Response of laying hens to asymmetrical interrupted lighting regimens: physiological aspects

1. There were no significant differences in the mean time of oviposition, distribution of ovipositions over the 24 h or proportion of eggs laid in the modal 8 h when conventionally-lit hens were compared with hens which received interrupted lighting with the same apparent daylength. 2. Intermittently-lit hens performed 25% less feeding activity than conventionally-lit hens, but without a significant reduction in mean food intake. There were genetic differences in response of feeding rate to interrupted lighting. 3. Intermittently-illuminated hens consumed about 20% of their food during the scotoperiods which interrupted the apparent day of a 1.5L:0.5D:10(0.5L:0.5D):4L:8D regimen, although there was significant genetic variation from 10 to 22%. None of the genotypes ate during the 8-h night. 4. Across 4 genotypes neither crop weight nor rate of crop emptying was affected by the lighting treatments, although a heavier mean crop weight under interrupted lighting approached significance in one breed (P less than 0.10). 5. Interrupted lighting did not cause any ocular disorders.     

Effects of different lighting regimes on diurnal feeding patterns of the domestic fowl

1. Male hybrid chicks were, from hatching, subjected to either a 12‐h photoperiod with uniform light intensity or a 12‐h photoperiod with a simulated “dawn” and “dusk” or to continuous light.

2. At 10 weeks of age the birds exposed to “dawn” and “dusk” were significantly heavier than those exposed to 12 h uniform illumination and these were heavier than those in continuous light.

3. From 15 to 25 weeks of age the birds in continuous light showed a marked diurnal rhythm in food intake, eating most in the period corresponding to normal daytime, while all birds subjected to 12‐h photo‐periods ate most at the end of the day, apparently having learnt to anticipate when their day would end.

4. When the birds subjected to continuous light were given one of the two 12‐h photoperiods, those given 12 h of uniform light intensity started by eating most food in the mornings, but later ate more towards the end of the day, while those with the “dawn” and “dusk”, ate more food at the end of the day during most of the 20‐d experimental period.

5. It is concluded that the birds preferred to eat most at the end of the day, probably to ensure adequate stores of food in the crop during the night. However, it was necessary for them to learn when their day would end, and this they did much sooner with the presence of a “dusk” than without it.

6. It is suggested that the difference in growth rate among the three treatments can be accounted for by differences in the efficiency of food conversion and also by differences in food intake.     

Energy expenditure and physical activity in domestic fowl kept on standard and interrupted lighting patterns

1. The energy expenditure (H) and physical activity of laying hens were measured under lighting regimes of 14L:10D (standard), 2L:10D:2L:10D (interrupted) and (15 X (13 min L:47 min D]: 9D (fragmented). 2. Neither of the intermittent regimes produced a significant change in total daily energy expenditure, although large alterations occurred in the distribution of H between the lighting phases. The absence of change in total H resulted from the combined effects of greater H in the light in the intermittent regimes, greater H in darkness during the interrupted day than at night and slightly greater H at night in the intermittent regimes. 3. Physical activity count, like H, was redistributed over time but, unlike H, was also significantly reduced in total; changes in the energy cost of unit activity, however, were such that no reduction occurred in the total amount of H attributable to activity. 4. In the standard groups, 90% of total activity costs were incurred in the light; in the fragmented-day and interrupted-day groups, respectively, 7% and 55% of total activity costs were incurred in the light periods and 85% and 30% in daytime darkness. 5. In terms of both H and activity, there was clear differentiation between night darkness and subjective-day darkness. 6. Even when the energy cost of activity was excluded, significant differences remained between H at night, H in the light and H in daytime darkness.     

Noise output of hens subjected to interrupted lighting regimens

1. Noise output from domestic hens subjected to an interrupted lighting regimen began before dawn of the apparent day. 2. Noise output did not cease during the scotoperiod(s) which interrupted the apparent day. 3. Differential noise outputs during the 30 min. 4 h and 10 h scotoperiods of a 1L:7(30D:30L):4D:2L:10D regimen indicated that the hen's interpretation of darkness, even within the apparent day, was complex and probably dependent on several factors. 4. Noise output data suggested that the intense feeding behaviour at the end of the apparent day, effected by the interrupted lighting regimen, appeared to prevent the pre-dusk reduction in activity observed in conventionally lighted birds. 5. Noise output was negligible during the scotoperiod which the hen interpreted as night.     

