A dark-light interface that the animal seems to interpret as the start of the day or subjective day. A light-dark interface that the animal seems to interpret as an end.
GENERAL INTRODUCTION 2. LITERATURE REVIEW
PHOTOPERIOD AND OVIPOSITION TIME .1 The open period for LH release
PHOTOPERIOD AND EGGSHELL QUALITY
FEEDING TIME AND EGGSHELL QUALITY .1 Calcium metabolism and eggshell formation
THE EFFECT OF PHOTOPERIOD ON OVIPOSITION TIME OF BROILER BREEDERS
INTRODUCTION
MATERIALS AND METHODS 3.3 RESULTS AND DISCUSSION
THE EFFECT OF FEEDING TIME ON BROILER BREEDER EGGSHELL
PHOTOPERIOD AND OVIPOSITION TIME
- The open period for LH release
- Length of the photoperiod and/or scotoperiod and entrainment of oviposition
- Photoperiod and eggshell thickness
- Time of calcium intake and eggshell quality
- Calcium supplementation via free choice feeding
- Feeding time and broiler breeder performance
The effect of the light-dark cycle on the time of egg laying was investigated by Warren and Scott (1936). In addition, the phase angle of the open period within the photoarray is determined by the duration of light and dark, as shown in Figure 2.2. In experiments as shown in Figure 2.3 (Etches et al., 1984), the periodicity of the open period for LH release was shown to be the same as the period of the light-dark cycle.
The length of the photoperiod was found to affect the pattern of egg laying. Bhatti and Morris (1988) attributed this change in oviposition pattern to a variable phase relationship between dusk and the onset of the open period. Similar findings were reported by Etches (1990), who found a relationship between the mean time of egg laying and the duration of the scotophase (Figure 2.11). about with r-.
Relationship between the mean time of oviposition after lights-out and the length of the scotophase. At the end of the feeding period, half of the ingested feed remained in the digestive tract. Three hours after feeding, only a third of the feed remained in the digestive tract.
1983c) conducted an experiment to determine the importance of the timing of Ca introduction on eggshell quality of broilers.
FEEDING TIME AND OVIPOSITION TIME
THE NEED FOR FURTHER RESEARCH
Furthermore, because egg timing is important in the commercial operations of broiler breeders in relation to egg collection and grading, such research is of practical importance. Reduced shell quality can negatively affect fecundity, with thinner shells associated with reduced hatchability and increased embryonic mortality (McDaniel et al., 1981; Roque and Soares, 1994). Therefore, a study of the effect of photoperiod on eggshell quality of breeder birds is needed, especially because many breeder bird producers provide birds with photoperiods longer than required for maximum egg production.
The effect of feeding time on oviposition time and eggshell quality of broiler breeders was reported. However, not all bird breeds lay their eggs at the same time when they get a normal day length; egg-laying in brown-egg hybrids, for example, is consistently about 1.5 hours earlier than in white-egg hybrids (Lewis, 1987; . Lewis et al., 1995). In contrast, both types of chickens show a similar rate of change in oviposition time for a given change in photoperiod (Lewis et al., 1995).
However, there is a lack of information on the effect of photoperiod on laying time for control-fed broiler breeders. This chapter reports the findings of two experiments in which the egg-laying time of breeding birds was measured for photoperiods ranging from 8 to 16 h.
MATERIALS AND METHODS
A genetic difference in the setting of the open period phase for LH release is thought to be a likely reason for this discrepancy. The second experiment used the same genotype but with 60 hens in individual cages in each of two light-tight rooms; one room on an 8-hour and the other on a 16-hour light period. Light was provided by 100 incandescent lamps with an average light intensity of 34 ± 1.8 lux on the inlet trough of the upper, middle and lower layers of the cages.
As in the first experiment, eggs were cleaned on the preceding evenings, and collections were made continuously throughout each day's egg-laying period. Six collections were made over three 2-d periods during the 37th and 38th weeks of age. Oviposition times for hens in the second experiment were later than those in the first experiment because age-related increases in egg weight cause egg laying to be progressively delayed as hens age (Lewis and Perry, 1991).
Data for the proportion of eggs laid before dawn were divided into two sets with regression lines above and below a hinge point, as described by Lewis et al.
RESULTS AND DISCUSSION
The breakpoint was determined by iterating at 0.25-hour intervals to identify the model that minimized the residual sums of squares around the fitted model. Table 3.1. Average laying time and time at which 50% of eggs were laid (h.min) relative to the start of the photoperiod in which egg laying occurred for the given broiler breeders. Regression of !Uean oviposition time (using day lengths :::; 14 h and adjusted data for experiment 2) on photoperiod showed that it advanced by about 0.5 h for each 1-h increase in photoperiod between 8 and 14 h relative to initial dusk (but delayed by 0.5 hours relative to current dawn).
