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A review of lighting for broiler breeders
a
Dr P.D. Lewis
a
University of KwaZulu-Natal, Animal and Poultry Science, Pietermaritzburg, South
Africa
Available online: 18 Jan 2007
To cite this article: Dr P.D. Lewis (2006): A review of lighting for broiler breeders, British Poultry Science, 47:4, 393-404
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2. British Poultry Science Volume 47, Number 4 (August 2006) pp. 393—404
REVIEW ARTICLE
A review of lighting for broiler breeders
P.D. LEWIS
University of KwaZulu-Natal, Animal and Poultry Science, Pietermaritzburg, South Africa
INTRODUCTION breeding birds from becoming sexual mature in
the same year in which they are hatched, even
Lighting programmes recommended for broiler though they may be somatically mature. The
breeders are very similar to those advocated for adult form of PR causes gonadal regression
laying hens. They usually involve the provision of in advance of unfavourable environmental con-
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an 8-h photoperiod during the rearing period, a ditions. The mechanism involved in ending the
transfer to 11 or 12 h at about 20 weeks, and a breeding season is thought to be initiated at the
subsequent series of weekly increments to reach same time as that which stimulates sexual
a maximum of 15 or 16 h by 23 to 25 weeks. maturation at the beginning of the season, with
Whilst it might be construed, since the pro- the length of the season being determined by the
grammes are similar (though an egg-type hybrid relative rates at which these two processes reach
will be photostimulated 3 to 5 weeks earlier), that completion (Dawson, 2001).
the two types of fowl have the same lighting This paper reviews the responses to constant
requirements, this is not so, because a broiler and changing photoperiods in broiler breeders
breeder’s response to light is strongly modulated grown to a typically recommended 2Á0 to 2Á2 kg
by two factors irrelevant to the lighting of egg- body weight at 20 weeks of age, contrasts these
type hybrids: controlled feeding and photore- with how egg-type hybrids respond, and
fractoriness (PR). describes the involvement of PR in, and the
Meat-type genotypes are principally selected modifying influence of body weight on, these
for body weight gain, feed conversion efficiency photoperiodic responses. It also briefly covers
and body conformation. As a result, feed intake the effects of illuminance, wavelength, source of
and growth of the parent stock have to be light and season.
controlled during the rearing period to achieve
the appropriate body weight and carcass compo-
CONSTANT PHOTOPERIODS
sition for satisfactory reproductive performance.
The degree to which growth is restricted affects
Sexual maturation
reproductive performance through altered
rates of body weight gain and fat deposition When broiler breeders are exposed to a constant
(Fuller et al., 1969; Leeson and Summers, 1983; photoperiod from soon after hatching they reach
Bornstein et al., 1984; Brody et al., 1984; Soller sexual maturity about one day earlier for each
et al., 1984; Hocking et al., 1987) and through one-hour longer photoperiod up to 10 h
a modification of the bird’s response to the (Figure 1). This rate of advance is similar to
imposed lighting regimen (Yuan et al., 1994; that observed in early genotypes of egg-type
Gous and Cherry, 2004; Melnychuk et al., 2004; hybrids (Lewis et al., 1998a), but only a quarter of
Lewis, 2006). that reported for modern egg-type stock, where
Photorefractoriness is a natural phenom- the selection for egg numbers has accelerated
enon that prevents animals becoming sexually sexual maturity in pullets reared on 8- to 10-h
active when the ensuing environmental condi- days but not in those reared on very short days
tions are inopportune for successfully raising (Lewis and Morris, 2005). When broiler breeders
offspring. The juvenile form of PR stops seasonal are given photoperiods between 10 and 13 h,
Correspondence to: Dr P.D. Lewis, Northcot, Cowdown Lane, Goodworth Clatford, Andover, Hants. SP11 7HG, UK. E-mail: peter.lewis@dsl.pipex.com
ISSN 0007–1668(print)/ISSN 1466–1799 (online)/06/040393—12 ß 2006 British Poultry Science Ltd
DOI: 10.1080/00071660600829092

3. 394 P.D. LEWIS
age at sexual maturity (ASM) is markedly During the rearing period, broiler breeders
delayed, with birds maintained on 13 h maturing maintained on 8-h photoperiods have signifi-
between 3 and 4 weeks later than birds held on cantly lower plasma LH concentrations than
10 h. Thereafter, maturity is advanced by about birds held on 16-h days (Lewis et al., 2005c),
0Á8 d per one hour of photoperiod (Lewis et al., and this reflects the situation in egg-type
2004a). The responses to photoperiods longer hybrids reared on 8- or 14-h photoperiods
than 10 h are in complete contrast to those of (Lewis et al., 1998b).
