The leg strength of two commercial strains of meat chicken subjected to different incubation profiles

Lower egg shell temperatures (EST) during the first 2 weeks of incubation, notionally known as Slow start incubation, extended the standing time of a 5-week-old fast feathering meat chicken parent line. This study was designed to evaluate the effect of Slow start incubation on the standing ability of commercial meat chickens. Eggs from two strains of meat chickens, Strains 1 and 2, were incubated using either the Slow start incubation, (the initial EST was 36.75°C followed by a gradual increase in EST, reaching 37.8°C at day 16 of incubation), or Control incubation (EST 37.75°C to 38°C from the start of incubation until day 18 of incubation). Eggs were observed every 6 h from 468 h until 516 h of incubation to identify chick hatch window. At 516 h of incubation all chicks were taken out of the incubator (take-off). Chicks from each Strain and incubation treatment were randomly selected for assessment of chick weight, chick length, yolk sac weight, serum Ca and P, and femoral bone ash (BA). All unhatched eggs were inspected to determine the stage of embryo failure. Remaining chicks were grown for 5 weeks in floorpens. Weekly feed intake (FI), chick weight and feed conversion ratio (FCR) were determined. At 35 days of age the standing ability of visibly male birds was assessed in a latency-to-lie test. Compared to the Control, Slow start incubation delayed the average hatch time of both strains by ∼13 h, and reduced hatchability with 4.6% live but unhatched chicks, which was most evident in Strain 2. Significant differences due to main effects only were observed at take-off. Strain 1 chicks were significantly heavier and longer with higher serum Ca but significantly lower BA and serum P than Strain 2. Slow start incubation generated significantly heavier chicks that were shorter, but had significantly heavier yolk sacs, lower serum Ca but higher serum P than Control incubated chicks. During the 1^st week post hatch Strain 1 Control incubated chicks had significantly higher FI and higher FCR than all other Strain and incubation treatments. At 35 days of age Slow start incubated birds of both Strains stood significantly longer than those from the Control incubation. This experiment clearly demonstrated the ability of Slow start incubation of commercial meat chickens to improve their leg strength.     

Earlier hatching time predisposes Cobb broiler chickens to tibial dyschondroplasia

Fertile eggs from Cobb 500 broiler breeder hens were incubated to provide low starting egg shell temperatures (EST; 36.9°C to 37.3°C) which were gradually increased to 37.8°C during the first 7 to 15 days of incubation compared with eggs incubated with a constant EST of 37.8°C (standard conditions) over the first 18 days of incubation. Time of individual chick hatching (measured at 6 h intervals from 468 h of incubation), chick weight, chick length and yolk weight were measured at take-off and BW was measured at 7, 14, 28, 34 and 42 days of age. Male birds at 34 and 42 days of age were assessed for their ability to remain standing in a latency-to-lie test. At 34 and 42 days, male birds were examined for leg symmetry, foot pad dermatitis, hock bruising and scored (scale 0 to 4, where 0=no lesion and 4=lesions extending completely across the tibial growth plate) for tibial dyschondroplasia (TD) lesions. The lower EST profiles caused chicks to hatch later than those incubated under the standard EST profile. Chicks which hatched at ⩽498 h incubation grew faster over the first 7 days than those that hatched later. There were significantly more birds (only males were studied) that hatched from the lower EST profiles with TD scores of 0 and 1 and fewer with score 4 at 34 days than those hatched under the standard profile. Male birds at 34 days with TD lesions ⩾3 stood for significantly shorter times than males with TD scores ⩽2. Moreover, male birds at 34 and 42 days with TD lesion scores of ⩾3 hatched significantly earlier and grew significantly faster over the first 2 weeks of age than did male birds with TD scores ⩽2. It appears possible to decrease the severity and prevalence of TD in the Cobb 500 broiler by ensuring that the birds do not hatch before 498 h of incubation.     

