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Rearing Leghorn Pullets on a Photoperiod of 1 Hour of Light and 11 Hours of Darkness with Respect to Growing and Laying Performance as Influenced by Age at Housing and Strain
Rearing Leghorn Pullets on a Photoperiod of 1 Hour of Light and 11 Hours of Darkness with Respect to Growing and Laying Performance as Influenced by Age at Housing and Strain A. GOLDROSEN1 and R. B. BUCKLAND Department of Animal Science, Macdonald College ofMcGill University, Ste. Anne de Bellevue, Quebec, Canada HOA ICO (Received for publication July 13, 1976)
Poultry Science 56:741-746, 1977 INTRODUCTION
In a continuing effort to attain maximum productivity with least cost, many forms of feed restriction have been imposed on chickens during all phases of production. These have been reviewed by Lee et al. (1971) and Balnave (1973). Intermittent lighting has received much attention with respect to broiler production, and this material was recently reviewed by Buckland (1975). In his review, Buckland suggests that improved feed efficiency may be the most consistant advantage of using intermittent lighting programs for broiler production. Limited work has been conducted with respect to intermittent lighting for egg-type chickens. King (1961) observed that providing light in 2, 4 or 6 periods per day hastened sexual maturity when compared to birds receiving the same amount of light per day in a single period. In comparing ten minute periods of light every 4 hours with 17 hours of continuous light per 24 hours during the laying period, Bell (1974) reported no effect on egg production. He did re-
1 Present address: Plant Products Division, Agriculture Canada, Ottawa, Canada.
port in two trials that intermittent light resulted in increased egg size. The objective of the work reported here was to determine the effect of growing Leghorn pullets on two cycles of 1 hour of light and 11 hours of darkness every 24 hours with respect to performance during the growing and laying period.
MATERIALS AND METHODS
Experimental Stocks. Two commercial strains of Single Comb White Leghorns were used in each of two trials. In the first trial both strains (7Y5 and 19) were hatched on April 12, 1973, and in the second trial both strains (7Y7 and 7X) were hatched on May 7, 1974. Growing Period. All birds were reared in insulated, light-tight, negatively ventilated pens measuring 3.64m. X 3.65m. (150 birds per pen) giving each bird an area of 0.08 sq. m. Four pens were used per trial (2 per treatment) with the strains grown intermingled. Each bird was provided with 4cm. of feeding space and 1.27 cm. of watering space. Standard brooding practices (hot water heat with hoovers) were used throughout and the birds were vaccinated for Mareks, Newcastle, bronchitis and laryngo-
741
Downloaded from http://ps.oxfordjournals.org/ at NERL on May 23, 2015
ABSTRACT Two trials in two years, each involving 2 commercial strains of White Leghorns, were conducted to compare the growing of Leghorn pullets on: (1) one hour of light and 11 hours of darkness (1L:11D) from day 4 to housing; vs. (2) a program of 8 hours of light and 16 hours of darkness (8L:16D). Lighting treatment had a significant effect on body weight in trial 1 with birds grown on 8L:16D being heavier at 4 and 8 weeks of age, while those grown on 1L:11D were heavier at 16 weeks of age. Birds grown on 1L:11D did consume less feed to 20 weeks than those grown on 8L:11D in trial 1 (6.24 kg. vs. 6.61 kg.) and in trial 2 (6.75 kg. vs. 7.60 kg.) where the effect was significant (P<0.05). Birds grown on 1L:11D had a greater age at 50 percent production in both trials. In trial 2, it was found that this effect could be modified by housing birds at different ages. There was no effect of lighting program during the growing period on subsequent percent egg production in trial 1 though in trial 2 the effect was significant (P<0.05) (1L:11D, 77.2% vs. 8LT6D, 75.8%) as was the interaction of lighting treatment by strain (P<0.05). There was no effect of lighting treatment on kg. of feed per dozen eggs, but in trial 2 birds grown on 1L:11D laid significantly (P<0.05) heavier eggs. Birds grown on 1L:11D showed a greater return over feed and chick costs for one strain in trial 1 and for both strains in trial 2 at an average of 30 cents per bird. In neither case were the differences significant.
