Biomedical subjects

T R Morris

Publications and source records attributed to T R Morris.

At least 19 recordsLinked to original sources

PubMed2001

The influence of pelleted feed on the response of growing pullets to photoperiods of less than ten hours.

1. An experiment was designed to test the hypothesis that delayed sexual maturity in pullets reared on very short (4 h) constant photoperiods might be partly attributable to limitation of food intake and that offering a pelleted feed might circumvent this effect. 2. The factors investigated were 2 strains (Amber Link and Hyline Brown), 3 photoperiods (4, 7 and 10 h) and 2 forms of food (mash throughout rearing or crumbs from 0 to 4 weeks followed by pellets). All 12 combinations of these factors were tested with 14 replications of 18 pullet chicks allocated to each combination. 3. Mean ages at first egg for 4, 7 and 10 h rearing photoperiods were 189, 184 and 162 d respectively. Pullets given the pelleted diet ate 2% less food to 20 weeks but were 6% heavier at that age. However, the pellet-fed birds were 6 d later in mean age at 50% lay. There was no interaction between form of food and photoperiod in the data for age at first egg. 4. It is concluded that constant short photoperiods during rearing cause delayed sexual maturity entirely due to the effect of light on gonadal development and that limitation of food intake is not a factor in this response.

Animal Feed↗

PubMed2001

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.

Age Factors↗

PubMed2001

Supplementary dim light differentially influences sexual maturity, oviposition time, and melatonin rhythms in pullets.

The addition of two 3-h periods of very dim light, one before and one after a normal 8-h photoperiod, advances sexual maturity in pullets by about a week. This trial tested the hypothesis that dim light given before a short day of normal intensity is linked to form a more stimulatory day length and that dim light given after it is photosexually ignored. Pullets were reared from 2 d of age on 8-h photoperiods. From 10 wk, they were continued on 8-h photoperiods, transferred to 16 h, or given an 8-h period of dim light (0.09 lx) immediately before or after the main 8-h photoperiod. The bright/dim and dim/ bright groups matured at the same age, thus disproving the hypothesis tested. Both groups matured 1 wk earlier than the 8-h controls but 5 wk later than birds transferred to 16-h photoperiod. Oviposition time was similar for 8-h controls and bright/dim hens and delayed by 3 h for 16-h birds, but phase advanced by 2.4 h for dim/bright hens. Plasma melatonin rhythm was phase-advanced by about 5 h in the dim/bright hens and retarded by about 5 h in the bright/dim hens, suggesting a 13-h subjective day. However, these treatments were not regarded as fully stimulatory, as a transfer to a normal 13-h photoperiod at this age advances maturity by 5 to 6 wk. These findings show that the addition of a period of dim light to a normal nonstimulatory photoperiod differentially affects the clocks that control sexual maturation, plasma melatonin concentration, and oviposition time.

Aging↗

PubMed2000

Ultraviolet radiation and laying pullets.

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.

Animals↗

PubMed2000

Effect of age of release from light or food restriction on age at sexual maturity and egg production of laying pullets.

1. Lohmann Brown pullets, in one trial, and Hyline Brown pullets in another, were reared from day 2 on short daylengths, and from week 8 in trial 1 (week 16 in trial 2) on food restriction. These restrictions were lifted at various times during the rearing period as a means of determining the relative importance of the day length and food restriction stimuli on the attainment of sexual maturity and subsequent laying performance. 2. A total of 2304 pullets were used in each trial. The birds were reared in light proof rooms, and subjected to 8L:16D until they were moved to a laying facility where a light stimulus of 16L:8D was applied. In trial 1 the six ages at which light stimulation was applied were 115, 122, 129, 136, 143 and 171 d. Within each light treatment, food restriction of pullets, which consisted of feeding 72 g of food/bird d, was lifted at six different ages, namely, 115, 129, 143, 157, 171 and 185 d. In trial 2 both the light stimulation and the lifting of food restriction occured at 111, 125, 139, 153, 167 and 181 d of age, producing 6x6=36 treatments in both trials. 3. The first trial was terminated when the pullets were 28 weeks old, soon after all the birds had commenced laying, because of an outbreak of Egg Drop Syndrome. However, because age at maturity was the variable of major interest, data from this experiment could be used in the analysis. The second trial ended when the birds reached 40 weeks of age. Variables measured were age at maturity, food intake and body weight gain subsequent to the lifting of restrictions and, in the second experiment, rate of lay, peak rate of lay and egg weight at various ages. 4. The mean age at sexual maturity was influenced by the date of release from light restriction (P<0.001) and from food restriction (P<0.001) in both trials. In addition, the interaction between the age at release from light and from food restriction was significant. Regression equations were produced for each trial to describe the relationships between the age at sexual maturity and the age at release from light restriction and food restriction. 5. There was an effect of both light restriction (P<0.001) and of food restriction (P<0.001) on the increase in food intake (g/bird d) in the week following release from food restriction in both experiments. These effects were not independent: the effect of the interaction of light and food restriction on this increase in food intake was also highly significant. The longer the birds were subjected to light restriction, the less dramatic the increase in food intake when food restriction was lifted. The more sustained the period of food restriction, the higher the increase in food intake in the week following release from the restriction. 6. Mean egg weight was 4 g heavier at 22 weeks of age in birds released from food restriction at 16 and 18 weeks, than from those released at 24 and 26 weeks of age. However, by 30 weeks of age, birds restricted for longer produced heavier eggs than their earlier-maturing counterparts. This effect continued to the end of the trial at 40 weeks of age, at which time there was a 2.3 g difference in egg weight between these treatments. 7. Both light and food restriction have an effect on the age of maturity in laying hens. The length of time between the release from light or from food restriction to the onset of laying depended on the age of the pullets when the release occurred. Egg weight at a given age was significantly affected by the age at release from food restriction, but not from light restriction.

