Photorefractoriness in broiler breeders: sexual maturity and egg production evidence

1. Photorefractoriness was assessed in two lines of broiler breeders. In one trial, male-line and female-line pullets were reared on the floor and transferred to individual cages at 15 weeks. Birds were either maintained on 8-, 11- or 16-h photoperiods or transferred from 8- to 16-h photoperiods at 67 or 124 d. In the second trial, female-line pullets were concurrently housed in the same rearing facilities as trial 1 and transferred to adult floor-pens at 12 weeks. These birds were either maintained on 11- or 16-h photoperiods or transferred from 8- to 11-h or from 8- to 16-h photoperiods at 140 d. 2. In the cages, male-line and female-line birds responded similarly to the lighting treatments, but with the male-line maturing 1 to 2 weeks later than the female-line in each case. Birds on constant 11-h photoperiods matured 3 to 8 d earlier than constant 8-h birds, but 3 weeks earlier than constant 16-h birds. Birds photostimulated at 67 d matured at a similar time to constant 16-h birds, but almost 7 weeks later than those transferred from 8 to 16 h at 124 d. In the floor facilities, constant 11-h birds matured 3 weeks earlier than constant 16-h birds, but almost 2 weeks later than either of the photostimulated groups. Birds transferred from 8 to 16 h matured 4d earlier than those transferred from 8 to 11 h. 3. Caged birds maintained on 16 h or transferred from 8 to 16 h at 67 d laid at least 24 fewer eggs, and had more hens not laying at 58 weeks, than birds maintained on 11-h days or those transferred from 8 to 16 h at 124 d. In the floor-pens, constant 11-h and both photostimulated groups produced about 20 more eggs to 56 weeks of age than the constant 16-h controls. 4. Collectively, these findings indicate that conventionally managed broiler breeders exhibit photorefractoriness. Additionally, a combination of photorefractoriness and controlled feeding appears to prevent broiler breeders from being photoresponsive until at least 10 weeks of age, and to cause some individuals still to be photoperiodically non-responsive at 18 weeks.     

Effect of exogenous oestradiol and lighting regime on age at first egg in domestic pullets

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 (P<0.05). 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.     

Effect of constant and of changing photoperiod on plasma LH and FSH concentrations and age at first egg in layer strains of domestic pullets

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. FSH 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.     

Effects of body weight at, and lighting regimen and growth curve to, 20 weeks on laying performance in broiler breeders

1. A total of 4000 Ross broiler breeders were reared to a 20-week target body weight of 1.55, 2.16 (standard), 2.50 or 2.84 kg, using either a convex or concave growth curve. Each treatment group was either exposed to a conventional broiler breeder lighting regimen, with a series of weekly one-hour increments in photoperiod from 8h at 19 weeks to a 16-h maximum, or maintained from 4d on a 17-h photoperiod. 2. Each 100 g increment in body weight at 20 weeks was associated with a significant increase of 0.55 kg in cumulative food intake, and a 1.5-d advance in sexual maturity. However, leaner body weights at 20 weeks resulted in smaller body weight gains between 20 and 60 weeks (-2.4 g/d/kg body weight at 20 weeks), and an increased production of double-yolked eggs. Neither egg production nor mean egg weight was affected by 20-week body weight. 3. Birds fed to produce more rapid early growth had higher feed intakes to 20 weeks, but reached sexual maturity 7 d later than birds permitted accelerated growth from 15 weeks. Growth curve did not influence body weight gain in lay, egg production or mean egg weight. 4. Birds maintained on 17-h photoperiods reached sexual maturity 27 d later, produced 7 fewer eggs to 60 weeks, and had a mean egg weight 1.2 g heavier than birds photostimulated at 19 weeks. Lighting treatment did not affect food intake to 20 weeks, the proportion of double-yolked eggs or body weight gain between 20 and 60 weeks. 5. Birds fed to have a faster growth early in the rearing phase and maintained on 17-h photoperiods produced 11 fewer eggs than those fed to have accelerated growth at the end of the rearing phase, yet there was only one egg difference between the growth-curve groups for the conventionally lighted birds, which was not significant. 6. The earlier sexual maturity of the conventionally lighted birds compared with those maintained on 17-h photoperiods either indicates that broiler breeders require an increment in photoperiod to stimulate rapid gonadal development or that broiler breeders exhibit juvenile photorefractoriness that takes longer to be dissipated when birds are not given a period of short days. 7. The findings suggest that a nutritional stimulus late in rearing is only necessary for satisfactory egg production if birds have not received a concurrent increment in photoperiod.     