742
GOLDROSEN AND BUCKLAND for each period, egg weight based on one day's production per group for each period, mortality based on cumulative mortality until the end of the last laying period, and shell thickness and Haugh units as measured during the sixth 28day period in each trial. Profitability in both trials was also calculated as returns over chick and feed costs. The effect of lighting treatment during the growing period on strain, replicate, 28-day period and age at housing (in trial 2 only) and their interactions were determined for both trials by analysis of variance using subclass means. All percents were converted to the arc sine for purposes of analysis. RESULTS Light treatment had a significant effect (P<0.05) on body weight at 4, 8 and 16 weeks of age in trial 1 with the birds grown on 8L: 16D being heavier at 4 and 8 weeks while at 16 weeks the birds grown on 1L:11D were heavier (Table 1). In trial 2 there was no significant effect of light treatment on body weight at any age (Table 1) nor was the interaction of light treatment by strain significant in either trial. Birds grown on 1L:11D consumed less feed than those grown on 8L:16D in both trials (Table 2). This difference was significant only in trial 2 at 18 (P<0.05), 20 (P<0.01) and 22 (P<0.01) weeks of age, but again the trend was consistent at all ages for birds grown on 1L: 11D to eat less feed. Neither light treatment nor strain had a significant (P<0.05) effect on percent mortality during the growing period in either trial (trial 1: 1L:11D, 0.8% vs. 8L:16D, 0.1%; trial 2: 1L: 11D, 8.0% vs. 8L:16D, 6.5%). Age at sexual maturity was delayed in both trials among birds grown on 1L:11D (P<0.01) (Table 3). Strain also had a significant effect (P<0.01) on age at sexual maturity in both trials while housing birds at older ages increased age at sexual maturity in trial 2 (P<0.01). Lighting treatment during the growing period had no effect on subsequent overall egg production (Table 3) in trial 1 but did (P<0.05) in trial 2 (1L:11D, 77.2% vs. 8L:16D, 75.8%). Strain (P<0.05) and 28-day period (P<0.01) each had a significant effect in both trials while the effect of age at housing on overall production was non significant in trial 2. The interaction of lighting treatment by strain (P<0.05), strain by housing age (P<0.01), light treatment
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tracheitis. The birds received an 18 percent protein chick starter ration from 0 to 8 weeks and a 16 percent protein grower ration from 8 weeks until housing. All birds were exposed to 24 hours of continuous light for the first day and for the next 2 days the birds were given 23 hours of light. At 4 days of age the experimental lighting programs were initiated. Treatment one consisted of 11 hours of darkness and 1 hour of light intermittently twice a day (1L:11D), while treatment two was a control of 8 hours of light and 16 hours of darkness per day (8L:16D). One twenty-five watt light bulb was used per pen giving a light intensity of between 10 and 11 lux at the feeder level. Performance during the growing period was evaluated by the determination of body weight and feed consumption at 4, 8, 12, 16 and 20 weeks in trial 1 and at 4, 8, 12, 16, 18, 20 and 22 weeks in trial 2. Percent mortality was calculated at the end of the growing period for each trial. In trial 1, the birds were transferred to the laying house at 20 weeks of age while in trial 2 a proportion of the birds were housed at each of 16, 18, 20 and 22 weeks of age. The effect of lighting treatment, strain and replicate and their interactions on body weight, feed consumption and mortality (arc sine) was determined by analysis of variance using subclass means. Since the strains were reared intermingled, the effect of strain on feed consumption during the growing period could not be evaluated. Laying Period. The Leghorns in both trials received 14 hours of light and were fed a 16 percent protein laying ration. They were housed in semi-stair step cages at 2 birds per cage measuring 30.4cm. X 40.6cm. in trial 1 and 25.4cm. X 40.6cm. in trial 2. In both trials the birds were housed in four replicates. In trial 1 twenty birds were housed per treatment group (two lighting treatments X two strains) per replicate and handled as a group. In trial 2, eight birds were housed per treatment group (two lighting treatments X two strains x four housing ages) per replicate and handled as a group. The laying period in both trials consisted of eight 28-day periods. Performance was evaluated with respect to age at sexual maturity (50 percent production for 3 consecutive days for each group), percent egg production calculated on a hen-housed basis for each period, feed conversion calculated as kg. of feed per dozen eggs
PHOTOPERIOD AND PERFORMANCE
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PHOTOPERIOD AND PERFORMANCE
