The tryptophan requirements of young laying pullets

1. Two experiments were conducted with laying pullets between 32 and 47 weeks of age. In each trial 1 728 White Leghorn and 1 728 crossbred pullets were used.

2. A series of diets of increasing protein content was offered. Protein quality was identical in all diets and tryptophan was demonstrated to be the most limiting amino acid in the protein mixture used.

3. The daily tryptophan requirement of the individual pullet was estimated, by indirect methods, to be 2.25 mg/g egg output plus 10.25 mg/kg body weight. Response curves for flocks of pullets are illustrated. Calculated optimum intakes of tryptophan for various ratios of costs of input to value of output are tabulated.

4. It is estimated that for a flock of mean body weight 1.5 kg, producing 55 g egg mass/hen d and consuming 110 g food/hen d, the optimum dietary tryptophan concentration is 1.7 g/kg when the marginal cost of supplying 1 kg tryptophan is 20 times the marginal value of 1 kg egg output.     

Some effects of confinement on laying pullets

Laying WLH pullets were housed individually in cages with floor areas of either 930 cm² (group 1) or 3700 cm² (group 2). Half the birds from each group were killed after 35 d confinement and the other half on the 70th d. Balance studies were conducted from 25th to 35th d and from 60th to 70th d.

The more severely confined birds had depressed plasma alkaline phosphatase activity but a raised plasma cholesterol level after 35 d. The alkaline phosphatase activity returned to normal after 70 d but the hypercholesterolaemia persisted. Acid phosphatase activity and plasma protein levels were unaffected by the treatments.

Pullets in the smaller cages laid fewer eggs but egg weight was unaffected.

Neither percentage metabolisable energy nor metabolisable nitrogen of the diet was affected by the severity of confinement, though less dietary nitrogen was retained by either group in the first half of the confinement period.

Severe confinement resulted in higher values of percentage metabolisable calcium and phosphorus by the 35th d but these decreased by the 70th d. In the less severely confined birds these values by the 70th d were higher than those at the 35th d.     

Pasteurella haemolytica as a co-pathogen in pullets and laying hens

Pasteurella haemolytica was isolated from internal organs of laying hens and pullets of four flocks in which five incidents of increased mortality had occurred. There was inflammation of the trachea in all cases, and infectious laryngotracheitis virus was identified in three of the incidents. Rapid response to antimicrobial therapy was seen in two out of three outbreaks in the pullets. P. haemolytica was regarded as a significant secondary invader in these cases.     

The protein requirements of two strains of laying pullets

Diets with 16.5, 14.5, 12.5 and 10.5 per cent protein and 2765 k cal. metabolisable energy per kg. and a fifth diet containing 10.5 per cent protein and 2165 k cal. M.E./kg. were fed to Rhode Island Red x Light Sussex pullets and to “hybrid” pullets which weighed 33 per cent less and produced 20 per cent more eggs. Both strains had protein requirements of the order of 20 g./bird/day. It is possible that the assumed higher requirement of the “hybrid” pullets for productive purposes was offset by a smaller requirement for maintenance and growth. Expressed as a percentage of a 2765 k cal. diet, the small strain required at least 16.5 per cent protein and the large strain no more than 12.5 per cent protein for maximum performance. Both strains performed well on the 2165 k cal., 10.5 per cent protein diet, illustrating that high energy diets are not essential for small strains of pullets.

Egg size was reduced by protein restriction in the heavy strain but not in the light strain. On isocaloric diets the light strain consumed more food only at the lowest protein level whereas the heavy strain tended to eat progressively more as the protein was reduced from 16.5 to 12.5 per cent. When offered the low energy diet both strains ate more food, but substantially fewer calories, than when given diets of 2765 k cal. M.E./kg. Protein restriction had a marked effect in reducing live‐weight gains. Energy level of the diet had a large effect on weight gain and also on fat deposition in the carcass.

The greatest differences in performance due to diet did not occur at the time of maximum egg output. The evidence indicates that a diet which is too low in protein to support peak egg production will also fail to support normal egg production at any later stage of the laying year.     

Seroprevalence of Histomonas meleagridis in pullets and laying hens determined by ELISA

Serum samples from 1120 layers from 56 flocks and 400 pullets from 20 flocks were tested by an indirect sandwich ELISA to investigate the prevalence of antibodies to Histomonas meleagridis in chickens kept in alternative husbandry systems. The overall prevalence of antibodies to H meleagridis in layers was 37.3 per cent, and positive birds were identified in 50 flocks. This was significantly higher than in pullets, where only 8.3 per cent of the birds tested positive. Optical density (OD) values obtained from pullet sera were much lower than the OD values from layers; however, positive birds were detected in half of the pullet flocks. In particular, all birds from an organic pullet flock were found to be positive, with high OD values. Overall, the highest prevalence of positive sera was obtained from birds kept in free-range flocks. Attempts to reisolate live histomonads from birds in 18 layer flocks were unsuccessful.     

