Reducing the crude protein content in layer diet

Abstract

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.

Background

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).

Reference	Age (wk)	Strain	CP%	AA%	Egg prod %	Egg mass (g. h/d)	Egg wt (g)	Feed intake (g)	FCR	E level (ME/Kg)	Nitrogen Excretion g/d
Nassiri, MH et al., 2012	70-76	Hy-line W36	14.3	Met+ Lys	76.8	52.3	68.1	126.55	2.95	2756
			12.87	Met+Lys	76.8	53.0	68.9	126.79	2.93	2756
Bouyeh & Gevorgian, 2011	52-56	Hy-line W36	13		68.75b		59.77	99.27b	2.54	2863
			14		72.75a		60.37	111.95a	2.65	2860
Rama Rao et al., 2011	21-72	Babcock	15	Met 0.08+Lys HCl 0.34	88.71		51.99	102.1	2.37	2350
			16.5	Met 0.10+Lys HCl 0.29	84.31		52.61	103.6	2.35	2350
			18	Met 0.12+Lys HCl 0.23	84.01		52.48	103.3	2.35	2350
Rama Rao et al., 2011	21-72	Babcock	15	Met 0.08+Lys HCl 0.19	86.68		52.45	102.9	2.27	2600
			16.5	Met 0.10+Lys HCl 0.09	85.94		52.58	101.8	2.26	2600
			18	DL-Met 0.12	84.98		52.61	101.6	2.28	2600
Latshaw and Zhao, 2011	29-57		13g/d	Synthetic AAs meeting NRC (1994)	88.4	52.1	59.1	98.7
			15g/d	Synthetic AAs meeting NRC (1994)	89.6	52.4	58.5	92.2
			17g/d	Synthetic AAs meeting NRC (1994)	91.1	52.8	58.0	93.6
Mousavi et al., 2013	25-33	Hy- line W36 & Lohman LSL	15.5	DL-Met- 0.14%	92.32	49.93c	55.92b	104.14a	1.908a	2900
			16.5	DL-Met- 0.16%+ L- Lys-0.07 + L- Thr-0.013	93.22	50.91bc	56.76a	100.91b	1.853b	2900
			17.5	DL-Met- 0.18%+ L- Lys-0.14 + L- Thr-0.05	93.63	51.70b	56.73a	102.20b	1.835b	2900
			18.5	DL-Met- 0.20%+ L- Lys-0.20 + L- Thr-0.08	92.64	53.08a	57.07a	101.90b	1.836b	2900
Burley et al.,2013	18-51	Lohmann LSL	21.88		96.68	56.84	60.49		1.92	2864
			20.35		96.68	56.28	60.43		1.91	2864
			19.90		96.94	56.13	60.03		1.92	2864
Torki et al., 2014	52-60	Lohmann LSL	16.5	DL-Met-0.04	79.1a	50.6a	64		2.03	2720
			15	DL- Met- 0.07	78.7a	50.1a	64.3		2.01	2720
			13.5	DL- Met- 0.11+ L-Try-0.01	79.0a	50.3a	63.7		1.96	2720
			12	DL- Met- 0.14 +Lys- HCl-0.06 +L-Try-0.03	76.0ab	47.1ab	61.9		2.02	2720
			10.5	DL- Met- 0.17 +Lys- HCl- 0.16 +L-Thr- 0.05+L-Try-0.04	70.0b	43.1b	61.5		2.10	2720
Rojas et al.,2015	30-42	Hy-line W36	15.5		86	51.0	59.3	101.4	1.99	2894
			13	Ile+Thr	79.6	46.7	58.7	102.5	2.20	2894
			13	Trp+Ile+ Thr	87.7	52.4	59.8	101.6	13.2	2894
Alagawany et al., 2016	20-42	Lohmann Brown	16	Lys HCl+DL-Met	72.50	40.23b	54.55b	100.65	2.50a	2800	1.57b
			18	Lys HCl+DL-Met	76.45	45.10a	58.65a	102.85	2.28b	2800	1.95a
Kumari et al .,2016	25-44	WLH	13.38	Lys HCl 2.15+ DL- Met- 1.45	89.48		53.37		2.27	2700	39.09%
			15.58	Lys HCl 2.30+ DL- Met- 1.29	88.90		54.97		2.38	2700	45.83%
			17.00	Lys HCl 1.45+ DL- Met- 1.80	92.19		53.92		2.34	2700	48.03%
Azzam et al., 2016	28-40		16		94.55a	60.21a	63.67	117.66	1.96abc	2842
			14	Dig Thr-0.43	89.58b	5613b	62.69	113.86	2.03a	2849
			14	Dig Thr-0.49	94.39a	59.65a	63.19	117.11	1.96abc	2849
			14	Dig Thr-0.57	95.66a	60.54a	63.28	116.56	1.93bc	2849
			14	Dig Thr-0.66	96.07a	61.39a	63.90	116.52	1.90c	2849
			14	Dig Thr-0.74	94.28a	59.14a	62.73	118.97	2.01ab	2849
Alagawany et al.,2020	18-34	Lohmann Brown	16	DL- Met+Lys- HCl	73.30		55.02b		2.50a	2800
			18	DL- Met+Lys- HCl	76.48		58.15a		2.27b	2800