Neither the main effects nor their interactions had a significant effect, in either trial, on Haugh units, shell thickness, laying house mortality or returns over chick and feed costs. However, in trial 2 birds grown on 1L:11D did show an increased return of 30 cents per bird (P=0.10) and in trial 1 7Y5 strain birds grown on 1L:11D showed a greater return by 24 cents. On the other hand, strain 19 birds in trial 1 grown on 8L:16D showed a greater return by $1.06. DISCUSSION
Growing Period. With respect to body weight the results reported here indicate that light restriction (1L:11D) during the growing period does not have a deleterious effect on Leghorn pullet body weight except perhaps at early ages as evidenced in trial 1. Rather, as housing age approaches (16+ weeks of age), birds grown on 1L:11D are slightly heavier than those grown on a standard program of 8L:16D. Coupled with the consistent, though only significant in trial 2, reduced feed consumption of the birds on 1L:11D compared to those grown on 8L:16D, this indicates that birds grown on 1L:11D not only consumed less feed but utilized it more efficiendy. This agrees with the literature on market chickens and turkeys as reviewed by Buckland (1975) and demonstrates that substantial feed savings can be realized by growing Leghorn pullets on light restriction programs such as 1L:11D. When applied at 4 days of age the lighting program of 1L:11D seemed to have no effect on the birds finding the feed or water as judged by the fact that light treatment did not have a significant effect
on growing mortality. Laying Period. The delay in sexual maturity by growing birds on 1L:11D in both trials was expected based on the concept that longer day lengths stimulate reproduction in the chicken. The larger effect noted in trial 1, particularly for strain 19, was not expected but may have been related to the fact that in trial 1 some birds were poorly debeaked. Detailed classifications of debeakings were not performed to substantiate or refute this. The authors believe the results in trial 2 more clearly reflect the effect of growing birds on 1L:11D compared to 8L: 16D with respect to age at sexual maturity. The earlier sexual maturity of birds housed at younger ages in trial 2 agrees with the results of Harrison et al. (1969) and demonstrates that a delay in sexual maturity by growing Leghorn pullets on a program of 1L:11D can be overcome by housing (lighting) them slightly earlier. The significant effect of strain on age at sexual maturity indicates that age for light stimulation may be different for different strains, but the lack of an interaction of lighting treatment or housing age with strain suggests similar trends in most Leghorn strains. The lack of significant effect of lighting program on subsequent egg production in trial 1 and the higher egg production of birds grown on 1L:11D in trial 2 suggests that this lighting program had no deleterious effects on overall production. In fact, the birds were able to recover from the few eggs lost due to delayed sexual maturity during the eight 28-day production periods. The lighting treatment by strain interaction in trial 2 does indicate the effect on subsequent egg production may be affected by strain which agrees with work of Proudfoot and Gowe (1967) who reported that not all Leghorn strains react in the same manner to all lighting programs. The interaction of strain by housing age on subsequent production further substantiates the possible importance of this interaction. The significant effect of 28-day period would be expected due to the normal production curve. The interactions involving 28-day period in trial 2 indicate that lighting treatment during the growing period, housing age and strain can affect the slope of the production curve. The lack of any significant effects of kg feed per dozen eggs was somewhat surprising in view of the significant effects noted with respect to percent egg production. The greater egg size for birds grown on 1L:
Downloaded from http://ps.oxfordjournals.org/ at NERL on May 23, 2015
by 28-day period (P<0.01), strain by 28-day period (P<0.01) and housing age by 28-day period (P<0.01) were significant in trial 2. Neither of the main effects nor their interactions had a significant effect on kg. feed per dozen eggs (Table 3) in either trial. With respect to egg weight the effect of light treatment during the growing period was significant (P<0.05) in trial 2 only (1L:11D, 58.0g. vs. 8L:16D, 57.lg.) although a similar trend was apparent for strain 7Y5 in trial 1 (Table 3). Strain had a significant effect (P<0.01) on egg size in trial 1 and the effect of 28-day period was significant (P<0.01) in both trials. The interactions of 28day period by light treatment were significant in trial 1 (P<0.05) as was the interaction of light treatment by housing in trial 2 (P<0.05).