egg-type hybrids (Figure 1), and show that broiler
breeders exhibit PR. Unwittingly, the prolonged Body weight and feed intake
selection for egg numbers in egg-laying stock
appears to have virtually eliminated PR (Morris Body weight at 20 weeks of age for pullets given
et al., 1995). The 3- to 4-week difference in the same daily allocation of feed during the
maturity between broiler breeders reared on 10- rearing period decreases by about 15 g for each
and 13-h photoperiods, though economically one hour of day-length and is a likely conse-
important to the poultry industry, is much quence of the bird’s energy expenditure being
smaller than that seen in exotic avian species higher during light than dark (MacLeod et al.,
(for example, partridges—Woodard et al., 1980) 1988). However, because the photoperiod also
and shows that the dissipation of PR in broiler influences the rate of gonadal maturation, which
breeders is only accelerated by, and is not is not linear (Figure 1), body weight at 50% egg
dependent upon, exposure to short days. production is more closely linked to ASM than to
the photoperiod that influenced it. Combined,
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Although there is a dearth of information on
the response of modern meat-type breeder males the effects of photoperiod on energy expendi-
to constant photoperiod, the data for semen ture and gonadal development increase the feed
required to reach sexual maturity by about 0Á6 kg
production in Figure 1 (Renden et al., 1991)
for each one hour of photoperiod (Lewis et al.,
show that the effect of constant photoperiod on
2005a).
the rate of gonadal development is likely to be
similar for both sexes.
The marked difference between the ASM of Egg production
birds maintained on short photoperiods ( 10 h)
Commercially, broiler breeders are unlikely to
and those reared on constant 13-h days agrees experience constant photoperiods from one day
with endocrinological evidence that the critical old through to depletion unless they are kept in
and saturation photoperiods for luteinising open-sided, non-illuminated housing close to the
hormone (LH) release in broiler breeders equator. Thus the following descriptions of their
reared on 8-h day-lengths lie between 10Á5 and biological responses to photoperiod are, in the
12Á75 h (Dunn and Sharp, 1990). main, of academic interest only.
Total eggs laid to a typical 60-week depletion
age for broiler breeders given a constant photo-
period throughout life are strongly influenced by
220 205 ASM (Figure 2) and, because ASM is not linearly
related to photoperiod, the relationship of egg
Broiler breeder maturity (d)
Egg−type maturity (d)
205 Broiler breeder 190 production with photoperiod is also non-linear.
A hinge analysis of data for various photoperiods
190 175
Early egg-type
between 1 and 16 h (McCluskey and Parker,
175 160 1963; Lewis et al., 2003, 2005a), with differences
among trials removed by fitting constants by least
160 Modern egg-type 145 squares, showed that the early sexual develop-
ment of birds maintained on 10-h photoperiods
145 130 (Figure 1) results in these birds also having the
0 3 6 9 12 15 18 21 24
Photoperiod (h)
highest egg production to 60 weeks of age. Egg
production falls by about 8 eggs for each one-
Figure 1. Mean age at first egg for broiler breeders with a hour shorter photoperiod below the 10-h hinge
mean body weight of between 1Á9 and 2Á4 kg at 20 weeks of age and by 3 to 4 eggs for each one-hour increase
and maintained on constant photoperiods from 2 d of age (f,
above the hinge (Figure 3). A description of the
m, i Lewis et al., 2003; œ, g Lewis et al., 2004a) and mean
age at initial semen production for broiler breeder males
hinge analysis is given in Lewis et al. (1998a).
weighing 2Á9 kg at 24 weeks of age ( Renden et al., 1991). Reproduction terminates in most seasonal
Differences among trials were removed by least squares analysis. breeding wild birds after prolonged exposure to
The broken line shows the response of early egg-type hybrids stimulatory day-lengths because of the onset of
(Lewis et al., 1998a) and the dotted line the response of modern adult PR (Dawson et al., 2001); a condition that
egg-type hybrids (Lewis and Morris, 2005). serves the same function as juvenile PR, namely,

4. LIGHTING FOR BROILER BREEDERS 395
180 160
175
140
Eggs per bird (n)
Eggs per bird
170
165 120
160
155 100
150
80
145 0 2 4 6 8 10 12 14 16 18
185 195 205 215 225 235 Photoperiod (h)
Age at sexual maturity (d)
Figure 3. Egg production to 60 weeks of age for broiler
Figure 2. Egg production to 60 weeks of age, regressed on breeders maintained on various constant photoperiods from 2 d
age at sexual maturity, for modern broiler breeders maintained of age (f Lewis et al., 2003; m Lewis et al., 2005a; g
on various constant photoperiods from 2 d of age (m, g Lewis McCluskey and Parker, 1963). Differences among trials were
et al., 2003; f Lewis et al., 2005a). Differences among trials removed by least squares analysis.
were removed by least squares analysis.
