

In the rearing phase, the S-BP group consumed a feed containing 0.80, 0.70, and 0.74 % of SID-Lys for the grower, developer, and pre-layer phase, respectively. The S-BP feeds in the laying phase contained 0.68, 0.66, 0.63, 0.61, and 0.58% of SID-Lys, respectively for each layer phase (Table 2). The remaining nutrients and energy in the feed were as recommended by the guideline [22].

Table 2.

Composition and nutritional content of experimental feeds in the laying phase.

Composition (%) Layer 1 (19–26 Weeks) Layer 2 (27–46 Weeks) Layer 3 (47–66 Weeks) Layer 4 (67–82 Weeks) Layer 5 (83–102 Weeks)
Standard Low High Standard Low High Standard Low High Standard Low High Standard Low High
Corn (8.8%) 59.0 65.0 53.0 61.1 67.0 55.3 61.9 67.5 56.2 63.3 68.5 58.0 63.4 68.7 58.1
Soybean meal (45%) 16.1 10.1 22.0 18.4 13.0 23.9 16.9 11.6 22.3 16.6 11.7 21.4 16.1 11.9 20.2
Wheat bran 3.75 6.00 1.49 2.35 4.70 - 2.50 5.00 - 2.50 5.00 - 2.50 5.00 -
Potassium carbonate 0.450 0.560 0.340 0.386 0.470 0.302 0.425 0.525 0.325 0.408 0.500 0.315 0.425 0.510 0.340
Corn gluten (60%) 7.50 5.00 10.0 5.43 2.55 8.30 5.76 2.95 8.56 5.01 1.95 8.07 4.54 1.10 7.98
Soybean oil 1.07 0.890 1.25 0.725 0.610 0.840 0.680 0.570 0.790 0.566 0.580 0.552 0.670 0.660 0.680
Dicalcium phosphate 1.31 1.30 1.32 1.16 1.14 1.17 1.11 1.09 1.14 1.11 1.09 1.14 1.01 0.98 1.04
Limestone 9.11 9.17 9.06 9.46 9.51 9.41 9.77 9.82 9.72 9.77 9.82 9.72 10.4 10.4 10.3
Salt 0.307 0.279 0.336 0.323 0.290 0.356 0.292 0.275 0.310 0.270 0.260 0.280 0.275 0.280 0.270
Sodium Bicarbonate 0.155 0.200 0.110 0.132 0.183 0.080 0.139 0.168 0.110 0.174 0.190 0.157 0.166 0.160 0.172
Vitamin and Mineral Premix 1 0.200 0.200 0.200 0.200 0.200 0.200 0.200 0.200 0.200 0.200 0.200 0.200 0.200 0.200 0.200
DL-Methionine (99%) 0.066 0.041 0.090 0.065 0.047 0.082 0.052 0.036 0.068 0.048 0.038 0.059 0.044 0.038 0.050
L-Lysine HCl (78%) 0.099 0.119 0.078 0.015 0.029 - 0.019 0.038 - 0.011 0.022 - - - -
Choline chloride (60%) 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100 0.100
Inert 2 0.822 1.023 0.621 0.075 0.150 - 0.165 0.159 0.171 0.026 0.052 - 0.248 - 0.495
Total 100 100 100 100 100 100 100 100 100 100 100 100 100 100 100
---------- Calculated nutritional content (%) ----------
AMEn (kcal/kg) 3 2795 2795 2795 2785 2785 2785 2785 2785 2785 2785 2785 2785 2770 2770 2770
Crude protein 4 18.1 15.6 21.4 17.0 14.6 20.6 16.1 13.3 20.2 16.0 11.7 18.7 14.8 11.4 18.7
Crude Fibre 4 3.68 3.97 3.92 3.66 3.67 3.91 3.65 3.81 3.9 3.57 3.18 3.69 3.46 3.49 3.50
Starch 4 40.0 41.3 39.3 39.7 41.3 37.3 41.3 42.4 37.4 40.9 43.4 39.0 43.0 43.2 40.7
Digestible Lysine 0.680 0.544 0.816 0.655 0.524 0.786 0.625 0.500 0.750 0.605 0.484 0.726 0.580 0.464 0.696
Digestible Methionine + Cystine 0.600 0.480 0.720 0.580 0.464 0.696 0.560 0.448 0.672 0.540 0.432 0.648 0.520 0.416 0.624
Digestible Threonine 0.571 0.459 0.683 0.570 0.459 0.681 0.555 0.446 0.664 0.540 0.433 0.647 0.524 0.420 0.627
Digestible Tryptophan 0.157 0.123 0.192 0.163 0.131 0.196 0.156 0.124 0.188 0.153 0.123 0.183 0.148 0.121 0.176
Digestible Isoleucine 0.633 0.486 0.781 0.630 0.484 0.776 0.612 0.468 0.755 0.590 0.450 0.731 0.570 0.434 0.707
Digestible Valine 0.716 0.563 0.869 0.706 0.553 0.859 0.689 0.539 0.839 0.666 0.518 0.813 0.644 0.499 0.789
total Calcium 3.95 3.95 3.95 4.05 4.05 4.05 4.15 4.15 4.15 4.15 4.15 4.15 4.35 4.35 4.35
Available Phosphorus 0.440 0.440 0.440 0.410 0.410 0.410 0.400 0.400 0.400 0.400 0.400 0.400 0.380 0.380 0.380
Sodium 0.175 0.175 0.175 0.175 0.175 0.175 0.165 0.165 0.165 0.165 0.165 0.165 0.165 0.165 0.165
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1 Content/kg of feed: Vit. A 9700 Ul, Vit. D3 2700 Ul, Vit. E 15.8 Ul, Vit. K3 2.39 mg, Vit. B1 2.40 mg, Vit. B2 6.00 mg, Pantothenic acid 8.65 mg, Vit. B6 3.04 mg, Vit. B12 15.4 mcg, Niacin 0.032 g, Folic acid 1.00 mg, Biotin 0.083 mg, Choline chloride 0.187 g, Iron 0.044 g, Copper 9.00 mg, Manganese 0.050 g, Zinc 0.050 g, iodine 1.00 mg, selenium 0.250 mg, Phytase 600 FYT. 2 Inert—Washed sand. 3 Nitrogen-corrected apparent metabolizable energy. 4 Values represent the mean analysed composition by near-infrared spectroscopy (NIR).

