The Effects of Ahemeral Light and Dark Cycles on Growth and Sexual Maturity in Chickens R. J. ETCHES Department of Animal and Poultry Sciences, University ofGuelpb, Guelph, Ontario, Canada NIG 2WI (Received for publication November 10, 1976)
In recent years, a large body of evidence has a c c u m u l a t e d which implicates circadian rhythms in the control of most physiological systems. In birds, circadian rhythms have been recognized in the mechanisms which control the timing of ovulation (Morris, 1973) and in the mechanism which controls the sensitivity of the gonads to photostimulation (Follett, 1973). Body temperature is also subject to circadian rhythmicity (Cain and Wilson, 1974). The plasma concentrations of corticosterone are also regulated by circadian rhythms (Boissin and Assenmacher, 1970) and such functions as energy metabolism and food intake are also influenced by circadian rhythms (Aschoff and Pohl, 1970). More recently, John and George (1972) have identified circadian rhythms in plasma concentrations of free fatty acids. In general, circadian rhythms will adapt to light-dark cycles which recur at 20 to 30 h. intervals. Beyond these limits, the rhythms usually revert to an endogenous rhythm which approximates 24 h. Biological growth can be viewed as the end product of intermediary metabolism. In view of the apparent ubiquitous occurrence of circadian rhythms in the substrates of and mechanisms controlling metabolism, it was hypothesized that growth should be regulated by circadian rhythms. In an attempt to demonstrate this hypothesis, replacement pullets were reared under light-dark cycles which recurred at 21, 24 and 28 h. intervals. MATERIALS AND METHODS The chicks were purchased from
Shaver
Poultry Breeding Farms Ltd. They were reared in environmentally controlled chambers in which the temperature was maintained within 0.5 C. of the preset value. The temperature during the first week was 32.5 C. and was decreased by 2.5 C. during each subsequent week. After 6 weeks of age the temperature was maintained at 20 C. The lighting regimes were 14L:7D (21 h. cycles); 14L:10D (24 h. cycles) and 14L:14D (28 h. cycles). Therefore, at 20 weeks of age there were 160 "days" of 21 h. cycles, 140 "days" of 24 h. cycles and 120 "days" of 28 h. cycles. The birds were weighed individually to the nearest gm at 0, 2, 4, 8, 12 and 16 weeks of age. The age of sexual
E - 800
Solar
weeks
FIG. 1. Body weights of replacement pullets reared in 14L:7D, 14L.10D and 14L:14D. At 16 weeks of age the pullets in 14L:7D, 14L:10D and 14L:14D photoperiods were exposed to 128, 112, and 96 light-dark cycles, respectively.
1039
Downloaded from http://ps.oxfordjournals.org/ at Florida International University on June 6, 2015
ABSTRACT Replacement pullets were reared in environmentally controlled chambers in which the lighting schedule was 14L:7D, 14L:10D or 14L:14D. Both temperature and humidity were constant throughout the experiment. Neither body weight nor age at sexual maturity were altered by these lighting schedules. It was concluded that a unifying hypothesis to explain the various effects of photoperiods on growth and sexual maturity would probably not involve circadian rhythms. Poultry Science 56:1039-1040, 1977
1040
ETCHES TABLE 1. — The analysis of variance table for body weights of pullets reared in ahemeral light-dark cycles
Source
d.f.
Light-dark cycle Age Age X light-dark cycle Error
2 5 10 1092
M.S.
Fcalc.
16576 4177512 23970 5169
3.21* 8080** 4.64**
*P 0 . 0 5 , F = 1.41) by t h e lighting schedule. T h e pullets reared in 21 h., 24 h. and 28 h. light-dark cycles laid their first eggs at 134, 131 and 135 days of age, respectively. T h e analysis of b o d y weight likewise d e m o n strated t h a t t h e pullets did n o t i n t e r p r e t each light-dark cycle as a solar day. T h e m e a n b o d y weights are illustrated in Figure 1. T h e lack of a difference in t h e p a t t e r n of g r o w t h b e t w e e n pullets reared in 21 h., 24 h. and 2 8 h. cycles argues against t h e regulation of g r o w t h b y a circadian r h y t h m . It would, therefore, appear" t h a t a unifying t h e o r y which would explain t h e m a n y and varied effects of different p h o t o periods during g r o w t h and m a t u r a t i o n w o u l d n o t include circadian r h y t h m s . T h e analysis of variance of b o d y weight indicated a significant interaction b e t w e e n age and lighting schedule (Table 1). D u e t o t h e
REFERENCES Aschoff, J., and H. Pohl, 1970. Rhythmic variations in energy metabolism. Fed. Proc, Amer. Soc. Exp. Biol. 29:1541-1552. Boissin, J., and I. Assenmacher, 1970. Circadian rhythms in adrenal cortical activity in the quail. J. Interdisc. Cycle Res. 1:251—265. Cain, J. R., and W. O. Wilson, 1974. The influence of specific environmental parameters on circadian rhythms of chickens. Poultry Sci. 53:1438—1447. Follett, B. K., 1973. Circadian rhythmicity and time measurement in avian photoperiodicity. In: The Environment and Reproduction in Mammals and Birds. Edited by J. S. Perry and I. W. Rolands, Blackwell, Oxford, J. Reprod. Fert. Suppl. 19:5-18. John, T. M., and J. C. George, 1972. Circadian rhythm of free fatty acid level in plasma and pectoralis muscle of pigeon. J. Interdisc. Cycle Res. 3: 37-39. Morris, T. R., 1973. The effects of ahemeral light and dark cycles on egg production in the fowl. Poultry Sci. 52:423-445.
