The effects of early and late maturity on the protein requirements of pullets

Growing pullets were exposed to two light patterns which caused a difference in sexual maturity of 5 weeks. From 28 to 38 weeks of age they were fed diets containing crude protein levels of 7.0, 8.5, 10.0, 11.5, 13.0 and 14.5 per cent. Yellow maize provided 45 per cent and soyabean meal 55 per cent of the protein in all six diets.

Rate of lay, egg weight and body weight were greater in the late maturing flock than in the early flock at the start of the assay and throughout the assay period. The late maturing pullets required more protein to reach and maintain their maximum potential than the early birds, presumably because their potential output was greater. The late birds showed a diminishing but continued response to protein up to the highest level fed (14.5 per cent corresponding to 23 g. protein per bird day). The early maturing pullets showed no response to dietary protein levels beyond 11.5 per cent and their estimated protein requirement was about 16 g. per bird day.

When limiting amounts of protein were fed (7.0–10.0 per cent of the diet) the two flocks achieved similar levels of egg output. In both flocks and throughout the assay, body weight and egg weight fell at the two lowest levels and increased at the three highest levels of protein.

It is concluded that the protein requirements of early maturing and late maturing flocks of pullets may differ, but only in a way which corresponds directly with their different potential outputs. In the late flock, which had the higher protein requirement, excellent production was obtained with a diet containing 14½ per cent crude protein all of which came from vegetable sources.     

Changes in dietary protein level during the pullet year

A “High” protein diet (14 per cent crude protein, 2490 k cal. ME/kg.) and a “Low” protein diet (10.5 per cent protein, 2420 k cal. ME/kg.) were fed to two types of laying pullet. One type was a small commercial hybrid weighing about 1.6 kg. and the other was a large first cross weighing about 2.4 kg. at 20 weeks. After 12 weeks and 24 weeks of lay, groups were transferred from the High to the Low protein diet and vice versa.

In the heavy strain birds the High and Low protein diets both supported good egg production throughout the trial and changing from High to Low protein had no effect on rate of lay. The opposite change from Low to High, made after 12 weeks of lay, stimulated an increase in rate of lay above the level of birds which had received the High protein diet throughout.

In the small hybrid pullets the low protein diet did not support a normal rate of lay. Attempts to reduce dietary protein by switching from High to Low after 12 or 24 weeks caused a fall in rate of lay. Groups transferred from Low to High increased their rate of lay to a level comparable with controls kept on High protein throughout.

Egg weight and body weight were affected by dietary protein level in both strains. Changes in the diet caused corresponding changes in both egg weight and body weight.

It is concluded that there is little scope for reducing the level of protein in the diet during the laying year. If a diet is inadequate in the early stages of production it is likely to remain inadequate for any later stage. On the other hand, some unexpected benefit was obtained in one strain by increasing the dietary protein beyond the level which was adequate for maximum egg production in the first 3 months of lay.     

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.     

The recovery of laying birds from a period of low protein feeding

Laying pullets which had been fed diets containing 7, 8½, 10, 11½, 13 and 14½ per cent crude protein for 10 weeks were returned to a normal diet containing 14½ per cent crude protein. For birds which had received the lowest protein diet, rate of lay improved from about 30 per cent to over 80 per cent in 4 weeks. Egg weight, body weight and food consumption also increased rapidly. In the period from 3 to 20 weeks after restoring a normal diet the pullets which had previously been fed 7 per cent and 8½ per cent crude protein showed a rate of lay and an average egg weight substantially better than that of control birds which had always received the 14½ per cent crude protein diet.

It is concluded that a period of low protein feeding does not impair the subsequent ability of the laying bird to reach normal levels of output. On the contrary, birds which are denied a normal protein intake for a time tend to compensate when returned to normal feeding by laying more eggs and bigger eggs. However, in this experiment, the compensation was not enough to offset the loss in yield incurred during low protein feeding.     

Efficiency of egg production of three types of caged layers fed diets containing maize, oats or barley as the main cereal ingredient

The results of two similar experiments, each using 204 pullets in cages, are presented. In each experiment, a type of light commercial hybrid, heavier commercial hybrids and Brown Leghorn×Light Sussex cross‐breds were compared, in factorial design, on diets containing either 65 per cent barley, 55 per cent maize or 35 per cent oats and 15 per cent bran. Individual records of egg production, egg weight, food conversion and body weight were kept for eight 28‐day periods, starting when the pullets were in full production.

There were no significant differences in egg production between diets but in both experiments a significantly improved food conversion ratio was obtained on the high maize diets, which also gave the highest level of energy consumption.