2.4. Performance Data and Egg Components Measurement

The number of eggs produced, and mortality were daily recorded. Every week, all eggs produced were weighed and the egg mass (rate of egg produced × egg weight) was calculated. The feed leftovers were weighed fortnightly and adjusted by mortality to calculate the food intake. The cumulative feed intake was expressed on g/bird for the rearing (eight to 18 w-old) and the rearing plus laying phases (8–102 w-old). Hen-housed egg production was calculated based on the number of eggs produced in the entire experiment period per number of housed hens at 19 w-old.

2.5. Body Composition

On the first day of the trial, eight birds per treatment were randomly selected and identified for body composition measurements by dual-energy X-ray absorptiometry (Hologic-QDR® model 13.4.2., Marlborough, MA, USA). Throughout the experiment, the same hen was scanned on the last day of every feeding phase. Prior to each scan, hens were fasted for five hours, weighed, anesthetized with isoflurane (2%) diluted in 100% of oxygen, and positioned in dorsal decubitus with the wings and legs flexed [23]. Measures collected were fat mass (g), lean mass (water + protein content, g), bone mineral content (g), and bone mineral density (g/cm²). Data collected were converted to contents of body protein, fat, and ash by applying the equations published by Alves et al. [23].

2.6. Egg Components

At the end of each laying cycle (28 days), a total of nine eggs per experimental unit were collected (three eggs per three sequential days). On each day, the eggs were broken apart individually to measure the albumen, yolk, and shell weights. Before measurement, the eggshell was washed with tap water and dried using a forced oven at 55 °C for 24 h. The percentages of albumen, yolk, and eggshell were then calculated.

2.7. Statistical Analysis

The collected data were examined for outliers, normality, and homoscedasticity. The data of cumulative feed intake and hen-housed egg production were analysed as One-Way ANOVA with a Tukey test to evaluate the differences between dietary balanced protein levels, using a generalized linear model. Two-factor repeated measure design was employed to determine the effects of dietary balanced protein over time, using a mixed model. One factor is represented by the three groups receiving the different series of dietary balanced protein feeds and the other factor is the age of hens. Each experimental unit was the repeated measures factor. Differences were considered to be significant at a probability of 5%. The Statistical Analysis System (SAS Institute Inc., Cary, NC, USA) was used to perform both a One-Way ANOVA and the Two-factor repeated measure analyses procedures. The data was analysed considering 21 cycles of four weeks each.

To test whether the responses differed between dietary balanced protein levels over time, non-linear regression with groups was used, the groups being the dietary balanced protein [24]. The average data per replicate were treated as the experimental unit. Two exponential models were applied and that with the lower Akaike information criterion [25] value was used to describe the response variable. The model used were:

Linear plus exponential: y=A+B×Rage+C×age (1)

where A and C are the y-intercept and slope of the linear segment, respectively, B is the y-intercept of the exponential segment, and R is the exponential base.

Exponential: y=A1+B1×R1age (2)

where A1 + B1 is the y-intercept, and R1 is the exponential base.

3. Results

The reduction and increase of dietary balanced protein in the laying feed did not affect the cumulative feed intake (p > 0.05, Table 3), being on average 4.44 kg (p = 0.986) and 67.7 kg of feed per bird (p = 0.485) in the growth and whole period, respectively. The reduction of dietary balanced protein affected the hen-housed egg production (p < 0.01), with similar results between hens from the S and H groups (p > 0.05).

Table 3.

Cumulative feed intake and hen-housed egg production (± standard deviation) of laying hens from 8 to 102 weeks old in response to age in three dietary balanced protein levels.

Treatments 1 Cumulative Feed Intake, kg/Bird Hen Housed Egg Production 2, und
8 to 18 Weeks 8 to 102 Weeks
S 4.44 ± 170 67.2 ± 1.82 516 ± 15 a
L 4.45 ± 131 67.4 ± 2.88 485 ± 24 b
H 4.43 ± 151 68.4 ± 1.72 529 ± 22 a
p-value 0.986 0.485 0.001
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1 S—standard, formulated to meet the nutritional recommendation of Lohmann-LSL guideline; L—20% reduction of balanced protein from S; and H—20% increase of balanced protein from S; 2 Distinct letter in the same column is significantly different by Tukey’s.

There was an interaction between dietary balanced protein and hens age for feed intake, egg production, and egg mass (p < 0.05, Table 4). For feed intake, differences between treatments were observed only at 26 weeks of age (p < 0.05). For egg production, differences were observed mainly at the beginning (first three laying cycles) and the end (after 74 w-old) of the laying cycle, whereas for egg mass the differences between groups of hens were consistent during the whole experimental period (Table 4).

Table 4.

Performance of laying hens from 8 to 102 weeks old in response to three dietary balanced protein feeds.