Temperature alterations during embryogenesis have a sex-dependent influence on growth properties and muscle metabolism of day-old chicks and 35-day-old broilers

Broiler eggs were either incubated at 37.8°C during the whole incubation period (control), or at higher (38.8°C, group H) and lower temperatures (36.8°C, group L) from embryonic day (ED) 7 up to ED 10 (ED 7 to 10) or from ED 10 up to ED 13 (ED 10 to 13). Before and after this temperature treatment the eggs were incubated at 37.8°C. The day-old chicks were weighted, sexed and fed up to day 35. On days 1 and 35 samples were taken from the breast and leg muscles for analyzing of the mitochondrial respiratory activity (MRA) and from the breast muscles for analysis of the cross-sectional areas (CSA) and the glycogen phosphorylase (GP), phosphofructokinase (PFK), lactate dehydrogenase (LDH), citrate synthase (CS) and cytochrome oxidase (COX) activities. Statistical analysis showed that treatment (control, group H, group L), sex and their interaction, but not the treatment period (ED 7 to 10; ED 10 to 13), significantly influenced the results. Group H chicks had lower (P⩽0.05) body and heart weights but higher (P⩽0.05) liver weights, CSA values, leg MRA as well as PFK, LDH, CS, GP and COX activities compared with the group L chicks. The results of the control chicks differ (P⩽0.05) from those of the group H (body, heart weight, COX), the group L chicks (liver weight, PFK, LDH, CS, GP) or the birds of both other groups (CSA). The group H broiler had higher (P⩽0.05) body and leg weights as well as LDH, CS, COX and GP activities than the group L broilers. The BWs and the LDH and GP results of the control broiler differ (P⩽0.05) from those of both other groups or from the results of the group H (CS) and group L broiler (COX). Female broilers had lower (P⩽0.05) body, breast and leg weights, but higher (P⩽0.05) CSA, LDH, CS and GP activities than the male animals. Analysis of treatment×sex interaction showed that group H hens had higher (P⩽0.05) body and breast weights, LDH and GP activities compared with the group L hens, whereas in the male broiler no effect of the interaction could be found, except for the lower (P⩽0.05) CSA values in the group H than group L cocks. The treatment effects are probably due to altered embryonic activity and related molecular mechanisms. The sex-related differences in the broiler indicate that these alterations already occur in the embryos and chicks, but become significant with the sexual dimorphism after hatch.     

Effect of heat treatment on pre-stocking of Turkey eggs and its impact on incubation and hatching

Egg stocking is used to meet housing demands in the hatchery industry. Stocking periods longer than 10 days of occur commonly, despite the fact that this practice causes productive losses during the incubation process. To minimize these losses, eggs are heated before incubation to stimulate the embryo, thereby reducing the range of birth intervals. The objective of this study was to determine whether heat treatment (37.5 °C) prior to incubation would improve hatching rates. We also determined the heat-exposure time necessary to improve productivity. We stored 5376 Nicholas pedigree eggs, aged between 40 and 51 weeks, for seven days. These eggs were distributed in three groups: groups 1 and 2 received 4 and 6 h of heat treatment, respectively; group 3 was used as control (no heat treatment, remaining at 17 °C). After heat treatment, the eggs were stored for 7 days at 17 °C, together with eggs from the control group. We found significant variation in the cumulative dispersion of birds born during the hatch window; greater numbers of birds were born in group 1 that underwent the 4-h heat treatment with a 24-h hatch window and in group 3 that underwent the 6-h heat treatment with a 12-h hatch window. Hatch rate, yolk retention and the relationship between average chick weight/average egg weight did not differ between treatments. These data suggest that heat treatment modulates the hatch window; nevertheless, the treatment did not influence the average weight the chicks, the number of chicks born, the percentage of hatching or yolk retention.     

Spread of hatch and delayed feed access affect post hatch performance of female broiler chicks up to day 5