745
746
GOLDROSEN AND BUCKLAND
ACKNOWLEDGEMENTS The authors thank Shaver Poultry Breeding Farms of Cambridge, Ontario, for donating the Leghorn chicks for both trials and thank Agriculture Canada for the support from Operating
Grant Number 3076. REFERENCES Balnave, D., 1974. The effect of feeding low-protein diets to pullets from hatch to point-of-lay and the quantitative restriction of food during the subsequent laying periods. British Poultry Sci. 15:395403. Bell, D. D., 1974. Intermittent feeding and lighting of layers. Proc. 1974 Aust. Poultry Sci. Conv. 1-10. Buckland, R. B., 1975. The effect of intermittent lighting programs on the production of market chickens and turkeys. World's Poultry Sci. J. 31: 262-270. Harrison, P. C , G. Shumaier and J. McGinnis, 1969. Reproductive development and response of white Leghorn pullets to increasing daylengths at different ages. Poultry Sci. 48:1021-1026. King, D. F., 1961. Effects of increasing, decreasing and constant lighting treatments on growing pullets. Poultry Sci. 40:479484. Lee, P. J., A. L. Gulliver and T. R. Morris, 1971. A quantitative analysis of the literature concerning the restricted feeding of growing pullets. British Poultry Sci. 12:413437. Proudfoot, F. G., and R. S. Gowe, 1967. The effect of photoperiodism and rearing period feed restriction on the performance of five Leghorn strains. Poultry Sci. 46:1056-1072.
Downloaded from http://ps.oxfordjournals.org/ at NERL on May 23, 2015
11D in trial 2 is probably related to the delayed sexual maturity of birds grown on this lighting program. This agrees with the results of Harrison et al. (1969) who found that egg size was directly related to age at sexual maturity. The effect of strain and 28-day period on egg size would be expected and the interactions involving 28-day period in trial 2 indicate that lighting program during the rearing period and age at housing can modify the effect of age of the hen on egg size. The generally greater, though nonsignificant return over feed and chick costs for birds grown on 1L:11D is largely due to the feed saved during the growing period and in part to the slightly greater egg production and egg size of birds grown on 1L:11D.
Poultry Science 56:741-746, 1977 INTRODUCTION
In a continuing effort to attain maximum productivity with least cost, many forms of feed restriction have been imposed on chickens during all phases of production. These have been reviewed by Lee et al. (1971) and Balnave (1973). Intermittent lighting has received much attention with respect to broiler production, and this material was recently reviewed by Buckland (1975). In his review, Buckland suggests that improved feed efficiency may be the most consistant advantage of using intermittent lighting programs for broiler production. Limited work has been conducted with respect to intermittent lighting for egg-type chickens. King (1961) observed that providing light in 2, 4 or 6 periods per day hastened sexual maturity when compared to birds receiving the same amount of light per day in a single period. In comparing ten minute periods of light every 4 hours with 17 hours of continuous light per 24 hours during the laying period, Bell (1974) reported no effect on egg production. He did re-
1 Present address: Plant Products Division, Agriculture Canada, Ottawa, Canada.
port in two trials that intermittent light resulted in increased egg size. The objective of the work reported here was to determine the effect of growing Leghorn pullets on two cycles of 1 hour of light and 11 hours of darkness every 24 hours with respect to performance during the growing and laying period.