Age, Feed Intake, g/Bird/Day Egg Production, % Egg Mass, g
Weeks S 1 L 2 H 3 SEM 4 p-Value S L H SEM p-Value S L H SEM p-Value
11 56.0 55.8 53.5 1.16 0.3930 - - - - - - - - - -
15 56.4 56.9 56.8 1.39 0.9740 - - - - - - - - - -
18 61.6 61.8 63.4 1.61 0.7450 - - - - - - - - - -
22 79.2 75.9 80.2 1.26 0.1090 36.6 27.0 45.7 1.51 <0.0001 17.4 13.1 20.9 0.927 <0.0001
26 97.5 95.6 102 1.21 0.0060 94.3 91.9 96.8 1.41 0.0320 52.8 49.7 55.6 0.927 0.0010
30 104 102 103 0.94 0.7870 96.7 90.4 97.5 1.32 <0.0001 56.8 51.4 58.4 0.927 <0.0001
34 109 105 109 1.20 0.1570 97.3 92.6 97.4 1.32 0.0100 58.6 54.3 60 0.994 0.0010
38 109 110 110 1.25 0.7140 97.3 94.4 98.0 1.32 0.0990 60.6 56.7 61.9 0.927 0.0020
42 107 106 110 1.08 0.1850 97.7 94.6 98.0 1.32 0.1140 60.6 56.9 61.3 0.927 0.0060
46 108 109 108 0.78 0.6660 97.3 93.8 96.9 1.32 0.1130 60.4 56.1 61.4 0.927 0.0010
50 109 110 110 1.09 0.8910 96.5 91.9 95.8 1.41 0.0240 60.8 55.7 60.6 0.927 0.0010
54 109 110 111 0.86 0.4860 97.1 92.8 97.3 1.41 0.0220 61.6 57.2 61.6 0.927 0.0040
58 108 110 110 0.92 0.5500 95.8 91.7 94.9 1.51 0.0660 60.6 56.3 60.7 0.995 0.0040
62 111 113 113 1.07 0.6690 92.2 88.7 92.2 1.41 0.0790 59.5 56.1 60.1 0.994 0.0190
66 112 115 115 1.04 0.2590 95.8 95.1 94.9 1.32 0.8650 63.0 61.4 62.9 0.927 0.4860
70 113 115 115 0.900 0.4980 95.4 93.4 94.7 1.51 0.5670 61.9 58.7 62.0 0.995 0.0460
74 113 113 115 1.28 0.5940 95.1 92.1 94.8 1.51 0.2160 62.3 56.8 62.5 0.927 <0.0001
78 109 109 111 1.04 0.5720 93.3 89.5 95.4 1.51 0.0070 61.1 55.0 62.5 0.927 <0.0001
82 101 103 103 1.65 0.7180 91.8 86.4 90.9 1.41 0.0070 60.1 53.5 59.1 0.927 <0.0001
86 107 106 110 1.29 0.1760 86.4 82.5 89.3 1.51 0.0020 56.1 49.5 59.1 0.994 <0.0001
90 109 108 107 1.46 0.6820 87.4 79.6 92.6 1.61 <0.0001 57.4 49.4 61.3 0.994 <0.0001
94 107 109 107 1.73 0.6230 84.5 81.3 89.9 1.41 <0.0001 55.4 49.9 60.2 0.994 <0.0001
98 109 114 111 1.97 0.2150 83.2 82.7 87.7 1.61 0.0190 54.9 51.7 57.1 0.994 0.0020
102 109 111 110 1.90 0.7850 79.9 81.0 85.0 1.41 0.0160 52.7 50.7 56.1 0.995 0.0020
Main effects
Age <0.0001 <0.0001 <0.0001
Balanced Protein 0.7210 <0.0001 <0.0001
Interaction 0.0070 <0.0001 <0.0001
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1 S—standard, formulated to meet the nutritional recommendation of Lohmann-LSL guideline; 2 L is low, formulated with 20% reduction of balanced protein from S; 3 H is high, formulated with 20% increase of balanced protein from S; 4 Standard error of the mean.

The exponential equation was used to demonstrate the changes in feed intake and the line plus exponential equation had the best fit for egg production and egg mass (Table 5). The regression with groups identified that a single equation could be used to describe the feed intake between groups, whereas for egg production and egg mass the regression analysis indicates a necessity for different equations for laying hens inside each dietary balanced protein group (Figure 1).

Table 5.

Coefficients from an exponential equation for feed intake of laying hens from 8 to 102 weeks old and coefficients from a linear plus exponential equation for egg production and egg Mass of laying hens from 19 to 102 weeks old in response to age in three dietary balanced protein levels.

Parameters Feed Intake, g/Bird/Day Egg Production, % Egg Mass, g
S 1 L 2 H 3 S L H
A 111.4 108.0 102.0 104.0 65.30 61.40 63.10
B −163.1 −5,150,000 −51,900,000 −272,000,000 −63,700 −77,000 −489,000
C - −0.2280 −0.1940 −0.1510 −0.0870 −0.0980 −0.0380
R 0.9210 0.5990 0.5410 0.4960 0.7200 0.7140 0.6530
SEM 4 6.040 2.920 2.960
R2 5 88.80 95.00 91.00
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1 S—standard, formulated to meet the nutritional recommendation of Lohmann-LSL guideline; 2 L is low, formulated with 20% reduction of balanced protein from S; 3 H is high, formulated with 20% increase of balanced protein from S; 4 Standard error of the mean; 5 Coefficient of determination.

Figure 1.

Figure 1

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Observed and predicted feed intake ((a) ◊, – –) of laying hens from 8 to 102 weeks old and of egg production (b) and egg mass (c) of laying hens from 19 to 102 weeks old in response to age in three dietary balanced protein levels: standard (□, —), low (∆, - -), and high (○, ∙∙∙).

