Protein and energy requirements of laying hens and broiler breeders.

Abstract

64 PROTEIN AND ENERGY REQUIREMENTS OF LAYING HENS AND BROILER BREEDERS Simon Bornstein Division of Poultry Science, Agricultural Research Organization Volcani Center, Bet-Dagon, Israel CALCULATING AMINO ACID REQUIREPTENTS Layer and Breeder rations are still evaluated, as a rule, on the basis of their protein content, expressed as 'percent protein'. This is the easiest and most practical criterion, but unfortunately it is a relative measure, depending on general feed consumption. The latter hardly relates to the productive traits of the hen, being dependent primarily on the energy content of the feed and on the environmental temperature, with body weight of the birds coming only in third place, and with performance having even less of an effect, Expressing the requirements of laying hens as grams protein per hen per day is a great improvement over '$ protein', but this measure does not take into account two groups of factors which should determine, even on a purely intuitive basis, the quantity of protein needed by the layer, namely: performance characters (rate of production and egg size) and the amino acid pattern of the dietary protein. The more the latter resembles that of the egg protein, the less feed protein is required. Since recommendations for dietary protein levels must t;ike into consideration its amino acid make-up, a number of research workers have studied the requirements of laying hens for various amino acids, Unfortunately several of them have reverted to the above mistake of expressing these requirements as $ of the diet, However, even in terms of mg/hen/day, and for all lo-12 essential amino acids, there remain decided variations among the recommendations of different authorities, due to differences in laying performance and body weight, besides the influence of variations in experimental techniques, Some poultry nutritionists (Fisher 1998; Scott- -* 1960; et al Combs 1961) came to the conclusion, therefore, that there could not exist a single set of requirements which would fit all conditions. As an alternative they proposed to express the biological requirements by mathematical partition equations. The latter were based on requirements for thre'e functions: body maintenance, body weight gain and egg However, the algebraic sum of these three types of requireproduction. ments always resulted in a decided underestimate of the requirements as determined empirically. This difference between actual and calculated requirements was attributed to the relative inefficiency of the hen in converting feed protein to egg protein (Scott 1961). iJloran and Chiah (1971) expressed, rather incidentally, a thought which has bothered us for a long time, without drawing the necessary conclusion, namely, that the egg albumen was secreted by the oviduct in such a short time, that this amount of protein could not possibly come directly from the digestive tract and/or the muscosal lining of the oviduct, Whereas the formation of egg yolk is a continuous process, egg white formation (including shell membranes) is a short spurt-like process of approximately 4 hours, during which almost 4 g protein are secreted, Considering a 85% absorption of nitrogenous 65 TABLE 1. Selected amino acid composition of various proteins and its requirement for body maintenance (Hurwitz and Bornstein 1973) compounds (Lepkovsky et al. 1965; Hurwitz et al. 1972) and relatively low feed consumption during albumen secretion (Mongin 1971), synthesis and secretion of almost 1 g protein per hour directly from dietary amino acids appears rather improbable. As a consequence of the above considerations, we assumed that part (or even most) of the amino acids needed for egg white and shell membrane formation was derived from the breakdown of tissue protein, which together with intestinal absorption supplies the free amino acid pool, represented by the plasma pool (Salter et al 1971). The m-0 importance of storage protein in egg formation has been pointed out by Harms et al, (1971). Compared to tissue protein, albumen contains six amino acids in slightly hi her concentrations, and about twice as much sulphur amino This difference in the respective composition of acids (Table 1 7 . storage site and target thus determines the efficiency of utilization of the former? two units of tissue protein being needed for the formation of one unit of albumen protein. Hence it appears, that the movement of amino acids in the body, rather than the overall processes of 'utilization' , may account for the inefficiency of the conversion