Response to long‐term selection for egg production in laying hens

1. A White Leghorn line was selected for part‐record hen‐housed number of eggs from 1962 to 1990. Genetic changes were estimated as deviations from its unselected control line.

2. Over the first 10 generations with selection almost exclusively for number of eggs to the age of 273 d, all traits, except rate of mortality, showed significant changes. Regressions per year were: 273 d production, 3.07 eggs; 497 d production, 5.18 eggs; production from 274 to 497 d, 2.43 eggs; age at first egg, ‐2.33 d; mean weight of first 10 eggs, ‐0.82 g; body weight at 497 d, ‐19.02 g and rate of mortality, 0.19%.

3. Over the rest of the period increasing selection pressure for egg weight has been applied. This resulted in positive changes for this trait and no or small negative changes in egg number.

4. In general, heritabilities and genetic correlations did not change over the period of selection. The heritability of the main trait of selection, production to 273 d was 0.19 ± 0.04 and heritabilities of egg size traits about 0.50.

5. The genetic correlation between egg production to 273 d and mean weight of first 10 eggs was estimated as ‐0.37 ± 0.06 but from the observed response a realised genetic correlation of ‐0.97 was calculated.     

Effect of selected dietary antioxidants on fatty liver‐haemorrhagic syndrome in laying hens

1. Single comb White Leghorn hens of an inbred line highly susceptible to fatty liver haemorrhagic syndrome (FLHS) were fed supplemented dietary ascorbic acid (200 mg/kg), α‐tocopherol (75 mg/kg), or L‐cysteine (3 g/kg, and 6 g/kg) for 28 d in order to evaluate the potential therapeutic effect of these compounds against the disease.

2. Supplementation of ascorbic acid, α‐tocopherol, or a low level of L‐cysteine (3 g/kg) did not significantly affect any of the hepatic variables evaluated. Hepatic glutathione was not increased by the supplementation of dietary L‐cysteine.

3. L‐cysteine supplemented at a level of 6 g/kg decreased hepatic dry matter and fat contents without affecting the hepatic malondialdehyde or the liver haemorrhagic score.

4. Because one of the predisposing factors of FLHS is a high hepatic fat content it was concluded that dietary supplementation of L‐cysteine (6 g/kg) may be useful in the prevention of the disease.     

Disease outbreak in laying hens arising from the consumption of fumonisin‐contaminated food

1. During the last quarter of 1995 an unusual disease outbreak characterised by black sticky diarrhoea, severe reduction in food intake, egg production and body weight follow by lameness and death was observed in 2 layer farms in Andhra Pradesh. A total of 6700 hens of 64 weeks age and 3000 hens of 36 weeks age were affected.

2. Around 10% mortality and a 20% reduction in egg production was observed. Postmortem examinations showed pale yellow coloured livers with peripheral congestion, mild haemorrhage in the proventriculus and watery accumulations in the intestine.

3. The disease was traced to a new batch of food and its withdrawal improved the health status of the flocks.

4. Analysis of the diet indicated contamination with fumonisin B₁ up to 8–5 mg/kg and with aflatoxin B₁ up to 0.1 mg/kg.

5. Diarrhoea was induced in day old cockerels by feeding the suspect diet containing 8.5 mg/kg fumonisin Bi, and in laying hens by feeding a normal diet with fumonisin B₁ additions of 8 and 16 mg/kg.     

A comparison of three methods of food restriction of laying‐type pullets on growth and laying performance

1. Three methods of restricting the growth rate of pullets from 8 to 20 weeks of age were compared. They were: quantitative food restriction, a diet low in lysine and arginine and a low protein diet.

2. Food consumption up to 20 weeks of age was significantly reduced by all three treatments; mortality was increased and sexual maturity was delayed.

3. Greatest uniformity was observed amongst pullets fed on the low protein and the low lysine diets

4. By 70 weeks there were no significant differences in food conversion based on food consumed between 20 and 70 weeks of age, but based on consumption between 8 and 70 weeks the quantitatively restricted birds converted food most efficiently.

5. The most favourable method of restriction appeared to be the feeding of a low lysine or low protein diet, since rearing costs were low, and the performance of the pullets on these treatments was high.     

A diet formulated from by‐products and indigenous foodstuffs for laying hens

1. The performance of six commercial stocks of laying hens fed on a diet composed of home‐produced foodstuffs, not usually used for human consumption, was compared with that of birds fed on a conventional diet.

