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).     

A comparison of the effects of two low‐calcium diets on egg production in the domestic fowl

1. Hens fed on a diet containing 0–05% calcium virtually ceased egg laying (production <4%) whereas those fed on a diet containing 0–5% Ca maintained production at between 20 and 30%.

2. After a return to a normal diet (3% Ca) egg weight, shell weight, ovarian characteristics and oviduct size were of a similar nature in the two groups, though the differences in egg weight, shell weight and shell calcium were significant at the 1 % level.

3. Bone weight and bone ash did not differ significantly between the groups but after a return to normal rations, bone weight and bone ash became higher in the group that had received the 0.05% Ca diet.

4. There were no clinical signs of bone demineralisation during the experiments.     

The effect of reserpine on plasma LH concentrations in intact and Gona‐dectomised domestic fowl

1. Reserpine was found to inhibit the secretion of luteinising hormone when injected into intact and gonadectomised fowl at a dose rate which caused heavy sedation.

2. This could indicate that reserpine or its derivatives should not be used for breeding poultry.     

Ultrastructural changes of osteoclasts on hen medullary bone during the egg‐laying cycle

1. The ultrastructure of osteoclasts on hen medullary bone during the egg‐laying cycle was observed by electron microscopy.

2. At 0 to 6 h after oviposition, osteoclasts lacking ruffled borders were attached to the bone via the clear zone and appeared to have ceased bone resorption. Small vacuoles were scattered throughout this cytoplasm.

3. At 9 to 21 h after oviposition, most of the osteoclasts had ruffled borders and appeared to be resorbing bone. The ruffled borders at 15 h were well developed, whereas at 9, 18 and 21 h they were poorly developed or showed similarities in structure to the clear zone. The small vacuoles were concentrated under the ruffled borders at 9 h and then decreased.

4. These results demonstrate cyclic changes in osteoclasts during the egg‐laying cycle, indicate that ruffled borders form at the beginning of bone resorption and suggest that they are derived from the clear zone and the small vacuoles. The results also indicate that the ruffled borders fuse into the clear zone and disappear at the completion of bone resorption.     

Faecal measurements of oestradiol and testosterone allow the non‐invasive estimation of plasma steroid concentrations in the domestic fowl

1. Radioimmunoassays were validated for oestradiol and testosterone in faecal and plasma samples from domestic fowls. Faecal samples were prepared in phosphate buffer. A delay of up to 24 h between defaecation and the freezing of a dropping did not affect faecal steroid concentrations.

2. Differences in plasma concentrations of testosterone and oestradiol between cockerels and hens were clearly reflected in faecal hormone concentrations. Faecal concentrations of oestradiol were low in males and did not overlap with much higher concentrations in females, whereas there was some overlap between the sexes in faecal concentrations of testosterone.

3. The correlation coefficients (r²) between plasma and faecal steroid concentrations were 0.464 for testosterone and 0.852 for oestradiol (log‐transformed data). The coefficients did not increase when the mean hormone concentrations for several droppings produced by each bird during a collection period were used.

4. Faecal steroid concentrations can be used as a measure of plasma steroid concentrations and hence of gonadal activity in chickens. The resolution of the faecal steroid method is less than if plasma measurements were used, but it offers a practical alternative to blood sampling that is non‐invasive and does not require birds to be handled.     

The structure of the ileo‐caeco‐golic junction of the domestic fowl (Gallus Gallus L.)

1. The structure of the ileo‐caeco‐colic junction of domestic fowl aged from 3 to 12 weeks was investigated by histological techniques and the preparation of latex casts of the lumina.

2. The caeca open ventro‐laterally from the cranial end of the colon. At this level a muscular ring of tissue, formed from the circular muscle of the lamina muscularis of the ileum, projects into the colon lateral to the caecal openings. The location of this muscular ring is discussed in relation to the possible mechanisms of caecal filling.

3. The longitudinal muscle of the lamina muscularis of the caudal region of each caecum is continuous with that of the colon and ileum. The circular muscle of the lamina muscularis of each caecum begins in the muscularis mucosa of the colon at a distance of 1 to 2 mm from the caecal openings. At the level of the caecal openings the musculature is complex, consisting of parts of the lamina muscularis of the colon, caeca and ileum.

4. The openings of the caeca from the colon are narrow and filled with villi. It is suggested that the junction may be involved in filtering material during the filling of the caeca.     

Pencilled and double‐laced plumage pattern phenotypes in the domestic fowl

1. An investigation was conducted among the progeny from crosses between Partridge Wyandotte and Indian Game bantams into the relationship between two plumage pattern phenotypes, pencilling and double lacing.

2. The F₂ generation consisted of 5 phenotypes, three of which could be attributed to the effect of Pg in the absence of Ml. The other two phenotypes were double lacing and an intermediary between double lacing and pencilling, with presumed genotypes Ml/Ml and Ml/ml+ respectively, indicating that Pg and Lg are one and the same gene for which I retain the symbol Pg.

3. The action of Ml when homozygous is therefore to both add an outer lace and increase the width of the inner rings of eumelanin, so changing pencilling into double lacing.     