Differences in body weight influenced by dietary balanced protein were observed in 30 w-old hens (p < 0.05, Table 6), with heavier hens in the H group, followed by the S and L groups, respectively. Laying hens in the higher dietary balanced protein feed was fatter (p < 0.05) from 38 w-old and forward (Table 6).

Table 6.

Body weight and body lipid of laying hens from 8 to 102 weeks old in response to three dietary balanced protein feeds.

Age, Body Weight, g Lipid, g
Weeks S 1 L 2 H 3 SEM 4 p-Value S L H SEM p-Value
8 518 530 527 8.23 0.9820 38.4 41.1 41.8 1.66 0.8587
11 894 899 926 13.2 0.8608 80.3 81.6 87.7 2.25 0.9586
15 1010 1046 1038 26.1 0.8312 94.6 102 101 4.59 0.9544
18 1152 1148 1229 28.9 0.2692 116 119 139 5.63 0.5461
22 1370 1366 1471 38.5 0.1935 146 154 163 11.2 0.7326
26 1398 1384 1504 46.9 0.1139 176 186 215 19.8 0.3234
30 1422 1374 1533 49.8 0.0349 167 159 198 15.8 0.1676
34 1477 1412 1564 52.5 0.0514 181 174 217 16.5 0.0970
38 1479 1449 1616 46.9 0.0186 170 184 234 11.9 0.0151
42 1485 1466 1641 47.0 0.0092 184 182 232 15.4 0.0351
46 1514 1485 1657 45.2 0.0141 191 198 243 15.7 0.0402
50 1507 1480 1681 46.9 0.0026 205 195 268 14.5 0.0025
54 1523 1472 1689 52.2 0.0011 192 195 268 16.3 0.0014
58 1548 1470 1695 43.7 0.0014 208 180 238 16.1 0.0312
62 1484 1445 1679 52.7 0.0012 183 175 243 17.8 0.0119
66 1550 1479 1724 58.5 0.0004 197 182 263 17.8 0.0006
70 1460 1454 1703 49.2 0.0001 196 176 286 20.2 <0.0001
74 1467 1454 1743 47.3 <0.0001 186 182 280 17.6 <0.0001
78 1483 1441 1740 44.0 <0.0001 213 169 281 18.6 <0.0001
82 1462 1397 1696 41.5 <0.0001 180 162 256 15.3 <0.0001
86 1463 1373 1733 40.4 <0.0001 194 141 250 16.8 <0.0001
90 1452 1357 1714 32.2 <0.0001 184 163 233 19.2 0.0553
94 1477 1374 1672 48.2 <0.0001 172 137 212 14.2 0.0061
98 1501 1398 1675 44.6 0.0002 172 139 214 12.7 0.0079
102 1344 1341 1689 37.1 <0.0001 149 137 229 14.5 0.0051
Main effects
Age <0.0001 <0.0001
Balanced Protein 0.0032 0.0147
Interaction <0.0001 <0.0001
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1 S—standard, formulated to meet the nutritional recommendation of Lohmann-LSL guideline; 2 L is low, formulated with 20% reduction of balanced protein from S; 3 H is high, formulated with 20% increase of balanced protein from S; 4 Standard error of the mean.

Body contents of ash and protein increased along time for all groups (p < 0.05, Table 7). For body ash, differences were observed from 50 w-old and body protein from 30 w-old, and still relatively constant until the end of the trial.

Table 7.

Body protein and ash of laying hens from 8 to 102 weeks old in response to three dietary balanced protein feeds.

Age, Protein, g Ash, g
Weeks S 1 L 2 H 3 SEM 4 p-Value S L H SEM p-Value
8 73.0 73.2 74.0 1.52 0.9171 18.3 18.9 18.0 0.401 0.8248
11 132 131 140 1.93 0.6790 29.6 28.6 30.3 0.594 0.6182
15 153 154 159 3.87 0.8188 33.9 33.4 34.3 3.89 0.8631
18 178 173 189 5.08 0.4017 39.3 37.1 40.2 0.600 0.1094
22 218 214 227 7.77 0.5049 45.4 45.7 47.2 12.1 0.5528
26 214 206 223 6.50 0.2032 45.2 45.7 47.2 9.23 0.4427
30 220 212 237 7.07 0.0168 47.1 45.4 47.7 11.9 0.3555
34 226 215 235 6.38 0.0651 46.3 45.4 47.7 12.8 0.3993
38 231 223 245 6.61 0.0548 46.1 46.7 49.4 5.00 0.1220
42 234 226 252 6.34 0.0086 47.1 47.1 49.7 9.32 0.1954
46 241 223 250 6.29 0.0096 48.7 47.4 50.6 4.63 0.1569
50 224 224 254 6.72 0.0006 46.5 47.7 51.3 12.9 0.0130
54 227 220 248 6.01 0.0031 47.2 47.3 51.3 11.9 0.0137
58 243 227 262 5.57 0.0004 47.8 47.2 51.3 4.97 0.0331
62 236 232 259 7.02 0.0070 46.8 47.3 50.6 13.5 0.0499
66 242 229 259 7.74 0.0077 48.7 47.7 52.4 13.8 0.0139
70 235 225 242 7.14 0.2201 47.7 49.2 50.2 12.7 0.5501
74 229 220 256 6.67 0.0002 46.8 49.6 52.4 12.8 0.0321
78 223 223 253 6.17 0.0016 47.9 50.0 52.3 14.4 0.0478
82 226 221 253 6.23 0.0017 48.3 47.8 52.7 4.86 0.0121
86 233 213 261 5.68 <0.0001 50.7 48.9 53.6 10.9 0.0431
90 241 228 262 9.90 0.0870 48.1 51.9 54.5 15.4 0.0072
94 235 216 260 6.76 <0.0001 49.5 50.5 53.9 13.8 0.0697
98 230 222 260 5.21 0.0004 51.1 50.5 53.2 10.2 0.3497
102 219 213 266 7.01 <0.0001 48.3 48.7 54.7 5.81 0.0018
Main effects
Age <0.0001 <0.0001
Balanced Protein 0.0100 0.0704
Interaction <0.0001 0.0072
Open in a new tab

1 S—standard, formulated to meet the nutritional recommendation of Lohmann-LSL guideline; 2 L is low, formulated with 20% reduction of balanced protein from S; 3 H is high, formulated with 20% increase of balanced protein from S; 4 Standard error of the mean.

