The Amino Acid Requirements of Laying Hens: Models for Calculation. I Physiological Background

Estimation of Nitrogen Maintenance Requirements and Potential for Nitrogen Deposition in Fast-Growing Chickens Depending on Age and Sex

Experiments were conducted to estimate daily N maintenance requirements (NMR) and the genetic potential for daily N deposition (ND(max)T) in fast-growing chickens depending on age and sex. In N-balance studies, 144 male and 144 female chickens (Cobb 500) were utilized in 4 consecutive age periods (I: 10 to 25 d; II: 30 to 45 d; III: 50 to 65 d; and IV: 70 to 85 d). The experimental diets contained high-protein soybean meal and crystalline amino acids as protein sources and 6 graded levels of protein supply (N1 = 6.6%; N2 = 13.0%; N3 = 19.6%; N4 = 25.1%; N5 = 31.8%; and N6 = 37.6% CP in DM). The connection between N intake and total N excretion was fitted for NMR determination by an exponential function. The average NMR value (252 mg of N/BW(kg)0.67 per d) was applied for further calculation of ND(max)T as the threshold value of the function between N intake and daily N balance. For estimating the threshold value, the principle of the Levenberg-Marquardt algorithm within the SPSS program (Version 11.5) was applied. As a theoretical maximum for ND(max)T, 3,592, 2,723, 1,702, and 1,386 mg of N/BW(kg)0.67 per d for male and 3,452, 2,604, 1,501, and 1,286 mg of N/BW(kg)0.67 per d for female fast-growing chickens (corresponding to age periods I to IV) were obtained. The determined model parameters were the precondition for modeling of the amino acid requirement based on an exponential N-utilization model and depended on performance and dietary amino acid efficiency. This procedure will be further developed and applied in the subsequent paper.

Studies on requirement and excess of isoleucine in laying hens

Three production trials and one nitrogen balance trial were conducted with Lohmann Brown hens to determine the requirement for and effects of an excess of isoleucine in layers at different ages (24 to 32 and 46 to 54 wk of age). The trials were designed as dose-response studies where isoleucine-deficient basal rations with 11.4 MJ metabolizable energy per kilogram were supplemented with varying amounts of L-isoleucine. In the production trials, dietary isoleucine concentrations ranged from 0.37 to 1.05%. In the three production trials, maximum daily egg mass was achieved at dietary isoleucine concentrations of between 0.39 and 0.75% (25 to 32 wk of age, daily egg mass 53 g), 0.40 and 0.57% (24 to 32 wk of age, daily egg mass 57 g), and 0.40 and 0.81% (46 to 54 wk of age, daily egg mass 56 g). The corresponding ranges of daily isoleucine intakes were 412 to 770 mg, 436 to 624 mg, and 431 to 874 mg. In the nitrogen balance trial, maximum total nitrogen retention was achieved at dietary isoleucine concentrations of between 0.43 and 0.57%. Dietary isoleucine concentrations higher than 0.8% caused a reduction in hen BW. Dietary isoleucine concentrations higher than 1.0% additionally caused a reduction in the daily egg mass. The study thus shows that the margin between requirement and excess of isoleucine is narrow in laying hens.

Lysine: Amino acid requirements of broiler breeders

Because feed intake is controlled in broiler breeders, amino acid supply is determined by the composition of the feed and the level of feed intake. Controlling amino acid supply during the laying cycle can be facilitated by the use of a model for calculating requirements. A possible model is outlined and the various components discussed. Typical calculations suggest that the model can provide a useful basis for practical feeding decisions. Model elements include: levels of animal performance; utilization of amino acids for egg production, maintenance, and tissue growth; population structure; and the variation of feed intake and the covariance between feed intake and requirements.

