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This selection was originally to have been made by Professor Trevor Morris, but sadly Trevor passed away on 2 February 2009, and so I wish to dedicate this paper to him as an acknowledgement of the...

1. A total of 7960 Cobb and Ross broiler males were reared on various photoperiods or continuous illumination in two trials to 35 or 40 d. Tibial breaking strength was measured in both, and tibial ash content determined in the first of the two trials. 2. Tibial breaking strength was significantly affected by photoperiod, body weight, testicular weight, and genotype. Although peak bone strength occurred at about 7 h for Ross and at 12 h for Cobb, with reductions in strength for both shorter and longer photoperiods than these peaks, the removal of body weight effects showed that tibial breaking strength was negatively correlated with photoperiod per se. However, after removal of photoperiodic influences, breaking strength was positively correlated with both body weight and testicular weight. 3. Ross birds had greater tibial breaking strengths than Cobb, irrespective of whether the comparisons were made at the same photoperiod, the same body weight, or the same ash content. 4. Ash content increased according to the logarithm of photoperiod, but was unrelated to body weight. Tibial breaking strength increased with ash content. Ash contents were similar for Ross and Cobb birds. 5. Despite the significant differences in breaking strength and ash content, there were no broken bones or signs of leg abnormality in any of the 300 birds sampled. Tibial breaking strength data may therefore be of limited value in assessing the benefits of photoperiod to welfare in modern broilers.

Poultry, unlike humans, have a fourth retinal cone that allows them to see in the UVA part of ultraviolet radiation. This ocular function is principally used by poultry to modify various behavioural functions such as feeding, peer recognition, mate selection, mating activity, and social encounters. Retinally perceived UVA controls the release of melatonin in the pineal gland of dark-adapted birds. Ultraviolet radiation has shorter wavelengths than visible light, and, as a result, is unable to penetrate to the hypothalamus to induce a photosexual response; UV is thus minimally involved in avian reproductive function. UVA and UVB have anti-rachitic properties which catalyse the synthesis of vitamin D3 from 7-dehydroxycholesterol in the skin of feet and legs, a function that prevents rickets, minimises the incidence of tibial dyschondroplasia, and normalises growth and bone ash in young birds fed diets deficient in vitamin D3; surprisingly, there is sufficient UVA in white fluorescent light to produce these benefits. UVC from the sun is filtered out by the atmosphere's ozone layer, so does not occur in sunlight, but artificially produced UVC has germicidal properties and has been shown to protect domestic fowl from aerogenic viral infections, however, vaccination has made this property superfluous to the modern poultry industry. Recently, the introduction of lamps that emit both visible light and UV has made the provision of UVA to poultry a practical proposition, and so it is opportune that the responses of poultry to UV radiation are reviewed and its relevance to modern poultry production assessed.

1. Ross broiler breeders were reared at a nominal illuminance of 15, 20 or 45 lux and transferred to a nominal illuminance of 25, 55 or 70 lux at 20 weeks. 2. There were no significant interactions between the response to illuminance during rearing and in lay. This means that it matters not whether illuminance is increased, decreased or held constant on transfer to the laying house, provided it equals or exceeds the biological optimum for satisfactory egg production. 3. Whilst there were no significant effects of illuminance in either the rearing period or laying periods on egg numbers, peak rate of lay, terminal rate of lay, egg mass output or liveability, meta-analyses of these and other data indicated biological optima of 15 lux during rearing and 7 lux in the laying period. Birds reared at 45 lux had a lower mean egg weight (and earlier sexual maturity) than birds reared at 15 lux, and hens illuminated at 25 lux in the laying period laid more eggs on the floor than at either 55 or 70 lux. 4. Typical primary breeder recommendations of 10-20 lux during rearing and 30-60 lux in lay are appropriate for floor-housed birds; however, an illuminance of 7 lux could be used for caged birds, subject to welfare-code compliance.