The linear plus exponential function had the best fit for body weight and body components, and it was used to investigate the differences between hens consuming the different feeds (Table 8). A common coefficient R-value can be used to describe the changes in growth (p < 0.05), despite the levels of dietary balanced protein, except for fat (p < 0.05). However, the coefficients A, B, and C are different between groups (p < 0.05) and specific values are necessary to properly describe the changes in body weight and body composition between hens consuming the different levels of dietary balanced protein (Figure 2).

Table 8.

Coefficients from linear plus exponential equation for body weight and body composition of laying hens from 8 to 102 weeks old in response to age in three dietary balanced protein levels.

Parameters Body Weight, g Ash, g Fat, g Protein, g
S 1 L 2 H 3 S L H S L H S L H
A 1638 1631 1712 46.35 46.35 47.60 345.9 280.0 816.0 240.8 234.0 247.0
B −2019 −1949 −2176 −68.20 −68.20 −71.57 −382.6 −338.8 −839.0 −347.6 −326.0 −353.7
C −1.754 −2.569 −0.0916 0.0330 0.0330 0.0641 −1.648 −1.367 −4.780 −0.0775 −0.1303 0.1343
R 0.9164 0.8839 0.9637 0.9468 0.9809 0.9028
SEM 4 78.30 2.670 36.70 15.50
R2 5 91.90 89.50 67.70 87.70
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1 S—standard, formulated to meet the nutritional recommendation of Lohmann-LSL guideline; 2 L is low, formulated with 20% reduction of balanced protein from S; 3 H is high, formulated with 20% increase of balanced protein from S; 4 Standard error of the mean; 5 Coefficient of determination.

Figure 2.

Figure 2

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Observed and predicted body weight (a) and body components (ash (b), fat (c), and protein (d)) of laying hens from 8 to 102 weeks old fed three balanced protein feeds: standard (□, —); low (∆, - -) and high (○, ∙∙∙).

Overall, egg weight of laying hens was affected by dietary balance protein content (p < 0.05, Table 9). At 26 w-old, hens consuming the H feed produced heavier eggs, followed by hens from the S and L groups, respectively. Notably, egg weight was similar between groups of hens from 30 to 42 w-old and from 54 to 66 w-old (p < 0.05). The yolk percentage increased in all feed treatments as the hens aged (p < 0.05).

Table 9.

Egg weight and egg components of laying hens from 19 to 102 weeks old in response to three dietary balanced protein feeds.

Age, Egg Weight, g Yolk, %
Weeks S 1 L 2 H 3 SEM 4 p-Value S L H SEM p-Value
22 51.2 51.3 51.9 0.590 0.7920 21.6 20.9 21.5 0.280 0.2160
26 57.9 55.5 59.4 0.590 0.0010 24.0 23.9 24.3 0.230 0.5230
30 59.3 58.5 60.4 0.590 0.1710 25.1 24.5 25.3 0.200 0.0320
34 61.1 59.7 61.7 0.590 0.1370 25.6 25.5 25.4 0.180 0.8880
38 61.9 60.6 62.2 0.590 0.2640 26.2 26.2 26.3 0.220 0.9790
42 62.4 61.4 63.6 0.590 0.1130 26.5 26.0 26.7 0.230 0.1380
46 62.2 60.2 63.4 0.590 0.0080 27.1 26.5 26.9 0.200 0.1570
50 63.4 60.3 63.7 0.590 0.0010 27.4 27.0 27.0 0.220 0.3500
54 63.8 62.6 64.7 0.590 0.1210 27.4 26.9 27.1 0.210 0.2960
58 63.1 62.1 64.2 0.590 0.1090 27.3 26.6 27.0 0.200 0.0950
62 65.6 64.4 65.3 0.590 0.4560 27.3 26.9 27.5 0.250 0.3580
66 66.6 64.9 66.2 0.590 0.2390 27.6 27.2 27.8 0.260 0.2260
70 65.9 63.0 66.5 0.590 0.0010 27.6 26.4 27.8 0.320 0.0050
74 66.4 62.4 66.1 0.590 <0.0001 27.3 27.2 27.8 0.210 0.2200
78 66.2 62.0 67.5 0.590 <0.0001 27.0 26.6 27.4 0.220 0.0830
82 65.7 61.9 65.5 0.630 0.0000 27.1 27.1 27.7 0.230 0.1250
86 65.5 61.6 66.1 0.590 <0.0001 27.5 27.1 27.7 0.250 0.2540
90 66.9 61.3 67.6 0.590 <0.0001 27.0 26.1 27.5 0.330 0.0200
94 66.9 61.4 65.6 0.630 <0.0001 26.7 26.2 27.1 0.260 0.0910
98 66.9 62.1 66.8 0.590 <0.0001 26.8 26.3 27.1 0.260 0.1400
102 65.8 63.9 66.2 0.590 0.0620 27.1 26.7 27.6 0.310 0.1360
Main effects
Age <0.0001 <0.0001
Balanced Protein 0.0010 0.0600
Interaction <0.0001 0.0590
Open in a new tab

1 S—standard, formulated to meet the nutritional recommendation of Lohmann-LSL guideline; 2 L is low, formulated with 20% reduction of balanced protein from S; 3 H is high, formulated with 20% increase of balanced protein from S; 4 Standard error of the mean.

