L‐aspartic acid and urea supplementation of low‐protein layer diets1

1. Urea supplementation of low‐protein (125 g/kg) conventional‐type diets for layers, whether containing fish meal or not, did not appear advantageous.

2. Supplementation of the low‐protein diet with aspartic acid did not affect egg production rate or efficiency.

3. Soyabean meal supplementation of the low‐protein diet increased egg weight significantly whereas aspartic acid did not.     

Urea and aspartic acid supplementation of low‐protein broiler diets1

1. L‐Aspartic acid does not seem useful as a protein surrogate in conventionally formulated low‐protein diets for broiler chicks.

2. Urea as a protein substitute does not enhance the value of conventional broiler diets.

3. Urea does not improve broiler diets that have been supplemented with fish meal or crystalline amino acids to satisfy requirements for all indispensable amino acids.

4. Urea is absorbed into the bloodstream, but is not assimilated into body proteins.     

Differential effect of age on metabolisable energy content of high protein‐low energy and low protein‐high energy diets in young broiler chicks1

1. An experiment was carried out with 6‐d old male broiler chicks in an attempt to understand better the effect of age on dietary AME_n of high protein‐low energy (HPLE) and low protein‐high energy (LPHE) diets which are used in the determination of the AME_n content of grains when substituted for the entire diet. The experiment was carried out in a split‐plot design in which the effects of 2 diets (HPLE‐reference and LPHE‐test, containing maize) on food intake, faecal excretion, dietary AME_n and the utilisation of the nutrients were evaluated in 3 age periods (A = 11–13, B = 15–17 and C = 20–22 d of age).

2. Chicks fed on the HPLE diet consumed significantly less food than those fed on the LPHE diet during periods A and B, but not in G. They also produced a significantly larger amount of droppings during periods B and C. Food‐to‐droppings ratio, which was consistently and significantly lower in chicks fed on the HPLE diet, decreased markedly in period C only in these birds.

3. Absolute and relative retention (RR) of dry matter (DM) and starch, and RR of nitrogen (N) from birds fed on the HPLE diet, were consistently and significandy lower than from those fed on the LPHE diet, but fat retention (absolute and relative) was higher. RR of DM and of N in period C was significantly lower than in periods A and B, while RR of fat and of starch was not affected by age. The effect of age on RR of N was observed only with the HPLE diet.

4. AME_n of the HPLE diet, but not of the LPHE diet, in period C was significandy lower than in periods A and B, resulting in a significant interaction between age and diet and a general reduction with age. The calculated AME_n contents of the maize in periods A and B were essentially the same (14.91 and 14.85 MJ/kg, respectively), and lower than in period C (15.28 MJ/kg). It is concluded, therefore, that because of its effect on AME_n of the HPLE reference diet in chicks older than 17 d, bird age is of considerable importance in the determination of AME_n in grains when substituted for the entire diet.     

Evaluation of methanol‐grown bacteria as a source of protein and energy for young chicks

1. The inclusion of 100 or 200 g/kg spray‐dried methanol‐grown bacteria in unpelleted semi‐purified diets reduced growth rate and efficiency of food conversion of young chicks over a 14 d period.

2. Classical metabolisable energy values for the spray‐dried product, at relatively low inclusion rates, ranged from 9.55 to 10.92 MJ/kg dry‐matter (DM) and nitrogen‐corrected values ranged from 8.95 to 10.16 MJ/kg DM.

3. Inclusion of 96 g/kg flash‐dried methanol‐grown bacteria in unpelleted semi‐purified diets marginally increased growth rates, efficiency of food conversion and nitrogen utilisation of chicks, but higher inclusions of up to 290 g/kg caused adverse effects.     

The diagnostic value of plasma proteins and non‐protein nitrogen substances in birds

Summary

This paper summarises current knowledge of the diagnostic value of avian plasma proteins and non‐protein nitrogen substances.

Reference values for total protein, the albumin: globulin ratio, uric acid, creatinine, and urea for various avian species are presented. The importance of the albumin:globulin ratio and the urea:uric acid ratio is emphasised.     

