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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.

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.

During a broiler breeder trial with 3200 Cobb 500 hens, the effects of lighting treatment after 20 weeks’ feed allocation and of feed form on the length of time taken to consume the daily allocation of feed were measured. Pullets were reared on 8-hour photoperiods to 20 weeks, then transferred to one of four lighting treatments: permanently to 11 h or 16 hours, transferred temporarily to 11 hours, then given 2-hours increments at 40, 44 and 48 weeks to reach 17 hours or a commercially recommended step-up lighting programme (11 hours at 20 weeks, incrementing by 30 min per week to reach 16 h by 30 weeks). Feed was made available in mash or pelleted form, and hens received 160 g or 180 g by 30 weeks. This allocation was increased linearly from 100 g at 20 weeks. After 40 weeks, the daily feed allocation was reduced by 5 g/bird for each 5% reduction in rate of lay to a minimum of 150 or 160 g/bird. On five occasions, when the hens were 39, 40, 41, 45 and 54 weeks old, the time taken by the hens to consume all their feed was measured and scaled to min/100 g consumed. Hens learned to consume the feed more rapidly as the laying period progressed. The mean clean-up time over all treatments was 67.7, 62.1, 63.4, 47.1 and 40.2 min/100 g at the five ages. Over all treatments and ages, the time taken to consume all their feed was 40.0 min/100 g for birds fed 160 g, versus 72.2 min for those given 180 g of food daily, but this difference was greater at 39 weeks (43.5 versus 91.8) than at 54 weeks (34.0 versus 46.4 min/100 g, respectively). This effect was also evident with feed form, the difference in time taken to consume mash and pellets being greater at 39 weeks (69.2 versus 66.1) than at 54 weeks (54.7 versus 25.7 min/100 g, respectively). The lighting programmes also had an effect on the feed clean-up time. The main effects were 53.5, 56.3, 52.1 and 62.5 min/100 g for the 11-hour constant, 11 to 16 hours, 16-hour constant and step-up programmes, respectively. Significant interactions occurred between treatments. The main reason was the much longer time taken initially by birds receiving the step-up lighting programme and 180 g of pelleted feed to consume all their feed. The effects of these treatments on bird welfare are discussed. Keywords: Breeders, laying period, lipid reserves, welfare

1. Individually-caged Ross 308 broiler breeders were transferred temporarily at 147 d from 8 to 14-h photoperiods and back to 8 h at 5-d intervals from 5 to 25 d and at 32 d. Control birds were maintained on 8 h or transferred permanently to 14 h. 2. Five long days had minimal effect on age at first egg, between 10 and 25 long days progressively accelerated sexual development, and maximum advance was achieved by 32 long days. However, a model involving the ogive of a normal distribution with a mean of 14 long days and an SD of 5.3 indicated that 28 long days would be sufficient to maximise sexual development. 3. The similarity of this model for broiler breeders with one previously produced for egg-type pullets suggested a common physiological mechanism for photosexual responses to two opposing changes in photoperiod.

Ross 308 broiler breeder females, maintained in litter-floor pens, were reared from 2 d of age on 8-h photoperiods and transferred abruptly to an 11-, 12-, 13-, or 14-h photoperiod at 20 wk of age and at a mean BW of 2.09 kg. Four qualitative dietary treatments were superimposed upon each photoperiodic treatment, but, in the absence of any significant interactions of photoperiod with diet, only photoperiodic means are reported. Age at 50% egg production (ASM) was progressively advanced as photoperiod increased from 11 to 13 h but was similar for 13-h and 14-h birds. Egg production was significantly related to ASM, with peak egg numbers being stimulated by a transfer to 13-h photoperiods. Rate of lay after 48 wk of age declined more rapidly in the 14-h birds than in any of the other groups, suggestive of an earlier onset of adult photorefractoriness. More eggs were laid outside the nest box and more cracked and dirty eggs were produced by birds on 11- and 12-h photoperiods than on 13- or 14-h photoperiods. Mean egg weight was positively correlated with ASM but negatively related to photoperiod; the number of eggs thought to be double-yolked was not significantly affected by photoperiod. Total egg mass output was not significantly affected by photoperiod. Birds exposed to 11-h and 12-h photoperiods were heavier at 60 wk than birds transferred to 13- or 14-h photoperiods. These findings show that a transfer from 8 to 13 h at 20 wk optimizes egg-laying performance in broiler breeder females, especially when they are kept beyond 60 wk of age.

1. Broiler breeders were reared at an initial illuminance of 13, 21 or 44 lux and transferred at 20 weeks and a mean body weight of 2.06 kg to floor pens at 25, 55 or 71 lux, or to individual cages at various intensities between 3 and 138 lux. 2. Rate of sexual maturation was not significantly affected by the light intensity experienced during the rearing period, but was progressively accelerated by the provision of a brighter illuminance after 20 weeks, up to a ceiling of about 14 lux. There was no interaction between the pre- and post-20-week illuminance. 3. Cumulative egg numbers to 39 weeks were unaffected by illuminance in the rearing period, positively correlated with illuminance post 20 weeks up to an asymptote at about 8 lux, and highly correlated with age at sexual maturity. Peak rate of lay was both delayed and depressed at 3 lux. 4. It is concluded that the minimum light intensity required at bird-head height to achieve satisfactory photostimulation and an optimal peak rate of lay in broiler breeders is 10 lux, but that a higher illuminance would be prudent for broiler breeders kept in floor pen facilities to maximise nest-box usage.