1. Data from 9 experiments in which broiler breeder pullets had been photostimulated at two or more ages were integrated to produce a model to predict age at 50% egg production following a single increase in photoperiod during rearing. 2. It was clear that the photosexual response in broiler breeders was strongly influenced by the feed allowance and hence the rate of prepubertal growth. Regressions for birds given either a constant photoperiod or a single increase indicated that mean age at 50% lay advances by 2 d for every 100-g increase in body weight at 20 weeks. 3. The general response of broiler breeders was similar to that previously reported for egg-type pullets, but with important changes in the ages at which the birds progressed from one physiological state to the next, depending on body weight. 4. Broiler breeders, unlike modern egg-type pullets, exhibit juvenile photorefractoriness and, depending on their body weight, require up to 20 weeks to dissipate this (faster growth allows quicker dissipation). As a consequence, a group of birds grown to a typical weight of 2.1 kg at 20 weeks do not start to be photoresponsive until about 10 weeks and are not uniformly responsive until 19 or 20 weeks. A transfer to a stimulatory photoperiod before a bird has dissipated photorefractoriness causes a delay of about 3 weeks in its sexual development, and this results in a bimodal distribution of ages at maturity when a flock is photostimulated between 10 and 20 weeks. 5. Once photosensitive, the response of broiler breeders to an increment in photoperiod is between 0.50 and 0.65 of that observed in ISA Brown egg-type pullets. However, a flock of broiler breeders with typical feed restriction starts to mature spontaneously under the influence of the initial photoperiod from about 25 weeks. 6. There is a difference of only 1 to 3 d in age at 50% egg production between a flock transferred to 11 or 12 h followed by further increases to 15 or 16 h and one increased abruptly to one of these photoperiods, and so this model can be used to predict maturity in a commercial flock of birds even though they are likely to be given a stepped, rather than a single, increase in photoperiod.

1. Brown-egg pullets were reared on 8-h photoperiods and temporarily transferred at 80 d of age to 14-h photoperiods for 2, 4, 6, 8, 10 or 12 d. Controls were either maintained on 8 h or permanently transferred to 14 h at 80 d. 2. Pullets given 8 or 12 long days matured 8-9 d earlier than constant 8-h controls, but 22-23 d later than pullets transferred permanently to long days. Mean age at first egg for the groups given 2, 4, 6 or 10 d of 14-h days were not significantly different from the 8-h controls. The mean weight of first egg and body weight at first egg for the temporarily-photostimulated groups were not significantly different from constant 8-h controls, but egg weights were > or = 5.1 g and body weights at first egg > or = 200 g heavier than the birds transferred permanently to 14 h. 3. It is concluded that up to 6 temporary long days may be given (from 80 d of age) without affecting the timing of sexual maturity, but that the provision of 8 or more long days will accelerate sexual development, thought not to the extent of a permanent transfer, in most birds within a flock. A regression analysis of the ages at which the first and last birds in the groups given 6, 8, 10 or 12 long days matured suggested that about 20 d of photostimulation are required to achieve a mean age at first egg similar to that of birds permanently transferred to long days.

1. Cobb broiler breeders were fed to achieve typical body weight targets (2.1 kg at 20 weeks) on 6-, 8-, 10- or 16-h fully or intermittently illuminated (Biomittent) photoperiods in controlled-environment housing to 20 weeks, then moved to open-sided housing and 16-h photoperiods to 60 weeks. 2. At each photoperiod, birds given Biomittent lighting had heavier body weights up to 42 d, lighter body weights between 49 and 140 d, but similar body weights at sexual maturity. 3. Irrespective of lighting type, birds given 8-h photoperiods matured 3 to 4 d earlier than 6- or 10-h birds, but all matured=15 d before 16-h birds. 4. There were no significant differences between the 6-, 8- or 10-h groups for total eggs, mean egg weight or egg mass output, but all three produced=13 more, but =0.5 g smaller, eggs and =0.83 kg more egg mass to 60 weeks than 16-h birds. The proportion of abnormally large eggs was low (0.73/bird) and similar for all lighting groups. Egg production for a given period after sexual maturity was similar for all groups, and so differences among groups could be explained by the differences in age at sexual maturity.