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.

References	Age (wk)	Strain	CP	AA	Albumin %	Yolk%	Shell%	HU	Shell Breaking strength	Shell thickness mm	Sp. Gravity %
Latshaw and Zhao 2011	29-57		CP 13g/d		64.7	25.0	10.3	86.1
			CP 15g/d		64.8	24.9	10.3	85.7
			CP 17g/d		64.6	25.1	10.4	84.8
Nassiri, MH et al., 2012	70-76	Hy-line W36	14.3	Met+ Lys						0.380	1.062
			12.87	Met+Lys						0.381	1.063
Mousavi et al 2013	25-33	Hy- line W36 & Lohman LSL	15.5	DL-Met- 0.14%	62.09	27.81	10.10	79.39	3.79	0.319a	1.080
			16.5	DL-Met- 0.16%+ L- Lys-0.07 + L- Thr-0.013	63.13	27.17	9.69	81.67	3.52	0.312a	1.079
			17.5	DL-Met- 0.18%+ L- Lys-0.14 + L- Thr-0.05	63.06	26.99	9.95	80.68	3.67	0.312a	1.080
			18.5	DL-Met- 0.20%+ L- Lys-0.20 + L- Thr-0.08	63.02	27.31	9.67	80.29	3.57	0.304b	1.079
Burley et al.,2013	18-51	Lohmann LSL	21.88					93.57	4284.91g force at failure	0.36
			20.35%					94.15	4321.91g force at failure	0.37
			19.90					94.07	4370.26g force at failure	0.37
Torki et al. 2014	52-60	150 Lohmann LSL	16.5	DL-Met-0.04		40.12**		80.41		0.374	1.087
			15	DL- Met- 0.07		42.07**		79.78		0.370	1.088
			13.5	DL- Met- 0.11+ L-Try-0.01		39.44**		82.09		0.364	1.086
			12	DL- Met- 0.14 +Lys- HCl-0.06 +L-Try-0.03		40.08**		76.76		0.369	1.090
			10.5	DL- Met- 0.17 +Lys- HCl- 0.16 +L-Thr- 0.05+L-Try-0.04		44.20**		76.35		0.355	1.090
Azzam et al 2016	28-40		16					71.75	43.24*	0.36
			14	Dig Thr-0.43				73.15	41.48*	0.35
			14	Dig Thr-0.49				72.89	39.03*	0.37
			14	Dig Thr-0.57				75.81	38.24*	0.35
			14	Dig Thr-0.66				73.07	41.18*	0.36
			14	Dig Thr-0.74				75.73	42.07*	0.36
Alagawany et al 2020	18-34	Lohmann Brown	16	DL- Met+Lys- HCl	62.40	25.02	12.59	88.02		0.407
			18	DL- Met+Lys- HCl	63.16	23.97	12.82	86.07		0.383

^{*Shell strength in Newton units}; **Yolk index in %age

Conclusions

            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