Quantitative review of optimum amino acid intakes for young laying pullets

Data relating egg output to daily intakes of lysine, methionine, tryptophan, isoleucine and valine have been analysed using both published and unpublished sources. Amino acid requirements in mg/d for individual pullets were estimated by the following equations: (Table: see text) where E = egg output in g/d and W = body weight in kg. Response curves for flocks of pullets were calculated using the Reading model and optimum intakes were derived for various body weights, egg outputs and ratios of input costs to output values. Estimates of amino acid maintenance requirements were related to reported values for the adult cockerel and the amino acid requirement for egg output was related to the digestibility of amino acids and the composition of egg protein. Procedures are suggested for deriving response coefficients for other essential amino acids.     

Effects of constant environmental temperatures on the performance of laying pullets

1. Two experiments are described in which laying pullets maintained at constant temperatures were fed a range of diets with a view to defining optimum combinations of temperature and nutrient intake. 2. In the first experiment, all combinations of 6 temperatures (15 degrees, 18 degrees, 21 degrees, 24 degrees, 27 degrees and 30 degrees C) 9 diets (three protein concentrations and three energy contents) and two stocks were tested for 34 weeks using 4320 pullets. In experiment 2, all combinations of three rearing temperatures, three laying temperatures (18 degrees, 22.5 degrees and 27 degrees C) three diets (protein concentration) and two stocks were tested for 61 weeks using 2160 pullets. 3. As anticipated, higher dietary protein concentrations were needed to maintain egg output at higher temperatures. If diets suplying adequate amino acid intakes were provided, egg output was unaffected by temperatures in the range 15 degrees to 27 degrees C although, at the highest temperature, egg weight was slightly reduced and rate of lay (particularly in the later part of the laying year) was increased. At 30 degrees C, egg output was depressed whichever diet was fed. 4. Dietary energy content had small but significant effects on egg weight and egg output but did not interact with temperature. It was not possible to maintain egg weight or egg output at 30 degrees C by feeding a high energy, high protein diet. 5. Estimated heat output of the birds increased during the course of the experiment at the lower temperatures but decreased with time at 30 degrees C. Feather loss occurred earlier at the lower temperatures and this is interpreted as an effect of temperature on the timing of the annual moult, which also accounts for the better persistency of lay observed at 27 degrees C.     

Model for predicting egg output and metabolisable energy intake of laying pullets.

1. The data compiled by Marsden and Morris (1987) to examine the relationships between environmental temperature and the long-term, adapted responses of laying pullets were divided at random into two subsets of 99 and 113 observations. The first subset was used to estimate regression coefficients for an econometric model, and the second subset to validate the model. 2. Equations to predict inputs (costs) and outputs (returns) were estimated with a three-stage least-squares regression model. Three stage least-squares estimation is a technique which corrects for the simultaneity of variables within the model and correlation across equations of the model. This results in more efficient estimates of the regression coefficients. 3. The final output and output equations were: MEI = 253.86-190.31EM+5.766EM2-0.546EM3 + 0.7034T-0.004388T3 + 695.08BW-120.23BW2 + 397.37ME-13.132ME2-1.06MEXT; R2 = 0.86; EO = 119 + 0.025MEI -0.0000045MEI2-1.462T-0.0791T2-135.3BW + 38.31BW2-1.483T X BW + 0.0288T2 X BW + 0.673 delta BW; R2 = 0.59 where MEI = daily metabolisable energy intake (kJ/bird d), T = environmental temperature (degree C), EO = egg output (g/bird d), BW = body weight, and ME = metabolisable energy concentration (kJ/g). The values for R2 indicate very good fits considering that the data were recorded over a 26-year period in 14 different laboratories. 4. This statistical model can serve as the basis for an econometric model of egg production to determine the environmental temperature that maximises profits from laying pullets of different body weights.     

Changes in the protein requirements of pullets during the first laying year

A range of protein intakes (5 to 20 g protein/d) was achieved by feeding six diets containing 7 to 14½% protein to a total of 400 pullets for 10 weeks from 28 weeks of age. The same six diets and an additional diet with 16% protein were fed again for 10 weeks from 62 weeks of age. The resulting patterns of egg output were different at the two ages. The birds required more protein at the end of the laying year than at the beginning to sustain any given level of output. This difference in protein requirement was not accounted for by changes in body weight.

It is concluded that measurements of protein input‐output relationships made at one stage in the laying year do not form a satisfactory basis for predicting protein requirement at another stage.     

New intermittent lighting programme (the reading system) for laying pullets

1. Two intermittent lighting systems for laying hens are: the Biomittent system, using an asymmetric pattern of 0.25L:0.75D for 16 h followed by 8D, which entrains oviposition to 24 h cycles and, compared with standard lighting programmes, gives the same egg number and egg size but a smaller feed cost, and a symmetrical system (4[3L:3D]) which allows intervals between ovipositions to stretch, giving bigger eggs with thicker shells, but yielding fewer eggs and achieving no saving in food intake.