1. A total of 240 Shaver White and 240 ISA Brown pullets that had been reared in multi-bird cages on a 10-h photoperiod, and maintained at a light intensity of 3 or 25 lux, or changed from 3 to 25 lux or from 25 to 3 lux at 9 or 16 weeks of age, were moved into individual-bird cages at 20 weeks and transferred to 15-h photoperiods at 25 lux. 2. In both breeds, birds transferred from 3 to 25 lux at 16 or 20 weeks laid significantly more eggs than birds maintained on the brighter intensity from one day or increased to it at 9 weeks. 3. Mean egg weight, shell deformation, albumen height, feed intake and body weight gain in lay were not significantly affected by the light intensity treatments during the rearing period. There was, however, a small, but significant, negative correlation of egg numbers with mean egg weight, although this only partially explained the difference in egg numbers. The differences in egg production were unrelated to rate of sexual maturation.

1. Shaver White and ISA Brown pullets were reared to 140 d in groups of 8 in cages on a 10-h photoperiod of incandescent light and maintained at an illuminance of 3 or 25 lux, or transferred from 3 to 25 lux or from 25 to 3 lux at 63 or 112 d of age. 2. There was no significant difference in sexual maturity, measured as eggs per 100 bird.d at 139 and 140 d, for ISA Brown maintained on 3 or 25 lux, but Shaver White pullets exposed to constant 3 lux matured significantly later than those maintained on 25 lux. 3. In Shaver Whites, sexual maturity was significantly delayed by an increase from 3 to 25 lux at 63 and 112 d, and advanced by a decrease from 25 to 3 lux at 112 d. Sexual maturity of ISA Browns was not significantly affected by a change in illuminance at 63 or 112 d, though responses were in the same direction as for Shaver Whites. 4. In both breeds, total feed consumed to 112 d was higher for birds on 3 lux than 25 lux, but lower between 112 d and 140 d when birds on 25 lux underwent rapid sexual development. In both breeds, body weight at 63 d was higher for birds exposed to 3 lux than 25 lux, but body weight gain thereafter was similar for the two light intensities. 5. In both breeds, plasma luteinising hormone (LH) concentration at 63 and 112 d was lower in birds maintained on 3 lux than 25 lux. At 63 and 112 d, transfers from 25 to 3 lux depressed, whereas transfers from 3 to 25 lux at 63 d, but not at 112 d, increased plasma LH. 6. Advances or delays in sexual maturity induced by changes in illuminance were not correlated with differences in feed intake, body weight gain, or with changes in plasma LH. 7. One possible explanation for the inverse relationship between the direction of change in illuminance at 63 and 112 d in pullets exposed to a 10-h photoperiod and the age at which they became sexually mature is that changes in light intensity and/or spectral composition affect the entrainment of the circadian rhythm of photoinducibility, to effect a phase shift in the photoinducible phase and/or the responsiveness of phototransduction pathways.

1. Groups of ISA Brown pullets were transferred from 8- to 16-h photoperiods at 34, 44 or 54 d. In each group, 12 birds were injected on alternate days over a 12-d period starting 6 d before the change in photoperiod with beta-oestradiol-3-benzoate (1 mg/kg body weight) or with arachis oil vehicle (controls). Short-day controls were similarly injected from 28 to 40 d. Long-day (16 h) controls were also included in the trial but were not injected. Age at first egg (AFE) was recorded and plasma luteinising hormone (LH) concentrations were measured around the time of oestradiol treatment. 2. Mean AFE for birds photostimulated at 34 d was not significantly different from short-day controls. Birds photostimulated at 44 and 54 d matured at similar ages but 3 weeks earlier than short-day controls (P0.05). 3. There was a tendency for oestradiol to advance AFE for birds photostimulated at 34 d (P=0.15) but to delay AFE following photostimulation at 44 d (P=0.23). Oestradiol significantly delayed AFE for the birds photostimulated at 54 d (P=0.01). 4. Plasma LH levels during 6 d of oestradiol injection but before transfer from 8- to 16-h photoperiods tended to fall between 28 and 34 d, were relatively constant between 38 and 44 d, but declined significantly between 48 and 54 d. Following photostimulation at 34 d, increases in plasma LH levels for oestradiol-injected birds were significantly greater than for controls. Oestradiol treatment had no significant effect on changes in plasma LH concentrations after photostimulation at 44 or 54 d. 5. This trial confirms previous work showing that pullets are unresponsive to photostimulation before 6 weeks of age. It also demonstrates that raising circulating oestrogen levels by injecting 0.5 mg/kg oestradiol benzoate on alternate days enhances the LH response to photostimulation at 34-d, but only very slightly sensitises a 34-d old bird to an increase in photoperiod which, 10 d later, is capable of advancing AFE in control birds by 24 d. Increased circulating oestrogen might be a factor which allows pullets to advance AFE in response to an increase in daylength.

