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Light in broiler breeder


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Light in broiler breeder

  1. 1. This article was downloaded by: [UQ Library]On: 09 August 2011, At: 16:12Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: MortimerHouse, 37-41 Mortimer Street, London W1T 3JH, UK British Poultry Science Publication details, including instructions for authors and subscription information: 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 2007To cite this article: Dr P.D. Lewis (2006): A review of lighting for broiler breeders, British Poultry Science, 47:4, 393-404To link to this article: SCROLL DOWN FOR ARTICLEFull terms and conditions of use: article may be used for research, teaching and private study purposes. Any substantial or systematicreproduction, re-distribution, re-selling, loan, sub-licensing, systematic supply or distribution in any form toanyone is expressly forbidden.The publisher does not give any warranty express or implied or make any representation that the contentswill be complete or accurate or up to date. The accuracy of any instructions, formulae and drug doses shouldbe independently verified with primary sources. The publisher shall not be liable for any loss, actions, claims,proceedings, demand or costs or damages whatsoever or howsoever caused arising directly or indirectly inconnection with or arising out of the use of this material.
  2. 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-Downloaded by [UQ Library] at 16:12 09 August 2011 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: ISSN 0007–1668(print)/ISSN 1466–1799 (online)/06/040393—12 ß 2006 British Poultry Science Ltd DOI: 10.1080/00071660600829092
  3. 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,Downloaded by [UQ Library] at 16:12 09 August 2011 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. 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-Downloaded by [UQ Library] at 16:12 09 August 2011 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. 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.Downloaded by [UQ Library] at 16:12 09 August 2011 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. 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 toDownloaded by [UQ Library] at 16:12 09 August 2011 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. 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 lessDownloaded by [UQ Library] at 16:12 09 August 2011 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. 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 modernDownloaded by [UQ Library] at 16:12 09 August 2011 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. 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 kgDownloaded by [UQ Library] at 16:12 09 August 2011 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. 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 laidDownloaded by [UQ Library] at 16:12 09 August 2011 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.