Response of laying hens to asymmetrical interrupted lighting regimens: reproductive performance, body weight and carcase composition

1. The performance of brown egg laying hens was compared under conventional and asymmetrical interrupted-lighting conditions. 2. Egg numbers and mean weight were similar under the two conditions, provided the apparent day perceived by the hen was the same under both lighting treatments. 3. Daily food intakes of intermittently-illuminated hens were not significantly lower than those of conventionally-lit birds. However, the reductions were of the magnitude reported in the literature and observed under commercial conditions. 4. Shell quality was unaffected by interrupted lighting in the period up to 60 weeks of age in two of the 4 genotypes studied. All breeds had lower shell weights under interrupted lighting in the last three months of lay. 5. Intermittently-lit hens had lower body weights, which approached significance, and significantly less carcase fat. There were no differences in ash, protein (N x 6.25) or water contents of the carcases, or in fat content at a given body weight. 6. There were no significant differences in the production responses of the 4-brown-egg hybrids to interrupted lighting. 7. Diets with differing concentrations of energy and protein were included in both trials, but there was no evidence of interaction between these nutritional treatments and the lighting treatments.     

Magnesium metabolism in the laying fowl

Laying fowls were fed on synthetic diets containing 49, 118, 486, 655, 1242 and 2176 mg/kg magnesium. Magnesium intake and plasma concentration were significantly correlated: 49% of the plasma Mg was diffusible. The hens fed on magnesium‐deficient diets (49 to 118 mg/kg magnesium) were hypomagnesaemic while those receiving 2176 mg/kg were hypermagnesaemic. In the deficient hens the liver showed magnesium depletion, increased calcium content and decreased fresh weight. Skeletal muscle was unaffected by the dietary variations in Mg. The magnesium concentration in the femur was positively correlated with the plasma magnesium concentration. Femurs showed a loss of magnesium and increased mineralisation (especially of the medullary bone) in deficient hens, and a net gain of magnesium in the birds receiving 2176 mg/kg magnesium. The magnesium concentrations in egg shells, albumen and yolk were also positively correlated with the plasma magnesium concentration. The shells of eggs laid by magnesium‐deficient hens were thin, a reflection, apparently, of the reduced plasma calcium levels associated with the decreased bone mobilisation.     

Responses of sexually-maturing pullets to self-selection feeding under different temperature and lighting regimens

1. Pullets allowed to self-select nutrients from a protein concentrate and either a separate complete diet or cereal-based, energy-rich mixture showed preferences for protein and energy which varied in relation to the time of their onset of lay. 2. The selected protein:metabolisable energy (ME) intake ratio increased from 14 g protein per MJ of ME 2 to 3 weeks before sexual maturity to approximately 19 g protein per MJ of ME at and after sexual maturity. 3. This response to self-selection feeding was consistent with different temperatures, lighting patterns and dietary manipulations. 4. Egg mass output was improved by self-selection feeding at hot (25 degrees to 35 degrees C) temperatures in experiments 1 and 2 and at ambient temperatures in experiment 3. No beneficial response in egg mass from self-selection feeding was observed at cold (6 degrees to 16 degrees C) temperatures in experiment 1. 5. Providing 2 h of additional light during the dark (cool) part of the day, with or without 2 h of darkness in the middle of the extended light (hot) period, had no effect on the egg mass output of pullets at hot (25 degrees to 35 degrees C) temperatures.     

Effects of treadmill exercise on the transfer of plasma triglyceride into the ovary of the laying fowl

1. The effects of 90 min continuous treadmill exercise on the plasma-to-ovary transfer of 14C-labelled triglycerides in laying hens were examined. 2. Exercised birds showed a 4-fold increase in plasma free fatty acid concentration, a 15% decrease in plasma glucose concentration and unchanged plasma triglyceride concentration compared with resting controls. The mean plasma-to-ovary triglyceride transfer rate was approximately halved by exercise. 3. The surface area-specific triglyceride transfer rate was greatest for oocytes weighing 0.25-1.5 g and decreased with increasing oocyte size. The lowest rates were in the small (less than 0.25 g) white oocytes. This pattern was largely unaffected by exercise. 4. Factors that might be responsible for the reduction in triglyceride transfer into the oocytes during exercise include hormonal effects on the permeability of the oocyte envelope, increased competition for plasma lipids by the working muscles and reduced blood flow to the ovary, as a result of the release of vasoconstrictors.     

The effects of restricted feeding on adrenal cortical activity in the immature domestic fowl

1. The effect of reducing food intake to 75% of the ad libitum intake was determined from hatching to 8 weeks in young Light Sussex chickens.

2. Restricted birds were lighter throughout the experiment.

3. Relative adrenal weight tended to be greater in restricted birds but the difference decreased with time.

4. There was no depletion of adrenal cholesterol: from week 5 there was a significantly greater amount in the adrenals of restricted birds.