Poultry have four types of cone in the retina of the eye, and this means that they probably see colour differently from trichromatic humans. Notwithstanding the fact that humans and birds have maxi...

1. Responses to ultraviolet (UV) radiation were studied in two trials. In one trial, sexually mature pullets, that had been maintained on an 8L:16D regimen from 2 d of age, were exposed sequentially, for periods of 9 to 12 d, to a further 8 h of very dim visible light (VDV), to 8 h of UV radiation and, finally, to an extra 8 h of normal light (conventional 16L:8D). Individual ovipositions were recorded during the last 48 h of each treatment. In the second trial, sexually mature pullets which had been allowed to 'free-run' for 14 d under continuous normal illumination (LL), were given, in addition to the normal light, a 12-h period of UV radiation commencing at midday or midnight for a further 15 d. During the final 48 h oviposition times were recorded and 4 food intakes for each 12-h period were determined. 2. In trial 1, mean oviposition time under VDV and UV supplementation was not significantly different from that under the 8L:16D regimen. Transfer to a 16L:8D regimen altered mean time of oviposition by about 4 h. In trial 2, eggs continued to be laid almost at random in all groups. 3. Food intake was suppressed during the 12-h period of UV supplementation compared with that when the birds were not receiving UV. 4. It is concluded that the addition of 8 h of UV radiation (at the intensity used in these studies) to 8 h of normal light does not cause a phase shift in the timing of the 'open-period' for pre-ovulatory luteinising hormone release which determines the time of oviposition. Furthermore, the insertion of 12-h periods of UV into continuous illumination does not entrain egg laying. 5. The suppressing effect of UV on food intake but lack of influence on the timing of the ovulatory cycle suggests that UV (at the intensity used in this study) acts principally at the retinal level and, as a result, stimulates only behavioural responses in laying birds.

Evidence from published trials is reviewed to investigate whether there is any need to change the recommended optimal light intensity for laying fowls from 5 lux. Although some recent trials have r...

1. ISA Brown pullets were transferred at 6, 9, 12, 15, 18 or 20.3 weeks of age from an 8 h photoperiod to an 8, 10, 13 or 16 h photoperiod. Plasma follicle stimulating hormone (FSH) concentration was measured at transfer at 7 and 14 d afterwards, and age at first egg (AFE) was recorded. 2. Plasma FSH concentration in pullets reared on constant 8 h photoperiods generally increased with age but with a trough at 12 weeks. Plasma FSH increased during the first 14 d of photostimulation to a significantly higher concentration, compared with constant 8 h controls, when the photoperiod was increased to 13 or 16 h at 9, 12 or 15 weeks; but for the increase from 8 h to 10 h photoperiods FSH was only significantly higher than controls when the change was made at 12 weeks. 3. The change in plasma FSH concentration 14 d after photostimulation was significantly correlated with mean AFE (reported in Lewis et al., 1997) and appears to be a better predictor of gonadal development than concurrent changes in plasma LH concentration previously reported (Lewis et al., 1994).