Most breed differences were not significant but in Experiment 1 the crossbreds produced significantly fewer eggs than the hybrids and in Experiment 2 the light hybrids gave a significantly better food conversion ratio than the two heavier types. The crossbred pullets consumed the most energy in both experiments and in Experiment 1 had significantly the worst energetic efficiency of egg production.

There were no significant interactions between type of pullet and type of diet in either experiment. Thus there were no indications that, at the energy levels investigated, favourable effects may be expected from the feeding of higher energy diets to the lighter hybrid type pullet.

The practical significance of feeding a high barley diet is discussed.     

The effect of low‐protein grower diets on the subsequent response of pullets to quantitative food restriction during lay

1. The laying responses of pullets fed from 8 weeks of age on a 12.5% protein grower diet and subsequently subjected to food restriction commencing at various times between 20 and 40 weeks of age were compared with those of pullets reared on diets containing 12.5 or 16% protein and given access to food throughout lay.

2. Restricted feeding during lay of pullets reared on the low‐protein diet substantially improved laying performance, the best results being obtained from pullets fed the low‐protein grower diet and restricted from 20 weeks. The laying responses of pullets restricted after peak‐lay at 40 weeks of age were not significantly different from those of birds restricted prior to peak‐lay.

3. Maximal egg production of 81 % over the 48weeks of the experiment was attained on an average daily ME intake of 270 kcal (1130 kJ) and a FCR of 2.06 : 1.

4. It is suggested that food restriction of laying pullets previously reared on low‐protein diets may be successfully utilised prior to peak‐lay provided such restriction is not so severe as to retard the rate of attainment of mature weight and a continued slight gain in weight thereafter.     

Effect of feeding low lysine starters and developers on growth,sexual maturity and subsequent performance of broiler breeder pullets 1

Pullets that were fed diets containing 0.53 per cent and 0.42 per cent lysine grew at a slower rate and matured later than those that were given adequate amount of lysine. The latter pullets converted their food more efficiently than did the restricted pullets with the exception of the group fed the ration containing 0.53 per cent lysine for the first 12 weeks. The restricted pullets consumed less food during the growing period. A smaller bird was produced on less food. The restricted pullets were also lighter than the control pullets at the end of the laying season. A saving in food costs is indicated because the smaller hen would require less food for maintenance.

There was a higher mortality in the pullets fed a ration containing 0.53 per cent lysine during the growing period. The mortality in the group fed the ration containing 0.42 per cent lysine from 7 to 22 weeks of age was the same as that of the control. There were no differences in mortality during the laying season that could be related to methods of rearing the pullets.

During the laying season, the highest rate of lay was obtained from hens which had been fed the ration containing 0.42 per cent lysine from 7 to 22 weeks of age. Hens fed on the ration containing 0.53 per cent lysine from o to 4, 8 or 12 weeks of age showed no improvement in rate of lay as compared with controls.

Hens fed the ration containing 0.42 per cent lysine from 7 to 22 weeks laid fewer small eggs at the beginning of the laying season than did hens receiving adequate amounts of lysine throughout or fed the ration containing 0.53 per cent lysine from o to 4, 8 or 12 weeks. The hens fed the latter ration laid smaller eggs throughout the laying season.

No differences were found between the fertility, hatchability or embryonic mortality of eggs obtained from hens fed on lysine deficient diets during growth and those fed on diets adequate in lysine.     

Effects of age on the tryptophan requirement of laying hens

1. White Leghorn pullets which had been used for an assay of tryptophan requirement between 32 and 40 weeks of age were used for similar determinations between 63 and 73 and, after a moult, from 97 to 106 weeks of age.

2. A tryptophan‐limiting protein mixture was used and by dilution seven dietary protein contents were produced, supplying from 0.84 to 1–92 g tryptophan/kg diet. The diet of lowest protein content was also sup‐lemented with free tryptophan. These diets were fed in experiments using 24 groups of 72 pullets at 63 to 73 weeks and 45 groups of 21 hens at 97 to 106 weeks.

3. The relationship between egg output and tryptophan intake was the same in moulted hens as in young pullets, but pullets of 63 to 73 weeks of age yielded a different response curve; more tryptophan being needed for a given egg output.

4. It is concluded that tryptophan required, per day, does not decrease during the first laying year, despite a decrease in rate of egg output.     