Age Factors↗

PubMed1999

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).

Aging↗

PubMed1999

Light intensity and age at first egg in pullets.

Layer strain pullets were reared on litter and given an 8-h photoperiod to 10 wk of age. They were then transferred to cages in which light intensity at the feed trough varied from 5 to 14 lx. Thirty birds continued on 8 h light (L):16 h dark (D) (negative controls), and another 30 birds were given 14L:10D (positive controls). Two other groups of 30 birds were given a regimen of 3 dim:8 L:3 dim:10 D with intensity during the dim phase ranging from 0.03 to 0.42 lx (very dim) or from 0.6 to 3.0 lx (marginal). Mean age at first egg (AFE) differed by 30 d between the positive and negative controls. Birds receiving very dim lighting matured 10 d earlier than the negative controls but 20 d later than positive controls. It is concluded that either the very dim light was itself nonstimulatory but had a phase shifting effect upon the biological clock that caused the 8-h normal light to fall partly in the photoinducible phase, or the first 3 h of very dim light was added to the bright phase to form an 11-h photoperiod. Birds in the top tier of the room with marginal supplementary lighting received 1.7 to 3.0 lx and matured at the same age as the positive controls, whereas those in the bottom tier received 0.6 to 0.9 lx and matured at the same age as the negative controls. Birds in the middle tier showed an intermediate AFE. It is concluded that the threshold intensity at the feed trough for white light stimulation of the photoperiodic mechanism in caged pullets lies between 0.9 and 1.7 lx. However, very dim lighting, below the threshold required for stimulation of a photoperiodic response, may shift the biological clock with unexpected consequences and, as a result, there is no known intensity of dim light that can be equated with darkness for all purposes.

Animals↗

PubMed1998

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. 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.

Animals↗

PubMed1998

A model for the effect of constant photoperiods on the rate of sexual maturation in pullets.

1. This paper reviews evidence from 15 experiments, reported over a span of 44 years, in which pullets were reared from hatching to sexual maturity on 2 or more constant photoperiods. 2. The evidence strongly indicates that earliest age at first egg (AFE) was observed when pullets were held on constant 10 h days (though earlier maturity is easily induced by increasing the photoperiod during rearing). The pair of equations which best describe the relationship between AFE (y, d) and photoperiod (x, h) are for x < or = 10 h, y = 175.8-1.731x; for x > or = 10 h, y = 155.5 + 0.301x. 3. This 2-straight-line model, hinged at 10 h, should be used in preference to curvilinear models published earlier, which wrongly predict that pullets reared on long days (14 h to 17 h) mature faster than birds reared on constant 10 h.

Aging↗

PubMed1997

Effect of size and timing of photoperiod increase on age at first egg and subsequent performance of two breeds of laying hen.

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.

Aging↗

PubMed1997

Responses of immature pullets to repeated cycles of gradual increases and abrupt decreases in photoperiod.

1. Growing pullets were reared on constant 8, 11 or 14 h photoperiods or given 12 daily increments of 30 min followed by an abrupt 6 h decrease in photoperiod in 14 d cycles from 2 d of age to sexual maturity. 2. Birds on the experimental lighting programme matured earlier than constant 8-h controls, later than 11-h controls but at the same age and body weight as constant 14-h controls. 3. Weight of the first egg was correlated with age at first egg. 4. It is assumed that potential advances in maturity for the experimental birds from the 30 min increments in photoperiod were cancelled by the retarding influences of 6 h decreases in photoperiod, resulting in their maturity being similar to that of birds reared on a constant daylength equal to the longest photoperiod reached during the cycle.

Animals↗

PubMed1996

Poultry science: the next 20 years?