5. After 1 week of restriction plasma corticosterone concentration was 73% greater than in controls. It decreased progressively, falling within the normal range at 5 weeks.

6. Restricted birds were hypoglycaemic from weeks 2 to 7 and hyper‐lipacidaemic throughout. A negative correlation between plasma glucose and free fatty acids was found.     

Avulsion of the patellar ligament in osteopenic laying fowl

Metabolic bone disease in laying fowl has been associated with mortality and decreases in egg production. Recently there appears to have been an increasing incidence of the disease and the affected flocks have shown a variable response to dietary treatments. In 14 birds from eight recent submissions, avulsion of the patellar ligament together with part of its bony insertion was observed. Because the skeletons of the affected birds were judged from radiographs to be osteopenic, the lesions were probably pathological fractures. Histopathological studies of four birds revealed osteoporosis affecting cancellous bone trabeculae; in one bird, however, the medullary bone trabeculae were largely composed of unmineralized or poorly mineralised matrix, a finding which can be interpreted as osteomalacia.     

Effects of age, sex and housing on the trabecular bone of laying strain domestic fowl.

To determine the effects of age, sex and housing on trabecular bone volume, samples were collected from groups of male and female domestic fowl housed in cages or floor pens from four to 60 weeks old. Between 25 and 60 weeks old, trabecular bone volume decreased by 25 per cent in sections of free thoracic vertebrae (T5) from female birds, the loss occurring at an earlier age in caged birds. Over the sample period, TBV in male caged birds diminished by 35 percent, but male floor birds showed no reduction in trabecular bone volume. At 60 weeks, trabecular bone volume was 30 per cent greater in male caged birds and 40 per cent greater in male floor birds than in the corresponding females. In reproductively active females, no trabecular osteoid was observed, indicating no new trabecular bone formation. However, trabecular osteoid was present in two birds aged 60 weeks which had regressed ovaries. Osteomalacia was not seen in any of the bone samples.     

Allelomimetic feeding in the domestic fowl

Groups of 6 chickens were housed singly in battery cages with food available ad libitum and their feeding activity during 9‐h days was recorded. A significant tendency for the birds to feed as a group rather than as individuals extended over the entire day; it was ascribed to interaction between the birds rather than to external influences. Implications for animal welfare are discussed.     

Effects of experimental infection of fowl with EDS'76 virus,infectious bronchitis virus and/or fowl adenovirus on laying performance

Following BCI4 (EDS'76) virus infection of brown layer hens at 33 weeks of age, production of normally shelled eggs dropped from 87 per cent to 49 per cent within 3 weeks. The production of soft shelled and shell‐less eggs attained a maximum of 33 per cent 3 weeks after infection (p.i.). Shell quality recovered completely within 5 weeks p.i.

Egg production problems in White Leghorns infected with BCI4 virus were less severe and of shorter duration than in brown layers.

Both in brown layers and in White Leghorns total egg production, mean weight of normally shelled eggs, and internal egg quality were not affected following BCI 4 virus infection at 33 and 28 weeks of age, respectively. Besides shell abnormalities no clinical disease symptoms were observed. Vaccination with a commercial EDS'76 vaccine (Nobivac EDS'76^®) at 17 weeks of age had no adverse effects on laying performance and provoked adequate immunity against challenge at 33 weeks of age. The same observations were made following BCI4 virus infection at 17 weeks of age.

After infectious bronchitis virus (IBV) (H52 virus) infection of laying fowl the percentage of eggs with shell aberrations (rough, misshapen and/ or soft shells) increased to a maximum of 8 per cent, total egg production was depressed, mean egg weight was reduced I to 2 grams, and up to 10 Per cent of normally shelled eggs showed watery, not ropy thin albumen. This abnormally thin albumen was observed in a considerably higher proportion of eggs with shell defects than in normally shelled eggs. No turbidity of the thick albumen was observed and no symptoms of respiratory disease were noticed.

The severity and duration of adverse effects of IBV infection on laying performance depend very much on the stage of production in which the infection occurs. Following IBV infection at the onset of production a much severer drop in total production and in production of normally shelled eggs, a greater increase in the number of abnormally shelled eggs, and more lasting adverse effects on egg weight and internal egg quality were observed, in comparison with infection after peak production. Compared with single infections, a combined BC14 virus and IBV infection of brown layers at 33 weeks of age resulted in greatly potentiated adverse effects on total egg production, number of eggs with aberrant internal quality, and duration of production problems.

Following a combined BC14 virus and IBV infection, in a great proportion of eggs with shell defects and watery thin albumen, turbidity of the thick albumen was observed also, probably due to combined effects on the uterus of both IBV and BC14 virus.