Different from those observed for yolk, the albumen and eggshell percentages reduced with time (p < 0.05, Table 10). Nevertheless, egg components were similar between groups of hens (p > 0.05) with a tendency for yolk percentage (p < 0.06).

Table 10.

Egg components of laying hens from 19 to 102 weeks old in response to three dietary balanced protein feeds.

Age, Albumen, % Shell, %
Weeks S 1 L 2 H 3 SEM 4 p-Value S L H SEM p-Value
22 67.2 68.1 67.2 0.320 0.1280 11.2 11.0 11.3 0.100 0.2160
26 65.6 65.6 65.2 0.280 0.5660 10.5 10.5 10.5 0.100 0.9710
30 64.5 65.4 64.6 0.220 0.0250 10.4 10.1 10.1 0.100 0.0780
34 64.1 64.3 64.4 0.200 0.6040 10.3 10.2 10.2 0.100 0.3500
38 63.6 63.5 63.5 0.220 0.9890 10.2 10.3 10.2 0.100 0.6580
42 63.6 64.1 63.6 0.250 0.4150 9.91 9.92 9.67 0.100 0.0630
46 63.0 63.5 63.3 0.220 0.3620 9.94 10.1 9.87 0.100 0.1510
50 63.0 63.3 63.4 0.230 0.6030 9.59 9.73 9.58 0.100 0.3610
54 62.8 63.4 63.3 0.230 0.2690 9.74 9.71 9.64 0.100 0.6010
58 63.1 63.8 63.4 0.210 0.1160 9.63 9.65 9.65 0.100 0.9820
62 63.2 63.7 63.1 0.270 0.2490 9.54 9.36 9.46 0.100 0.5010
66 62.9 63.4 62.6 0.310 0.2880 9.46 9.49 9.54 0.100 0.8390
70 63.0 63.8 62.7 0.370 0.1240 9.41 9.45 9.49 0.100 0.8170
74 63.4 63.4 63.0 0.230 0.4200 9.28 9.43 9.26 0.100 0.4160
78 63.7 64.1 63.5 0.250 0.2890 9.32 9.28 9.08 0.100 0.2300
82 63.8 63.7 63.1 0.240 0.1560 9.13 9.21 9.15 0.100 0.8210
86 63.5 63.8 63.3 0.260 0.3130 9.06 9.10 9.09 0.100 0.9700
90 64.1 64.7 63.5 0.310 0.0400 8.99 9.2 9.06 0.100 0.3330
94 64.5 64.7 63.9 0.310 0.1980 8.81 9.15 9.05 0.100 0.0980
98 64.5 65.2 64.1 0.340 0.0790 8.72 8.81 8.85 0.100 0.7340
102 64.1 64.5 63.5 0.370 0.2020 8.79 8.76 8.79 0.110 0.9800
Main effects
Age <0.0001 <0.0001
Balanced Protein 0.1010 0.8480
Interaction 0.0970 0.1690
Open in a new tab

1 S—standard, formulated to meet the nutritional recommendation of Lohmann-LSL guideline; 2 L is low, formulated with 20% reduction of balanced protein from S; 3 H is high, formulated with 20% increase of balanced protein from S; 4 Standard error of the mean.

The exponential function had the best fit for egg weight and egg components (Table 11). The analysis indicates that all dietary balanced protein contents used in this study affected the egg weight (p < 0.05) and all equation coefficients need to be changed to estimate the egg weight of hens according to dietary balanced protein. The range in dietary balanced protein levels applied in this study was not sufficient to change the concentration in egg components (p < 0.05); therefore, a single exponential equation was used for each egg component. A tendency was observed for yolk percentage (p = 0.06), suggesting an influence of dietary balanced protein in this egg component. The equation used to describe the albumen percentage had a low R2 value, mainly because a drop in albumen percentage was observed around 68 w-old and followed by a consecutive increase (Figure 3), which was poorly predicted with the exponential equation used.

Table 11.

Coefficients for the exponential equation for egg weight and egg components of laying hens from 19 to 102 weeks old in response to age for three dietary balanced protein levels.

Parameters Egg Weight, g Yolk, % Albumen, % Shell, %
S 1 L 2 H 3 S L H S L H S L H
A1 66.60 62.50 66.40 27.10 63.6 8.23
B1 −45.60 −115.0 −56.20 −81.10 234.0 3.72
R 0.9450 0.8990 0.9340 0.8860 0.8300 0.9830
SEM 4 1.840 0.6540 0.7650 0.2030
R2 5 72.00 72.20 43.50 86.50
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1 S—standard, formulated to meet the nutritional recommendation of Lohmann-LSL guideline; 2 L is low, formulated with 20% reduction of balanced protein from S; 3 H is high, formulated with 20% increase of balanced protein from S; 4 Standard error of the mean; 5 Coefficient of determination.

Figure 3.

Figure 3

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Observed and predicted egg weight (a) of laying hens from 19 to 102 weeks old in response to age in three dietary balanced protein levels (standard (□, —); low (∆, - -), and high (○, ∙∙∙)), and egg components (b) yolk (□, —), albumen (∆, - -) and shell (○, ∙∙∙).