Various photoperiods and Biomittent lighting during rearing for broiler breeders subsequently transferred to open-sided housing at 20 weeks

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.     

Effect of temporary transfers to 14 h on age at first egg in domestic pullets reared on 8-h photoperiods

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.     

Effect of timing and size of photoperiod change on plasma FSH concentration and the correlation between FSH and age at first egg in pullets.

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).     

A comparison of the effects of feeding treatments and lighting on age at first egg and subsequent laying performance and carcase composition of broiler breeder hens

The effects of the growth curve from 15 to 20 weeks, age at photostimulation and pattern of photostimulus on sexual maturity, egg production and egg weight were evaluated in two trials with broiler breeder females to 56 and 34 weeks of age (housed in litter pens and individually caged, respectively). Carcase composition and reproductive morphology of hens varying in laying efficiency were measured in the second trial. Trial 1: Four growth curves were applied from 15 to 20 weeks to pullets housed in litter pens. Birds were transferred from 8- to 10-h photoperiods at 20 or 24 weeks of age, followed by weekly increments of one hour to reach a 16-h final photoperiod. Lower-than-recommended body weights at 20 weeks significantly delayed sexual maturity, reduced peak rate of lay, total eggs and mean egg weight. However, double-yolked egg production was lower, resulting in non-significant differences in settable egg numbers between body weight treatments. Birds reared to the heaviest body weight exhibited a significantly advanced sexual maturity, but total egg numbers, peak rate of lay and mean egg weight were not significantly affected. However, the laying of more double-yolked eggs resulted in a decrease in the number of settable eggs. Delaying photostimulation to 24 weeks significantly retarded sexual maturity, reduced total and settable egg numbers, and increased mean egg weight. A tendency for fewer double-yolked eggs was observed. Trial 2: At 19 weeks, birds were selected from the 4 body weight categories in Trial 1 and moved to individual cages in 8 rooms. Five lighting programmes were applied. The pattern of photostimulation applied did not affect any of the production traits measured. At 34 weeks, 24 birds were selected for the analysis of reproductive morphology, presence of internal or multiple ovulations, and carcase composition. Eight hens showing an early age at first egg and regular egg production records, 8 birds showing erratic laying performance and 8 non-layers were killed for this purpose. There were no differences in carcase composition or reproductive morphology between these groups. No internal ovulations or double or multiple ovarian hierarchies were observed. The results presented confirm that broiler breeders do not require a lighting stimulus in order to initiate ovarian activity and that, where no lighting stimulus is given, body weight or feeding level plays a critical role in stimulating the birds to attain sexual maturity. However, when a lighting stimulus is given, factors such as body weight and body composition become relatively less important in regulating the age at sexual maturity.     

Constant photoperiods and sexual maturity in broiler breeder pullets

1. Broiler breeder pullets were maintained on 10-, 11-, 12-, 13-, 14- or 16-h photoperiods to determine the effect of constant photoperiods on sexual development in broiler breeders. The birds were fed to achieve a 2100 g body weight at approximately 17 or 20 weeks to see if the photosexual response was modified by rate of growth. 2. In both body weight groups, pullets maintained on 10h were the first to reach sexual maturity (50 eggs/100 bird-d), and these and the 11-h pullets matured significantly earlier than any of the other photoperiod groups. Pullets maintained on 13 or 14 h matured latest, at about 3 weeks after the 10-h pullets, though both were only marginally later than the 12- or 16-h birds. These differences in maturation probably reflect the different rates at which photorefractoriness is dissipated in broiler breeders reared on photoperiods that vary in their degree of stimulatory competence. 3. There were no significant interactions among the photoperiods and the ages at 2100 g; faster-growing birds consistently matured about 10 d earlier than conventionally grown pullets.     