It is not rare that newly hatched chicks remain without feed for about 24 to 48 h before they are placed on farms due to a series of logistic operations. Furthermore, the spread in hatching time can also mount up to 30 to 48 h for late v. early hatchers. In other words, the practice is a complex combination of spread of hatch and delayed feed access. The present study was aimed to investigate the combined effects of hatching time with a delay in feed access of 48 h, starting from their hatch-time (biological age). When chicks had access to feed immediately after hatch, late hatchers had a higher feed intake and relative growth rate up to day 5 compared with their early hatched counterparts. Feed deprivation during the first 48 h resulted in retarded early growth rate, which was further aggravated by an impaired feed intake after refeeding. In addition, the differential effects of hatching time on relative growth rate and feed intake observed in immediately fed chicks were eliminated by the 48 h feed delay. The yolk utilization after hatch was faster for the late hatchers up to biological day 2 regardless of the feeding treatments. Hatching muscle glycogen content was higher in the late hatchers compared with that of their early counterparts at hatch and at biological day 2 independent of feeding treatment. Moreover, the liver glycogen content of the late hatchers was also higher at hatch. For the immediately fed chicks, the proportional breast muscle weight of the late hatchers was higher at biological day 2 and 5. For the starved chicks, on the other hand, this effect was only observed after they had access to feed (biological day 5). The different plasma T₃ levels at hatch may have contributed to the different post hatch performance. It is concluded that the spread of hatch influenced post hatch performance, especially appetite and growth at least until day 5. Moreover, the delay in feed access interacted with the hatching time and caused adverse effects on the post hatch performance.     

Hatch rate of laying hen strains provided a photoperiod during incubation

Implementing a photoperiod during incubation has been shown to be a potential next step to removing one more stressor for newly hatched poultry species. The distribution of hatch over time is a parameter that may be influenced by photoperiod that could benefit from a photoperiod but has not been studied at this time and is the objective of this paper. The impact on hatch rate for three strains of chicken, Barred Plymouth Rock (BR), Lohmann Brown (LB) and Lohmann Lite (LL), was measured following the provision of a 12L : 12D (12 h light : 12 h dark) photoperiod starting at 0, 9 or 17 days of incubation and compared with incubation in the dark. The cumulative number of chicks hatched eggs at four points in time (489, 498, 507 and 516 h of incubation) was analysed using repeated measures analysis in a 3 × 4 factorial arrangement of treatments. Repeated measures analysis was done to determine the main and interaction effects of photoperiod and bird strain, and a regression analysis was used to determine how these effects evolved over time. Lohmann Brown embryos provided a 12L : 12D photoperiod throughout incubation were first to reach 50% of total chicks hatched and rate of hatch from 50% to 75% of total chicks hatched as well. As the LB chicks did not begin to hatch earlier or finish later, the LB strain was the most synchronised when provided a 12L : 12D photoperiod from the beginning of incubation. Similar results were found for LL, but no difference on the percentage hatched over time was found when provided the 12L : 12D photoperiod at the beginning of incubation or at day 9. The BR strain only showed a significant difference in hatch window synchronisation when provided a 12L : 12D photoperiod at day 9 of incubation. These results indicate that the strain of chicken impacts the hatch window, and each strain responds to a photoperiod during incubation differently. This information could be useful for hatchery managers to deal with different strains of chicken for incubation.     

Egg storage duration and hatch window affect gene expression of nutrient transporters and intestine morphological parameters of early hatched broiler chicks

In recent years, researchers have given emphasis on the differences in physiological parameters between early and late hatched chicks within a hatch window. Considering the importance of intestine development in newly hatched chicks, however, changes in gene expression of nutrient transporters in the jejunum of early hatched chicks within a hatch window have not been studied yet. This study was conducted to determine the effects of egg storage duration before incubation and hatch window on intestinal development and expression of PepT1 (H⁺-dependent peptide transporter) and SGLT1 (sodium–glucose co-transporter) genes in the jejunum of early hatched broiler chicks within a 30 h of hatch window. A total of 1218 eggs obtained from 38-week-old Ross 308 broiler breeder flocks were stored for 3 (ES3) or 14 days (ES14) and incubated at the same conditions. Eggs were checked between 475 and 480 h of incubation and 40 chicks from each egg storage duration were weighed; chick length and rectal temperature were measured. The chicks were sampled to evaluate morphological parameters and PepT1 and SGLT1 expression. The remaining chicks that hatched between 475 and 480 h were placed back in the incubator and the same measurements were conducted with those chicks at the end of hatch window at 510 h of incubation. Chick length, chick dry matter content, rectal temperature and weight of small intestine segments increased, whereas chick weight decreased during the hatch window. The increase in the jejunum length and villus width and area during the hatch window were higher for ES3 than ES14 chicks. PepT1 expression was higher for ES3 chicks compared with ES14. There was a 10.2 and 17.6-fold increase in PepT1 and SGLT1 expression of ES3 chicks at the end of hatch window, whereas it was only 2.3 and 3.3-fold, respectively, for ES14 chicks. These results suggested that egg storage duration affected development of early hatched chicks during 30 h of hatch window. It can be concluded that the ES14 chicks would be less efficiently adapted to absorption process for carbohydrates and protein than those from ES3 at the end of the hatch window.     