2. The experimental diet was calculated to be low in energy and methionine and high in fibre by conventional standards. Birds ate up to 12% more of this diet, but the calculated intakes of energy and methionine were less than those of the corresponding controls.

3. White stocks fed on the experimental diet produced seven eggs less per bird than controls while the production of brown stocks was essentially unaffected.

4. The gross efficiency of energy utilisation for egg production was better with the experimental diet.     

Growth and laying performance of light‐hybrid pullets subjected to quantitative food restriction

1. Three degrees of quantitative food restriction producing body weights 88, 76 or 64% of controls at 20 weeks and three times of starting restriction 3, 6 or 9 weeks of age were compared with ad libitum‐fed pullets in a factorial experiment with 1800 light‐hybrid hens. Restrictions were applied such that the target weights were produced irrespective of time of starting.

2. Food intake was least when restrictions were started at 3 weeks.

3. Sexual maturity was delayed in proportion to the severity of restriction and resulted in lower percentages of small eggs.

4. Egg numbers decreased as restriction increased.

5. Mortality in restricted groups during rearing and laying was higher.

6. Optimal restriction was apparently intermediate between treatments producing 88 or 76% of ad libitum‐fed body weight. Body weight was so excessively affected by the most severe restriction that total production was adversely affected.

7. Restriction from 3 weeks was more profitable than restriction from 6 or 9 weeks, resulting in lower food cost during rearing and higher total egg production.     

Phosphorus requirements of laying hens fed on wheat‐based diets

1. Three experiments were carried out to determine the phosphorus (P) requirements of laying hens aged 34 to 58 weeks (experiment 1), 59 to 70 weeks (experiment 2) and 22 to 50 weeks (experiment 3) given diets containing wheat, sorghum and soyabean meals as the main ingredients. Dietary total P (P_t) varied between 3.2 and 7.3 g/kg (experiment 1), 3.2 and 4.6 g/kg (experiment 2) and 3.0 and 6.6 g/kg (experiment 3). Hens were housed at either 18° or 30°C (experiments 1 and 2) and uncontrolled temperature (experiment 3), and in experiment 2 diets were fed without or with a phytase supplement of 500 units/g.

2. Dietary P_t had no significant effect on production measures in any experiment. Increases in dietary P_t adversely influenced egg shell quality although uterine calcium (Ca), ATPase and carbonic anhydrase activities were unaffected.

3. A 3‐d‐feeding trial in experiment 1 gave maximum P_t retentions of 228 mg/d at 18°C and 204 mg/d at 30°C. These were obtained with diets containing, respectively, 4.6 and 6.0 g P_t/kg.

4. Plasma inorganic P (P_i) increased consistently with increases in dietary P_t at all temperatures but plasma total Ca, and tibia Ca and P, were unaffected.

5. The inclusion of the phytase supplement in diets containing 3.2 and 4.6 g P_t/kg had an adverse effect on egg production at both temperatures in experiment 2.

6. A dietary P_t concentration of 3.2 g/kg, providing a calculated 1.2 g available P (P_av) /kg, with a dietary phytase activity of less than 200 units/kg, satisfied the P requirements of the hens used in these studies. However, the data from experiment 3 suggest that the P_t requirement of some flocks fed on wheat‐based diets may be lower than 3.2 g/kg.     

Effects of lauryl sulphate on egg‐shell quality in laying hens

1. The effect of feeding the detergent, sodium lauryl sulphate at concentrations up to 10 g/kg diet on egg‐shell quality was examined in laying hens at 24, 36 and 48 weeks of age.

2. Lauryl sulphate at 2.5 g/kg or more in the diet significantly increased shell breaking strength, shell thickness and shell weight at 24 and 36 weeks. In 48‐week‐old hens only shell breaking strength was increased significantly. Egg production and egg weight were not affected significantly by lauryl sulphate.

3. Lauryl sulphate might increase these measures of quality by increasing shell deposition and/or shell elasticity.     

Effects of plastic anti‐pecking devices on food intake and behaviour of laying hens fed on pellets or mash

1. This study investigated effects of plastic anti‐pecking devices on food intake and behaviour to assess their applicability in commercial layer flocks.

2. In experiment 1, 72 individually caged ISA Brown pullets were fitted at 16 weeks of age (point of lay) with either ‘ring’ or ‘bumper’ beak devices or no device (control), half being fed on pellets and half on mash. The devices were held in place by lugs inserted in the nares.