MATERIALS AND METHODS
Experimental Stocks. Two commercial strains of Single Comb White Leghorns were used in each of two trials. In the first trial both strains (7Y5 and 19) were hatched on April 12, 1973, and in the second trial both strains (7Y7 and 7X) were hatched on May 7, 1974. Growing Period. All birds were reared in insulated, light-tight, negatively ventilated pens measuring 3.64m. X 3.65m. (150 birds per pen) giving each bird an area of 0.08 sq. m. Four pens were used per trial (2 per treatment) with the strains grown intermingled. Each bird was provided with 4cm. of feeding space and 1.27 cm. of watering space. Standard brooding practices (hot water heat with hoovers) were used throughout and the birds were vaccinated for Mareks, Newcastle, bronchitis and laryngo-
741
Downloaded from http://ps.oxfordjournals.org/ at NERL on May 23, 2015
ABSTRACT Two trials in two years, each involving 2 commercial strains of White Leghorns, were conducted to compare the growing of Leghorn pullets on: (1) one hour of light and 11 hours of darkness (1L:11D) from day 4 to housing; vs. (2) a program of 8 hours of light and 16 hours of darkness (8L:16D). Lighting treatment had a significant effect on body weight in trial 1 with birds grown on 8L:16D being heavier at 4 and 8 weeks of age, while those grown on 1L:11D were heavier at 16 weeks of age. Birds grown on 1L:11D did consume less feed to 20 weeks than those grown on 8L:11D in trial 1 (6.24 kg. vs. 6.61 kg.) and in trial 2 (6.75 kg. vs. 7.60 kg.) where the effect was significant (P<0.05). Birds grown on 1L:11D had a greater age at 50 percent production in both trials. In trial 2, it was found that this effect could be modified by housing birds at different ages. There was no effect of lighting program during the growing period on subsequent percent egg production in trial 1 though in trial 2 the effect was significant (P<0.05) (1L:11D, 77.2% vs. 8LT6D, 75.8%) as was the interaction of lighting treatment by strain (P<0.05). There was no effect of lighting treatment on kg. of feed per dozen eggs, but in trial 2 birds grown on 1L:11D laid significantly (P<0.05) heavier eggs. Birds grown on 1L:11D showed a greater return over feed and chick costs for one strain in trial 1 and for both strains in trial 2 at an average of 30 cents per bird. In neither case were the differences significant.
742
GOLDROSEN AND BUCKLAND for each period, egg weight based on one day's production per group for each period, mortality based on cumulative mortality until the end of the last laying period, and shell thickness and Haugh units as measured during the sixth 28day period in each trial. Profitability in both trials was also calculated as returns over chick and feed costs. The effect of lighting treatment during the growing period on strain, replicate, 28-day period and age at housing (in trial 2 only) and their interactions were determined for both trials by analysis of variance using subclass means. All percents were converted to the arc sine for purposes of analysis. RESULTS Light treatment had a significant effect (P<0.05) on body weight at 4, 8 and 16 weeks of age in trial 1 with the birds grown on 8L: 16D being heavier at 4 and 8 weeks while at 16 weeks the birds grown on 1L:11D were heavier (Table 1). In trial 2 there was no significant effect of light treatment on body weight at any age (Table 1) nor was the interaction of light treatment by strain significant in either trial. Birds grown on 1L:11D consumed less feed than those grown on 8L:16D in both trials (Table 2). This difference was significant only in trial 2 at 18 (P<0.05), 20 (P<0.01) and 22 (P<0.01) weeks of age, but again the trend was consistent at all ages for birds grown on 1L: 11D to eat less feed. Neither light treatment nor strain had a significant (P<0.05) effect on percent mortality during the growing period in either trial (trial 1: 1L:11D, 0.8% vs. 8L:16D, 0.1%; trial 2: 1L: 11D, 8.0% vs. 8L:16D, 6.5%). Age at sexual maturity was delayed in both trials among birds grown on 1L:11D (P<0.01) (Table 3). Strain also had a significant effect (P<0.01) on age at sexual maturity in both trials while housing birds at older ages increased age at sexual maturity in trial 2 (P<0.01). Lighting treatment during the growing period had no effect on subsequent overall egg production (Table 3) in trial 1 but did (P<0.05) in trial 2 (1L:11D, 77.2% vs. 8L:16D, 75.8%). Strain (P<0.05) and 28-day period (P<0.01) each had a significant effect in both trials while the effect of age at housing on overall production was non significant in trial 2. The interaction of lighting treatment by strain (P<0.05), strain by housing age (P<0.01), light treatment
Downloaded from http://ps.oxfordjournals.org/ at NERL on May 23, 2015