Physiological status of broiler chicks at pulling time and the relationship to duration of holding period

Newly hatched chicks may be held longer than 48 h and experience long periods of fasting in commercial hatcheries. Limited information is known about the physiological status of chicks in such situations, due to the difficulty of precisely recording time of hatch. This study investigated the effect of the time from hatch to pulling (holding period) on physiological measures/parameters in 109 broiler chicks. Fertile Ross 308 eggs were incubated in a custom built small-scale incubator. The individual hatching time of each focal chick was determined using eggshell temperature monitoring. At ‘pulling’ (512 h of incubation time), the quality of focal chicks was assessed using the chick scoring method and physiological parameters were measured including BW, organ (heart, liver and stomach) weights, blood values and plasma corticosterone level. The time from hatch to pulling varied from 7.58 to 44.97 h. Egg weight at setting was significantly correlated with chick BW and weight of organs at pulling, but had no effect on chick quality, blood values and plasma corticosterone. Relative BW at pulling was negatively associated with the duration of holding period (P=0.002). However, there was a positive correlation between relative stomach weight and the duration of the holding period (P<0.001). As the holding period duration increased, there was a trend that blood partial pressure of oxygen, haematocrit and haemoglobin also increased, and blood partial pressure of carbon dioxide, total carbon dioxide and bicarbonate decreased (P<0.05). A wide range of plasma corticosterone was observed from chicks that had experienced different durations of holding period. We conclude that shortening the hatch window and minimising the number of chicks that experience a long holding period before pulling may improve chick quality and physiological status, which may be due to unfavourable environmental conditions that include feed and water deprivation.     

Effect of elevated carbon dioxide on chicken eggs during the early and late incubation periods

Carbon dioxide (CO₂) is always maintained at ambient levels by ventilation in commercial egg incubators. However, elevated CO₂ levels during the early and late periods have been reported to improve the quality of chicks and shorten the hatch window. This study investigated the effect of precise CO₂ supplementation during the early and late periods of incubation on embryo growth and incubation performance by developing and using a CO₂ supplementation system to increase the CO₂ level in an experimental egg incubator. The CO₂ level was maintained at 1% in the early period (from the beginning to the 10th day of incubation, E0–E10) and in the late period (from internal pipping (IP) to the 21st day of incubation (E21), IP–E21) in an incubator for the treatment group, whereas the CO₂ level was maintained at the ambient level in the other incubators for the control group. A comparative assessment of embryonic development, hatching characteristics, and hormone and nutrient levels was conducted for each trial. The experiment comprised three trials, with 300 Jing Hong No. 1 breeding eggs in each incubator. The elevated CO₂ treatment significantly shortened the chick hatching time (H0) by 4 h (P < 0.05) and the hatch window by 3 h (P < 0.05) without affecting hatchability, chick weight at 1 d of age, brooding period, or quality score. At external pipping (EP), the heart weight, intestinal weight, relative intestinal weight, and relative heart weight in the treatment group were significantly higher than those in the control group (P < 0.05). In addition, the embryonic intestine, relative intestine, and relative heart weights of the newly hatched chicks in the treatment group were significantly higher than those in the control group (P < 0.05) at H0. The treatment significantly increased the concentration of corticosterone in the embryonic plasma during the period from IP to EP (P < 0.05), promoted the secretion of triiodothyronine and tetraiodothyronine (P < 0.05), and increased the glycogen content of the embryonic liver on E21 (P < 0.05). This result indicates that elevated CO₂ (1%) during the early and late periods of incubation accelerated embryonic organ development and shortened the chick hatching time and hatch window without affecting hatchability or hatchling quality, which can be explained by the synergistic functions of the secretion of plasma corticosterone and thyroid hormones and the accumulation of liver glycogen between the early and late periods of incubation.     