73
Mean egg weight (g)
72
the prevention of sexual activity when forth-
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coming environmental conditions are unfavour- 71
able for raising young. The phenomenon, which
occurs to a lesser extent in broiler breeders than 70
in truly seasonal breeding species, is one of the
69
causes of the more rapid decline in rate of lay
with age in meat-type, compared with egg-type, 68
hens. A higher proportion of non-laying birds in 9 10 11 12 13 14 15 16 17
60-week broiler breeders maintained on 16-h Photoperiod (h)
photoperiods, compared with others held on Figure 4. Mean egg weight to 60 weeks of age for broiler
11 h, provided evidence for the existence of adult breeders maintained on various constant photoperiods from 2 d
PR in meat-type genotypes (Lewis et al., 2003). of age (m Lewis et al., 2003; f Lewis et al., 2005a). Data
adjusted to a mean age of 202 d and mean body weight of 3Á5 kg
at sexual maturity (age adjustment ¼ þ0Á0329, body weight
Egg weight
adjustment ¼ þ2Á0694) and a bent-stick model fitted with
Mean egg weight (MEW) in broiler breeders is differences between trials removed by least squares analysis.
correlated with both age and body weight at first
egg (Lewis et al., 2005a), but, as in egg-type
hybrids (Lewis et al., 1994), a multiple regression 1996). However, egg-type hybrids are fed
of MEW on age at sexual maturity (ASM), body ad libitum, and this allows them to continue to
weight at sexual maturity (BWSM) and photo- increase feed intake at longer photoperiods and
period ( p) shows that MEW still varies with to use the extra nutrients to increase MEW; an
photoperiod even when the effects of ASM and option not available to control-fed broiler
BWSM have been removed: breeders.
MEW ¼ 53 Á 8 þ 2 Á 30 BWSM þ 0 Á 04 ASM Shell quality
þ 0 Á 10 p ðr 2 ¼ 0 Â 983, SD ¼ 0 Á 258,
Although this section describes the response of
P 0 Á 0001Þ: birds to constant photoperiods, it is also relevant
to birds that have been reared on short days
Although this revealed a significant linear effect and transferred to longer days. Shell quality,
of photoperiod, further analysis of the data as measured by shell weight or thickness index,
following adjustment to a 202-d ASM and is negatively correlated with photoperiod
3Á50-kg BWSM suggested that a bent-stick (Backhouse et al., 2005), decreasing by 30 mg
model (Morris, 1999) would provide a better fit. weight and 0Á57 mg/cm2 thickness index for each
Such a model indicated that MEW increased by one hour of photoperiod. This deterioration
about 1 g per one hour of photoperiod up to in shell quality with increasing photoperiod is
about 13 h, but levelled out thereafter (Figure 4), similar to that which occurs in egg-type hybrids
which contrasts with the continued photoperio- (Lewis et al., 1994). Although shell quality is
dic effect on MEW in egg-type hybrids (Lewis, known to be closely correlated with hatchability

5. 396 P.D. LEWIS
in broiler breeders (McDaniel et al., 1981; Roque photoperiod at the end of the rearing phase
and Soares, 1994), the direct effect of photoper- (Payne, 1975; Gous and Cherry, 2004; Lewis and
iod on hatchability has not been reported. Gous, 2006c). Data in the Table 1 show that
sexual maturity is markedly delayed and subse-
quent egg production significantly inferior when
Time of lay birds have not been given short days during the
Irrespective of whether a bird has been given rearing period.
constant or changing day-lengths, the timing of
events in the ovulatory cycle is determined by the
current lighting environment and almost com- Photoperiod in lay
pletely unaffected by lighting history. Mean time A single increment at about 20 weeks of age, for
of lay in broiler breeders occurs 0Á5 h later in the broiler breeders reared on 8-h photoperiods and
day for each one-hour extension of the photo- weighing about 2Á1 kg, significantly accelerates
period, a rate almost identical to that reported gonadal development, but the size of the advance
for egg-type hybrids (Lewis et al., 2004b). in ASM depends on the photoperiod to which
However, actual time of lay for broiler breeders the birds are transferred. Figure 5 shows a
exposed to a given photoperiod is one hour later curvilinear relationship between mean ASM and
than for white-egg hybrids and 2Á5 h later than for final photoperiod, with the earliest maturity
brown-egg hybrids, and, as a consequence, few occurring following a transfer to between 14
broiler breeder eggs are laid before dawn when and 16 h. The relationship is described by
the photoperiod is !13 h.