1. ISA Brown pullets were transferred from 8 to 14 h or from 14 to 8 h photoperiods at 35 or 56 d of age. Controls were maintained on constant 8 or 14 h photoperiods from day 1. 2. Blood samples were obtained immediately before each daylength change and subsequently at 7 d intervals until 1st egg in the treated groups and at 70 d of age and then at 14 d intervals until 1st egg in the constant photoperiod controls. Plasma luteinising hormone (LH) and follicle stimulating hormone (FSH) concentrations were determined using homologous radioimmunoassays. 3. Prior to 16 weeks, LH was consistently higher in birds on constant 14 h photoperiods than in those on constant 8 h, but was down-regulated as birds approached maturity so that LH concentrations in the 2 groups were similar during the final 10 d before the first egg was laid. FISH concentrations rose steadily with age but with a tendency for concentrations to be higher in the 8 h than in the 14 h treatment. Birds on constant 8 h daylengths matured 18.3 d later than those on constant 14 h photoperiods. 4. A 6 h increment in photoperiod given at 35 d or 56 d, resulted in an increase in LH within 7 d in both cases. FSH concentration did not respond to an increase in photoperiod at 35 d but rose following the same increase at 56 d. This was associated with a 3-week advance in sexual maturity, whilst age at 1st egg in birds photostimulated at 35 d was similar to the age with a constant 14 h photoperiod. 5. LH concentration fell when photoperiod was reduced from 14 to 8 h at either 35 or 56 d and remained below the constant 8 h controls for many weeks before rising to a concentration not significantly different from other groups in the final 10 d before 1st egg. FSH concentrations in birds exposed to a decreased daylength at 35 d, although more oscillatory, were similar to the constant 8 h photoperiod controls. In birds exposed to the same decrease at 56 d, FSH concentration initially tumbled but was similar in the 2 groups during the latter stages of rearing; neither differed significantly from the constant daylength controls during the 60 d before 1st egg. Sexual maturity in both groups given a reduction in photoperiod was delayed by about 2 weeks compared with constant 8 h controls. 6. Change in FSH concentration following an increase in daylength was a better predictor of age at 1st egg than change in LH. However, FSH concentrations after 14 weeks of age were rather similar in short day and long day controls and in the 2 groups given reductions in photoperiod at 35 d and 56 d, despite differences of nearly 5 weeks in mean age at 1st egg amongst these 4 treatments.

More energy efficient and longer lasting lamps are being used to replace incandescent lighting in poultry houses. This paper reviews the responses of domestic fowl, turkeys and geese to various sou...

1. ISA Brown and Shaver 288 pullets were changed from 8 h to 8, 10, 13 or 16 h photoperiods at 42, 63, 84, 105, 126 or 142 d of age. 2. Age at first egg (AFE) was curvilinearly affected by the size and timing of the change in photoperiod. AFE was advanced most by a photoperiod change from 8 to 13 h made at 63 or 84 d. ISA birds were generally more responsive than Shaver to the photoperiod changes. 3. Longer photoperiods significantly increased survivors' egg production, but decreased liveability to 504 d. so that eggs per hen housed were unaffected. Retarding AFE by 10 d reduced survivors' egg numbers by 7.0, but increased mean egg weight by 1.26 g. Egg output by Shaver birds was unaffected by AFE, but that of ISA was curvilinearly affected, with an apogee at an AFE of 135 d. In both breeds, egg weight and egg output were greater following an early or late, rather than a mid-term photostimulation. 4. Photoperiod significantly increased mean daily food intake during lay by 1.26 g/h. A 10 d retardation in AFE resulted in a reduction in food intake of 1 g/d. Efficiency of food conversion deteriorated according to the square of the photoperiod, and changed curvilinearly according to age at photostimulation. Food conversion efficiency improved by 0.05 g/g for each 10 d delay in AFE. 5. Shell quality was unaffected by AFE, but deteriorated with increasing photoperiod and was curvilinearly affected by age at photostimulation with the smallest shell weights associated with photostimulation at 63 d. The incidence of double-yolked (DY) egg production increased with photoperiod and decreased with delayed photostimulation. There was an exponential regression of DY eggs on AFE. 6. Body weight at first egg increased by 75 g/d delay in AFE, but body weight at 504 d of age was unaffected by AFE, photoperiod or age at photostimulation. Body weight gain during lay increased by 15 g/h increase in photoperiod, decreased by 6 g per 10 d delay in photostimulation and by 40 g per 10 d delay in AFE. Fat content at 504 d increased by about 10 g/kg and by 23 g/bird for each 10 d delay in AFE. 7. Mortality in lay increased by 0.8%/h increase in photoperiod, but was unaffected by either age at photostimulation or AFE.