Effect of hatching time on time to first feed intake,organ development,enzymatic activity and growth in broiler chicks hatched on-farm

The conventional commercial hatcheries used today do not allow the newly hatched chicks to consume feed or water. Combined with natural variation in hatching time, this can lead to early hatched chicks being feed-deprived for up to 72 h before being unloaded at the rearing site. This study investigated the effects of hatching time on time to first feed intake and development of organs, digestive enzymes and productivity in terms of growth and feed conversion ratio in chicks hatched on-farm. Chicks were divided into three hatching groups (early, mid-term and late), and assessed over a full production cycle of 34 days. The results revealed that chicks remain inactive for a considerable amount of time before engaging in eating-related activities. Eating activity of 5% (i.e. when 5% of birds in each hatching group were eating or standing close to the feeder) was recorded at an average biological age (BA) of 25.4 h and a proportion of 50% birds with full crop was reached at an average BA of 30.6 h. Considering that the hatching window was 35 h in this study, the average chick probably did not benefit from access to feed and water immediately post-hatch in this case. At hatch, mid-term hatchlings had a heavier small intestine (30.1 g/kg bw) than both early (26.4 g/kg bw) and late (26.0 g/kg bw) hatchlings. Relative length of the small intestine was shorter in late hatchlings (735 cm/kg bw) than in mid-term (849 cm/kg bw) and early (831 cm/kg bw) hatchlings. However, the relative weight of the bursa fabricii was greater in mid-term (1.30 g/kg bw) than in early hatchlings (1.01 g/kg bw). At hatch, late hatchlings were heavier than early and mid-term hatchlings (P < 0.05), but by 3 days of age early hatchlings were heavier than mid-term and late hatchlings (P < 0.01). The only effect persisting throughout the study was a difference in the relative weight of the small intestine, where late hatchlings had heavier intestines than early hatchlings (P < 0.05). Thus, while there were differences between hatching groups, this study showed that the hatchlings seemed capable of compensating for these as they grew.     

Effects of feeding high dosages of vitamin E to laying hens on thyroid hormone concentrations of hatching chicks.

Long-term experimental feeding of 20,000 ppm alpha-tocopheryl acetate to laying hens caused a significant (P < 0.05) decrease in hatching rates as compared to the control group, which was fed a diet containing 19 ppm alpha-tocopherol. When the thyroid hormones in the developing chicks were checked on incubation days 16, 19, 21, and 22, the following results were ascertained: During the latter part of incubation, increases in plasma concentrations of thyroxine and triiodothyronine were observed. No significant differences in hormone concentrations (P > 0.05) between the control and the treatment group were observed during incubation days 16, 19, and 22. However, on the day of hatching (day 21 of incubation) significantly lower (P < 0.05) triiodothyronine concentrations in chick embryos of piped eggs were found in the treatment group. Moreover, thyroxine concentrations in non-piped eggs and in hatched chicks were found to be significantly higher as compared to the control group. Given these results, one concludes that extremely high dosages of vitamin E may affect thyroid hormone concentrations of hatching chicks, and therefore, the chicks might be inhibited in pipping the egg shell. Hypothetically, the hepatic enzyme 5'-monodeiodinase is involved in the mechanism of inhibition.     

Influence of temperature on hatching of winter eggs of fruit-tree red spider mite, Panonychus ulmi (Koch)

The effects of the duration and degree of chilling, and the temperature of incubation, on hatching of winter eggs of Panonychus ulmi (Koch) were investigated. For chilling, 0°C and 5°C were more effective than — 5° and 9°, and the limits for the reaction were close to — 10° and 15°. As the chilling period was increased from 60 to 200 days, the percentage hatch on incubation at 21° increased, and the mean incubation time and its variance decreased. Before the maximum effect of chilling was achieved, percentage hatch on incubation at 9° and 15° was higher than at 21°; 27° was lethal to most winter eggs though not to summer eggs. After chilling, the later stages of diapause development could occur at temperatures from 0° to 21°₎ i.e. above and below the threshold temperature for morphogenesis, 6–7° in both winter and summer eggs. Diapause development cannot, therefore, be a unitary process. The significance of the results is discussed in relation to forecasting the time of hatch in the field, and to the phenological aspects of hatching in the spring.     