4. Discussion

The aim of the study was to describe how three scenarios of protein levels elicited variations in the growth of laying hens and how such changes might affect long-term egg production and egg components. To our knowledge, this is the first study to investigate the influence of dietary balanced protein in laying hens, from the rearing period (eight w-old) until the end of laying cycle (102 w-old). Currently, there is a growing concept to keep laying hens for longer periods in production [1]. However, maintaining the egg production and egg quality of a flock of older hens is a challenge. Pieces of evidence demonstrate that body weight of laying hens at the onset of lay may affect the entire egg production [26] and the egg weight [27,28]. Specifically, the body composition of laying hens at the beginning of the laying phase could also affect the peak and persistence of egg production [29]. The dietary protein content is known to affect the growth of broilers and breeder pullets [30,31], and considering the higher cost of dietary protein [32] and the trend in reducing the nitrogen excretion in poultry farms [17], it might be convenient to investigate the effects of dietary protein over the growing and laying phase. Assuming that essential amino acids are required in constant ratios with lysine, in this study the concept of balanced protein was used as proposed by Eits et al. [33].

We observed that dietary balanced protein levels used in this study, poorly affected the daily feed intake of laying hens. A general theory for feed intake regulation was developed over the years [34,35,36], suggesting that feed intake is regulated by the first limiting component in the feed, being energy or essential amino acids. Evidence demonstrates that feed intake of growing broiler chicken and pullet of broiler breeder is affected by dietary protein [30,31]. For laying birds, the feed intake regulation seems to be more complex because the consumed nutrients are also used for egg production. A model proposed by Fisher et al. [37] and recently reviewed by Sakomura et al. [38] accommodated this problem, splitting the amino acid requirement for maintenance and egg mass, which was called the Reading model. Those authors introduced a methodology to predict the requirements of essential amino acids (mg/hen/day), highlighting the importance to understand the mechanisms related to feed intake regulation. In the present study, the higher level of dietary balanced protein elicited an increase in egg mass. According to the cited model, egg mass will affect the requirement of essential amino acids, which may explain why feed intake did not reduce for laying hens in the H group. On the contrary, laying hens in the L group reduced the egg mass, therefore, a lower amino acid was needed for egg production, which may have impacted the feed intake. An interesting behaviour of feed intake was observed after 74 weeks. Laying hens from all groups reduced their intake of feed. For egg production, comparing the values in the peak and that observed at week 74th, egg production reduced by about 2.6, 2.5, and 3.2 units, respectively for hens consuming the standard, low, and high dietary balanced protein feeds, which may be related to a reduction in laying hens needs, consequently, the feed intake.

On the other hand, when the cumulated feed intake was calculated per unit of egg produced, it was evidenced that laying hens in the L group consumed 130 g of feed per unit of egg produced, whereas the S and H groups consumed 122 and 120 g of feed per egg produced. The feed intake per unit of body weight was 50.3, 49.7, and 44.2 kg of feed per kg of body weight for the L, S, and H groups, respectively. Those results suggest that hens attempted to regulate their feed intake to compensate for the reduction in dietary balanced protein when the feed is deficient and reduce the feed intake when the dietary balanced protein is in excess. Recently, Kumar et al. [39] described a quadratic response of feed intake in function of the dietary balanced protein. Different from the study reported herein, laying hens (Lohmann-LSL) received a standard feed in the rearing phase. The laying hen’s current status, regarding body weight and body composition, seems to be an important factor that modulates their response and needs more attention in future studies.

Even though the reduction in dietary balanced protein may reduce the feed cost and nitrogen excretion [16,40], the feed intake per hen-housed egg increased. In this study, the number of eggs produced per hen-housed reduced 31 units for hens in the L group compared with the S group. Therefore, feeding cost (feed price x feed intake), revenue, and viability of hens should be accounted for to properly calculate the economic return. Viability observed in the L group was 85%, whereas for the S and H groups were 90 and 93%, respectively. Laying hens consuming the L feed demonstrated an acute reduction in body fat after 54 w-old. The ovulation cycle was demonstrated to be dependent on plasma-free fatty acids and the body lipid seems to be the main blood source of fatty acids [41]. We hypothesized that the ovulation cycle was affected by a reduction in body fat content, which reduces egg production in the L group. Eventually, a severe reduction of body fat might drastically affect the ovulation cycle and may stop egg production, reducing the viability of hens in the L group.

Laying hens from the H group had a body weight close to the recommendations in the guideline (Lohmann Tierzucht GmbH, Cuxhaven, Germany), whereas the hens from the S and L groups were 200 g lighter. The variation in body weight was mostly due to body fat, since after sexual maturity there is a reduction in body protein deposition, and the change in body weight is given by variations in body fat deposition [2,42]. The observations on body fat and egg production suggest that the hens in the H group did not have an excess of body lipid, as the laying performance was not affected. On the contrary, the persistence of egg production indicates that body fat in the H group was favourable. Milisits et al. [29] observed that laying hens with high body fat content at the onset of lay reduced the egg production in about 11 to 13 eggs when compared with hens with lower body fat content. There is a discussion about the importance of energy reserves as body fat; however, there is a lack of information on the desired body fat content that benefits longer-term egg production.

Using the first derivative of the linear plus exponential equation, the results demonstrated an increase in body fat content until 48 (L), 58(S), and 63 (H) w-old, followed by a linear reduction until 102 w-old. As cited before, few differences were observed between groups, where laying hens from the H group seem to have a delay in body fat mobilization, regarding the age. After the cited ages, the laying hens mobilize body fat, possible to maintain egg production, especially after 82 w-old, when the dietary metabolizable energy was reduced, as recommended by the guideline. Nonis and Gous [43] demonstrated that broiler breeders produce energy from body lipid if they are allowed to do it so, even though the concentration of dietary energy is above requirement, by regulating their feed intake. Similarly, Caldas et al. [44] observed a reduction in broiler breeders fat at the end of egg production phase. In line with our findings, Kumar et al. [17] observed a linear increase in body fat for laying hens consuming a feed with a crescent level of digestible lysine (ranging from 560 to 858 mg/hen/day). However, the authors investigated the effect of balanced protein in Lohmann-LSL Lite NA only until 66 w-old.