Downloaded from http://ps.oxfordjournals.org/ at Florida International University on June 6, 2015
**P
In recent years, a large body of evidence has a c c u m u l a t e d which implicates circadian rhythms in the control of most physiological systems. In birds, circadian rhythms have been recognized in the mechanisms which control the timing of ovulation (Morris, 1973) and in the mechanism which controls the sensitivity of the gonads to photostimulation (Follett, 1973). Body temperature is also subject to circadian rhythmicity (Cain and Wilson, 1974). The plasma concentrations of corticosterone are also regulated by circadian rhythms (Boissin and Assenmacher, 1970) and such functions as energy metabolism and food intake are also influenced by circadian rhythms (Aschoff and Pohl, 1970). More recently, John and George (1972) have identified circadian rhythms in plasma concentrations of free fatty acids. In general, circadian rhythms will adapt to light-dark cycles which recur at 20 to 30 h. intervals. Beyond these limits, the rhythms usually revert to an endogenous rhythm which approximates 24 h. Biological growth can be viewed as the end product of intermediary metabolism. In view of the apparent ubiquitous occurrence of circadian rhythms in the substrates of and mechanisms controlling metabolism, it was hypothesized that growth should be regulated by circadian rhythms. In an attempt to demonstrate this hypothesis, replacement pullets were reared under light-dark cycles which recurred at 21, 24 and 28 h. intervals. MATERIALS AND METHODS The chicks were purchased from
Shaver
Poultry Breeding Farms Ltd. They were reared in environmentally controlled chambers in which the temperature was maintained within 0.5 C. of the preset value. The temperature during the first week was 32.5 C. and was decreased by 2.5 C. during each subsequent week. After 6 weeks of age the temperature was maintained at 20 C. The lighting regimes were 14L:7D (21 h. cycles); 14L:10D (24 h. cycles) and 14L:14D (28 h. cycles). Therefore, at 20 weeks of age there were 160 "days" of 21 h. cycles, 140 "days" of 24 h. cycles and 120 "days" of 28 h. cycles. The birds were weighed individually to the nearest gm at 0, 2, 4, 8, 12 and 16 weeks of age. The age of sexual
E - 800
Solar
weeks
FIG. 1. Body weights of replacement pullets reared in 14L:7D, 14L.10D and 14L:14D. At 16 weeks of age the pullets in 14L:7D, 14L:10D and 14L:14D photoperiods were exposed to 128, 112, and 96 light-dark cycles, respectively.
1039
Downloaded from http://ps.oxfordjournals.org/ at Florida International University on June 6, 2015
ABSTRACT Replacement pullets were reared in environmentally controlled chambers in which the lighting schedule was 14L:7D, 14L:10D or 14L:14D. Both temperature and humidity were constant throughout the experiment. Neither body weight nor age at sexual maturity were altered by these lighting schedules. It was concluded that a unifying hypothesis to explain the various effects of photoperiods on growth and sexual maturity would probably not involve circadian rhythms. Poultry Science 56:1039-1040, 1977
1040
ETCHES TABLE 1. — The analysis of variance table for body weights of pullets reared in ahemeral light-dark cycles
Source
d.f.
Light-dark cycle Age Age X light-dark cycle Error
2 5 10 1092
M.S.
Fcalc.
16576 4177512 23970 5169
3.21* 8080** 4.64**
*P 0 . 0 5 , F = 1.41) by t h e lighting schedule. T h e pullets reared in 21 h., 24 h. and 28 h. light-dark cycles laid their first eggs at 134, 131 and 135 days of age, respectively. T h e analysis of b o d y weight likewise d e m o n strated t h a t t h e pullets did n o t i n t e r p r e t each light-dark cycle as a solar day. T h e m e a n b o d y weights are illustrated in Figure 1. T h e lack of a difference in t h e p a t t e r n of g r o w t h b e t w e e n pullets reared in 21 h., 24 h. and 2 8 h. cycles argues against t h e regulation of g r o w t h b y a circadian r h y t h m . It would, therefore, appear" t h a t a unifying t h e o r y which would explain t h e m a n y and varied effects of different p h o t o periods during g r o w t h and m a t u r a t i o n w o u l d n o t include circadian r h y t h m s . T h e analysis of variance of b o d y weight indicated a significant interaction b e t w e e n age and lighting schedule (Table 1). D u e t o t h e
REFERENCES Aschoff, J., and H. Pohl, 1970. Rhythmic variations in energy metabolism. Fed. Proc, Amer. Soc. Exp. Biol. 29:1541-1552. Boissin, J., and I. Assenmacher, 1970. Circadian rhythms in adrenal cortical activity in the quail. J. Interdisc. Cycle Res. 1:251—265. Cain, J. R., and W. O. Wilson, 1974. The influence of specific environmental parameters on circadian rhythms of chickens. Poultry Sci. 53:1438—1447. Follett, B. K., 1973. Circadian rhythmicity and time measurement in avian photoperiodicity. In: The Environment and Reproduction in Mammals and Birds. Edited by J. S. Perry and I. W. Rolands, Blackwell, Oxford, J. Reprod. Fert. Suppl. 19:5-18. John, T. M., and J. C. George, 1972. Circadian rhythm of free fatty acid level in plasma and pectoralis muscle of pigeon. J. Interdisc. Cycle Res. 3: 37-39. Morris, T. R., 1973. The effects of ahemeral light and dark cycles on egg production in the fowl. Poultry Sci. 52:423-445.
Downloaded from http://ps.oxfordjournals.org/ at Florida International University on June 6, 2015
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