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 sex-linked dwarf genes in chickens from two sources when introgressed into unrelated genetic backgrounds

1. Sex-linked dwarfing genes from 2 broiler stock origins (EU and US) were each introgressed into 2 White Leghorn populations that had been divergently selected for antibody response to sheep erythrocytes. 2. When the resulting backcrossed populations were 87.5% of their respective White Leghorn line, non-dwarf pullets were assessed for body weights, shank lengths, immunoresponsiveness, age and body weight at sexual maturity, egg production, average egg weight, and duration of fertility. For measurements where there were no differences between non-dwarf pullets from the 2 origins of the dwarfing genes, then the dwarf pullets (which were full sisters to the non-dwarfs) were compared. 3. Shank length at 8 weeks of age and mature (24-week) body weights were higher for dwarf pullets from EU than US dwarf origin. Immune response and several egg production traits were higher for dwarf pullets from the high antibody backcross than from those of the low antibody backcross. 4. There were few differences in expression of the dwarfing genes from 2 origins in the unrelated backcross populations used in this study. Also each of the dwarfing genes, when introgressed into different genomic backgrounds, was not discernibly different in its expression in terms of antibody response or egg production characteristics.     

An assessment of the optimal range of dietary sodium for inducing a pause in laying.

Laying hens were fed on a diet containing 0-9 g sodium/kg until 34 weeks of age, then groups were fed on diets containing 0-2, 0-3,0-4, 0-5, 0-6 or 0-9 g sodium/kg for 16 weeks before that containing 0-9 g sodium/kg was reintroduced for all birds. 2. Egg production and food consumption were depressed by the low-sodium diets in proportion to the dietary sodium content. 3. Birds receiving 0-3 to 0-6 g sodium/kg diet lost weight initially but subsequently gained weight; birds receiving 0-2 sodium/kg diet lost weight continouosly. 4. In birds receiving 0-2 g sodium/kg diet, the reproductive organs were completely regressed, whereas these organs resembled those of point-of-lay pullets in birds fed on 0-3 or 0-4 g sodium/kg. 5. When the control diet was reintroduced, birds which had received the low-sodium diets resumed normal egg production and food consumption and regained body weight. 6. The optimal range of dietary sodium for inducing a pause in egg laying is 0-3 to 0-4 g/kg.     

Nutritional and environmental factors involved in egg shell quality of laying hens.

1. Two experiments were conducted to assess the effects of lighting regime, dietary calcium source and sodium bicarbonate on production variables and egg shell quality of White Leghorn hens. In both experiments, hens were assigned to one of three lighting programmes that provided evening, morning or intermittent (midnight) lighting supplements in addition to natural daylight. Experimental diets used in the first study were formulated to contain (1) ground oyster shell flour, (2) limestone flour, or (3) and (4) the same +2/3 of the calcium source as hen-size oyster shell grit. The same 4 diets plus those containing hen-size limestone or hen-size limestone and oyster shells were used in experiment II. Additionally, diets in the first experiment contained either 0 or 10 g/kg sodium bicarbonate. 2. Hen-day egg production and food consumption were not affected by any of the experimental treatments. Hens fed on oyster shell diets or exposed to intermittent lighting regimes laid eggs of the highest specific gravity. Shell quality, as measured by specific gravity, was not affected by the addition of dietary sodium bicarbonate. 3. As expected, elevated temperatures (greater than 32 degrees C) significantly reduced egg shell quality. However, this effect was variable particularly in experiment II which used younger hens. 4. The shell quality of eggs from hens exposed to intermittent lighting in experiment II was significantly higher in each of the 4 sampling periods: morning (08.00-12.00), afternoon (12.00-16.00), evening (16.00-20.00) and night (20.00-08.00). 5. It is suggested that midnight lighting programmes provide a means of supporting egg shell quality of older laying hens during the summer months without a significant reduction in egg production.     