3. There was evidence of discomfort immediately after fitting the devices, but not thereafter. In the first week, the devices reduced food intake, and were removed from 7 (15%) birds that lost weight consistently. Between 16 and 21 weeks, however, there were no significant effects of beak treatment or food form on either total food intake or egg production with the 65 remaining birds.

4. Beak treatment did not affect feeding efficiency (food intake per minute of feeding). The only behaviour affected was pecking at birds in adjacent cages, which was reduced with the ring device.

5. At 21 weeks, the birds were placed together in groups of 4 to 6 in 12 pens, each group consisting of birds from one of the 6 original treatments, and their behaviour was observed in experiment 2 between 21 and 23 weeks.

6. The only effects of beak treatment on behaviour were that pecking at pen walls was increased with the ring device, while pulling and eating feathers from group mates was seen mainly with control birds fed on pellets. Two birds were cannibalised in a control group on pellets.

7. Devices came off 3 (7%) birds in experiment 1 and were replaced, and rings slipped over lower mandibles of 2 (5%) birds in experiment 2 and were corrected.

8. At 23 weeks, beak lengths were increased with ring and bumper treatments, and pecking damage scores were low with all treatments.

9. It is concluded that these devices are not applicable commercially, but further trials would be justified with new improved designs.     

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.     

Individual and combined effects of t‐2 toxin and das in laying hens

1. The individual and combined effects of T‐2 toxin and 4,15‐diacetoxyscirpenol (DAS) on laying hens were investigated in an experiment consisting of a 2 X 2 completely randomised factorial design with dietary concentrations of 0 and 2 mg/kg T‐2 toxin and 0 and 2 mg/kg DAS.

2. Individually, T‐2 toxin and DAS induced oral lesions in half of the hens and decreased significantly egg production and food intake.

3. The effects of T‐2 toxin and DAS were additive for reduced food consumption and incidence of oral lesions. However, a synergism for reduced egg production was observed during the last experimental period.

4. No effects on body weight were observed during this study. Mild changes in selected plasma enzymes activities and no change in liver malondialde‐hyde content were detected.

5. The combination of T‐2 toxin and DAS was more toxic than the single mycotoxins, for some parameters, and therefore, may pose a greater economic threat to the poultry industry than either of the toxins individually.     

Egg‐shell deposition and blood plasma inorganic phosphorus concentration in individual laying hens

1. The relationship between plasma inorganic phosphorus measured at the end of the dark period and the weight of the next egg shell produced was investigated in 30 Hisex Brown hens.

2. Hens received an adequate conventional layers’ diet and the lighting pattern was conventional (17 L:7 D). Observations were made early (31 to 40 weeks) and late (62 to 68 weeks of age) in the laying period.

3. Eggs were classified by position in the clutch sequence and significant negative correlations were found between shell weights of early eggs in the sequence and plasma phosphate at the end of the dark period.

4. No significant trends were found in plasma total calcium.

5. No significant differences were found in bone compositions of birds producing consistently more or less than average shell weight during the laying period.

6. The negative correlations between plasma phosphate and shell weight are consistent with the observations of Sauveur and Mongin (1983) and show that impairment of shell deposition is associated with skeletal mobilisation as indicated by increase in plasma phosphate. This is consistent with the observations on bone composition and indicates that selection for shell quality will tend to select birds which are not dependent on excessive skeletal mobilisation during shell formation.     

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.     

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.     

The egg‐laying response of the domestic hen to variation in dietary calcium

1. Eight diets (1 to 8) containing respectively 36.8, 30.9, 19.6, 9.7, 5.5, 1.9, 0.96 and 0.48 g of calcium/kg food were each fed for 11 weeks to 24 individually‐caged laying hens (Gallus domesticus) aged 24 weeks. After the experimental period, all birds were returned to a normal diet (34.9 g calcium/kg).

2. Food consumption and egg production decreased as dietary calcium decreased. Shell weight was unaffected on diets 1 and 2; on diet 3 there was slight reduction of shell weight and on diets 4 to 8 the reduction was marked. The proportion of calcium in the shell was affected particularly on diets 7 and 8, though those from diet 5 also showed a decreased shell calcium.

3. The values for calcium intake and calcium loss in the egg showed that, generally, birds restricted calcium loss to less than intake. Only on the very low concentrations of calcium (diets 6, 7 and 8) did output appear to exceed input.