The body ash content of laying hens suggested that laying hens did not use mineral reserves to produce an egg, as the body ash increased until the end of the laying cycle. The major portion of minerals used for egg formation is due to calcium carbonate necessary for eggshell formation given approximately 80% of eggshell is formed by this mineral [45]. Around 99% of total body calcium is found in the bone ash [46]. Evidence demonstrates that in a flock of older hens, there are individuals with a tendency to develop osteoporosis [47], and there are an increased number of eggs with thinner eggshells due to lower ability to uptake calcium and phosphorus from the intestinal lumen [48]. In this study, dietary balanced protein seems to have a low or no effect over the dynamics of body ash contents. Apparently, the advanced ages of laying hens used in this study was not sufficient to elicit a negative consequence in the bone structure; however, in all treatments, the eggshell percentage reduced with age, probably due to the increase in egg size with the age of laying hens [49].

The dynamic of egg components observed over time was similar to that reported by Bendezu et al. [5] for white laying hens from 18 to 60 w-old. As the laying hens aged, the yolk percentage increased, and the albumen and eggshell reduced, which was consistent with other reported literature [50,51]. The dietary balanced protein tended to influence yolk percentage. Compared with the L group, the hens consuming the H feed produced eggs with more percentage of yolk. The contribution of dietary protein to yolk formation is probably related to phosvitin as this is the major protein molecule found in egg yolk. Around 56% of the amino acid found in the phosvitin is serine phosphorylated [52,53]. According to Huang et al. [54], it is believed that the role of phosvitin in the egg is related to embryo development, which reinforces the importance of such a constituent in egg yolk. In the present study, the tendency of a lower percentage of yolk observed in eggs of the L group may be related to the lower amount of dietary serine, which is necessary to produce the phosvitin in the egg. With lower sources of dietary serine, essential amino acids might be used to overcome this deficiency.

Among the responses observed in this study, the body fat content between laying hens consuming the different levels of balanced protein was unexpected. Most reports in the literature demonstrate that growing birds would increase body lipid content when they are offered a low balanced protein feed [30,31]. The opposite result is reported when a growing bird consumes a high balanced protein feed. The regulation of body fat content in laying birds seems to be more complex and the prediction of body fat in laying hens should be done with caution. The increase in egg yolk percentage may contribute to a higher value of body fat content as 34% of egg yolk is constituted of lipid [55]. Hocking [56] investigated the effect of body weight and feed intake on the ovarium follicular dynamics and found that feed-restricted broiler breeders reduced the number of yellow follicles. We did not find a similar study for laying hens, which would contribute to a better understanding of the results observed, but we hypothesize that a pullet raised with high level of dietary balanced protein feed may increase the number and the weight of yellow follicles in the ovarium, resulting in more body fat content in laying hens.

5. Conclusions

As expected, the dietary balanced protein influenced the dynamics of performance, body content, egg production, and egg mass of laying hens in the laying phase. The performance of laying hens increased with higher levels of balanced protein but other responses such as the feeding cost also influence the economic return and need to be considered to making a nutritional decision. The hen-housed egg production reduced in laying hens consuming a feed with low levels of dietary balanced protein. In this study, body ash was not mobilized, indicating that the minerals consumed were sufficient for egg production and that the dietary balanced protein levels applied in this study did not influence this variable. On the contrary, a mobilization of body fat was observed, being more evident at the end of laying cycle. The dietary balanced protein levels investigated in this study slightly affected the yolk percentage but had no influence on albumen and eggshell percentages. More persistence of egg production was observed for laying hens consuming a high dietary balanced protein feed.

Acknowledgments

The authors would like to thank the CAPES—Brazil, grant number 88882.330322/2019-01. We are also grateful to the company Planalto Postura LTDA for the birds’ donation.

Author Contributions

Conceptualization, N.K.S., M.d.P.R. and J.B.K.F.; methodology, N.K.S., M.d.P.R., J.B.K.F. and I.P.T.d.N.; validation, N.K.S., J.B.K.F., M.d.P.R., I.P.T.d.N. and F.A.H.M.; formal analysis, M.d.P.R., I.P.T.d.N. and L.F.V.-B.d.F.; investigation, N.K.S., I.P.T.d.N., M.d.P.R. and F.A.H.M.; resources, N.K.S. and L.C.B.; data curation, I.P.T.d.N. and M.d.P.R.; writing—original draft preparation, M.d.P.R. and I.P.T.d.N.; writing—review and editing, M.d.P.R. and I.P.T.d.N.; supervision, N.K.S. and M.d.P.R.; project administration, N.K.S., L.C.B., I.P.T.d.N. and M.d.P.R.; funding acquisition, N.K.S. and L.C.B. All authors have read and agreed to the published version of the manuscript.

Institutional Review Board Statement

The study was approved by the Animal Care and Use Committee of Faculty of Agrarian and Veterinary Sciences of the São Paulo State University, Jaboticabal, São Paulo, Brazil (Process 012598/2018), prior to the beginning of the assays.

Informed Consent Statement

Not applicable, as this research did not involve humans.

Data Availability Statement

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.

Conflicts of Interest

The authors declare no conflict of interest.

Funding Statement

This research was funded by DSM Innovation & Applied Science—Brazil. This study was possible thanks to the scholarship granted from the Brazilian Federal Agency for Support and Evaluation of Graduate Education (CAPES), in the scope of the Program CAPES-PrInt (process number 88887.572699/2020-00).

Footnotes

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Associated Data

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Data Availability Statement

The data presented in this study are available on request from the corresponding author. The data are not publicly available due to privacy.

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