Effects on health and blood plasma parameters of laying hens by pure nivalenol in the diet

The effects of trichothecene nivalenol (NIV) on the health and production of laying hens were determined in a feeding study. White Leghorn hens, 55 weeks old, were fed diets containing 0, 1, 3 and 5 mg NIV/kg during 50 days. Feed intake was reduced by NIV, but there were no effects on body weight, egg production and egg quality. Traces of unaltered NIV were found in liver and bile. Alkaline phosphatase in the blood plasma increased in the hens fed 0, 1 and 3 mg NIV/kg diet but decreased in the birds fed 5 mg NIV/kg feed. Total protein and glucose were slightly reduced in hens fed 5 mg NIV/kg diet. Pathological examination revealed that 40-75% of hens fed NIV (3 and 5 mg/kg) supplemented diet showed gizzard lesions, haemorrhages in the duodenum and swollen cloaca and oviducts with immature eggs while certain birds in the 1 mg NIV group showed light and fragile livers. NIV and the metabolite de-epoxy-NIV in faeces were found to constitute up to 10% of ingested NIV.     

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.     

Rearing photoperiod and abrupt versus gradual photostimulation for egg-type pullets

1. Lohmann White and Lohmann Brown egg-type hybrids were reared on 6-, 8-, 10- or 12-h photoperiods, transferred to 12.5 h at 18 weeks and then given weekly increments to reach 14 h at 21 weeks. In a second experiment, Lohmann White pullets from the same rearing facility were transferred abruptly to 14 h at 18 weeks. 2. Body weight gain and feed intake to 6 and 18 weeks were positively correlated with rearing photoperiod in both breeds. Mortality to 18 weeks was unaffected. 3. Whether the photoperiod was increased abruptly or in a series of increments, Lohmann White pullets reared on 6 or 8 h matured 4 to 6 d later than pullets reared on 10 or 12 h. Rearing day-length had little effect on sexual maturity in Lohmann Brown pullets. 4. In both genotypes and each experiment, egg numbers, egg weight and shell strength increased with rearing photoperiod. Feed intake in the laying period was not significantly affected by rearing day-length, but a meta-analysis of all data showed a significant, though small, increase in adult feed intake with rearing photoperiod. Despite Lohmann White birds reared on 6 and 8 h having lower body weights throughout the laying period, they had larger body weight gains between 18 and 70 weeks than those reared on 10 or 12 h. There were no clear effects of rearing photoperiod on albumen height or mortality. 5. The heavier eggs and stronger shells of the birds reared on the longer day-lengths were correlated with heavier body weights at 18 weeks, and the superior egg numbers and higher feed intake were associated with age at sexual maturity.     

Factors affecting direct and correlated responses in a White Leghorn population under long term selection for egg number

1. Data on 13,773 pullets, the progeny of 30 to 50 sires and about 135 to 220 dams per generation of a strain of White Leghorn under long term selection for part period egg production over 16 generations, were examined. 2. Realised genetic gain per generation was highly significant for egg production (2.55 eggs), egg weight (- 0.51 g), age at sexual maturity (- 2.30 d) and 40 week body weight (- 11.73 g). 3. The significant genetic response of 4.46 to 4.72 eggs per generation was realised in the first 8 generations only, which was accompanied by a marked decline in egg weight (- 1.67 and- 0.79 g per generation) and in age at sexual maturity (- 4.63 and- 6.39 d per generation). The 20 and 40 week body weights showed significant improvement in the last 4 generations. 4. Realised heritabilities were much lower in the last 8 than in the first 8 generation. 5. The additive genetic variance for most traits, except 20 week body weight and genetic covariances of egg production with egg weight and age at sexual maturity, declined significantly. 6. Natural selection did not seem to play any major role. No appreciable change in fitness traits was observed in the selected line. 7. The time trends were non-significant for all the traits in the control line, indicating its stability over generations.     