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.     

Laced and double‐laced plumage pattern phenotypes of the domestic fowl

1. An investigation was conducted among the progeny from crosses between Gold‐Laced Wyandotte and Silver‐Pencilled Wyandotte bantams into the relationship between two plumage pattern pheno‐types, lacing and double‐lacing, both of which are arrangements of eumelanin expressed on a background of phaeomelanic pigmentation.

2. The double‐laced phenotype had been presumed to be caused by the addition to the laced genotype of the gene Pg which causes pencilling. The error of this presumption was demonstrated by the appearance of double‐laced bantams in the F₂ generation of a mating specifically designed to avoid the addition of Pg to the laced genotype.

3. Examination of the F₂ generation demonstrated that the elimination of the eumelanin restrictor gene Co from laced fowl permits the double‐laced phenotype to be manifest.     

The effect of delaying the onset of laying in pullets with a low‐calcium diet on subsequent egg production

1. A low‐calcium diet (0.5 g calcium/kg) was used to prevent the onset of laying in young pullets.

2. It was fed at 16 weeks of age to five separate groups (groups 2 to 6) each of 50 to 60 birds.

3. Group 2 was fed on a normal layers’ diet at 23 weeks of age, group 3 at 27 weeks, group 4 at 31 weeks, group 5 at 35 weeks and group 6 at 55 weeks while the control group (group 1) of similar size to groups 2 to 6 was subjected to a normal commercial treatment for laying stock.

4. In all the experimental groups the onset of sexual maturity occurred normally, but only one or two eggs were laid before laying ceased under the influence of the treatment.

5. Laying re‐started when the hens were fed on a normal diet and production rapidly rose to a high level.

6. Groups 1, 2 and 3 differed little in the total number of eggs produced up to 72 weeks of age.

7. In all experimental groups there were fewer very small, small and medium eggs than in the control group.

8. It is suggested that the use of a low‐calcium diet before the onset of lay may have advantages which could be exploited on a commercial scale.     

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.     

The use of the plasma chemistry unit as an aid to the scanning electron microscope study of avian egg‐shell structure

1. In order to study the mammillary layer of the avian egg shell by scanning electron microscopy, it is necessary to separate the outer shell membrane from the calcified shell.

2. Chemical methods of effecting membrane removal are difficult to standardise due to variations in the strength of the membrane‐shell bond.

3. The use of reactive gas plasma provides an alternative, more efficient method for removing membranes without the risk of damage to underlying crystalline structures.     

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

Summary

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

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

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.     

Manipulations of germ‐cell populations in the gonad of the fowl

1. Embryos of the domestic fowl have been partially sterilised by injecting the drug busulphan into 24‐h incubated eggs.

2. Some of these embryos were injected with primordial germ cells (PGCs) after 55 h of incubation to attempt to repopulate the gonads.

3. Primordial germ cells transfected with a defective retrovirus containing the reporter gene lac Z were shown to settle in these sterilised gonads.

4. Quantitative histology of 6‐d embryos showed that busulphan produced 75% sterilisation but that PGCs could repopulate these gonads.

5. The technique of producing such germ line chimaeras is of value in studying cell kinetics, gonad differentiation and the production of transgenics.     

Chocolate: A sex‐linked recessive plumage colour mutant of the domestic fowl

1. A mating between Black Orpington bantams produced, in addition to blacks, a single female in which the black colouration was replaced by dark chocolate.

2. A mating of the chocolate‐coloured female with a black male, F₂ and backcross matings demonstrated that the chocolate phenotype is caused by a recessive sex‐linked gene to which I assign the symbol ?CHOC.

3. A mating of ‘chocolates’ inter se yielded all chocolate offspring.     

A note on changes in egg‐shell porosity with flock age and season during the first breeding cycle of domestic ducks

1. — Changes in egg weight and egg‐shell porosity with flock age and season are presented for domestic duck flocks in their first laying cycle.

2. — The first eggs laid are of low weight and shell porosity but generally by the fifth week of lay both characteristics have increased to the values found in the mature flock.

3. —For mature flocks porosity decreases in the summer and the consequences of this are considered in relation to the observed decrease in hatch‐ability at this time.     

The influence of the cuticle on egg‐shell strength

1. Sixty sound eggs, assumed to have shell cuticle, were paired according to egg‐shell deformation value.

2. Egg weight and shell quality characteristics were recorded for the eggs and the cuticle was then removed from one egg of each pair.

3. Egg weight and shell quality were re‐assessed for the eggs from which the cuticle had been removed.

4. The cuticle made a significant (P<0.01) contribution to shell thickness and removal of it appeared to reduce shell strength when measured directly, but the method of measurement was too variable to establish this with statistical significance.     

The microstructure of the cuticle‐less shell of the eggs of the domestic hen

1. Open pores were a notable feature of the shell of hens' eggs which were naturally devoid of cuticle.

2. In contrast with normal eggs, the surface of the cuticle‐less shell was irregularly contoured and, in many instances, deeply fissured.     

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.