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ASM ¼ 288 Á 2 À 13 Á 54 p þ 0 Á 463 p2
ðr 2 ¼ 0 Á 941, P 0 Á 001, SD ¼ 2 Á 46Þ
CHANGING PHOTOPERIODS
where ASM ¼ mean age at 50% egg production
Photoperiod during rearing (d) and p ¼ final photoperiod (h). Predicted
There is little difference in ASM among birds mean ASM for ad libitum-fed egg-type hybrids
that have been reared on 6-, 8- or 10-h photo- photostimulated at 10 weeks (equivalent ‘physio-
periods and abruptly transferred to 16-h days at logical age’ to 20-week-old control-fed broiler
20 weeks (Lewis and Gous, 2006c). This is breeders) using the models of Lewis et al. (2002)
because the slightly slower gonadal development and Lewis and Morris (2004) show that egg-type
expected for birds reared on 6- or 8-h photo- and meat-type fowl respond similarly to a change
periods (Figure 1) was countered by a larger, in photoperiod when reared initially on 8-h days.
more stimulatory increment in photoperiod at
20 weeks. However, this does not mean that day-
Age at photostimulation
length during the rearing period is unimportant,
but that 6-, 8- and 10-h day-lengths exert similar In a flock of broiler breeders grown to a mean
influences, because they are all neutral photo- 20-week body weight of 2Á1 kg, no individuals
periods, and so dissipate juvenile PR at compar- respond to an increment in photoperiod until
able rates. The situation is very different when they are about 9 weeks of age. The model in
broiler breeders are reared on a stimulatory day- Figure 6, created using data from Robinson et al.
length and receive little or no increase in (1996), Joseph et al. (2002b), Lewis et al. (2003),
Table. Mean age at sexual maturity and total egg production during the laying cycle for broiler breeders reared on 6 or 15 h
and transferred to 16 h at 168 d (Payne, 1975), maintained on 17 h or reared on 8 h and given one-hour increments weekly to
16 h from 133 d (Gous and Cherry, 2004), and maintained on 16 h or reared on 6, 8 or 10 h and transferred to 16 h at 140 d
(Lewis and Gous, 2006c)
Rearing photoperiod (h) Laying photoperiod (h) Transfer age (d) Sexual maturity (d) Total eggs per bird (n)
Payne (1975)
6 16 168 177Á2 152Á3
15 16 168 192Á7 139Á6
Gous and Cherry (2004)
8 1 h/week to 16 133 199Á8 151Á1
17 17 None 226Á5 143Á9
Lewis and Gous (2006c)
6 16 140 197Á0 163Á7
8 16 140 193Á5 165Á3
10 16 140 197Á5 167Á2
16 16 None 214Á5 150Á2

6. LIGHTING FOR BROILER BREEDERS 397
220 160 250
Broiler breeders
Eggh-type maturity (d)
Meat-type maturity (d)
210 150
235
Age at maturity (d)
200 140
220
190 130
180 120 205
170 Egg-type hybrids 110 190
160 100
6 8 10 12 14 16 18 20 175
Final photoperiod (h) 0 30 60 90 120 150 180 210 240
Age at transfer from 8 to 16 h (d)
Figure 5. Mean age at 50% egg production for broiler
breeders reaching a 2Á1 kg body weight at 20 weeks of age and Figure 6. A model for mean age at 50% egg production for
transferred from 8-h to various photoperiods (m Lewis et al., broiler breeders weighing about 2Á1 kg body weight at 20 weeks
2003; i Ciacciariello and Gous, 2005; f, Lewis and of age and transferred at various ages from 8- to 16-h
Gous, 2006b). Differences among trials were removed by least photoperiods (g [Shaver Starbro] Robinson et al., 1996; i
squares analysis. The broken line shows the predicted response [Ross] Joseph et al., 2002a; m [Cobb 500] Lewis et al., 2003;
of egg-type hybrids photostimulated at 10 weeks of age using the , œ [Ross] Ciacciariello and Gous, 2005; f [Cobb 500]
models of Lewis et al. (2002) and Lewis and Morris (2004). unpublished data, University of KwaZulu-Natal). It is assumed
that the rate at which photorefractoriness is dissipated forms a
normal distribution with a mean of 98 d and a SD of 15 d, that
the proportion of birds maturing spontaneously in response to
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Ciacciariello and Gous (2005), and unpublished an 8-h photoperiod forms a normal distribution with a mean of
data from the University of KwaZulu-Natal that 221 d and a SD of 9 d, and that constant 16-h birds mature
19 d later than constant 8-h birds.
