Nutrient management is of major concern for today’s animal science industry. A laying hen typically utilizes only 40% of consumed dietary protein, which is both costly to the integrator and wasteful in terms of nitrogen utilization. In 2003, the EPA promulgated regulations for concentrated animal feeding operations (CAFOs). The revised regulations expanded the number of operations falling under CAFO regulations and addressed the land application of manure (EPA, 2003). Nitrogen emissions, currently not directly regulated, fall under the National Ambient Air Quality Standards (NAAQS). The NAAQS were issued by the EPA in 1997 in an effort to reduce particulate matter (PM) with a diameter of 2.5 microns or less (Gay and Knowlton, 2005).
Particle matter of 2.5 is of particular concern because it has been implicated in respiratory distress as well as increased environmental haze. Volatilized ammonia from animal operations fall into this PM size, and the EPA has estimated that animal agriculture is responsible for 50 to 85% of man-made ammonia emissions in the U.S (Battye et al., 1994). Individual states are expected to submit their emissions plans to the EPA by April of 2008. In anticipation of the new guidelines, United Egg Producers have released a new version of their animal husbandry guidelines which reduced recommended house ammonia levels from 50 to 25 ppm (United Egg Producers, 2006).
Pre and post-excretion strategies are two approaches the animal industry implement to reduce nitrogen waste (Powers, 2002). Pre-excretion strategies focus on diet manipulation through either feed additives or crude protein reduction. Feed additives such as gypsum and zeolite reduce manure pH, which allows nitrogen to be excreted in a less volatile form (Nakaue and Koelliker, 1981; Keshavarz, 1991; McCrory and Hobbs, 2001). A number of studies have successfully reduced nitrogen excretion by feeding low crude protein diets with or without amino acid supplementation, but with mixed production effects (Schutte et al., 1992; Summers, 1993; Jais et al., 1995; Elwinger and Svensson, 1996; Jamroz et al., 1996; Blair et al., 1999). Post-excretion involves the addition of an acidifier to reduce ammonia production (Burgess et al., 1998; Moore et al., 1999; Do et al., 2005). This report focuses on the pre-excretion strategy of lowering dietary crude protein.
Adjusting TSAA:Lys in low protein diets
Protein and TSAA:Lys were varied in a 3x3 treatment arrangement to determine the effects of low protein diets on layer production. Hens were fed diets with 18.9, 17.0 or 14.4 g of protein/hen per day combined with 0.97, 0.85 or 0.82 TSAA:Lys from 20 to 43 wks of age (Phase I).
During Phase II (43 to 63 wks), hens consumed 16.3, 14.6 or 13.8 g of protein/ hen/ day and either 0.92, 0.82 or 0.72 TSAA:Lys. Body weight gain (BWG; Table 1) was reduced when feeding the low protein diet regardless of ratio used as compared to feeding the high or medium protein diets which gained similarly. Egg production (EP) and feed intake was reduced from 83.7 and 82.2% and 98.8 to 95.6 g (21.8 to 21.1 lbs/ 100 hens), respectively. Feed conversion ratio (FCR) was similar across treatments. Egg mass (EM) was maintained when feeding hens the high and medium protein diets, while reduced feeding the low protein diets.
Dry albumen, albumen protein percent and albumen solids (Table 2) were all affected by treatment. As noted with other production parameters, hens consuming high and medium protein diets performed similarly, while providing low protein diets significantly reduced the aforementioned parameters. Overall, yolk parameters (wet and dry percentage, solids and percent protein) were not affected by dietary protein. In terms of eggshell quality, specific gravity was influenced by protein level. Feeding high and medium levels of protein produced eggs with similar specific gravity, while feeding low protein produced eggs with reduced specific gravity. The ratio of TSAA:Lys had little influence on production outside of dry shell percentage. Feeding hens the high TSAA:Lys ratio increased dry shell percentage as compared to the feeding the medium ratio diets with low falling between high and medium during both phases. There was little difference between feeding high and medium protein diets in regards to hen performance and egg measurements. Faecal nitrogen was linearly decreased as dietary protein was reduced. A 5.6% drop in faecal nitrogen (Table 3) was observed when reducing dietary protein from high (18.9 and 16.3 mg/ d, Phase I and II) to medium (17.0 and 14.6 mg/ d, Phase I and II), while a 14% reduction feeding the low protein diets. This finding, when applied to large scale production may reduce total house nitrogen.
Low protein diets supplemented with synthetic amino acids
Yakout and colleagues (unpublished) conducted two experiments designed to determine the effect of feeding varying levels of crude protein in combination with supplemental synthetic amino acids on performance from 24 to 67 weeks of age.
In order to mimic commercial production, Experiment I was divided into two phases: 24 to 36 wks of age and 38 to 50 wks of age.