2. A new system was devised to combine the increased egg size and shell thickness, characteristic of symmetrical intermittent lighting programmes, with the reduction in food intake which is a feature of programmes that reduce total activity time. The pattern tested was 24(0.25L:0.75D).

3. The results of 2 trials showed that this new system gives about 2% fewer eggs than conventional (Step Up) or Biomittent lighting with a 2% increase in mean egg size and a 3% improvement in shell thickness at the end of the laying year. Feed consumption with the new system was similar to that under Biomittent lighting and 6% lower than that recorded for Step Up lighting.

4. Mortality was lower with the new system than with Step Up lighting, but not significantly so. From the evidence of other trials it is argued that intermittent lighting programmes which provide less than 8 h total illumination in 24 h generally reduce laying house mortality and may be regarded as beneficial to the welfare of the hen.     

Effect of low protein diets for growing Leghorn pullets upon subsequent laying performance

An experiment was conducted with White Leghorn pullets to study the effect on laying performance of dietary protein content and amino acid supplementation during the growing period. From 0 to 6 weeks of age birds fed on diets containing either 149 g protein/kg supplemented with methionine and lysine or 182 g protein/kg grew faster than those fed on a diet containing 149 g protein/kg alone. However, only those fed on the supplemented diet utilised their food more efficiently. From 7 to 20 weeks of age neither body weight gain nor food utilisation was affected by the dietary protein content. Pullets fed the low protein diet supplemented with 2 g methionine/kg and 2.5 g lysine/kg during the period of 0 to 6 weeks of age had significantly better egg production than birds fed the low protein diet alone. The dietary protein content during 7 to 20 weeks of age did not influence subsequent egg production.     

Comparison of equations for predicting the metabolisable energy intake of laying pullets.

1. The accuracy of equations to predict metabolisable energy intake of laying hens was compared using a random sample of the data set of Marsden and Morris (1987). 2. The equation of Pesti et al. (1992) was found to be significantly better at predicting metabolisable energy intake than the equations of Byerly (1941), Emmans (1974), Byerly et al. (1980), and the National Research Council (1984) when equation residual mean square errors were tested. 3. The equation of Pesti et al. (1992) had the highest coefficient of determination (R2), the smallest average residual, and smallest mean square error. The NRC equation predicted the average metabolisable energy intake best, indicating that over- and under-predictions offset each other. 4. The equations of Emmans (1974) and Pesti et al. (1992) were essentially without bias across temperature zones: less than 20, greater than = 20 less than 25, greater than = 25 less than 30, and greater than = 30 degrees C. The equation of Byerly (1941) over-predicted below 25 and above 30 degrees C, but under-predicted between 25 and 30 degrees C. The equation of Byerly et al. (1980) under-predicted below 30 degrees C while the NRC (1984) equation under-predicted above 20 degrees C.     

Comparison of nutritive values of groundnut oil cake and Niger oil cake for laying pullets

1. The nutritive value of Niger oil cake (Guizotia abyssinica, Cass.) as a protein supplement for layers’ diets has been assessed.

2. Replacing groundnut oil cake (GNC) by Niger oil cake (NC) on an isonitrogenous basis, did not affect egg production, egg weight or the amount of food required per dozen eggs.

3. The percentage retention of nitrogen from diets containing 30% GNC or 30% NC was similar.

4. The ME value of NC used was 3025 kcal/kg.

5. It is concluded that NC can replace GNC in layers’ diets.     

The protein requirement of laying pullets with changing seasons in the tropics.

1. The protein requirements of White Leghorn laying pullets were evaluated in summer and winter using isocaloric diets containing 12-8, 15-0, 16-6, 18-5 and 21-6% protein. 2. The age at 50% production of summer-raised pullets was about 2 weeks later than that of winter-raised pullets irrespective of the concentration of dietary protein. 3. Egg production in summer-increased with increasing concentrations of protein up to 18-5%; further increases had no significant effect: in winter, egg production was similar provided the diet contained at least 15-0%. 4. The data on egg production, food consumption and egg weight indicated that the protein requirement of White Leghorn pullets is met by diets containing about 19% protein in summer and 15% in winter.     

The determination of the methionine requirement of laying pullets by a diet dilution technique

A method for the determination of amino acid requirements of laying hens is described. This involves the dilution of a high protein “ summit” diet with an isocaloric nitrogen‐free mixture. By ensuring that the amino acid to be assayed is first‐limiting in the summit diet, the response to dilution can be interpreted as a response to a single amino acid.

The method is applied to the determination of methionine requirement and it is shown that the response to methionine obtained is virtually independent of the protein level of the diet and is not influenced by direct effects of the dilution mixture.

From the results of the present and other published experiments, the “ available “ methionine required for maximum egg yield of pullets in the early stages of lay is estimated to be 275 mg per bird per day.