Evaluation of methanol‐grown bacteria and hydrocarbon‐grown yeast as sources of protein for poultry: Studies with young chicks

1. In a series of five trials, conducted with broiler chicks during the starting period, two types of dietary single‐cell protein were tested: Pruteen (PR), a protein concentrate produced from methanol‐utilising bacteria, and a Lavera‐type yeast (LA) utilising the normal paraffins of heavy gas oil.

2. The inclusion of 90 to 150 g PR or LA/kg diet depressed growth rate by 14 to 16% and 9 to 10%, respectively. This effect was slightly counteracted (about 6 percentage units) by the addition of L‐arginine.

3. The growth depression can be explained completely in the case of PR or almost completely in that of LA on the basis of reduced food intake, without a decided effect on food utilisation.

4. The reduced consumption of PR‐containing diets is not due to a petroleum‐ether‐soluble factor, nor to the high and low concentrations of sodium and potassium, respectively, in PR.     

Responses of laying hens to a low‐protein diet supplemented with essential amino acids,l‐glutamic acid and/or intact protein

1. Three sequential experiments, each lasting 8 weeks, were carried out on 576 singly‐caged light hybrids.

2. In experiment 1 egg production was 84% using a conventional control diet, 61% with a basal low‐protein diet, and 79% with the basal diet supplemented with 10 essential amino acids + L‐glutamic acid (GA).

3. In experiment 2 supplementation with lysine and methionine (L + M) alone increased egg production significantly from 54 to 72%, compared with 83% with the conventional diet.

4. In experiment 3 egg production was 55% with the basal diet, 71% with the basal diet + L + M, 75% with a diet containing 141 g protein/kg + L + M, and 73% with the conventional diet.

5. In all three experiments supplementation with GA alone either gave no significant response or a depression in production.

6. Daily intakes of 1.24 g nitrogen as non‐essential amino acids and 13 to 14 g total crude protein per bird resulted in good egg production. Supplementation of the basal diet with L + M resulted in a daily intake of 413 mg methionine/bird day which was considered adequate, and a daily intake of 710 mg lysine which was considered slightly inadequate.     

The effect of feeding low‐protein diets to pullets from hatch to point‐of‐lay and the quantitative restriction of food during the subsequent laying period

Pullets from two commercial breeds were fed on diets of similar energy content but with 19% or 16% crude protein to 8 weeks of age and from 8 to 20 weeks of age on one of three isoenergetic diets containing either 12, 14 or 16% crude protein. At 20 weeks the birds were offered a conventional layers’ diet containing 16% crude protein either ad libitum or on a daily food intake of 100 g for a further 32 weeks.

The results indicate that with certain breeds the dietary protein levels can be lowered to approximately 16% during the o to 8‐week period and to approximately 12% during the 8 to 20‐week period without adversely affecting egg production. However, variations in the laying performance of the different breeds appear to be dependent on the amount of protein fed in the first eight weeks of life. Significant breed effects were observed throughout the experiment and although restricted feeding during the laying period substantially reduced the food intake it also had a detrimental effect on the rate of egg production and on the total weight of eggs produced.     

Evaluation of methanol‐grown bacteria and hydrocarbon‐grown yeast as sources of protein for poultry: Performance of broilers during the finishing period

1. Three trials were carried out with male broilers during the 5‐ to 8‐week period, for the evaluation of two types of single‐cell protein (SCP) in practical‐type broiler finisher diets. The SCP tested were: Pruteen, produced from methanol‐utilising bacteria, and a Lavera‐type yeast which utilises the normal paraffins of heavy gas oil.

2. The inclusion of 90 to 100 g of either type of SCP/kg of the diet caused a 2 to 3% reduction in weight gain, a 3 to 5% decrease in food consumption, and up to a 2% improvement in food utilisation. The reduced growth rate could be fully explained by the decrease in food intake, with essentially no effect on food : gain ratio.