tracheitis. The birds received an 18 percent protein chick starter ration from 0 to 8 weeks and a 16 percent protein grower ration from 8 weeks until housing. All birds were exposed to 24 hours of continuous light for the first day and for the next 2 days the birds were given 23 hours of light. At 4 days of age the experimental lighting programs were initiated. Treatment one consisted of 11 hours of darkness and 1 hour of light intermittently twice a day (1L:11D), while treatment two was a control of 8 hours of light and 16 hours of darkness per day (8L:16D). One twenty-five watt light bulb was used per pen giving a light intensity of between 10 and 11 lux at the feeder level. Performance during the growing period was evaluated by the determination of body weight and feed consumption at 4, 8, 12, 16 and 20 weeks in trial 1 and at 4, 8, 12, 16, 18, 20 and 22 weeks in trial 2. Percent mortality was calculated at the end of the growing period for each trial. In trial 1, the birds were transferred to the laying house at 20 weeks of age while in trial 2 a proportion of the birds were housed at each of 16, 18, 20 and 22 weeks of age. The effect of lighting treatment, strain and replicate and their interactions on body weight, feed consumption and mortality (arc sine) was determined by analysis of variance using subclass means. Since the strains were reared intermingled, the effect of strain on feed consumption during the growing period could not be evaluated. Laying Period. The Leghorns in both trials received 14 hours of light and were fed a 16 percent protein laying ration. They were housed in semi-stair step cages at 2 birds per cage measuring 30.4cm. X 40.6cm. in trial 1 and 25.4cm. X 40.6cm. in trial 2. In both trials the birds were housed in four replicates. In trial 1 twenty birds were housed per treatment group (two lighting treatments X two strains) per replicate and handled as a group. In trial 2, eight birds were housed per treatment group (two lighting treatments X two strains x four housing ages) per replicate and handled as a group. The laying period in both trials consisted of eight 28-day periods. Performance was evaluated with respect to age at sexual maturity (50 percent production for 3 consecutive days for each group), percent egg production calculated on a hen-housed basis for each period, feed conversion calculated as kg. of feed per dozen eggs
PHOTOPERIOD AND PERFORMANCE
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PHOTOPERIOD AND PERFORMANCE
Neither the main effects nor their interactions had a significant effect, in either trial, on Haugh units, shell thickness, laying house mortality or returns over chick and feed costs. However, in trial 2 birds grown on 1L:11D did show an increased return of 30 cents per bird (P=0.10) and in trial 1 7Y5 strain birds grown on 1L:11D showed a greater return by 24 cents. On the other hand, strain 19 birds in trial 1 grown on 8L:16D showed a greater return by $1.06. DISCUSSION
Growing Period. With respect to body weight the results reported here indicate that light restriction (1L:11D) during the growing period does not have a deleterious effect on Leghorn pullet body weight except perhaps at early ages as evidenced in trial 1. Rather, as housing age approaches (16+ weeks of age), birds grown on 1L:11D are slightly heavier than those grown on a standard program of 8L:16D. Coupled with the consistent, though only significant in trial 2, reduced feed consumption of the birds on 1L:11D compared to those grown on 8L:16D, this indicates that birds grown on 1L:11D not only consumed less feed but utilized it more efficiendy. This agrees with the literature on market chickens and turkeys as reviewed by Buckland (1975) and demonstrates that substantial feed savings can be realized by growing Leghorn pullets on light restriction programs such as 1L:11D. When applied at 4 days of age the lighting program of 1L:11D seemed to have no effect on the birds finding the feed or water as judged by the fact that light treatment did not have a significant effect
on growing mortality. Laying Period. The delay in sexual maturity by growing birds on 1L:11D in both trials was expected based on the concept that longer day lengths stimulate reproduction in the chicken. The larger effect noted in trial 1, particularly for strain 19, was not expected but may have been related to the fact that in trial 1 some birds were poorly debeaked. Detailed classifications of debeakings were not performed to substantiate or refute this. The authors believe the results in trial 2 more clearly reflect the effect of growing birds on 1L:11D compared to 8L: 16D with respect to age at sexual maturity. The earlier sexual maturity of birds housed at younger ages in trial 2 agrees with the results of Harrison et