Experiment II utilized the same set of hens, but was re-randomized due to the poor performance of hens on the lowest protein diet. The purpose of the following research was to reduce feed cost, while maintaining hen performance.
Experiment I
Three hundred and eighty four commercial Hy-Line W-36 White Leghorn hens at 24 wk of age were housed four per pen at a density of 54 in2/hen. Laying hens were assigned to one of four dietary treatments. Each of the four treatments was assigned to 24 replicate cages. Diets were fed in mash form and consisted of: a 19% CP diet with synthetic Met; a 17% diet with synthetic Met and Lys added to meet the requirements of the 19% CP diet; a 15% CP diet with synthetic Met, Lys and Thr added to meet the requirements of the 17CP diet; a 13% CP diet with synthetic Met, Lys, Thr and Trp added to meet the requirements of the 15% CP diet.
Similar treatments were developed with protein levels of 18, 16, 15 and 13% replacing phase I diets containing 19, 17, 15, 13% CP, respectively. All protein containing feedstuffs were analyzed for protein and dry matter to determine digestible amino acids using AminoDat 2.0 (Degussa International). Diets were formulated on a digestible amino acid basis using these calculated values.
Feed intake (FI) and egg production were calculated weekly from 24 to 50 wks of age. Body weights (BW) and uniformity were obtained by pen at 0, 4th, 8th and 12th week of each phase. Feed conversion ratio (FCR), egg mass (EM) and egg weight were calculated or obtained weekly and reported as an average for the twelve-week trial. Mortality was recorded daily with a description of any known cause determined by necropsy. Egg specific gravity (SG) and components (percent albumen, yolk and shell) were measured every other week.
Data reported in the following tables are average values for the entire experiment, while phase data is discussed to provide a sense of how hens responded to feeding programs during pre and post peak production. Feed intake (Table 4) during the trial decreased as dietary protein was reduced from recommended to 13% CP, despite supplementation of synthetic amino acids. Feed intake was similar when hens were provided diets containing 15% or more CP during each of the 12-week phases. Feed conversion ratio was similar across treatments and ranged from 1.963 to 1.701 g/g. Egg production was reduced by 5.55% when CP was reduced from 19 to 13%. Feeding intermediate levels, 17 and 15%, allowed for production comparable to feeding hens the 19% CP diet. Body weight and uniformity were similar at the beginning of the trial; however, at 50 weeks of age, hens fed the 13% CP diet lost 34 g/hen.
While minimal loss was noted during Phase II, hens fed the lowest protein diets lost on average 107 g/hen indicating that reducing dietary protein during early production is more detrimental on performance. It was also observed that hens fed as low as 15% CP had comparable gain as birds fed 17 or 19% CP diets. Hens fed the 13% CP diet were less uniform (87%) as compared to hens provided more protein (> 90.5% - data not shown).
Egg weight, EM and SG followed similar trends as FC and EP when reducing dietary protein (Table 5). Egg weight was decreased from 55.21 g (43.7 lbs/ case) to 52.20 g (41.4 lbs/ case) as dietary protein decreased from 19% to 13%, respectively during phase I. Similar reduction was noted during Phase II (49.34 to 45.97 lbs/ case) as dietary protein decreased from 18% to 13%, respectively. Egg mass was higher when hens consumed diets containing at least 15% CP compared to 13% CP. Specific gravity was also decreased when reducing dietary protein from 15% (1.0818) to 13% (1.0802) CP.
Wet albumen and albumen solids were decreased when reducing dietary protein from recommended to 13% (Table 6). Yolk solids were not affected by dietary treatments during the trial; however, wet yolk increased as dietary protein was reduced from recommend CP (19% - 25.32%; 18% - 28.52%) to 13% (26.08; 29.09%) during Phase I and II, respectively. Decreasing dietary protein from 19 to 13 % reduced dry albumen percentage by 11.09%, while increasing dry shell percentage by 3.16 %. During Phase II, dry albumen percentage was reduced by 11.35%, while there was not affect on dry shell. The increase in shell percentage is most likely due to decreased egg size since there were only numerical differences in SG. Reducing dietary protein to 13% reduced albumen solids (10.90%) when compared to feeding the commercially recommended diet (18% CP - 11.79%). The same result was observed when evaluating wet albumen; 59.94% compared 62.84% for 13 and 18% CP, respectively.
Feeding 19, 17 or 15 % CP diets with varying levels of supplemental Met, Lys and Thr allowed for similar production in regards to egg production, egg weight and conversion. Egg components were also similar during Phase I. Based on the information gathered in this trial, feeding the 15% CP diet with supplemental Met, Lys and Thr matched the EP and EM of the high protein diet and may be a viable feeding program for the 24 to 36 wk of age to save feed cost and possibly reduce ammonia emissions. Feeding the 13% CP diet with supplemental Met, Lys, Thr and Trp is not a feasible option for producers at this time. Feeding the lowest CP diet resulted in reduced production and performance and increased feed cost. As in phase I, the numerical increase in shell percentage is probably due to a decreased egg size since there were no differences in SG.