Significance of chick quality score in broiler production

The quality of day old chicks is crucial for profitable broiler production, but a difficult trait to define. In research, both qualitative and quantitative measures are used with variable predictive value for subsequent performance. In hatchery practice, chick quality is judged on a binomial scale, as chicks are divided into first grade (Q1-saleable) and second grade (Q2) chicks right after hatch. Incidences and reasons for classifying chicks as Q2, and potential of these chicks for survival and post-hatch performance have hardly been investigated, but may provide information for flock performance. We conducted an experiment to investigate (1) the quality of a broiler flock and the relation with post-hatch flock performance based on a qualitative score (Pasgar©score) of Q1 chicks and based on the incidence of Q2 chicks and (2) the reasons for classifying chicks as Q2, and the potential of these chicks for survival and post-hatch growth. The performance was followed of Q1 and Q2 chicks obtained from two breeder flocks that hatched in two different hatching systems (a traditional hatcher or a combined hatching and brooding system, named Patio). Eggs were incubated until embryo day 18, when they were transferred to one of the two hatching systems. At embryo day 21/post-hatch day 0, all chicks from the hatcher (including Q2 chicks) were brought to Patio, where the hatchery manager marked the Q2 chicks from both flocks and hatching systems and registered apparent reasons for classifying these chicks as Q2. Chick quality was assessed of 100 Q1 chicks from each flock and hatching system. Weights of all chicks were determined at days 0, 7, 21 and 42. There were no correlations between mean Pasgar©score and post-hatch growth or mortality, and suboptimal navel quality was the only quality trait associated with lower post-hatch growth. Growth was clearly affected by breeder flock and hatching system, which could not be linked to mean Pasgar©score or incidence of Q2 chicks. Q2 chicks showed lower post-hatch growth compared to Q1 chicks but effects on flock performance at slaughter weight were limited because early mortality in Q2 chicks was high (62.50% at 7 days). We concluded that chick qualitative scores and the incidence of Q2 chicks may be informative for the quality of incubation, but are not predictive for post-hatch flock performance. Culling Q2 chicks after hatch is well-founded in terms of both animal welfare and profitability.     

Delayed Egg Hatching and Semivoltinism in the Nearctic Stonefly Megarcys signata (Plecoptera: Perlodidae)

Delayed egg hatching can influence the survival of aquatic insects by reducing exposure to competitors, predators, parasites, or unfavorable environmental conditions. We examined egg development in a Colorado population of the stonefly, Megarcys signata (Plecoptera: Perlodidae), whose larvae inhabit high altitude streams in the Rocky Mountains of western North America. Five-thousand fertilized eggs were collected from 40 different females and incubated in the East River, Gunnison County, Colorado, until late fall, at which time unhatched eggs were transported to incubation chambers in Ithaca, New York. We used three different combinations of photoperiod and temperature (10L:14D, 4°C; 10L:14D, 8°C; 8L:16D, 8°C) in an attempt to induce hatching. Eggs in the treatments with temperatures elevated above normal winter temperatures in the East River (8°C) began developing after 6 months, whereas eggs in the treatment most closely simulating natural stream conditions (4°C) did not hatch after 10 months of incubation. Our data indicate that this population of Megarcys signata has an extended egg stage that persists for almost a year, and that it is semivoltine at these elevations of 2885 and 2895 meters.     

Incubation prior to clutch completion accelerates embryonic development and so hatch date for eggs laid earlier in a clutch in the great tit Parus major

The ability of parents to respond to changes in food supply within a season will have a large effect on fitness through the number and quality of chicks fledged. Great tits, Parus major, attempt to synchronise their production of chicks with a seasonal food peak, but when food supply fails, hatching asynchrony of chicks provides a mechanism by which some young can be fledged because more developed chicks outcompete their less developed siblings for the reduced parental food supply. We tested whether female great tits can potentially control the degree of hatching asynchrony by using incubation before clutch completion, so that early laid eggs develop faster and hatch sooner. The temperature of an artificial egg placed in 29 nests during the laying period was measured with data loggers, and nocturnal incubation of eggs similar to incubation post clutch completion was recorded in all nests. We then demonstrated that eggs removed from the nest for 72 hour periods prior to clutch completion hatched later than eggs remaining in the nest for the entirety of the laying period. Our results show that variable pre clutch completion incubation (which was mostly nocturnal) can lead to faster embryo development and earlier hatching, so potentially providing a mechanism for adaptive female control of degree of hatching asynchrony.     