Broiler breeders do not respond positively to photoperiodic increments given during the laying period

1. Broiler breeders were given a 3-h increase in photoperiod to 11 h at 20 week and then a series of increases to reach 16 or 17 h either immediately after the initial increment or in 30-min, 1- or 2-h increments starting at various ages after peak rate of lay. Controls were maintained on 11 h from 20 weeks. Changes in plasma LH concentration (after 7 d) were measured in birds that had been transferred to 11 or 16 h at 20 weeks and given further increases in photoperiod at 41 or 61 weeks of age. 2. Birds that were transferred to 16- or 17-h photoperiods, irrespective of when and how the maximum photoperiod was reached, had inferior rates of lay between 52 and 60 weeks of age to birds maintained on 11 h from 20 weeks. However, the 11-h birds laid more eggs on the floor and produced a larger number of cracked and dirty eggs, resulting in similar numbers of settable eggs. 3. Although transferring birds from 11- to 16-h photoperiods at 41 weeks of age significantly increased plasma LH concentration, there was no effect on egg production during the ensuing 12 d. None of the other increases in photoperiod significantly increased plasma LH, whether given at 41 or 61 weeks. 4. It is concluded in broiler breeders, that increases in photoperiod applied during the laying period, from 11 or 16 h, have little or no effect on LH secretion, do not compensate for age-related declines in egg production, and adversely affect rate of lay.     

Model to predict age at sexual maturity in broiler breeders given a single increment in photoperiod

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.     

Changes in ovarian function of female turkeys photostimulated at 18, 24 or 30 weeks of age and fed ad libitum or restricted until point of lay.

1. Females from a medium body weight strain of turkeys were fed ad libitum or restricted to 0.6 of ad libitum-fed body weight at sexual maturity and were photostimulated at 18, 24 or 30 weeks of age. Ovarian follicular structure was assessed in 8 birds from both rearing treatments at photostimulation, after photostimulation for 6 or 12 weeks and at 55 weeks of age. 2. The patterns of small white follicles and of larger yellow follicles were similar in restricted and in ad libitum-fed turkeys for birds in lay at the same age, regardless of the time elapsed since photostimulation. 3. Among birds in lay the number of normal yellow follicles and the proportion of multiple yellow follicles declined with age. A relatively low proportion of restricted birds photostimulated at 18 and 24 weeks were in lay after 12 weeks of photostimulation. 4. For birds in lay the number of white follicles 1.4 to less than 1.8 mm in diameter increased and the number greater than 1.8 mm declined with age. There was a corresponding increase in the rates of atresia in follicles 1.8 to less than 5.0 mm in diameter.     

Effect of age and body weight at photostimulation on the sexual maturation of broiler breeder pullets transferred from 8L:16D to 16L:8D