The effects of formic acid-treated shrimp meal on laying performance and egg quality in aged laying hens

An experiment was carried out to measure the suitability of using formic acid-treated shrimp meal (TSM) as a protein source for aged laying hens. Shrimp meal (SM), air-dried shrimp waste was treated with 3% formic acid (w/v) at room temperature for 20 min, sun-dried, ground to pass through 1.0 mm mesh screen and then ready to use as the TSM. A total of 56 Single Comb White Leghorn hens, 85 wk of age, were placed in individual cages and assigned randomly into 7 dietary groups of 8 birds each. A control diet, diets containing 5, 10, and 15% SM and diets containing 5, 10, and 15% TSM were prepared. Diets and water were given ad libitum during the 30-d experimental period. Hen-day egg production, egg mass, feed intake, and feed conversion ratio (FCR) were deteriorated with increasing levels of the SM in the diets (P < 0.05). In contrast, these parameters were unchanged with increasing levels of the TSM in diets and compatible with the control group. No significant improvements were observed in exterior or interior egg quality among the dietary groups, except for eggshell weight, strength and yolk color, which were significantly increased in SM and TSM groups when compared to the values in control group (P < 0.05). It is concluded that inclusion of TSM up to 15% in laying hen diets may have beneficial effects on laying performance along with improved eggshell quality and yolk color, and suggested that TSM is a promising combined source of protein and calcium in aged laying hens.     

Comparison between wheat, triticale, rye, soyabean oil and strain of laying bird on the production, and cholesterol and fatty acid contents of eggs.

1. The effects of feeding three types of cereal grain (wheat, triticale or rye) and soyabean oil (0 or 20 g/kg) over a 12-week period on the production, yolk cholesterol and yolk fatty acid concentrations of three strains of laying pullets were studied. 2. Pullets fed on wheat- or triticale-based diets had higher body weight gains, egg productions, egg weights, egg mass and lower yolk cholesterol concentrations than pullets fed on rye-based diets. However, there were no significant differences between the cereals in yolk cholesterol content. 3. There were no significant differences between the three cereals in total food consumption of pullets nor of yolk weight nor yolk concentration of palmitic, stearic and oleic acids. 4. Pullets fed on triticale-based diets had higher yolk linoleic acid concentrations and lower yolk oleic acid: linoleic acid ratios than pullets fed on rye- or wheat-based diets. 5. Soyabean oil supplementation increased egg production, egg mass, yolk linoleic concentration and yolk unsaturated to saturated fatty acid ratio, but reduced yolk oleic acid: linoleic acid ratio. 6. There were differences between strains of pullets in weight gain, food consumption, rate of lay, egg weight and yolk cholesterol, but not in yolk fatty acid concentrations. 7. It was concluded that wheat- or triticale-based diets gave good production of eggs of lower cholesterol content, that soyabean oil supplementation gave eggs with a high unsaturated to saturated fatty acid ratio and that two strains of layers produced eggs with lower yolk cholesterol concentrations than a third strain.     

The use of a methanol bacterial mass in multigenerational studies in the hen. 2. Laying period

In a multi-generation trial with 120 or 96 hens of the breed White Leghorn per group the effect of diets containing 7.5% or 15.0% of methanol-grown dried bacterial cells was examined. The hens were kept in conventional three-stage battery. In two of the three experiments the feed intake was decreased if it was used methanol-grown bacterial cells as a protein source. The period of intensive laying (50% egg production) started later and the egg production has been decreased by using the bacterial cells. For the traits egg weight and mortality no relation to the nutrition could be found. The feeding of methanol-grown bacterial cells showed in two incubatory trials no negative effects on reproductive ability of the hens. The cock's sperm quality was not influenced in two experiments. In one trial the sperm volume was reduced and the sperm concentration was raised if diets contained methanol-grown dried bacterial cells. Indications of toxic influences of the methanol-grown bacterial cells were not found.     

Effect of low-energy cereals and cereal by-products and of a vegetable fat supplement on egg production and food conversion in caged layers

The aim of this work was to ascertain the value of alterations in the energy concentration in layers' diets by the incorporation of high‐energy cereals and fat in diets composed of ingredients commonly used in the United Kingdom. Two similar experiments, employing 22 individually‐fed Light Sussex pullets on each diet, were carried out using cereal and cereal by‐products in four diets containing 1200, 1050, 1000 and 880 k cal. M.E./lb. Significant improvements in food conversion efficiency were found when low energy cereals were replaced by maize. Furthermore, the diet of lowest energy content led to a considerable reduction in the total energy intake of the pullets accompanied by a fall in production. There is evidence that the efficiency of utilisation of M.E. for egg production is not affected by the dietary level of M.E. over the range of energy concentration studied in these experiments.