Calcium and phosphorus levels in the diet of laying birds

Two hatches of crossbred pullet chicks were brooded and reared to 18 weeks of age on diets which conformed to the recommendations of the National Research Council (N.R.C.) of America for calcium and phosphorus. The pullets of each hatch were then divided at random into six laying groups. Three groups were fed diets containing 2.25, 3.14 and 5.0 per cent respectively of calcium without supplementary phosphorus and the other three groups were fed diets of the same graded calcium levels but with supplementary phosphorus to give a total inorganic phosphorus content of 0.45 per cent. When the rate of egg production in the groups receiving 2.25 per cent calcium exceeded 70 per cent an ad libitum supply of limestone grit was provided and the intake recorded. Over the twelve months of lay this resulted in an average total dietary intake level of nearly 2.65 per cent calcium.

Egg yield was not significantly influenced by the diets, except that the production of birds fed on the diet containing 5 per cent calcium without supplementary phosphorus was significantly depressed. Food intake was not adversely affected by the higher levels of ground limestone; in fact, there was a positive regression of food consumption on the percentage of calcium in the diet. Because of the greater food intake and the lower egg production, food consumed per dozen eggs and cost of food per dozen eggs were higher in the groups receiving 5 per cent dietary calcium without phosphorus supplementation, compared with groups which received lower dietary levels of calcium. There were, however, no significant differences between the various groups in income or in the margin of income over costs, per bird or per dozen eggs.

The data on egg grading showed that over the two experiments and at all levels of calcium there was no evidence of any influence of phosphorus on the combined percentage of large and standard eggs. The average percentage for the two diets with the 5 per cent level of calcium was significantly greater than the combined average for all the other diets.

The average percentage of cracked eggs for the groups with diets containing 5 per cent calcium was 9.4 per cent compared with an average of 11.1 per cent for all the other diets, but the difference was not significant.

The results suggest that there is no economic advantage in raising the calcium content of the basal diet used in these experiments beyond the level of 3.14 per cent and that at this level there appears to be no need with this basal diet to supplement the phosphorus content.     

Effect of diet and natural variations in climates on the performance of laying hens

1. Laying hens raised in 3 natural tropical environments were fed on 2 series of diets with a view to defining the optimum combination of climate and dietary energy.

2. A combination of 3 growing climates, 3 laying climates (temperate, hot dry, hot humid), and 2 dietary energy concentrations (10.03 and 11.70 MJ ME/kg with protein concentrations proportional to energy) were tested for 46 weeks using 432 point‐of‐lay pullets.

3. Both growing and laying climates significantly affected most traits measured during the laying period. The patterns of egg production showed good persistency in all environments and differences observed reduced with age.

4. The difference between the high and low energy intake reduced at high ambient temperatures. Feeding low energy diets did not affect mean age at first egg, rate of lay or the egg output in the hot dry environment, nor egg weight in either hot dry or hot humid climates. Rather, feeding low energy diets resulted in improved body weight change in all 3 laying environments.

5. The growing climate and diet interacted significandy on body weight change, while highly significant interactions between laying climate and diet occurred on rate of lay, food and energy intake and egg weight during the laying period.     

A study of the effect of variation in the calorie‐protein ratio of a medium energy diet and a high energy diet containing sucrose on the efficiency of egg production in caged layers

Literature pertaining to the variation in the protein content of layers’ diets is discussed and the lack of information on the effect of calorie‐protein ratio on food conversion is mentioned. The experiment described in the present paper was designed to test the effect of variations in calorie‐protein ratio on food conversion on a diet of high energy content (1340 k cal/lb.) based on sucrose supplementation and on a medium energy diet (1160 k cal/lb.). At the same time three types of pullet, Thornber 606, Thornber 404 and Light Sussex x Brown Leghorn pullets were compared on the two types of diet, each being fed at three nominal protein levels of 13, 15 and 17 per cent giving a total of eighteen treatments. The pullets were individually recorded for egg production, egg weight and food consumption. Meta‐bolisable energy crude protein determinations were carried out on each of the six diets employed and the actual calorie‐protein ratios calculated.

There was no significant effect on egg production when the calorie‐protein ratio of the diet was raised from 69 (i.e. k cal M.E./lb. per 1 per cent protein) to 90 but an increase to 103 reduced production and egg weight. It was found that maximum efficiency of food conversion was realised at ratios of 76 to 78.

The efficiency of conversion of dietary energy was unaffected by energy concentration in the diet.

The lightweight hybrid (Thornber 606) produced eggs more efficiently than either the Thornber 404 or the crossbred type.     