Optimum threonine requirement of laying hens

1. One experiment was conducted with medium weight laying hens to determine their threonine requirement between 28-38 weeks. 2. Two threonine-limiting diets of identical protein quality (summit-dilution) were used and, by dilution, ten protein contents were produced supplying 2.7 to 5.4 g total threonine/kg diet. The diet with the lowest protein was also supplemented with synthetic L-threonine. Each diet was fed to 5 groups of 24 laying hens. 3. The daily threonine requirement of the individual laying hens was estimated by direct methods to be 8.7 mg/g egg output plus 43.49 mg/kg body weight for this experiment. Calculated optimum intakes of threonine for various ratios of costs of input to value of output are tabulated. For example, for a flock of medium weight laying hens producing an average of 50 g daily egg mass, the optimum threonine intake (mg/hen d) varied between 700 and 710 for cost ratios (k-values) varying between 0.002 and 0.001.

Optimum isoleucine requirement of laying hens and the effect of age

1. Medium weight laying hens were used for an assay to determine their isoleucine requirement between 26 and 36 weeks of age and again between 46 and 56 weeks of age. 2. Two isoleucine-limiting mixtures were formulated with similar amino acid profiles, one containing 198 g and the other 110 g crude protein per kg diet. These mixtures were blended to give a series of 11 diets with isoleucine contents ranging from 7.6 to 3.8 g/kg. The lowest protein diet was also fed with a supplement of L-isoleucine. Each of the 12 diets was given to 5 groups of 24 laying hens. 3. The daily isoleucine requirement of individual laying hens was estimated to be 9.48 mg/g egg output plus 44.47 mg/kg body weight per day for the 1st period and 12.11 mg/g egg output plus 6.86 mg/kg body weight per day for the 2nd period. Calculated optimum intakes of isoleucine for various ratios of cost of input to value of output are tabulated. For example, for a flock of medium weight hens producing an average of 50 g daily egg mass, the optimum isoleucine intake (mg/hen d) varied between 760 and 890 varying for ratios of costs to egg prices. 4. It is concluded that the isoleucine required per day does not decrease during the first laying year despite a decrease in rate of egg output.

Performance of laying hens as affected by split time and split composition dietary regiments using ground and unground cereals

A factorial experiment was conducted to study the effects on the performance of White Leghorn X Australorp laying hens of diets based on unground cereal grains, small morning and large afternoon meals, and morning and afternoon meals of different composition. From 10 to 21 weeks of age the pullets' food intake was restricted, using either a diet in which the wheat fraction (600 g/kg) was unground or a fully ground diet of similar composition. In the laying period the birds received either a diet (U) in which the limestone was granulated and most of the cereal fraction (wheat and oats or wheat and sorghum) was unground or a fully ground diet (G) of similar composition. Both laying diets were offered ad libitum (A), with 25% issued in the morning and 75% in the late afternoon (T) or as a protein concentrate (250 g/kg of total diet) in the morning and cereal/limestone fraction (750 g/kg) in the late afternoon (C). Rearing and laying performance were unaffected by rearing diet. Laying diet U resulted in a 5.2% increase in food intake and a 0.9 g increase in average egg weight compared with diet G. From 21 to 56 weeks of age, when the cereal/limestone fraction of the diet included oats (240 g/kg of total diet), diet U resulted in fewer (4.8/bird) eggs and a lower financial margin than diet G. From 56 to 80 weeks of age, when oats were replaced by sorghum, this trend was reversed (-3.5 eggs). Birds on diet C produced fewer (16.9) eggs of lower (1.5 g) average weight than birds on diet A, ate less (1.39 kg) food and had a lower financial margin.(ABSTRACT TRUNCATED AT 250 WORDS)

Calculation and evaluation of energy: amino acid ratios for the egg-production type hen

Published equations for estimating the daily energy needs of laying hens were combined with published equations for estimating the daily amino acid needs to derive estimated energy:amino acid ratios for laying hens at different stages of production and environmental temperatures. Two feeding trials were conducted using various percentages of the suggested ratios to determine their applicability. The results of these studies indicate that the calculated energy:amino acid ratios appeared to support production levels comparable with those of hens fed higher nutrient levels. The use of temperature-adjusted energy:amino acid ratios appears to be a valid and feasible means of formulating diets to meet the changing nutritional needs of laying hens.