In two further experiments four groups of 48 Brown Leghorn x Light Sussex pullets were fed diets containing three levels of vegetable fat as groundnut oil to give dietary concentrations of 1170, 1240, 1270 and 1340 k cal. M.E./lb.

The results show that fat addition had no significant effect on egg production or egg size.     

Quantitative review of the effects of environmental temperature on food intake, egg output and energy balance in laying pullets

1. Data from 30 published experiments have been analysed to examine the relationships between environmental temperature and the long-term, adapted responses of laying pullets, measured as metabolisable energy intake, egg output and body weight change. Heat production was also estimated indirectly from the other three variables. 2. The majority of experiments employed White Leghorns, but there were 8 large trials in which brown crossbred pullets had been compared directly with White Leghorns. These trials were used to estimate differences in energy intake and heat output between brown and white birds. 3. A total of over 26,000 birds was involved in the analysis. Individual trials varied in scale from 9 birds to 2,280 birds per treatment and in duration from 8 to 61 weeks. The constant temperatures investigated ranged from 10 degrees C to 34 degrees C, but there were no data for brown pullets beyond 30 degrees C. 4. The relationship between temperature and metabolisable energy intake is curvilinear, with food intake declining more steeply as ambient temperature approaches body temperature. Adapted heat production per bird is also a curvilinear function of temperature, tending towards a value of zero when extrapolated to the point at which ambient temperature equals normal body temperature. However no satisfactory data are available for fully adapted responses in the range 34 to 42 degrees C because egg production declines continuously when these temperatures are maintained for long periods. 5. When energy intake and heat output are expressed as functions of metabolic body size (kg 0.75) they can be represented as linear functions of temperature within the range 15 to 30 degrees C, but the slope must change outside this range. 6. It is calculated that the energy available for production is at a maximum at 23 degrees C for brown birds and at 24 degrees C for White Leghorns. Gross energetic efficiency is at a maximum at 30 degrees C, but egg output is reduced at this temperature. The optimum operating temperature for laying houses will depend upon the local cost of modifying ambient temperature and on the cost of supplying diets of appropriate protein content.     

The effects on rearing and subsequent laying performance of rearer diets containing two levels of protein and dried poultry manure or urea

1. Six hundred and seventy‐two light‐hybrid pullets aged 6 weeks were allocated to eight experimental treatments and cage‐reared to 18 weeks of age when they were transferred to single‐bird battery cages and fed on a common layer diet.

2. In the 6‐ to 12‐week period four dietary treatments were applied: a diet containing about 160 g crude protein (CP)/kg with or without 50 g dried poultry manure (DPM)/kg (diets 2 and 1 respectively) and a diet containing about 140 g CP/kg with or without 50 g DPM/kg (diets 4 and 3). In the 12‐ to 18‐week period two additional diets were fed: diets 1 and 3 supplemented with 10 g urea/kg (diets 5 and 6 respectively). Diets containing DPM were formulated to utilise the CP, energy, calcium and 50% of the phosphorus content of DPM.

3. Pullets fed on diets 1, 2 and 5 (high‐protein) were significantly heavier at 18 weeks than those fed on diets 3, 4 and 6 (low‐protein). In the laying period total estimated egg weight, food intake and conversion were significantly greater, and the age at first egg was significantly less (2.4 d).

4. Dietary DPM had no significant effect on the 18‐week body weight but food consumption was significantly less and conversion was significantly improved. There were no significant effects on subsequent laying performance. Dietary urea caused no significant effects on rearing or laying performance.     

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.     

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.     