BC14 virus infection did not reinforce the adverse influence of IBV infection on egg weight.

The same observations as described for the combined BC14 virus and IBV infection were made following BC14 virus infection of fowl previously infected with IBV.

It is concluded that changes of internal egg quality in field cases of EDS'76 are most likely due to subclinical IBV infections.

After infection of brown layers at 33 weeks of age with fowl adenovirus 66 (FA V 66) neither symptoms of clinical disease were observed nor effects on egg production, egg weight, and egg quality. Also, in a combined infection with FA V66, IBV, and BCI4 virus, no pathogenic significance could be attributed to the FAV.     

Lecithin--cholesterol--acyltransferase activity in the plasma of immature, oestrogenised and laying fowl (Gallus domesticus).

A study was made of the role of the lecithin-cholesterol-acyltransferase (LCAT) enzyme in the changes in the concentrations and fatty acid composition of the plasma cholesteryl esters of the fowl associated with oestrogen treatment and sexual maturity. Although there was a considerable increase in the concentration of free cholesterol in the plasma of oestrogen treated and laying birds, only in the oestrogen treated birds was it associated with an increased rate of cholesterol esterification. In both laying and oestrogen treated birds, changes in the fatty acid composition of the plasma cholesterol esters could be attributed to related changes in the fatty acid specificity of the LCAT enzyme. Evidence is provided to indicate that the cholesterol esters in the plasma of the fowl are synthesised mainly by the plasma LCAT system. The changes in the rates and fatty acid specificity of the LCAT system in the plasma of the fowl associated with sexual maturity or oestrogen treatment are discussed in relation to the extensive alterations shown to occur in the lipoprotein pattern of the plasma.     

Comparison of various anesthetic regimens in the domestic fowl

Three anesthetic agents (equithesin, metomidate, and ketamine) combined with diazepam were tested in the domestic fowl. Laparotomy and thoractomy were possible with the equithesin/diazepam combination, but only laparotomy was possible with the metomidate/diazepam combination. The combination of ketamine/diazepam did not result in the depth of anesthesia required for surgical procedures. Repeated blood pressure and heart rate measurements were recorded by use of a modified noninvasive Doppler technique. Equithesin/diazepam was our combination of choice for long-duration surgical anesthesia. The depth of anesthesia could be modulated by increasing the dose of diazepam. Metomidate/diazepam was useful when short-term anesthesia was required. In contrast to equithesin/diazepam, the metomidate/diazepam combination provided unstable anesthesia of varying depth and duration. Adverse reactions with metomidate indicated caution when using this drug in chickens; the drug also caused marked bradycardia. Ketamine/diazepam combination cannot be recommended as an anesthetic agent for use in chickens. The combination may be useful for minor surgical procedures or treatment, but not for experimental procedures that involve major surgery. Diazepam alone had a slight tranquilizing effect.     

Effects of feeding on the plasma disposition kinetics of the anthelmintic albendazole in laying hens

1. To optimise the use of albendazole (ABZ) as an anthelmintic in hens, the effects of fasting and type of diet on the plasma kinetics of ABZ and its metabolites were evaluated.

2. Twenty-four hens were distributed into 4 groups: In experiment I the Fed group were fed ad libitum, while the Fasted group was fasted over a 12-h period. In experiment II the Pelleted group was fed with pelleted commercial food, while the Grain group was fed with cereal grains. All the groups were treated with ABZ by oral route. Blood samples were taken and plasma analysed by HPLC.

3. ABZ and its metabolites albendazole-sulphoxide (ABZSO) and albendazole-sulphone (ABZSO₂) were recovered in plasma in all the groups. The 12-h fasting period did not modify the disposition kinetics of ABZ in hens. The type of feed affected ABZ kinetics. ABZSO concentration profile was higher and detected for longer in the Grain group compared to the Pelleted group. Statistical differences were not found for AUC_0-∞ values, whereas the T_1/2for and T_1/2el were different between groups.

4. Factors affecting ABZ kinetic behaviour should be taken into account to optimise its use to ensure the sustainability of the limited available anthelmintic therapeutic tools in avian parasite control.     

The effects of partial defeathering on energy metabolism in the laying fowl

1. The effects of a complete removal of feathers from the neck and/or breast on the energy metabolism of laying hens were measured by indirect calorimetry.

2. The daily heat production of fed birds was significantly increased if feathers were removed from the entire neck plus breast region but not if the neck only or breast only were denuded.

3. Removal of feathers from the neck plus breast led to a 10% increase in food consumption.

4. The partially‐defeathered birds laid more eggs.