had been adjusted for differences among trials by
least squares analysis, shows that broiler breeders
transferred from 8- to 16-h days before 9 weeks of
age respond as if they have been reared on and standard deviation (9 d) of the ASM for birds
constant 16-h days (plotted at 0 d) and so mature maintained on 8-h photoperiods. The gradient of
about 3 weeks later than birds maintained on 8 h. the slope for a transfer to 16 h at between 19 and
The model also predicts that a flock will be about 30 weeks, when all birds are responsive to an
19 weeks of age before all individuals are increase in day-length, is similar to that between
responsive to an increase in day-length, though 9 and 20 weeks for a typical white-egg hybrid, but
the earliest mean ASM following photostimula- only 0Á73 (k value) that for a brown-egg hybrid
tion will occur a little earlier, at about 18 weeks. (Lewis et al., 2002). However, in commercial
Thereafter, the stimulatory effect of a transfer to conditions it is more common for broiler
long days decreases by 0Á36 d for each one-day breeders to be initially transferred to 11 or 12 h
delay in photostimulation until, about 10 d and the respective k values for these photoper-
before the latest maturing members of a flock iods are 0Á59 and 0Á63.
spontaneously commence egg production (%30 Although the two egg-type genotypes
weeks), none of the birds is responsive. responded significantly differently from each
There is a bimodal distribution in ASM other, there was no indication of any variation
where photostimulation has occurred in the in the responses of the three genotypes (Ross,
period between 9 and 19 weeks, with some Cobb 500 and Shaver Starbro) used to create the
birds still photorefractory and maturing as if broiler breeder model.
maintained on long days (ASM delayed by about The differences between meat-type and egg-
3 weeks) and others responding by accelerating type genotypes in the ages at which they attained
their gonadal development. This results in a photosensitivity, experienced the biggest advance
mean ASM that is intermediate between a flock in ASM and commenced sexual maturation
photostimulated before 9 weeks, when all birds spontaneously are consequences of juvenile PR
are photorefractory, and one in which all birds and the retarding effects of feed restriction in
are responsive at the time of photostimulation. broiler breeders. The model suggests that the
It is assumed that the age at which individuals levels of restriction typically applied in feeding
dissipate PR and become responsive to an broiler breeders retards them to the extent that
increment in photoperiod forms a normal they respond to an increase in photoperiod as it
distribution, and that the proportion of sensitive were given to an ad libitum-fed bird half its age,
birds may be calculated using a mean of 98 d and that is, at 18 weeks of age they respond to a
a standard deviation of 13Á2 d. The proportion of lighting stimulus as if it were given to a non-
birds maturing spontaneously at the end of the restricted bird at 9 weeks of age. A relaxation of
rearing period is also assumed to form a normal feed control during rearing, which obviously
distribution that is described by the mean (221 d) results in faster growth, expedites the dissipation

7. 398 P.D. LEWIS
of PR so that birds can be photostimulated at a or ovarian morphology (Joseph et al., 2002b;
younger age and sexual maturation advanced; Lewis and Gous, 2006a).
conversely, a tightening of feed control hinders
PR dissipation and delays the age at which birds
can successfully be transferred to long days. Male fertility
The consequences of altering growth to facilitate There are few data for the effects of photoperiod
changes in the age at photostimulation are on male performance, but Brake (1990) sug-
described in a latter section that discusses the gested that broiler breeder males may have a
interaction of lighting with body weight. lower threshold for photostimulation than
females. His findings also showed a consistent
improvement in fertility for birds transferred
Egg production from 8- to 10-h photoperiods at 18 weeks
compared with others held on 8 h, which, in the
Figure 7(a) shows that birds transferred to 16 h, absence of any significant effects on the female
despite having an earlier ASM, lay fewer total reproductive performance, was attributed to the
eggs during the laying period than birds trans- male input.
ferred to only 11 or 12 h. This is most likely due
to a combination of an earlier onset of adult PR
and higher daily energy expenditure by the 16-h ILLUMINANCE, WAVELENGTH, LIGHT
birds (MacLeod et al., 1988). Figure 7(b) shows SOURCE AND SEASON
that if birds are initially transferred to a less
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stimulatory day-length, for example, to 11 or Illuminance
12 h, before being given further increments to Notwithstanding the dearth of experimental data
16 h, egg production will be superior to that of for the responses of broiler breeders to illumi-
birds abruptly transferred to 16 h. These findings nance, recommendations in primary breeders’
support the hypothesis of Dawson (2001) that the management guides are in reasonable agreement
initial increment in photoperiod triggers the (for example, Aviagen, 2001). Most advocate an
mechanisms for initiating sexual maturation intensity of about 60 lux for the first 2 d, followed
and the onset of adult PR, and that the processes by a gradual reduction to between 5 and 10 lux by
proceed to completion at a slower rate if the 7 to 21 d. This intensity is then maintained until
transfer is to a less stimulatory photoperiod. about 20 weeks, after which it is increased to
There is no evidence that giving further between 15 and 40 lux for the duration of the
increases in photoperiod after birds have reached laying period. In a 2 Â 2 factorial trial in which
peak egg production, be they 15-min, 30-min or broiler breeders were reared on 8 h of incandes-
one-hour increments, has any effect on rate of lay cent light at 20 lux or a mixture of incandescent
(a) 160
Eggs per bird
155
150
145
Trial 1 Trial 2 Trial 3
(b) 200
Eggs per bird
180
160
140
Trial 2 Trial 3 Trial 4 Trial 5
Figure 7. (a) Total egg production for broiler breeders abruptly transferred at 20 weeks from 8 to 16 h (open bars) or from 8 to 12 h
(solid bars) in Trial 1 (Lewis et al., 2003) or to 11 h in Trials 2 and 3 (Lewis and Gous, 2006a). (b) Total egg production for broiler
breeders abruptly transferred at 19 or 20 weeks from 8 to 15 or 16 h (open bars) or given a step-up regimen to 15 or 16 h (solid bars).