Studies on the effect of lysine and methionine supplementation of a high‐protein maize‐soyabean diet and of a low‐protein barley‐white fish meal diet on the performance of caged layers

Selected literature relating to the amino acid supplementation of layers’ diets is reviewed and the results of two experiments are presented.

In the first experiment a basal soyabean meal diet (14.3 per cent crude protein) was supplemented with L‐lysine and DL‐methionine, singly and together. Supplementation of the basal soyabean diet with the amino acids caused no significant effects on egg production, mean and total egg weight or food conversion efficiency. None of the soyabean diets proved as satisfactory for egg production or food conversion efficiency as a fish meal control diet (16.9 per cent crude protein).

In the second experiment the effect of adding 0.1 per cent each of L‐lysine and DL‐methionine or 0.2 per cent each of l‐lysine and DL‐methionine to a low fish meal diet (2.5 per cent fish meal) was examined. The addition of 0.2 per cent of each amino acid caused an increase in egg production.

Mean egg weight was improved by the addition of amino acids at both levels although this effect was not statistically significant. Comparison of the low fish meal diets with a fishmeal control diet (10 per cent fishmeal) showed that at the 0.2 per cent addition of amino acids, egg production, total egg weight and food conversion efficiency were better than on the 10 per cent fish meal control diet.

Two breeds, light and medium hybrids were used in both experiments.

The results are discussed with reference to their practical significance.     

The effect of maize and maize oil on egg weight

In two short‐term experiments involving about 1500 laying pullets it was confirmed that the direct substitution of maize for wheat in a laying diet leads to a small but significant increase in egg weight.

It was further shown that when oat hulls were added to a diet containing 55 per cent maize to make it isocaloric with a diet containing 55 per cent wheat, there was still a significant improvement in egg weight with the maize diet. The addition of 2 ‐5 per cent and 5 per cent maize oil to a 55 per cent wheat diet resulted in increases in mean egg weight of 0.7 g. and 1.3 g. respectively. The same response to 2 .5 per cent maize oil was obtained when oat hulls were added to make the diet isocaloric with the basal diet.

It is concluded that maize has an effect on egg weight which is not attributable to the differences in dietary energy normally associated with the substitution of one cereal for another in practical diets. The effect is associated specifically with the oil content of the maize.     

The influence of manganese in association with other dietary components on certain shell characteristics

Four groups of pullets were given, from 17 weeks of age, a high‐Mn diet, or one of three low‐Mn diets. Hens given low‐Mn diets laid eggs with poor shells, judged by appearance, strength and thickness at the start of lay, but only one low‐Mn diet (diet 4), was associated with poor shells throughout 12 months of egg production. Supplementary Mn (100 mg/kg) added to low‐Mn diets after 12 months had no significant effect during the next 2 months on shell appearance score, strength or thickness.

In a second experiment, four groups of pullets aged 16 weeks were given diets of low or high Mn content and high or moderate P content. At the start of the laying period there was a significant interaction between Mn and P, a high level of P increasing shell defects caused by low Mn. At a later stage, 4 months after the start of egg laying, high P significantly reduced shell strength and thickness but had no effect on appearance score: low Mn had only a small non‐significant effect on any shell characteristic at this stage.

In a third experiment pullets of five White Leghorn type hybrids aged 16 weeks were given diets of low or high Mn and high or low Ca until the point of lay, when all birds received the high‐Ca diet but continued receiving the level of Mn given from 16 weeks of age. Only shells produced at the start of lay were studied. Type of hybrid influenced the number of soft shells produced but had no significant effect on other characteristics. Manganese significantly influenced all shell measurements and a high level of Ca increased the number of soft shells, decreased strength and thickness but had no effect on appearance score. There were no significant interactions.     

A study of digestibility and biological value of protein in diets fed to colostomised laying pullets to determine their protein requirement

Hybrid pullets were colostomised just after the commencement of laying. A nitrogen‐free diet was used to determine metabolic faecal nitrogen (MFN) and endogenous urinary nitrogen (EUN). The mean figure obtained for MFN/kg. wt./100 g. dry matter/day was 67.2 mg. and for EUN/kg. body weight 3/4/day was 83.3 mg.

High energy diets of about 1350 k cal./lb. containing 13, 15 and 17 per cent protein and medium energy diets of 13 and 17 per cent protein were fed to colostomised pullets to determine their digestibility, biological value and net protein value. In a further experiment a maize‐fishmeal diet of 1370 k cal. ME/lb. and 17 per cent protein, a soyabean‐maize diet of 1330 k cal. ME/lb. and 14 per cent protein and the latter diet supplemented with methionine and/or lysine were also examined. The mean BV and NPV values of the diets considered in Experiment 1 were 60 and 52 respectively.