of feed protein to egg protein. DEVELOPMENT OF MODELS In the original paper (Hurwitz and Bornstein 1973) two models were used, both based on partitioning the egg proteins according to the following proportional groupings: In both models the hen is considered to be in a 'steady state' with regird to body maintenance, body weight gain and yolk formrtion. The models differ with respect to the need for tissue breakdown in the synthesis of egg white proteins, the assumption being in both cases that the amino acid composition of the protein(s) broken down in this process is represented by that of the tissues of the chicken as detailed in Table 1. In Model A the assumption was made that all amino acids needed for albumen and shell membrane formation are derived fromt he breakdown of tissue protein, whereas Model B is based on the premise, as detailed in the original paper (Hurwitz and Bornstein 19'73), that the ovalbumins of the egg white are also continuously synthesised (and stored in the magnum), and only the synthesis of ovoglycoproteins and shell membrane proteins involves the inclusion of tissue-derived amino Due to their high cystine content, shell membrane proteins acids. contain an almost four-fold concentration of sulphur amino acids than does tissue protein (Table l),thus seriously affecting the efficiency of this conversion. The actual calculations are performed in two stages: (a) the determination of the amino acid requirements in terms of mg/hen/day, and (b) using the latter as part of a least-cost linear computer program, allowing 'protein' to run free, Table 2 presents a set of simplified formulae for 11 essential amino acids (or their combinations). These formulae require knowledge or estimates of anticipated egg mass ($ production x g egg weight), body weight and body weight gain, as well as daily feed consumption per hen for computer programming. The rations obtained on the basis of these two models were reasonable and practical, and moreover resulted in a marked saving in protein under Israeli feed ingredient conditions, PRACTICAL APPLICATION OF THE MODELS So far seven experiments have been conducted with egg-type layers: Leghorn and crossbreds, in cages and on litter, during peak of lay and (once) toward the end of the laying year. Comparisons between Models A and B shobred, that Model A overestimated the requirements while Model B-based diets produced an egg mass restricted to the target, thus being a good approximation of the true amino acid requirements, at least with regard to the most limiting ones0 As an example of the type of trials performed, the results of the first experiment of this series are summarized in Tables 3 and 4. Rate of production was significantly lower in birds receiving the Model B diet than in those fed the Model A diet or in the control birds, In terms of egg mass, egg production of Model A hens exceeded the target The feed function, whereas Model B birds produced exactly as planned. intake of the latter was slightly higher than anticipated, but their The experimental diets body weight slightly exceeded tht predicted. were purposely formulated for performance lower than the genetic 67 capacity of the birds, in order to better test the models, and the decisive point is the resemblance between target and actual performance data, The models were also tested in four broiler breeder experiments, with equal success. Table 5 briefly summarises one such The hens were fed ad lib., in order to prevent the introduction trial. of confounding factors. During a lo-week period of peak production (74s of 66 g eggs, i.e, an egg mass of 49 g/day) the Model B birds consumed per day only 21.9 g protein containing merely 870 mg lysine but 890 mg sulphur amino acids. to hen of the The very fact that one set of equations is flexible enough fit such different conditions as represented by the light Leghorn and the heavy broiler-type White Rock hen, and their varied types production performance, seems to indicate that the principles behind calculations are sound. ENERGY REQUIREMENTS Once amino acid requirements can be calculated in terms of daily intake, feed restriction of laying hens (egg layers or broiler breeders) can finally be put 'on a sensible basis. Feed restriction 68 which limits the consumption of aJ& nutrients for the laying bird, cannot possibly be the aspired goal. The latter should be the feeding to requirement of all nutrients , plus certain margins of safety, rather than the quantitative restriction of a diet containing certain excesses to begin with, Since under - lib, conditions all layers, and ad especially broiler