Trial 2 was initially transferred to 11 h at 20 weeks then 15-min weekly increments from 35 weeks of age, Trial 3 was initially
transferred to 11 h at 20 weeks then one-hour increments every 4 weeks from 38 weeks of age, Trial 4 was initially transferred to 12 h at
19 weeks then one-hour increments from 20 weeks (Lewis and Gous, 2006d), and Trial 5 was initially transferred to 11 h at 20 weeks
then one-hour increments from 21 weeks (Robinson et al., 1998).

8. LIGHTING FOR BROILER BREEDERS 399
and natural light at 800 lux and exposed to 16 h was iso-illuminant to the birds, there was a
of incandescent light at 10 or 1000 lux during the significant increase in both locomotion and the
laying phase, illuminance had no significant number of attempted matings by males given
effect on reproductive performance (Brake and the UV-A ( Jones et al., 2001). In a second trial,
Baughman, 1989). Similar conclusions were females that were allowed to see a male
drawn for a mixture of dwarf and normal size illuminated with 2, 17, 77 or 135% supplemen-
genotypes reared on 2 lux and transferred to tary UV-A spent most time inspecting males
10 lux at 16, 18 or 20 weeks of age (Proudfoot that were illuminated with 17% added UV-A.
et al., 1984). These findings, together with measurements of
Recent work at the University of KwaZulu- the reflective properties of broiler breeder
Natal shows that the response of broiler breeders plumage under UV-A lighting (Prescott and
to photoperiod is in many ways more akin to Wathes, 1999a), suggest that UV-A is involved
turkeys than to laying hens, presumably because in sexual recognition between males and females
they both, in contrast to laying hens, exhibit PR. and that its provision in artificially illuminated
There have been several studies of the effect of environments (in which there will be minimal
illuminance on egg production in turkeys, and UV-A) may have a beneficial influence on
these suggest that, if the broiler breeders and fertility, especially when given in a proportion
turkeys do respond in a similar way, primary close to that of natural sunlight (%7% of natural
breeder recommendations for broiler breeders white light).
are apposite for optimising egg production. A
comparison of the response of early and modern
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egg-type pullets to illuminance (Lewis and Light source
Morris, 1999) showed that the early hybrids, There is no scientific evidence that light source
which would be more like broiler breeders in consistently affects any aspect of reproductive
terms of their reproductive potential, were more performance in broiler breeders (Colman and
affected by suboptimal illuminance than modern Minear, 1981; Ingram et al., 1987; Van Krey and
hybrids, and so broiler breeders may well require Weaver, 1988).
a brighter illuminance during the laying period
than the 5 to 10 lux recommended for modern
egg-type hens. Seasonal influences
Broiler breeders that are reared in non-light-
Wavelength proof housing and hatched in the spring (often
called out-of-season flocks) mature later than
There are no scientific publications that describe (Vandenberghe et al., 1999), and have inferior
the response of broiler breeders to different egg production to (Brake and Baughman, 1989),
wavelengths of light, and lamp manufacturers’ ‘in-season’ flocks that are hatched in the autumn
claims that red compact fluorescent lamps and become sexually mature in the spring.
beneficially influence egg production and shell Whereas part of the poor performance may be
quality (Gasolec, 2006) are not supported by attributed to the light intensity during the laying
scientific research. Application of the findings period being lower than during the rearing
that red light is more sexually stimulatory period (Brake and Baughman, 1989), the main
than other colours of light to commercial reason is the lack of exposure to short days
coloured lamps is misguided because the original during rearing, because this slows up the dissipa-
research (Benoit et al., 1950) used truly tion of PR, delays sexual maturation and reduces
monochromatic light sources; emissions from egg numbers. Rearing spring-hatched flocks in
commercial coloured fluorescent lamps are far ‘brown-out’ housing on short, artificial photoper-
from monochromatic (Lewis and Morris, 2006). iods results in some improvement in perfor-
It should also be appreciated that white mance, but it is still unlikely to be as good as that
light includes all colours of light, and so there of autumn-hatched flocks (Timmons et al., 1983;
is no need to replace white lamps with red lamps Brake and Baughman, 1989).
to provide the birds with red light, particularly
where incandescent lamps are used,
because these emit 70% red light (Lewis and INTERACTIONS WITH BODY WEIGHT
Morris, 2000).