1. In two trials, broiler breeders were grown to a mean body weight of 2.0 to 2.2 kg at 20 weeks on 8L:16D and transferred to 16L:8D at various ages between 69 and 175 d of age at mean body weights varying between 1.0 and 2.7 kg. Other groups were grown to have a mean 20-week body weight 0.87, 1.15, 1.25 or 1.37 of the normal birds and photostimulated simultaneously with the normal weight birds. Controls were held on 8L:16D in each weight group. In a third trial, broiler breeders were transferred from 8L:16D to 16L:8D at 45 (ad libitum fed), 75 or 90 d (mild feed control), when the mean body weight of each group had reached 2.1 kg. Controls weighing 2.0 kg at 20 weeks were held on 8L:16D or 16L:8D. 2. In trial 1, photostimulating normal weight birds at 69, 76, 83 or 97 d delayed maturity and widened the spread of individual maturities, whilst transferring to 16L:8D at 111 or 125 d advanced maturity. Increasing the mean 20-week body weight to 2.8 kg advanced maturity in birds transferred to 16L:8D at 97, 111 or 125 d. Birds photostimulated at 69, 76 and 83 d matured at a similar age to controls held on 8L:16D. 3. In trial 2, transferring normal weight birds to 16L:8D at 91, 112, 133, 147, 161 or 175 d advanced maturity. Reducing the 20-week mean body weight to 1.91 kg delayed maturity in birds photostimulated at 91 or 112 d, but advanced it in birds photostimulated at 112, 133, 147, 161 or 175 d. Sexual maturity was similar for birds with a 20-week mean body weight of 2.54 or 2.74 kg, with advances for all groups photostimulated between 91 and 175 d. 4. In trial 3, birds maintained on 16L:8D matured later than birds held on 8L:16D, but maturity was advanced when birds were transferred to 16L:8D at 45, 75 or 90 d at a common body weight of 2.1 kg.     

Effect of one or two pre-pubertal long days on age at first egg in domestic pullets

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.     

Illuminance and UV-A exposure during rearing affects egg production in broiler breeders transferred to open-sided adult housing

1. Broiler breeders were reared in light-proof accommodation on 8-h photoperiods at an illuminance of 10 (W10), 40 (W40) or 100 lux (W100) from warm-white fluorescent lamps, or 10 lux (UV10) from Arcadia bird lamps (white light plus UV-A emission). At 20 weeks, 200 birds from each group were transferred to open-sided housing and a 16-h mixture of natural and warm-white fluorescent light. 2. Mortality during rearing and body weight at 20 weeks were similar for all groups. 3. The W10 birds matured 2 d later, had inferior rates of lay over peak production and laid 9 fewer eggs to 60 weeks than the other groups. Mean egg weight, extra large egg production and mortality between 20 and 60 weeks were unaffected by lighting during the rearing period. The UV10 birds had a significantly better rate of lay between 52 and 60 weeks than any of the groups reared on white light. 4. The findings suggest that ultraviolet radiation does not directly affect hypothalamic activity, but that retinally received UV during the rearing period prolongs the laying cycle through a modification of the hormonal control of photorefractoriness.     

Normal sexual maturation and reproductive function in domestic hens following unilateral adrenalectomy

The ovulation-inducing properties of adrenal hormones and the anatomical juxtaposition of the left adrenal gland and the ovary suggest that a functional relationship exists between these two endocrine organs. To test this hypothesis, the effect of unilateral adrenalectomy on sexual maturation and reproductive function was examined in left and right adrenalectomized SCWL pullets. Between 9 and 13 weeks of age, 24 and 12 pullets were either left or right adrenalectomized, respectively; 12 birds were sham operated and 7 birds served as unoperated controls. Blood samples were obtained immediately before and after surgery, 48h after surgery and at 14, 19 and 23 weeks of age. All samples were analyzed for plasma corticosterone by radioimmunoassay. At 20 weeks of age all birds were weighed and the photoschedule was changed from 8L:16D to 16L:8D. During the first 52 days following photostimulation the age at first egg and the distribution of ovipositions within the 24h photoschedule were recorded.Mean plasma corticosterone levels of the unilaterally adrenalectomized hens were not significantly different (P > .05) from those of control birds 48h after surgery or at 14, 19 and 23 weeks of age. Unilateral adrenalectomy had no effect on body weight at 20 weeks, average age at first egg, or percent hen-day production. In addition, 95% of the eggs laid in the first 52 days after photostimulation were restricted to a 10 hour period of the day regardless of the surgical treatment. These observations indicate that the removal of either the left or the right adrenal gland does not affect plasma levels of corticosterone, sexual maturation, or the open period for LH release as evidenced by the times of oviposition and fail to support the hypothesis of a localized functional relationship between the left adrenal gland and the ovary.     