3 In diets containing Pruteen, arginine was second limiting after the sulphur amino acids.

4 An odd‐numbered fatty acid (17 carbons, unsaturation unknown) of Pruteen was not found in the carcass lipids of broilers fed on a diet containing 120 g Pruteen/kg.     

Comparison of a 19.7%‐protein wheat (triticum aestivum L), three 13.5%‐protein wheats,and corn (zea mays) in broiler diets with different protein and lysine contents

An experiment using broiler chicks up to 3 weeks of age was conducted to examine the use of corn (Zea mays), Glenlea, Pitic 62, 13.5%‐protein Neepawa and 19.7%‐protein Neepawa wheats (Triticum aestivum L) as ingredients in broiler diets. Two dietary protein contents (calculated as 18.5 and 23.0%) with and without supplementary lysine (0.3%) were used in the diets containing each of the five grains. The desired dietary protein contents were obtained by varying the proportions of the grains and soybean meal.

Grain, dietary protein and added dietary lysine significantly affected body weights and efficiencies of food conversion.

Significant first‐order interactions between grain x protein, grain x lysine and protein x lysine were found for both body weights and efficiencies of food conversion and resulted mainly from responses obtained with the 19.7%‐protein Neepawa wheat supplemented with lysine when compared with the responses obtained to the other grains. When substituted into the higher‐protein diet, supplemented with lysine, the 19.7%‐protein Neepawa wheat supported a similar performance in chicks to other grains fed under similar conditions.     

Response of broiler chickens to well‐balanced protein mixtures

1. Four experiments were conducted on broiler chickens between one and three weeks of age to determine their response to dietary protein concentrations.

2. Diets prepared by serial dilution of a concentrated protein mixture, well‐balanced with respect to all essential amino acids, were fed in three experiments, while in a fourth experiment, a lysine‐deficient protein mixture was used.

3. Response curves relating body‐weight gain to increasing concentrations of protein and of lysine intake are presented.

4. A table is presented from which optimum protein intakes can be calculated according to changes in input and output costs and changes in growth potential of the chickens.     

The effect of sodium sulphate and methionine on the utilisation of non‐protein nitrogen by laying hens

1. The response of layers to adding diammonium citrate (DAC), sodium sulphate or methionine to a basal diet containing 136–3 g protein/kg was determined.

2. Supplementing the diet with DAC equivalent to 25 g protein/kg did not improve egg production, the efficiency of food utilisation, egg weight, nitrogen retention or the apparent absorption of lysine and methionine; increases in food intake and in the concentration of methionine in the serum and liver were observed.

3. Adding sodium sulphate, alone or with DAC, did not affect the variables noted above.

4. Supplementation of the basal diet with methionine increased egg production, egg weight, food intake and the concentrations of lysine in the serum and liver.

5. It is concluded that the supplemental NPN was used only in serum protein synthesis.     

Effect of dietary protein,essential and non‐essential amino acids on the performance and carcase composition of male broiler chickens

1. The present study was conducted to determine the possibility of using low‐protein broiler diets supplemented with synthetic amino acids. The effects on performance, carcase composition and nitrogen retention were evaluated.)

2. A starter diet was given, ad libitum, from 7 to 21 and a finisher diet from 21 to 42 d of age. Body weight, weight gain, food intake and food conversion (FC) were determined at 3 and 6 weeks of age. Abdominal fat deposition (AFD), carcase yield, carcase fat and protein and nitrogen retention were determined at 6 weeks of age. During the starter period chicks were given a 231 g/kg crude protein (CP) diet and a low protein diet supplemented with synthetic amino acid, a: to National Research Council recommendations, b: to the concentration of the control diet, and c: in agreement with the pattern of body composition. Glutamic acid and glycine were added to some diets as sources of non‐essential amino acids (NEAA). All diets contained 12.62 MJ metabolisable energy (AME_n)/kg. The diets administered between 3 and 6 weeks were comparable to the starter diets, except that they contained more AME_n (12.85 MJ/kg) and less protein.