4. The main mechanism for controlling calcium loss involves the regulation of the number of eggs produced, i.e. the number of ovulations. Alterations in shell quality are of less importance with respect to calcium balance, although shell strength was impaired on the more restrictive diets (5 to 8).     

Effects of tryptophan supplementation to a maize‐based diet on lipid metabolism in laying hens

1. Experiments were conducted with laying hens to determine the effects of supplementing 0, 1.0, 2.0 and 3.0 or 4.0 g trp/kg diet to a maize and soyabean meal‐based laying ration (basal tryptophan = 1.66 g/kg) on tissue lipid concentrations.

2. Plasma cholesterol, triglycerides and nonesterified fatty acids were increased by supplementing the diet with 1.0 g trp/kg diet and decreased with 3.0 or 4.0 g trp/kg diet. A significant quadratic effect of supplemental tryptophan was observed on plasma lipids in most cases. The observed effects diminished with time. No consistent changes were observed in plasma glucose concentrations.

3. Total liver lipids were reduced by supplemental tryptophan at all concentrations.     

Responses of the reproductive vascular system during the egg‐formation cycle of unanaesthetised laying hens

1. Vascular adjustments to the process of egg formation were examined in the unanaesthetised laying hen, by the radioactive microspheres method.

2. Three‐ to four‐fold increases in blood flow were found in segments surrounding the egg during its passage along the oviduct, possibly due to an enhanced metabolic activity in the muscle layer of the oviduct.

3. Shell‐gland blood flow was minimal in the absence of an egg and increased gradually to a maximum (5‐fold) about 5 h after entrance of the egg into the shell gland. This parallels the rate of calcification of the egg shell.

4. Changes in blood flow in the ovarian follicles and other parts of the oviduct were small while the egg was in the shell gland. This might be typical for the reproductive system of the fowl, which undergoes little structural alteration during egg formation.     

Ovarian morphology and rates of ovarian follicular development in laying broiler breeders and commercial egg‐producing hens

1. Ovaries from a light‐bodied egg laying strain and a broiler breeder strain were compared at 26 and 82 weeks of age.

2. The rate of lay in both strains was lower in the older hens. The 82‐week‐old hens were subdivided into good and poor layers: the poor layers produced eggs at about half the rate of the good layers.

3. The yellow‐yolky ovarian follicles in both strains were smaller, more numerous and more closely ranked in hierarchies in 26‐week‐old hens than in 82‐week‐old hens.

4. No marked differences were seen between the strains at 26 or 82 weeks of age in the sizes, numbers or hierarchical arrangements of yellow‐yolky ovarian follicles.

5. The ovaries from 82‐week‐old good and poor layers from both strains contained similar numbers of yellow‐yolky follicles.

6. After feeding a fat‐soluble dye, the number of days over which eggs containing dye were laid did not differ between 26‐, 52‐ and 113‐week‐old hens from an egg laying strain. However, fewer eggs with dyed yolks were laid by the older hens.

7. These observations suggest that the decrease in egg production with age is due initially to a reduction in the rate of recruitment of yellow‐yolky follicles. Towards the end of the laying year it may also be due to an increased incidence of follicular atresia, internal ovulation and the production of membraneous or soft shelled eggs.     

Battery gage shape: The laying performance of medium‐ and light‐body weight strains of hens

1. One thousand two hundred and ninety‐six medium‐ and 1296 lightweight hens were housed, four to a cage, in deep (conventional) cages, 405 mm wide by 460 mm deep, or shallow cages, 610 mm wide by 305 mm deep, between 18 and 70 weeks of age. The performance of the hens during different periods of the laying stage and over the full laying year was measured.

2. Egg number per medium‐weight hen housed in shallow cages was significantly higher than of hens housed in deep cages between 18 and 30 weeks and 31 and 42 weeks. Thereafter significant differences were not found. With the light‐weight hens the increase was significant only in the 18‐ to 30‐week period. Apart from the 19‐ to 30‐week period hens of both strains housed in shallow cages consumed significantly less food than those in deep cages, the reduction over the full year being about 4%. In all periods the hens housed in the shallow cages converted food more efficiently. Gage shape had no significant effect on mortality.

3. The incidence of hair‐cracked, cracked and broken eggs between 60 and 70 weeks of age from hens housed in shallow cages was lower than that from hens housed in the deep cages but only with the light‐weight hens did this difference reach significance. Shell thickness, shell weight and albumen quality of eggs laid by hens housed in the different shaped cages were not significantly different.