Feeding 18, 16 or 15% CP diets with varying levels of supplemental Met, Lys and Thr resulted in similar EP, EW and FCR. Egg components of these treatments were also similar during the 12-week trial. Feeding the 15% CP diet with supplemental Met, Lys and Thr matched the EP and EM of the high protein diet and may be a viable feeding program for the 38 to 50 wk of age period to save feed cost. Feeding the low protein diet (13%) with supplemental Met, Lys, Thr and Trp is not a feasible option for producers at this time. The 13% CP treatment resulted in reduced production, which is exacerbated with lower feed intake.
Experiment II
Three hundred eighty four Hy-Line W-36 commercial white leghorn hens at 55 weeks of age were housed 4 per pen at a density of 54 in2/hen. Hens were assigned to one of four dietary treatments according to body weight. Each of the 4 treatments was assigned to 24 replicate cages until 67 weeks of age. Dietary treatments were fed in mash form and consisted of: a 17.5% CP diet with synthetic Met; a 16.5% diet with synthetic Met and Lys added to meet the requirements of the 17.5% CP diet; a 15.5% CP diet with synthetic Met, Lys and Thr added to meet the requirements of the 17.5% CP diet; a 14.5% CP diet with synthetic Met, Lys, Thr and Trp added to meet the requirements of the 17.5% CP diet. Diets were analyzed and formulated based on digestible amino acid values as indicated above. Methods for evaluating production were carried out identically to Experiment I.
The present study was conducted to determine the effect of feeding varying levels of crude protein in combination with supplemental synthetic AA on protein retention and performance from 55 to 67 weeks of age. All data reported are averages for the production period, 55 to 67 weeks of age. Experimental diet analysis showed that values for crude protein were slightly lower as compared to calculated, while lysine content was slightly higher across all diets as compared to calculated. All other amino acids were similar to calculated values.
Feed intake during the trial was not affected as dietary protein was reduced from 17.5% to 14.5%. Feed efficiency was also not affected by dietary treatments during the 12 week trial with hens fed 17.5 or 14.5% performing similar but numerically improved as compared to hens fed the 16.5 and 15.5% CP diets, respectively. Hen day egg production during the trial was numerically reduced by 6.02% (12 week average) when dietary protein was reduced from 16.5 to 14.5%, while feeding the highest CP diets (17.5%) resulted in similar egg production as hens consuming the 15.5% CP diet (70.87 vs. 70.22 %). Hen body weight was similar across treatments (1550 to 1580 g/hen) at the beginning and end of the trial; however, hens consuming the 14.5% CP diet lost weight while hens on higher CP diets gained during the 12 weeks as a result of reduced feed consumption. Flock uniformity as measured by CV was also similar at the start and end of the trial, however feeding the 14.5 or 16.5% CP diets improved CV while feeding the 17.5% CP diets reduced CV during the trial. This was probably the result of body weight changes during the trial (data not shown).
Egg weight, EM and SG responded similar to feeding hens dietary treatments, as did FC and EP. Egg weight was numerically decreased from 63.74 to 62.99 g (50.54 to 49.54 lbs/ case) decreasing dietary protein from 17.5 to 14.5% CP. Egg mass was similar across all four dietary treatments with only a 0.72 g difference in EM between hens feed 17.5% CP and 14.5% CP. Lastly, specific gravity was numerically decreased reducing dietary protein from 17.5 to 14.5% (1.0784 vs. 1.0768).
Wet and dry albumen percentage and solids were significantly decreased when reducing dietary protein. Reducing dietary protein from 17.5 to 14.5% reduced dry albumen percent by 4.99%, while albumen solids were reduced by 3.98%. Dry yolk percent and solids were not affected by dietary treatments, however, wet yolk increased as dietary protein was reduced from 17.5% (49.96%) to 14.5% (50.17%). Neither wet nor dry shell percentage was affected by dietary treatments during the current trial.
In the current trial, feeding a diet containing 14.5% CP with supplemental Met, Lys, Thr, and Trp supported egg production, efficiency, and egg mass comparable to an industry standard diet (17.5% CP). Dry albumen percentage and solids were reduced when supplying hens the lowest CP diet. This result would be detrimental for producers marketing dry egg products. Feeding a diet with 15.5% CP supported all production parameters evaluated from 55 to 67 weeks of age. Further analysis of excreta nitrogen will quantify the nitrogen reduction achieved by reducing dietary protein.