1. Data for modern egg-type hybrids reared on constant daylengths show that, as expected, they mature more quickly than earlier genotypes. However, the constant photoperiod which gives earliest sexual maturity has not changed as a result of selection and is 10 h for both early and modern genotypes. 2. Further analysis showed that the rate of delay in sexual maturity for constant photoperiods above 10 h is similar for modern and for early hybrids (+0.29 d for each incremental one hour of photoperiod), the response of modern hybrids below 10 h (+4.22 d for each one-hour reduction in photoperiod) is more than double that of early hybrids (+1.71 d/h).

1. The effects of constant photoperiods and of single (5 h) changes in photoperiod applied at 12 or 17 weeks of age upon age at first egg (AFE) were studied using ISA Brown and Shaver 288 pullets. 2. Birds reared from 2 d of age until after maturity on constant 10 h photoperiods matured 8 d earlier than birds reared on constant 8 h and 5 d earlier than the average for 13 or 18 h photoperiods. 3. A single increment in photoperiod from 8 to 13 h advanced AFE by 23 d (compared to 8 h constant day controls) when applied at 84 d, but by only 6 d when given at 119 d. An increase in photoperiod from 13 to 18 h advanced AFE by only 4 d, averaged across breeds and age at increase. A reduction in photoperiod from 13 to 8 h delayed AFE by 22 d when given at 84 d and by 16 d at 119 d. A similar 5 h reduction in photoperiod, but from 18 to 13 h, retarded maturity by 11 d in ISA Brown pullets, but only when given at 84 d, and delayed AFE in Shaver 288 by 12 d, but only when given at 119 d. This interaction may be partly explained by the different physiological stages reached by the two breeds when the photoperiod was changed. 4. Under constant daylengths cumulative food intake before first egg was positively correlated with photoperiod, but the early AFE for birds on 10 h photoperiods resulted in this group having the lowest cumulative food intake to first egg. 5. A 5 h increase in photoperiod at 84 d significantly reduced the food consumed to first egg, but had no effect when given at 119 d. A 5 h decrease in photoperiod generally increased the food consumed to first egg, but the effect was only significant when the daylength was reduced from 13 to 8 h at 119 d. Food intake to first egg in birds subjected to a change in photoperiod was highly correlated with AFE. 6. The data confirm that sexual development in growing pullets responds more to changes in photoperiod than to the absolute daylength, that changes made at different daylengths are not equivalent and that sensitivity changes with age.

1. Data from intermittent and conventional lighting trials were analysed to investigate the effect of daily illumination upon mortality during the laying period and in 49‐d‐old broilers. 2. Iiveability in laying hens was improved by the use of intermittent lighting: the degree of improvement was proportional to the reduction in daily illumination achieved by the intermittent programme. 3. The reduction in mortality with intermittent lighting in laying hens was not the result of intermittent lighting per se. Intermittent regimens which did not reduce daily illumination did not reduce mortality. 4. Mortality in both conventionally‐lit laying hens and 49‐d old‐broiler chickens increased with photoperiod.

1. ISA Brown pullets were given an 8-h photoperiod and fed ad libitum to 63 d of age. At 63 d the photoperiod was either kept at 8 h or increased to 13 h, and the photostimulated birds were subjected to 1 of 3 feeding systems: ad libitum, 8 h daily access to food or a daily individual allocation of food equal to that given to the 8 h control group. 2. Mean age at first egg (AFE) of the groups given the photoperiod increase was on average 33 d earlier than that of the 8 h controls. Within the photostimulated groups, limiting daily feeding opportunity to 8 h delayed maturity by 4 d compared with ad libitum feeding. The mean AFE of the birds which were given allocated quantities of food was intermediate and not significantly different from either of the other groups. 3. Light was the principal factor which determined AFE, but moderate food restriction had a small modifying influence, consistent with earlier evidence. 4. The 3 groups given a 5-h increase in photoperiod consumed similar quantities of food to first egg, which was laid around 15 weeks of age. The 8 h control group ate a similar amount of food to this age, but needed more than 40% extra food to reach their first egg at 20 weeks.