1. The theme of the lecture is that research in poultry science has moved too far in the direction of molecular biology and away from studies with whole animals. This has happened partly because exciting prospects are opening up in the field of gene manipulation but mainly because of the use of inappropriate referees to evaluate research proposals. 2. Agricultural research is defined as work intended to benefit agriculture and directed towards those problems which seem capable of solution. Science research is something else. Too much of the money allocated for agricultural and biotechnology research is being spent on science research. The system of rewarding agricultural scientists needs to be adjusted away from counting papers published. 3. Some examples are given of problems in poultry science which seem likely to be soluble by gene manipulation. These include "essential" amino acid synthesis within the chicken, improvement of shell strength, the prevention of many diseases, but probably not the improvement of quantitative traits or of behavioural adaptation to intensive husbandry. 4. Examples are also given of problems likely to require empirical solutions, such as the benefits of acclimatisation or the long-term response to a lighting programme. Here the need is to develop better theories to guide modelling activities. 5. The author concludes that there is much research that can and should be done in poultry science in the next 20 years but calls for a recognition that some problems cannot be solved by a "fundamental" approach but will need experiments with whole animals coupled with model-building activities.

Animal Husbandry↗

PubMed1996

Effect of 5 hour increases in photoperiod and in feeding opportunity on age at first egg.

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.

Aging↗

PubMed1996

Effects of changes in photoperiod and feeding opportunity on the performance of two breeds of laying hen.

1. ISA Brown and Shaver 288 hens, fed ad libitum, were given a 5-h increase or a 2, 5 or 10-h decrease in photoperiod at 215 d of age. Hens of both breeds were also maintained on constant 10, 13 or 18 h photoperiods. Other groups had their photoperiod increased from 8 to 13 h, or were held on constant days but had their access to food limited to 8 h per day. 2. Both breeds on ad libitum feeding exhibited curvilinear rate of lay and egg output, and linear food intake, responses to photoperiod change. Shaver hens reduced their egg output and rate of lay to a greater extent than ISA Brown hens when photoperiod was decreased. 3. In both breeds the beneficial effect on egg production of the 5-h increase in photoperiod was less than the adverse effect of the 5-h decrease. 4. The influence of light change per se generally had a greater effect on performance than the influence of feeding opportunity, but significant effects of changing feeding opportunity were demonstrated. 5. The reduction in mean rate of lay and egg output following a reduction in photoperiod was partly caused by some birds ceasing lay, but all birds showed some decrease in both variates.

Analysis of Variance↗

PubMed1996

Lighting and mortality rates in domestic fowl.

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. Liveability 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.

Animals↗

PubMed1996

Effect of constant and of changing photoperiods on age at first egg and related traits in pullets.

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.

Aging↗

PubMed1995

Effect of photoperiod on the mean oviposition time of two breeds of laying hen.

1. Oviposition times were recorded for brown and white egg-laying hybrids under 8, 10, 13 and 18 h photoperiods. 2. Mean oviposition time for both breeds was advanced relative to dusk by approximately 0.5 h for each 1 h extension of photoperiod. 3. Mean oviposition time for the brown egg hybrid was 1.2 to 1.4 h earlier than that of the white egg hybrid under each lighting regimen. 4. A genetic difference in phase setting of the Open Period for Luteinising Hormone (LH) release is the likely reason for the difference in mean time of lay of the two breeds. The difference is possibly one between brown and white hybrids generally, rather than between the particular varieties of hen used in this trial. 5. The proportion of the day in which eggs are laid is shorter under long photoperiods presumably because light at the end of the photoperiod inhibits the pre-ovulatory surge of LH.

Animals↗

PubMed1995

New intermittent lighting programme (the Reading system) for laying pullets.

1. Two intermittent lighting systems for laying hens are: the Biomittent system, using an asymmetric pattern of 0.25L:0.75D for 16 h followed by 8D, which entrains oviposition to 24 h cycles and, compared with standard lighting programmes, gives the same egg number and egg size but a smaller feed cost, and a symmetrical system (4[3L:3D]) which allows intervals between ovipositions to stretch, giving bigger eggs with thicker shells, but yielding fewer eggs and achieving no saving in food intake. 2. A new system was devised to combine the increased egg size and shell thickness, characteristic of symmetrical intermittent lighting programmes, with the reduction in food intake which is a feature of programmes that reduce total activity time. The pattern tested was 24(0.25L:0.75D). 3. The results of 2 trials showed that this new system gives about 2% fewer eggs than conventional (Step Up) or Biomittent lighting with a 2% increase in mean egg size and a 3% improvement in shell thickness at the end of the laying year. Feed consumption with the new system was similar to that under Biomittent lighting and 6% lower than that recorded for Step Up lighting. 4. Mortality was lower with the new system than with Step Up lighting, but not significantly so. From the evidence of other trials it is argued that intermittent lighting programmes which provide less than 8 h total illumination in 24 h generally reduce laying house mortality and may be regarded as beneficial to the welfare of the hen.

Aging↗