3. Performance equal to that of high protein controls was obtained with birds fed a low protein diet supplemented with synthetic essential and NEAA to the amounts in the control diet or based on the amino acid profile of body protein. This was not achieved with low protein diets supplemented with synthetic amino acids to the amounts recommended by NRC.

4. Without altering performances, the efficiency of protein utilisation of birds fed on low protein diets was superior to that of birds fed on the commercial control diet and their nitrogen excretion was reduced by 26%. The percentage carcase yield and protein was unaffected by the dietary regimen but carcase fat content and AFD increased as the protein content of the diet decreased.

5. These results show that it is possible to obtain the same performances with low protein diets supplemented with synthetic amino acids, using an ideal amino acid balance. However, low protein diets result in a higher carcase fat content.     

Genotype‐level of protein interaction for growth rate in broilers

1. Two groups of White Plymouth Rock which were related to each other as half‐sibs were fed on diets containing either a normal or reduced amount of protein.

2. Compared with the normal diet the low‐protein diet caused a decrease in growth rate which at 38 d was 37% and 25% for male and female chickens, respectively.

3. A genotype‐level of protein interaction was demonstrated for weight at 38 d. Expressed as a genetic correlation for the same trait and measured in the two feeding environments the values were about 0.33.

4. In estimating the genetic correlation the interaction as well as the covariance method were used. The two methods did not give the same estimates.

5. Heritabilities for weight at 38 d tend to be larger in the low‐protein environment.     

Maximum nutritional response to poor‐quality protein and amino acid utilisation

1. Although the theory of responses to amino acids suggests that, providing sufficient of the limiting amino acid is fed, it should be possible to elicit maximum growth response, maximum response is not usually elicited by poor‐quality proteins.

2. It has been suggested that this failure to elicit maximum response is a reflection of poorer limiting amino acid utilisation from poor‐quality proteins. This interpretation conflicts with the theory of general amino acid imbalance which proposes that amino acid excesses do not impair the utilisation of the limiting amino acid.

3. Three protein mixtures of different quality were made by mixing maize gluten meal and soyabean protein concentrate in constant proportions, supplementing with tryptophan, threonine and arginine to adequacy and varying amino acid score (0'62, 0^‐71 or = 1–0) by varying additions of free lysine. The 3 mixtures were diluted with protein‐free ingredients to produce 3 diet series, each providing 3–7, 6–5, 9–2, 120, 14–8 and 17–5 g lysine per kg. Each diet was fed to 4 cages of 2 chickens each from 4 to 14 d of age in a randomised block experiment. Food intake, body‐weight and body‐nitrogen gain were measured.

4. Differences in protein quality were confirmed by regression analyses of body‐weight response to protein intake (Net Protein Ratio) and body‐nitrogen response to nitrogen intake (Net Protein Utilisation) in the linear range. Regression analyses in the linear range of body‐weight or body‐nitrogen response to lysine intake showed no adverse effect of protein quality on lysine utilisation. Curvilnear analysis (Reading flock response model) confirmed this finding.

5. Maximum response could not be obtained with the poorest protein quality. It is illogical to invoke impaired utilisation of the limiting amino acid to explain this. A small decrease in net energy yield of the diet may be sufficient to explain the effect, but it is more likely that the depletion of the limiting amino acid from tissue (muscle) protein which results from feeding poor‐quality protein explains the effect.     

The use of n‐paraffin‐grown yeast as the main source of protein in diets for chicks

1. n‐Paraffin‐grown yeast and a mixture of soyabean meal and fish meal were compared in the net protein utilisation (NPU) test, and as protein supplements in diets for broilers up to 4 weeks of age.

2. The difference between the NPU values, 0.66 for yeast and 0.80 for the soyabean meal and fish meal mixture, could largely be attributed to the high nucleic acid content of the yeast.

3. Chicks given the diet containing yeast (190 g/kg) did not grow as rapidly as those given the soyabean meal and fish meal reference diet, and the reduced growth could only partly be explained by a marginal deficiency of methionine.