Postnatal effects of incubation length in mallard and pheasant chicks

Eggs of mallard ducks ( Anas platyrhynchos ) and ring-necked pheasants ( Phasianus colchicus ) were incubated in clutches arranged to stimulate embryos to hatch earlier or later than normal. This manipulation of hatching time was achieved by combining eggs of different age in the same clutch. To ensure hatching synchrony, embryos communicate with each other during the last stage of incubation, resulting in either a delay or an acceleration of hatching. Embryos of both species that accelerated their hatching time suffered a higher mortality rate after hatching. Combining mortality with the proportion of hatchlings that suffered from leg deformities, impeding their movements, resulted in a cost also to pheasant chicks delaying their hatching. Chicks of both species accelerating hatching time had a lower minimum mass and a shorter tarsus length than control chicks, whereas chicks delaying hatching time either grew as well or slightly better than control chicks. Mallard chicks had better balance and mobility immediately after hatching the longer they stayed in the egg. This indicates that the period immediately before hatching, is an important period for muscular and organ maturity. Reducing this period results in costs affecting post-hatching survival. The strategy to assure synchronous hatching in mallards and pheasants probably reflect a trade-off between the negative effects of shifting the age at hatching away from normal and differences in predation risk during different stages of reproduction.     

Interaction between eggshell temperature and carbon dioxide concentration after day 8 of incubation on broiler chicken embryo development

Carbon dioxide (CO₂) is considered to be an important factor during incubation of eggs. Effects attributed to higher CO₂ concentrations during experiment might be due to confounding effects of other environmental conditions, such as incubation temperature. To disentangle effects of eggshell temperature (EST) and CO₂ concentration, an experiment was conducted. A total of 630 Cobb 500 hatching eggs from 37 to 45 wk commercial breeder flocks were collected and incubated according to treatments. The experiment was setup as a complete randomized 2 × 3 factorial design, resulting in 6 treatments. From day 8 of incubation onward, broiler eggs were exposed to one of two EST (37.8 or 38.9 °C) and one of three CO₂ concentrations (0.1, 0.4 or 0.8%). Eggs were incubated in climate-respiration chambers and metabolic heat production was determined continuously. At day 18 of incubation and at 6 h after hatching, embryo and chicken quality were determined by evaluation of organ weights, navel condition, blood metabolites and hepatic glycogen. Hatching time and chicken length at 6 h after hatching showed an interaction between EST and CO₂ concentration (both P = 0.001). Furthermore, no effect of CO₂ concentration was found on embryo development or chicken quality. Metabolic heat production between day 8 and 18 of incubation was not affected by either EST or CO₂. At day 18 of incubation, an EST of 38.9 °C resulted in a higher egg weight loss, longer embryos, higher yolk free body mass (YFBM) and lower heart weight than an EST of 37.8 °C (all P < 0.008). At 6 h after hatching, an EST of 38.9 °C resulted in a higher residual yolk weight and lower YFBM, liver weight and heart weight than an EST of 37.8 °C (all P < 0.003). Lactate, uric acid and hepatic glycogen were not affected by EST at either day 18 of incubation or at hatch. Glucose was not affected by EST at day 18 of incubation, but at hatch, it was higher at an EST of 37.8 °C than at an EST of 38.9 °C (P = 0.02). It can be concluded that effects of CO₂ concentration (at concentrations ≤0.8%) on embryonic development and chicken quality appear to be limited when EST is maintained at a constant level. Moreover, a higher EST from day 8 of incubation onward appears to negatively affect chicken quality at hatch.     