Domestic fowl, unlike humans, are able to In one extreme, ad libitum-fed broiler breeder
perceive the UV-A component of ultraviolet females mature earlier, have heavier body
radiation (Prescott and Wathes, 1999b). When weights at first egg, produce more double-
groups of broiler breeders were kept under ovulations, have inferior rates of lay, higher
white fluorescent light with or without 20% mortality, and sometimes a lower MEW than
supplementary UV-A at an intensity that birds given the same lighting treatment but

9. 400 P.D. LEWIS
weighing 2Á0 to 2Á2 kg at 20 weeks (Katanbaf high proportion of under-weight birds (5% of
et al., 1989; Yuan et al., 1994; Heck et al., 2004; birds 20% below the mean), should not be
Melnychuk et al., 2004), whilst in the other, sexual transferred to long days until it has achieved the
maturation is completely suppressed when the recommended weight for photostimulation
degree of feed restriction is such that it prevents (commonly about 2Á1 kg). This delay in transfer
growth (Dunn and Sharp, 1992). Dwarf broiler to a stimulatory photoperiod will result in
breeders that had had their body weight pegged significantly better egg production than if the
at 1Á00 kg did not start egg production until the flock had been photostimulated at the normal
feed allocation had been increased, despite being age but at a suboptimal weight (Lien and Yuan,
transferred from 8- to 20-h photoperiods at 22, 1994).
32 or 52 weeks of age. Between these two Although the photosexual response seems to
extremes, unpublished data from the University be independent of growth rate when birds are
of KwaZulu-Natal show that increases or given constant day-lengths (Figure 8), body
decreases in growth alter ASM by about 2 d for weight has a profound effect on ASM when the
each 100-g change in 20-week body weight, but birds are given an increase in photoperiod. Data
the accelerating effect on gonadal development in Figure 9 show that ASM for birds weighing
of a relaxation in feed control appears to be 2Á06 kg at 20 weeks was retarded following a
independent of the photoperiodic effect when transfer from 8 to 16 h at 98 d (because they
birds are given constant photoperiods (Lewis were still photorefractory) and was not advanced
et al., 2004a); Figure 8 shows a consistent by an increment until the birds were !112 d of
difference between birds fed to reach 2Á1 kg
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age (Ciacciariello and Gous, 2005). Increasing
at 21 weeks and those managed to achieve this mean 20-week body weight to 2Á82 kg resulted in
weight at 17 weeks of age. none of the groups having their ASM delayed
Variability in individual body weights within and a significant advance in ASM when birds
a flock is correlated with differences in the rate of were photostimulated at !98 d. It was assumed
gonadal development (Robinson and Robinson, that this was a consequence of the relaxation in
1991), and so an improvement in body weight feed control permitting a more rapid dissipation
uniformity will result in a sexually more uniform of juvenile PR.
flock, especially when the smaller members Commercial experience and research has
would otherwise have been photostimulated shown that 2Á1 kg is the optimal body weight at
below the threshold body weight for successful which to photostimulate broiler breeders and, in
gonadal development (Soller et al., 1984; many trials (Leeson and Summers, 1983;
Melnychuk et al., 2004). Notwithstanding that Ciacciariello and Gous, 2005; unreported trials
delays in photostimulation marginally retard at the University of KwaZulu-Natal), the level of
sexual maturation, a flock of broiler breeders feed restriction has been varied to enable this
whose mean body weight is below target, weight bird to be transferred to stimulatory
particularly if this is due to an unacceptably day-lengths at different ages. An analysis of data
from these trials shows that modifying the age at
which a flock reaches 2Á1 kg alters its mean ASM
220
Age at 50% lay (d)
210
200 240
2.06 kg at 140 d
Mean age at first egg (d)
225
190
210 Constant 8-h photoperiods
180
9 10 11 12 13 14 15 16 17 195
Constant photoperiod (h) 180
2.82 kg at 140 d
Figure 8. Mean age at first egg for broiler breeders reaching 165
a 2Á1 kg body weight at 17 (f) or 20 ( ) weeks of age and
150
maintained on constant photoperiods from 2 d of age 60 70 80 90 100 110 120 130
(Lewis et al., 2004a). The curves between 10 and 13 h Age at transfer 8 to 16 h (d)
assume that the rate at which a photoperiod gains stimulatori-
ness forms a normal distribution and that the proportional Figure 9. Mean age at first egg for broiler breeders reaching
increase may be calculated using a mean of 11Á5 h and a 2Á06 kg (f and solid lines) or 2Á82 kg ( and broken lines)
standard deviation calculated to minimise the residual sums of body weight at 20 weeks of age and transferred from 8-h to 16-h
squares when fitting the curve to the data (0Á57 h for 17 weeks, photoperiods at 69, 76, 97, 83, 111 or 125 d of age
0Á51 for 20 weeks). (Ciacciariello and Gous, 2005).