4. Food conversion efficiency with the yeast diet was improved by maize oil while responses to α‐tocopheryl acetate and sodium selenite were inconsistent.

5. Chicks grew well when yeast replaced fish meal in the mixture of soyabean meal and fish meal, and when fish meal (194 g/kg diet) was the sole protein supplement.     

Comparison of storage time‐temperature effects on sensory and hedonic attributes of frozen and deep‐frozen chickens

1. Broilers were stored at ‐12±1°G and ‐18±1°C for nine periods of up to 24 and 36 months respectively and compared with birds stored at ‐43 ± 2°C.

2. There were negligible differences in preference between the experimental and reference grilled breast meats.

3. Odour preference differences for thawed, uncooked birds were significant after 1 month of storage at ‐ 12 °C and after 9 months at ‐ 18 °G.

4. In comparison with the reference birds the redness of frozen and thawed birds decreased more regularly during storage at ‐ 12°C than at ‐18 °C.

5. Packaging the birds in Cryovac instead of in polythene resulted, in the raw birds, in a greater difference in surface redness. This redness decreased more rapidly during storage than that of birds packaged in polythene.     

Relationship between energy and protein intakes and laying characteristics in individually‐caged broiler breeder hens

1. Individually‐caged broiler hens, which had been reared on an advised rationing programme, were fed allowances of 1.88, 1.61, 1.32 or 1.13 MJ apparent metabolisable energy/bird d at four different protein intakes (27, 23, 19.5 or 16.5 g crude protein per bird d) from 21 to 60 weeks of age.

2. Age at first egg, body‐weight gain and egg production were affected by energy allowance. Birds on the lower energy allowances came into lay later than birds on the higher energy allowances and at a lower body weight.

3. Body‐weight gain decreased with decreasing energy allowance. The decrease in egg output in response to decreasing energy allowance resulted from more birds ceasing to lay and fewer birds laying on more than 3 d per week. Similar changes in the distribution of rates of lay were observed on each treatment as the flock aged.

4. The relationship between body‐weight gain and egg number on each treatment was negative from 21 to 36 weeks, but became less consistent with age.

5. Protein intake had little effect on body weight. At the lowest energy allowance, egg number and egg weight decreased with increasing protein allowance. This effect was not observed on the higher energy allowances.     

Influence of protein concentration on the sulphur‐containing amino acid requirement of broiler chickens 1

1. Two experiments were conducted with male broiler chickens from 3 to 6 weeks of age to determine the effect of dietary protein content on the requirement for sulphur amino acids (SAA). In experiment 1, 0, 0.5, 1.0 or 1.5 g DL‐methionine/kg were added to diets calculated to contain 200, 240 or 280 g protein/kg. In experiment 2, 0, 0.6, 1.2 or 1.8 g DL‐methionine/kg were added to diets calculated to contain 160, 180 or 200 g protein/kg.

2. In experiment 1, the SAA requirement for body weight gain increased as dietary protein content increased. Regression analysis indicated a requirement of 38 g SAA/kg protein.

3. In experiment 2 in which lysine supplementation provided a minimum of 10 g/kg, the requirement for SAA per unit of diet increased only slightly as protein concentration increased indicating that below 200 g protein/kg of diet, the SAA requirement increases per unit of protein with supplementation of the second‐limiting amino acid.

4. Abdominal fat percentage declined in a linear manner with each increment of SAA added to diets containing 160 to 200 g protein/kg. Adding methionine to diets containing 240 or 280 g protein/kg did not affect abdominal fat content. A lower limit of abdominal fat was achieved with a protein concentration of 240 g/kg.

5. It is concluded that the requirement for SAA of finishing broiler chickens is directly related to protein content at concentrations of 200 or more g protein/kg but increases per unit of protein at lower protein concentrations when a minimum lysine concentration is specified. Abdominal fat content reaches a minimum between 200 and 240 g protein/kg of a maize‐soyabean meal diet regardless of SAA content.