Addition of methionine to the maize‐soyabean diet increased the BV from 43.9 to 61.6, the addition of lysine to 43.0 and the addition of both to 67.1.

A factorial method of calculating the daily protein requirement of the pullet based on the data for MFN and EUN and the NPV of each diet is presented. The estimate of 13.3 g. protein per day for the hybrid pullet is compared with other estimates in the literature.     

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.     

A comparative study of energy utilisation by the laying hen from diets containing a high proportion of fat and diets made up mainly from carbohydrate sources

An experiment was carried out in which laying hens were fed diets containing about 30 per cent tallow at three protein levels. Productive performances of hens on these diets were compared with those of hens fed either a diet containing 15 per cent arachis oil, a diet containing 15 per cent sucrose or a conventional cereal‐based control diet.

It was found that the best performance was obtained with hens fed the control diet. Gross energetic efficiency of egg production was slightly lower in the birds fed the diets containing arachis or sucrose. It appeared that the lower efficiency was due to the higher mean body weight of birds on these diets. Egg size was significantly increased by feeding the diet containing arachis oil.

Performance of hens given diets containing tallow was unsatisfactory. For each diet egg production was significantly less than that recorded for the control diet and the gross energetic efficiency of egg production was much lower than that on the control diet.     

The use of rapeseed meals and a mustard seed meal as a protein source in diets for laying pullets

1. Three experiments with laying pullets were carried out in which rapeseed meals (B. napus and B. campestris) and a mustard seed meal (B. juncea) formed 12% of the diet.

2. Dietary rapeseed had no effect on the onset of lay when fed from 17 weeks of age but caused a delay when fed from 10 weeks of age: changing to a control soyabean diet for the laying period resulted in normal egg production.

3. Diets containing B. napus but not B. campestris consistently depressed egg production and reduced egg weight in one experiment. Mustard seed meal did not affect performance.

4. Significant number of eggs with a “fishy” taint were laid by brown‐egged birds fed on a diet containing rapeseed.

5. Thyroids of birds fed on rapeseed meal diets during the laying period were significantly heavier than those of birds fed on diets containing mustard seed or soyabean.

6. The enlargement of the thyroid gland is probably related to the oxazolidinethione content of the rapeseed.     

The influence on shell formation of the pre‐laying period for which a low‐manganese diet is given

The effect of a low‐Mn diet on egg shells was assessed by recording the number of soft shells laid at the beginning of lay, and the shell thickness of subsequent eggs. Observations were made on eggs from two batches of pullets: one that had been fed the low‐Mn diet from 1 month before egg laying began and the other from 2 months before onset of lay. The 2 month period gave fewer soft shells but thinner firm shells than the 1‐month period.

Similar observations were made with groups having mean pre‐laying periods on the low‐Mn diet of 46, 33, 21 and o d. There was a tendency for more soft shells and thinner shells to be produced the longer the period of low‐Mn feeding before laying began.

Pullets that had been in lay for 6 months or low‐ or high‐Mn diets were given an enforced rest period for 6 weeks. On recommencing to lay the low‐Mn birds produced a large number of soft shells and slightly thinner shells than similar birds that had been allowed to continue laying on the same diet.     

Comparison between concentrated complete diets and self‐selection for feeding sexually‐maturing pullets at hot and cold temperatures

1. Pullets in late growth and early lay were maintained at hot (25° to 35°C) or cold (6° to 16°C) ambient temperatures and either fed complete diets or allowed to self‐select nutrients from separate energy‐ and protein‐rich foods.

2. Manipulating the metabolisable energy (ME) and/or nutrient density (ND) of complete layer diets failed to improve egg output at hot temperatures to that obtained at cold temperatures.

3. At both temperatures self‐selection increased protein, but not ME, intake. This increased egg output and body weight gain at the hot, but not cold, temperatures. At the hot temperatures pullets fed by self‐selection were the only ones to gain weight between sexual maturity and 28 weeks of age.

4. Nutrient intake patterns, related to each pullet's physiological age of sexual maturity, identified distinctive changes in protein intake and the selected protein: ME intake ratio of pullets fed by self‐selection. Pullets attempted to maintain a preferred protein:ME intake ratio, irrespective of the markedly different intakes of ME and protein at the two temperatures.

5. Pullets trained to self‐select nutrients from separate energy‐ and protein‐rich foods are better able to sustain egg output and body weight at sexual maturity when food intake is limited by high ambient temperatures.