Feeding the 15.5% CP diet may be a viable option to further reduce nitrogen excretion, while feeding the 16.5% diet was the most cost affective in terms of feed cost to produce a lb of egg mass. Feeding the low protein diet (14.5%) with supplemental Met, Lys, Thr and Trp is not a feasible option for producers at this time, as a result of it’s increased cost to feed and numeric reductions in egg production and mass and significant reduction in dry albumen percent and solids. Another AA may be to fault for this reduction in performance and needs further examination to make it an option for the industry. All data was generated in a research setting, which while similar to industry standards, may not always equate to similar responses in the field, but warrants the next step to determine its applicability in the field.
Experiment I and II - Overall conclusions
The above experiments demonstrate the feasibility of utilizing low protein diets in layer production. During early production, feeding very low protein diets (13% CP) negatively impacts hen and egg production, even when synthetic amino acids supplemented. A significant production loss would negate the benefit of reduced feed costs. In experiment I, CP included at the three highest levels offered appeared to have minimal production impact. However, the lowest levels of CP inclusion resulted in depressed production despite synthetic amino acid supplementation.
The influence of energy and low protein on performance and brain catecholamine levels
Providing low protein diets to laying hens is normally associated with a reduction in feed intake as noted in aforementioned projects. Previous research conducted at Virginia Tech showed that reducing energy in a low protein diet (12%) during late egg production increased feed intake. Increased feed intake subsequently resulted in increased egg production, egg weight and hen body weight. Birds typically eat to meet their energy requirements. In an effort to minimize the negative impact low protein diets have on feed intake, different levels of metabolizable energy were combined with varied levels of dietary protein (Parsons et al., 2007).
At 33 wks of age, seventy-two Bovans White Leghorn pullets were housed three per pen at a density of 72 in2/hen. Each pen was randomly assigned one of four dietary treatments which were each replicated six times. Dietary treatments were fed through 55 wks of age and consisted of combining recommended and low dietary protein with recommended and low ME: 13% CP + 2850 kcal/kg ME, 13% CP + 2780 kcal/kg ME, 18% CP + 2850 kcal/kg ME, 18% CP + 2780 kcal/kg ME. Mortality and cause of death were observed daily. Egg production, feed intake, feed efficiency and egg weight and mass were recorded or calculated weekly. Egg specific gravity and components were determined every other week. Specific gravity was measured on all eggs collected during a 24hr period. For egg components two eggs per pen were selected and from these, percent albumen, yolk and shell were determined. Body weights and flock uniformity were recorded on a monthly basis. In order to study the affects of low protein on appetite, brain catecholamine levels were measured at 36 wks of age. Brain tissue samples from twelve birds per treatment were collected and analyzed for norepinephrine (NE), epinephrine (EPI), dopamine (DOP), homovanillic acid (HVA), serotonin (SER), 5-hydroxyindol,3-acetic acid (HIAA), and 3,4-dihydroxyl-L-phenylalanine (DOPAC). Tissue samples were prepared according to the Jussofie (1983) method and analyzed blind by the Virginia-Maryland School of Veterinary Medicine using HPLC with electrochemical detection.
Hens fed a low protein diet lost body weight as compared to those fed the recommended level of protein which gained during the trial (Table 7). Body weight was not influenced by dietary energy level. However, combining low protein and energy improved weight gain as compared to combining low protein and recommended energy. Neither dietary protein nor energy impacted flock uniformity. Feeding low protein diets, resulted in a negative body weight gain and decreased feed consumption, egg production and egg weight. Decreased egg production and egg weight in layers fed low protein diets suggests that dietary energy and nutrients were shunted from egg production for use in meeting maintenance energy requirements. It would appear that reducing ME in a low protein diet improves egg production, but not egg weight as compared to feeding hens the recommended ME/low protein diet. Feeding low protein diets resulted in decreased NE concentration and increased SER and HIAA levels (Table 8). The change in catecholamine appears to be correlated with decreased feed intake.
Conclusions
The aforementioned trials were performed on layers ranging from 20 to 67 wks of age. Nutritionally, this is a vital production period as it encompasses pre-lay through peak production. Generally, lowering crude protein 2 to 3 percentage points below NRC requirements resulted in production loss (Table 9). This production loss occurred despite amino acid supplementation, suggesting that limiting amino acids may not have been added back in sufficient levels. However, diets which included CP just below the minimum recommendation (a reduction of approximately one percentage point) were able to maintain hen performance. In these instances, utilizing lower protein diets in combination with amino acid supplementation could maximize economic return. Nitrogen excreted and subsequent volatilization has become an increasing concern for today’s producers. Lowering dietary protein content has been shown to lower nitrogen excretion and subsequent emission.
References are available on request
From Proceedings of the “Midwest Poultry Federation Convention”, St. Paul, Minnesota, U.S.A.
Curtis NOVAK
Catalina TROCHE
Department of Animal and Poultry Sciences,
Virginia Tech, Blacksburg, VA
U.S.A.