10. LIGHTING FOR BROILER BREEDERS 401
by about 4 d for each 10-d change (Figure 10). CONCLUSIONS
The equation describing the regression is:
1 Broiler breeders respond to light, in particular
ASM ¼122 Á 6 þ 0 Á 42 A photoperiod, differently from modern egg-type
hybrids because they still exhibit PR, and so the
ðr 2 ¼ 0 Á 991, P 0 Á 001, Slope SE ¼ 0 Á 036, provision of 8-h day-lengths during the rearing
SD ¼ 1 Á 70Þ period is sound practice. However, the delay in
sexual maturation when they are not reared on
where ASM ¼ mean age at 50% egg production short days questions the appropriateness of
(d) and A ¼ age at 2Á1 kg body weight and providing a day-length equal to the longest
photostimulation (d). However, the lack of anticipated natural day-length when out-of-
advance in ASM when birds were photostimu- season flocks are reared in poorly light-proofed,
lated at 45 d (2Á1 kg achieved by feeding ad curtain-sided or open-sided rearing accommoda-
libitum) indicates that, even when body weight tion. Indeed, whilst there was only a 3-d
is not limiting, juvenile PR takes between 45 and difference in age at 50% egg production in
75 d to be dissipated in broiler breeders. These winter-hatched broiler breeders (latitude 30 S)
findings agree with data for (ad libitum-fed) truly given either a simulated naturally increasing or
seasonal breeding species that 9 to 12 weeks of decreasing day-length to 20 weeks and birds
short days are needed before the birds are reared on constant 14-h days (Lewis et al.,
maximally responsive to long days, for example, 2005b), the latter group subsequently laid
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Red-legged partridge (Creighton, 1988). between 6 and 10 fewer eggs to 60 weeks than
The sooner a broiler breeder reaches 2Á1 kg the simulated ‘naturally lit’ groups when they
body weight, the quicker it will have dissipated were transferred to open-sided housing and 16-h
PR and the earlier it can be photostimulated to days, and with no compensatory increase in egg
advance ASM (Figure 10), but accelerating weight. This is contrary to the response of
growth above that recommended by the primary egg-type hybrids, which, if exposed to increasing
breeding company has invariably resulted in day-lengths during the rearing period, become
inferior performance. In addition to having sexually mature prematurely and lay undesirably
poorer rates of lay, accelerated-growth birds, small eggs.
despite using less feed to reach 2Á1 kg, consume 2 The superior egg production of birds initially
more feed to, and have a heavier body weight at, transferred to a mildly stimulatory day-length
50% egg production (Figure 11), whilst the (11 or 12 h) but then given further increments to
proportion of eggs suitable for setting are 16 h, compared with the performance of birds
reduced by an increased number of multiple increased abruptly to 16 h, supports the step-up
ovulations (for example, Leeson and Summers, lighting regimen recommended by the primary
1983; Yu et al., 1992; Hocking, 1993, 1996, 2004; breeding companies. However, the consistently
Yuan et al., 1994; Hocking et al., 2002; Gous and poorer egg production of birds maintained on, or
Cherry, 2004; Ciacciariello and Gous, 2005; abruptly or incrementally transferred to 16 h,
Lewis and Gous, 2006a, b).
20 3.5
210
19
3.3
Body weight (kg)
200
Feed intake (kg)
18
Age at 50% lay (d)
190 17 3.1
180 16 2.9
15
170 2.7
14
160
13 2.5
150 85 95 105 115 125 135 145
40 55 70 85 100 115 130 145 160 175
Age at 2.1 kg body weight (d)
Age at 2.1 kg and photostimulation (d)
Figure 11. Cumulative feed intake to (solid line), and body
Figure 10. Mean age at 50% egg production for broiler weight at (broken line), 50% egg production for broiler breeders
breeders transferred from 8 h to a stimulatory photoperiod (11, grown to reach 2Á1 kg body weight and transferred to
12, 14 or 16 h) at various ages and at approximately 2Á1 kg stimulatory photoperiods at different ages (m Leeson and
body weight (f Leeson and Summers, 1983; Ciacciariello Summers, 1983; f Gous and Cherry, 2004; g Ciacciariello
and Gous, 2005; g, œ unpublished data from University of and Gous, 2005; œ Lewis and Gous, 2006a; Lewis and
KwaZulu-Natal). Differences among trials were removed by Gous, 2006b). Differences among trials were removed by least
least squares analysis. squares analysis.