breeders, tend to consume more energy.than required, feed restriction is a means to obtain enera restriction,as long as it can be safeguarded that the former does not cause a suboptimal intake of any other essential nutrients, In other words, the more severe the feed restriction, the higher the required concentration of all nutrients 69 (with emphasis on the amino acids) except for energy. Minimum energy requirements can be determined experimentally or calculated on the basis of partition equations. The literature on the latter CLpproach has been adequately reviewed in recent publications (Leeson et al 1973 ; Gleaves et al. 1973; Ivy and Gleaves 1973). Good - -0 examples of the empirical approach with egg layers and broiler breeders are the papers of Auckland and Fulton (1973) and Chaney and Fuller (1975L respectively, TVJO experiments have been performed with broiler breeders, during 1%week periods of peak performance, in windowed litter pens during Israeli winter conditions of two consecutive years. The temperatures ranged from an average minimum of about 10�C at night to an Fach trial consisted average maximum of around 2Ooc during daytime. of 3 or 4 graded degrees of feed restriction, and one lot of hens fed ad lib., (4 pens of 42 White Rock layers each per treatment), all birds having a uniform daily intake of amino acids. On the basis of both of these experiments it is suggested, that White Rock hens weighing approximately 3.5 kg and laying 65-g eggs at rates of 75% and 73$, can be restricted to 4.52 and 448 kcal (ME)/hen/day, respectively, with only a slight decrease in egg size (1.0 and 2.0 g, respectively), The latter is an advantage rather than a disadvantage with broiler breeders after more than 3 months production (when many eggs tend to become too large for efficient use as hatching eggs). These restrictions constituted approximately 86% and 79$, respectively, of the daily energy intake of control hens fed ad lib. 7n TABLE 5. The performance of Whit: Rock broiler breeders during a 15week period Chaney and Fuller (1975) reported that a 20% reduction in energy intake decreased rate of production and egg size significantly during the cold winter months, but had no effect on performance during Combs (1968) suggested the following equation to the summer months. calculate daily energy needs of egg layers, expressed as ME kcal/hen: where T is temperature (in degrees F), W = body weight (in g), G = daily body weight change (in g), and EM = egg mass (in g/hen/day). When this formula is applied to the above data (for an ambient temperature of 60�F),. the calculated requirement amounts to about 465 kcal/hen/day. The empirical and calculated results are thus in good agreement, and appear to indicate that careful energy restriction in broiler breeders may be a convenient means to reduce excessive egg size. SUMMARY The evolvement of a method for calculating the amino acid requirements of egg layers and broiler breeders (in terms of mg/hen/day) has been described, and a set of simplified formulae for 11 essential 71 amino acids has been presented. The latter appear to be a good approximation of the true requirements, if to judge by seven trials with egg layers in which Model B-based diets produced an egg mass closely resembling the planned The above models were also tested in four broiler target performance. breeder experiments with equal success0 Knowledge of the amino acid requirements of laying hens, on a mg/hen/day basis, should enable the use of energy restriction (by means of feed restriction) without causin g a suboptimal amino acid intake. Broiler breeder hens averaging 3.5 kg body weight, and housed in pens with a natural temperature cycle ranging, on the average, from 1OoC to 20�C, were able to produce at a lo-week average rate of 74$, eggs weighing 65 g, when restricted to 450 kcal/lnen/day of metabolisable energy, The latter represent about 83$ of the daily energy intake of hens fed ad lib, On the basis of these data it appears possible to 'tailor' diets to a.11 given circumstances, REFERENCES Auckland, J.N., and Fulton, R.B. (1973). Effects of` restricting the energy intake of laying hens. &. Poult, Sci. & 5.79-588. Chaney, L.W., and Fuller, H.L.(1975). The relationof obesity to egg production in broiler breeders. Poult. Sci. 2: 200-208. A method for calculating thexethionine requirements Combs, G,F.(1960). of the laying hen, Feedstuffs, 32 (19): 18-24, Combs, G.F.(1961). Amino acid needsof laying hens. Feedstuffs, 2 (21): 62-630 Combs, G.F.(1968). Amino acid requirements of broiler and laying hens. 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