Mean oviposition time relative to the preceding dusk for Cobb 500 broiler breeders maintained at different photoperiods (e Experiment 1, ~ modified Experiment 2); The dotted line represents a regression for 1SA Brown hybrids with brown eggs and the dotted line a regression for Shaver288 hybrids with white eggs (from Lewis et al., 1995). A 'hinge' analysis indicated that the number of eggs laid before dawn will be minimized by providing a photoperiod of ~12.25 hours, and that for day lengths shorter than this number will increase by approximately 0.045 for each 1-hour reduction in photoperiod.
The change in the proportion of eggs laid before dawn for photoperiods between 12.25 and 16 h is negligible and for practical reasons can be considered constant at less than 0.01.
INTRODUCTION
Both shell weight and shell thickness index for commercial egg layers fed ad libitum have been reported to decrease with photoperiod (Lewis et al., 1994). However, increased egg production rate, heavier egg weight, and higher feed intake, which generally result from exposure of egg-type hybrids to longer photoperiods, have been discounted as reasons for quality differences. of the peel (Lewiset al., 1994). Instead, differences in the temporal relationship of shell formation to feeding patterns, plasma calcium concentrations, and hormonal events controlling the ovulatory cycle have been suggested as possible causal factors (Lewis et al., 1994).
Differences in the pattern of daily plasma melatonin concentration under the different photoperiods can also modify osteoblast and osteoclast activity (Cardinali et al., 2003), affecting the mobilization of calcium from medullary bone. However, this is a conjecture because the molecular mechanisms that support the complicated movements of calcium during the shelling process are still poorly understood (Etches, 1996b). The effect of photoperiod on shell quality is of practical importance because reduced shell quality can negatively impact fertility, with poorer (thinner) shells associated with greater weight loss during incubation (McDaniel et al., 1979), and reduced hatchability, and increased embryonic development. mortality for eggs with a specific gravity <1.080 (McDaniel et al., 1981; Roque and Soares, 1994).
Photoperiodic influences on shell quality in broiler breeders have not been reported, and therefore a study was undertaken to determine shell weight and shell thickness index data for 52-week-old broiler breeders maintained on six different photoperiods from 3 days of age.
MATERIALS AND METHODS
RESULTS AND DISCUSSION
Average egg weight, shell weight and shell thickness index of broiler breeders given different photoperiods (protocol1). Average egg weight, shell weight, and shell thickness index of eggs laid at different times for broiler breeders given 13- or 14-h photoperiods (protocol 2). A combination of the increasing egg weight and decreasing shell weight resulted in a significant decrease in the shell thickness index of 0.57 mg/cm2 for each 1-hour extension of the photoperiod (r2=0.696, slope SE =0.189, P=0.039).
While there were significant differences in laying rate between photoperiods, no significant relationship was found between shell thickness index and laying rate at 52 weeks. According to the second egg collection protocol, the effect of laying time on egg weight, shell weight and shell thickness index was investigated. Eggshell thickness index increased slightly during the day by 0.16 mg/cm2 per hour (P=0.315), and eggs laid by hens in 14-hour photoperiods tended to have thinner shell thicknesses than those laid in 13-hour photoperiods ( P=0.131).
It can be concluded that hens given longer photoperiods lay eggs that have lower shell weight and have a lower shell thickness index than those in shorter photoperiods. The significant deterioration in shell thickness index with increasing day length (0.57 mg/cm2 per photoperiod hour) exceeded the non-significant improvement in oviposition time of 0.16 mg/cm2 per hour for laid eggs. later in the day.
INTRODUCTION
In contrast, Wilson and Keeling (1991) reported a delay in egg-laying due to afternoon feeding in standard-size broiler breeders, but did not observe such a response in dwarf breeders. Due to contradictions in the literature, three experiments were conducted to determine the effect of feeding time on shell quality and egg-laying time in broiler breeders.
MATERIALS AND METHODS
- RESULTS AND DISCUSSION
Consequently, these hens must store most of the Ca in the bone and, therefore, the path that Ca takes to the eggshell. It is important to consider the proximity of chickens to different treatments in all experiments. The delay in MOT by min per hour of delay in feeding time (Figure 5.2) may thus be an underestimate of the effect of feeding time on laying time.
Mean oviposition time (h.min) relative to the onset of the photoperiod at which oviposition occurred for broilers fed at different times in Experiments 3, 4 and 5. 1981) Effects of Light Interruption Schedule on Oviposition Time and Luteinizing Hormone Levels , progesterone and corticosterone in domestic hen plasma. Effect of feeding time on calcium status in the digestive system and eggshell quality in broiler breeders.
A study of the influence of light and darkness on the reproductive performance of the bird. 1981). 1979) Plasma inorganic phosphorus concentration during eggshell formation - effect of the physical form of dietary calcium. 1971) 1,25-dihydroxycholecalciferol: identification of the proposed active form of vitamin D3 in the intestine. 1973) Phosphate excretion in the laying hen.
1994) Effects of eggshell quality and broiler breeder age on hatchability. 1996) Interaction of feeding time and temperature and their relationship to broiler broiler performance.