al. (1969) and demonstrates that a delay in sexual maturity by growing Leghorn pullets on a program of 1L:11D can be overcome by housing (lighting) them slightly earlier. The significant effect of strain on age at sexual maturity indicates that age for light stimulation may be different for different strains, but the lack of an interaction of lighting treatment or housing age with strain suggests similar trends in most Leghorn strains. The lack of significant effect of lighting program on subsequent egg production in trial 1 and the higher egg production of birds grown on 1L:11D in trial 2 suggests that this lighting program had no deleterious effects on overall production. In fact, the birds were able to recover from the few eggs lost due to delayed sexual maturity during the eight 28-day production periods. The lighting treatment by strain interaction in trial 2 does indicate the effect on subsequent egg production may be affected by strain which agrees with work of Proudfoot and Gowe (1967) who reported that not all Leghorn strains react in the same manner to all lighting programs. The interaction of strain by housing age on subsequent production further substantiates the possible importance of this interaction. The significant effect of 28-day period would be expected due to the normal production curve. The interactions involving 28-day period in trial 2 indicate that lighting treatment during the growing period, housing age and strain can affect the slope of the production curve. The lack of any significant effects of kg feed per dozen eggs was somewhat surprising in view of the significant effects noted with respect to percent egg production. The greater egg size for birds grown on 1L:
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by 28-day period (P<0.01), strain by 28-day period (P<0.01) and housing age by 28-day period (P<0.01) were significant in trial 2. Neither of the main effects nor their interactions had a significant effect on kg. feed per dozen eggs (Table 3) in either trial. With respect to egg weight the effect of light treatment during the growing period was significant (P<0.05) in trial 2 only (1L:11D, 58.0g. vs. 8L:16D, 57.lg.) although a similar trend was apparent for strain 7Y5 in trial 1 (Table 3). Strain had a significant effect (P<0.01) on egg size in trial 1 and the effect of 28-day period was significant (P<0.01) in both trials. The interactions of 28day period by light treatment were significant in trial 1 (P<0.05) as was the interaction of light treatment by housing in trial 2 (P<0.05).
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GOLDROSEN AND BUCKLAND
ACKNOWLEDGEMENTS The authors thank Shaver Poultry Breeding Farms of Cambridge, Ontario, for donating the Leghorn chicks for both trials and thank Agriculture Canada for the support from Operating
Grant Number 3076. REFERENCES Balnave, D., 1974. The effect of feeding low-protein diets to pullets from hatch to point-of-lay and the quantitative restriction of food during the subsequent laying periods. British Poultry Sci. 15:395403. Bell, D. D., 1974. Intermittent feeding and lighting of layers. Proc. 1974 Aust. Poultry Sci. Conv. 1-10. Buckland, R. B., 1975. The effect of intermittent lighting programs on the production of market chickens and turkeys. World's Poultry Sci. J. 31: 262-270. Harrison, P. C , G. Shumaier and J. McGinnis, 1969. Reproductive development and response of white Leghorn pullets to increasing daylengths at different ages. Poultry Sci. 48:1021-1026. King, D. F., 1961. Effects of increasing, decreasing and constant lighting treatments on growing pullets. Poultry Sci. 40:479484. Lee, P. J., A. L. Gulliver and T. R. Morris, 1971. A quantitative analysis of the literature concerning the restricted feeding of growing pullets. British Poultry Sci. 12:413437. Proudfoot, F. G., and R. S. Gowe, 1967. The effect of photoperiodism and rearing period feed restriction on the performance of five Leghorn strains. Poultry Sci. 46:1056-1072.
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11D in trial 2 is probably related to the delayed sexual maturity of birds grown on this lighting program. This agrees with the results of Harrison et al. (1969) who found that egg size was directly related to age at sexual maturity. The effect of strain and 28-day period on egg size would be expected and the interactions involving 28-day period in trial 2 indicate that lighting program during the rearing period and age at housing can modify the effect of age of the hen on egg size. The generally greater, though nonsignificant return over feed and chick costs for birds grown on 1L:11D is largely due to the feed saved during the growing period and in part to the slightly greater egg production and egg size of birds grown on 1L:11D.