Selection for heterosis from crossbred populations: estimation of the F1 heterosis and its mode of inheritance

The heterosis inheritance backcross evaluation technique (HI-BET) is proposed as a selection strategy for developing a pair of complementary strains from a crossbred population descended from a F1 population possessing considerable heterosis. These complementary strains are expected to produce a strain cross superior to the F1 population from which they were derived. In the first stage of an experimental evaluation of HI-BET, Australorp and White Leghorn hens were compared with their F1, F2 and F1 by parental breed backcross populations for a range of egg production traits. The substantial heterosis for survivors' egg production and total egg mass was largely lost in the F2 and backcross populations indicating that this heterosis was mainly due to parental epistasis. The uneven distribution of residual heterosis in the backcross populations suggests that about two-thirds of this parental epistasis was inherited from the White Leghorn line. As the Australorp line was substantially superior to the White Leghorn line for survivors' egg production and total egg mass, it most likely contained additive genes for both these traits that were not present in the White Leghorn line. It is suggested that HI-BET should be an effective strategy for incorporating these additive genes into the White Leghorn line, together with some brown egg shell genes if also desired, as a means of further improving the performance of the F1 cross.     

Heterosis for egg production in white leghorn Australorp crosses

1. Australorp and White Leghorn pullets were compared with their F_l, F₂ and F₃ crossbred offspring for a range of egg production variables.

2. The substantial hybrid vigour for efficiency of food conversion, hen‐housed egg production, hen‐day egg production and total egg mass of the F₁ crossbred populations was lost in the F₂ and F₃ crossbred populations.     

Effect of 1 alpha,25-dihydroxycholecalciferol on egg shell quality and egg production

1. The effect of replacing dietary cholecalciferol (D3) by 1 alpha,25-dihydroxycholecalciferol (1,25-(OH)2D3) on egg shell quality and egg production was tested on 32-week-old White Leghorn laying hens over 9 weeks. 2. Hens fed on a diet supplemented with 5 micrograms 1,25-(OH)2D3/kg diet, tended to lay more eggs, and the eggs had significantly higher specific gravity and percentage shell than eggs from control hens fed on a diet supplemented with 27.5 micrograms D3/kg diet. 3. The effect became apparent after about 4 weeks of treatment and persisted until the end of the test. 4. Hens fed on a diet without D3 supplement started to lay very thin or soft shelled eggs within 4 weeks, suggesting that the birds' reserves of D3 or its metabolites were depleted within this period. 5. The results suggest that 1,25-(OH)2D3 can be substituted for D3 in layer diets to improve egg shell quality.     

Evaluation of pearl millet and flaxseed effects on egg production and n-3 fatty acid content

1. A 6-week trial was conducted to evaluate the effects of pearl millet (PM) as a replacement for maize, in combination with flaxseed (FS), on productivity, egg trait parameters and egg n-3 fatty acid (FA) content in White Leghorn hens. 2. Six diet treatments were used: a control (CTL, maize-soybean meal based) diet, and diets containing 0, 2, 4, 8 or 12% FS, in which all maize was replaced by PM (PM-0, PM-2, PM-4, PM-8 and PM-12, respectively). All diets were isocaloric and isonitrogenous and met NRC (1994) requirements. Eight cage replicates per treatment were used (three hens per cage). At the end of each week, three eggs were randomly collected from each cage to measure egg trait parameters and yolks were separated, pooled and lyophilised for FA determination. Body weights and feed consumption were recorded weekly. Egg production (number of eggs and egg mass produced) was recorded daily. At the end of the experiment, all hens were killed to determine liver haemorrhage score. 3. Egg traits and flock performance parameters were not different among treatments except at week 4, when birds on the PM-12 diet produced smaller eggs than hens on the PM-0 and PM-2 diets. Yolk pigmentation scores were lower for the PM-0 and PM-2 diets (1.60 +/- 0.24 and 1.80 +/- 0.20, respectively), increased with higher inclusions of FS (2.75 +/- 0.47 for PM-12 diet) but did not reach control levels (6.00 +/- 0.01). Liver haemorrhage scores were not affected by dietary treatment. Hens given the PM-8 and PM-12 diets produced eggs with n-3 FA content higher than required to be considered as n-3 FA enriched eggs, and had a lower n-6/n-3 FA acid ratio than eggs of hens consuming CTL or the PM based diets with lower FS supplementation. 4. These results suggest that PM can be used to substitute for maize in the diets of layers and may reduce the amount of FS needed to obtain n-3 FA enriched eggs.