Changes in light intensity can influence age at sexual maturity in domestic pullets

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.     

Effects of photostimulation at 18, 24 and 30 weeks of age on the productivity of female turkeys fed ad libitum or restricted until point of lay.

1. Turkey females were fed ad libitum or restricted from 6 weeks of age to achieve mean body weights of 0.6 of ad libitum fed birds on photostimulation at 18, 24 or 30 weeks of age. Body weight, food intake, egg production and hatchability were recorded to 54 weeks of age. 2. Restricted turkeys were fed ad libitum after first egg or 36 weeks of age. Food intake after 30 weeks of age averaged 170 g/bird/d and was similar for all treatments. At 54 weeks of age, restricted turkeys photostimulated at 24 and 30 weeks were not as heavy as turkeys photostimulated at 18 weeks and ad libitum fed turkeys. 3. A large proportion of restricted turkeys photostimulated at 18 weeks of age did not commence lay until 30 to 40 weeks and a significant number of restricted birds photostimulated at 24 weeks had short laying cycles. Restricted birds photostimulated at 30 weeks came into lay and showed similar persistency of lay to ad libitum fed turkeys. 4. Ad libitum fed turkeys laid 115.0, 122.0 and 101.0 and restricted turkeys 92.4, 99.5 and 103.4 eggs when photostimulated at 18, 24 and 30 weeks, respectively. The number of non-settable eggs was lower in restricted compared with ad libitum fed turkeys and declined with age at photostimulation. 5. Egg size at the end of the experiment was similar for ad libitum fed turkeys and restricted birds photostimulated at 18 weeks but was 2.3 g lower for restricted birds photostimulated at 24 and 30 weeks of age. 6. Hatchability was higher, and the proportion of second quality poults was lower with eggs from restricted turkeys. The mean numbers of poults hatched were 59.9, 75.1 and 66.0 for ad libitum fed and 71.7, 65.7 and 79.4 for restricted turkeys photostimulated at 18, 24 and 30 weeks of age.     

Selection for early response to photostimulation in broiler breeders

1. To determine if selection for early response to photostimulation could be successful, 150 male broiler breeders were photostimulated at 8 weeks of age. The first 20 to produce a semen sample and have a reddened comb with an area > 10 cm2 were selected as responders (R) and 20 birds that did not show these signs of sexual development were chosen as non-responders (NR). Once sexually mature, 8 birds from each group that consistently produced a semen sample were mated with both egg-type hybrids and broiler breeder females to observe the response to 8-week photostimulation in the as-hatched offspring. 2. The AFE of the F1 females with NR or R paternity and egg-type hybrid layer maternity (F1L) were similar, but AFE was advanced in birds from R relative to NR paternity when they had broiler breeder maternity (F1B). 3. Date following a normal distribution of AFE were extracted from the overall data set. This group included offspring from both NR and R paternity, but AFE in F1L and F1B females with R paternity was advanced compared to those with NR paternity. 4. Mean testis weights, or age at most rapid testis growth predicted using parameters from Tyler and Gous (2009), of F1 males were not significantly different in birds with NR or R paternity. A strong correlation was found between predicted age at most rapid growth and AFE of full sibs and so it is likely that an advance in AFE in female offspring would also result in an advance in age of testis development of males. 5. There was no significant difference in 21-d body weight of F1B females of NR or R paternity, but the 21-d body weights of F1L females were higher from R than from NR sires, suggesting that although fertility and meat-type traits are often negatively correlated, there was no adverse effect of selection for responsiveness to early photostimulation and broiler growth rates to 21 d. 6. These findings showed that the response to early stimulation is heritable, and should be useful to the broiler breeder industry, where a reduction in photorefractoriness would improve egg production and fertility.     

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

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