Effect of a photoperiodic green light programme during incubation on embryo development and hatch process

This study was conducted to evaluate the effect of a 12-h light, 12-h dark (12L : 12D) photoperiod of green light during day 1 to day 18 of incubation time, on embryo growth, hormone concentration and the hatch process. In the test group, monochromatic light was provided by a total of 204 green light-emitting diodes (522 nm) mounted in a frame which was placed above the top tray of eggs to give even spread of illumination. No light–dark cycle was used in the control group. Four batches of eggs (n=300/group per batch) from fertile Ross 308 broiler breeders were used in this experiment. The beak length and crown–rump length of embryos incubated under green light were significantly longer than that of control embryos at day 10 and day 12, respectively (P<0.01). Furthermore, green light-exposed embryos had a longer third toe length compared with control embryos at day 10, day 14 and day 17 (P=0.02). At group level (n=4 batches), light stimulation had no effect on chick weight and quality at take-off, the initiation of hatch and hatch window. However, the individual hatching time of the light exposure focal chicks (n=33) was 3.4 h earlier (P=0.49) than the control focal chicks (n=36) probably due to the change in melatonin rhythm of the light group. The results of this study indicate that green light accelerates embryo development and alters hatch-related hormones (thyroid and corticosterone), which may result in earlier hatching.     

Stimulation with monochromatic green light during incubation alters satellite cell mitotic activity and gene expression in relation to embryonic and posthatch muscle growth of broiler chickens

Previous studies showed that monochromatic green light stimuli during embryogenesis accelerated posthatch body weight (BW) and pectoral muscle growth of broilers. In this experiment, we further investigated the morphological and molecular basis of this phenomenon. Fertile broiler eggs (Arbor Acres, n=880) were pre-weighed and randomly assigned to 1 of the 2 incubation treatment groups: (1) dark condition (control group), and (2) monochromatic green light group (560 nm). The monochromatic lighting systems sourced from light-emitting diode lamps and were equalized at the intensity of 15 lx at eggshell level. The dark condition was set as a commercial control from day 1 until hatching. After hatch, 120 male 1-day-old chicks from each group were housed under incandescent white light with an intensity of 30 lx at bird-head level. No effects of light stimuli during embryogenesis on hatching time, hatchability, hatching weight and bird mortality during the feeding trial period were observed in the present study. Compared with the dark condition, the BW, pectoral muscle weight and myofiber cross-sectional areas were significantly greater on 7-day-old chicks incubated under green light. Green light also increased the satellite cell mitotic activity of pectoral muscle on 1- and 3-day-old birds. In addition, green light upregulated MyoD, myogenin and myostatin mRNA expression in late embryos and/ or newly hatched chicks. These data suggest that stimulation with monochromatic green light during incubation promote muscle growth by enhancing proliferation and differentiation of satellite cells in late embryonic and newly hatched stages. Higher expression of myostatin may ultimately help prevent excessive proliferation and differentiation of satellite cells in birds incubated under green light.     

A Meta-Analysis of Experiments Linking Incubation Conditions with Subsequent Leg Weakness in Broiler Chickens

A series of incubation and broiler growth studies were conducted using one strain of broiler chicken (fast feathering dam line) observing incubation effects on femoral bone ash % at hatch and the ability of the bird to remain standing at 6 weeks of age (Latency-To-Lie). Egg shell temperatures during incubation were consistently recorded. Parsimonious models were developed across eight studies using stepwise multiple linear regression of egg shell temperatures over 3-day periods and both bone ash at hatch and Latency-To-Lie. A model for bone ash at hatch explained 70% of the variation in this factor and revealed an association with lower egg shell temperatures during days 4–6 and 13–15 and higher egg shell temperatures during days 16–18 of incubation. Bone ash at hatch and subsequent Latency-To-Lie were positively correlated (r = 0.57, P<0.05). A model described 66% of the variation Latency-To-Lie showing significant association of the interaction of femoral ash at hatch and lower average egg shell temperatures over the first 15 days of incubation. Lower egg shell temperature in the early to mid incubation process (days 1–15) and higher egg shell temperatures at a later stage (days 16–18) will both tend to delay the hatch time of incubating eggs. Incubation profiles that resulted in later hatching chicks produced birds which could remain standing for a longer time at 6 weeks of age. This supports a contention that the effects of incubation observed in many studies may in fact relate more to earlier hatching and longer sojourn of the hatched chick in the final stage incubator. The implication of these outcomes are that the optimum egg shell temperature during incubation for broiler leg strength development may be lower than that regarded as ideal (37.8°C) for maximum hatchability and chick growth.