1. Two trials were conducted, using 288 brown-egg hybrid pullets in each, to determine the effect on age at first egg (AFE) of exposure to one or two 'long days' during the rearing period. In the first trial, birds were given a single 'long day' of 10, 12 or 14 h at 75, 89 or 103 d of age, with controls maintained on 8-h photoperiods. All treatment groups were transferred to cages at 110 d, and half the birds from each treatment combination given a 6-h increment in photoperiod at 116 d, with the remainder held on 8-h photoperiods. In the other trial, birds were given one or two long days of 14 or 16 h at 96, 107, 117 or 128 d of age; controls were again held on 8-h photoperiods. All groups were moved to cages at 130 d but maintained on 8-h photoperiods. 2. AFE was not significantly affected by one or two pre-pubertal long days, irrespective of when the long day was given or its length. AFE was advanced by 2 to 3 weeks following a transfer from 8 to 14 h at 116 d, independently of whether or not the birds had received a previous long day exposure. 3. It appears that a full-fed egg-type hybrid requires more than two cycles of long days to initiate rapid gonadal development, and that exposure to a single long day during the rearing period will have minimal effect on the timing of sexual maturation and no influence on the response to a subsequent permanent transfer to long days.

A literature search was carried out for papers which described the intermittent lighting of laying hens and included information on mortality and behavioural responses. A review of 36 sets of morta...

1. Egg production records of 31 455 individually caged hens, 27 to 34 weeks of age and of 4 genotypes, were examined. 2. Sixty‐nine non‐layers were identified in the 30 to 40 week age group, and examined post mortem; an incidence of 2.1 per 1000. 3. Some of the 69 individuals had more than one abnormality. Forty‐two percent were internal layers, 34% had some form of neoplasia, 24% had an abnormal or diseased oviduct, 18% were sex reversals, 16% had a diseased ovary, 8% were of poor condition and considered culls, and 7% were in good condition, but with small, immature ovaries. 4. Of 54 birds not in lay at 27 weeks, 43 (80%) had come into lay by 34 weeks of age. 5. Genotype influenced the incidence of neoplasia and, in turn, the number of non‐layers.

1. A list of definitions is given for terms commonly used in animal photoperiodism. 2. A list of symbols and abbreviations commonly used in avian photoperiodism is included. 3. Methods are given for a standardised description of lighting regimens.

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.

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.

Lighting programmes recommended for broiler breeders are very similar to those advocated for laying hens. They usually involve the provision of an 8-h photoperiod during the rearing period, a trans...

SummaryA case of male pseudohermaphroditism (46XY) due to 17β-hydroxysteroid dehydrogenase deficiency in a 14-year-old child is reported. The patient, unambiguously brought up as a girl, had noted clitoromegaly 10 months before presentation, together with deepening of voice, facial acne and absence of breast development or menstruation. Inguinal testes were palpable. Serum androstenedione was greatly elevated, whereas testosterone and dihydrotestosterone were at the lower end of the normal adult male range; serum oestradiol, oestrone and gonadotrophins were elevated. Testicular biopsy showed pronounced hyperplasia of the Leydig cells and absence of spermatogenesis. Incubation of slices of testicular tissue with 17α-hydroxyprogesterone showed no significant conversion of androstenedione to testosterone, yet abundant androgen receptor activity was demonstrated

The body weight, carcase composition and component energy concentrations of laying hens were determined under 17L:7D and 2L:4D:8L:10D lighting regimens. 2. Hens subjected to 2L:4D:8L:10D lighting had lower body weights at end of lay and during most of the laying year, than the 17L:7D control birds. 3. Intermittently illuminated hens had similar absolute water, crude protein and ash contents to, but more water on a proportional basis than, controls. 4. Hens subjected to the 2L:4D:8L:10D lighting regimen had significantly less fat, in both absolute and proportional terms, than the controls. 5. There were no significant differences between the energy concentrations of the fat or fat‐free components of the two lighting groups. 6. There was no significant difference in the regression of fat content on body weight at end of lay for the intermittently and conventionally‐illuminated birds. 7. A prediction of the difference in daily energy requirement, based on egg output, body weight and mean daily body ...

Measurements of 30,140 eggs clearly indicated the average weight of the second quality removed at the packing station was significantly higher than that of the first quality. Subsequent grading of ...