Effects of oxygen concentration during incubation and broiler breeder age on embryonic heat production, chicken development, and 7-day performance

Older breeder flocks produce eggs with a relatively larger yolk and thereby a higher nutrient availability than young breeder flocks. To optimise nutrient utilisation and embryonic development throughout incubation and posthatch period, embryos originating from older breeder flocks may require a higher oxygen availability. The current study investigated effects of broiler breeder flock age and incubational oxygen concentration on embryonic metabolism and chicken development until 7-day posthatch. Similar sized eggs of a young (28-32 week) or old (55-59 week) Cobb 500 breeder flock were incubated at one of three oxygen concentrations (17%, 21% or 25%) from day 7 of incubation until 6 h after emergence from the eggshell. Posthatch, chickens were reared until 7 days of age. Egg composition at the start of incubation, heat production during incubation, and embryo or chicken development at embryonic day (ED)14 and ED18 of incubation, 6 h after hatch and day 7 posthatch were evaluated. An interaction was found between breeder age and oxygen concentration for yolk-free body mass (YFBM) at ED18. A higher oxygen concentration increased YFBM in the old breeder flock, whereas no difference was found between 21 and 25% oxygen in the young breeder flock. Yolk size was larger in the old compared to the young flock from ED0 until 6 h after hatch. Breeder flock age did not affect YFBM at ED14 and 6 h after hatch nor daily embryonic heat production, but there were some effects on relative organ weights. Chickens of the old compared to the young breeder flock showed a higher weight gain at day 7, but at a similar feed conversion ratio (FCR). A higher oxygen concentration during incubation stimulated embryonic development, especially between 17% and 21% of oxygen, in both flock ages_. Although this growth advantage disappeared at 7 days posthatch, a low oxygen concentration during incubation resulted in a higher FCR at 7 days posthatch. Results indicated that breeder flock age seemed to influence body development, with an advantage for the older breeder flock during the posthatch period. Oxygen concentrations during incubation affected body development during incubation and FCR in the first 7 days posthatch. Although an interaction was found between breeder flock age and oxygen concentration at ED18 of incubation, there was no strong evidence that nutrient availability at the start of incubation (represented by breeder flock ages) affected embryo and chicken development at a higher oxygen concentration.

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.

Effects of breeder age, broiler strain, and eggshell temperature on development and physiological status of embryos and hatchlings

Breeder age and broiler strain can influence the availability of nutrients and oxygen, particularly through differences in yolk size and shell conductance. We hypothesized that these egg characteristics might affect embryonic responses to changes in eggshell temperature (EST). This study aimed to investigate the effect of breeder age, broiler strain, and EST on development and physiological status of embryos. A study was designed as a 2 × 2 × 2 factorial arrangement using 4 batches of 1,116 hatching eggs of 2 flock ages at 29 to 30 wk (young) and 54 to 55 wk (old) of Ross 308 and Cobb 500. EST of 37.8 (normal) or 38.9°C (high) was applied from incubation d 7 (E7) until hatching. The results showed that breeder age rather than broiler strain had an influence on yolk size (P = 0.043). The shell conductance was higher in Ross 308 than in Cobb 500 (P < 0.001). A high EST resulted in a higher yolk free body mass (YFBM) compared to the normal EST at E14 and E16, but at 3 h after hatch YFBM was lower when eggs were incubated at high EST compared to normal EST (all P < 0.001). Cobb 500 eggs yielded embryos with a lower YFBM at E14, E18, and 3 h after hatch (all P < 0.05) than Ross 308 eggs. Breeder age had no effect on YFBM, but the RSY weight was higher in embryos from the old flock compared to the young flock embryos at E14 and E16 (both P < 0.05). A 3-way interaction among breeder age, strain, and EST was found, especially for incubation duration, navel quality, and relative heart and stomach weights at 3 h after hatch (all P < 0.05). Based on the results obtained, we conclude that oxygen availability rather than nutrient availability determines embryonic development, and the egg characteristics affected embryonic responses to changes of EST, especially for variables related to chick quality.

Development and nutrient metabolism of embryos from two modern broiler strains

A progressive selection for broiler live and processing performance traits has changed broiler growth patterns during the post hatch period. However, limited information is available to understand whether changes have also occurred during the embryonic stages. This study aims to examine influences of broiler strain on nutrient availability, embryonic development, and nutrient metabolism during incubation. Hatching eggs of Ross 308 and Cobb 500 fast feathering were selected from breeder flocks aged 43 to 46 weeks at an egg weight range of 60 to 63 g. Eggs were obtained in 2 batches, 120 eggs per strain per batch. For each batch, 20 eggs per strain were used to determine egg composition and nutrient availability. The remaining eggs were incubated separately in one of 2 climate respiration chambers at an eggshell temperature of 37.8°C. The results showed that Ross 308 eggs had a higher yolk:albumen ratio with 0.9 g more yolk and 0.7 g less albumen than Cobb 500. Albumen + yolk of Ross 308 eggs had a higher dry matter (Δ = 0.24 g) and crude fat (Δ = 0.23 g) than that of Cobb 500 eggs, but a similar amount of crude protein. Albumen and yolk of Ross 308 eggs had a higher energy content (Δ = 8.9 kJ) compared to Cobb 500 eggs. At 3 h after hatch, Ross 308 chicks were 0.2 cm longer and had a 0.6 g heavier yolk free body mass (YFBM) than Cobb 500 chicks. During incubation, Ross 308 embryos used 13.9 kJ more energy than Cobb 500, and the efficiency of converting energy used to YFBM (EYFB) was approximately 7.6% lower compared to Cobb 500. Ross 308 chicks hatched approximately 4 h later and had less hepatic glycogen (Δ = 5 mg) than Cobb 500 chicks. It can be concluded that, Cobb 500 and Ross 308 differ in egg nutrient availability and have different trajectories for embryonic development and nutrient metabolism during incubation.

Differences in egg nutrient availability, development, and nutrient metabolism of broiler and layer embryos

Selection for production traits of broilers and layers leads to physiological differences, which may already be present during incubation. This study aimed to investigate the influence of strain (broiler vs layer) on egg nutrient availability, embryonic development and nutrient metabolism. A total of 480 eggs with an egg weight range of 62.0 to 64.0 g from Lohmann Brown Lite and Ross 308 breeder flocks of 41 or 42 weeks of age were selected in two batches of 120 eggs per batch per strain. For each batch, 30 eggs per strain were used to determine egg composition, including nutrient and energy content, and 90 eggs per strain were separately incubated in one of two climate respiration chambers at an eggshell temperature of 37.8°C. The results showed that broiler eggs had a higher ratio of yolk: albumen with 2.41 g more yolk and 1.48 g less albumen than layers. The yolk energy content of broiler eggs was 46.32 kJ higher than that of layer eggs, whereas total energy content of broiler eggs was 47.85 kJ higher compared to layer eggs. Yolk-free body mass at incubation day 16 and chick weight and length at hatch were higher in broilers compared to layers. Respiration quotient of broiler embryos was higher than layer embryos during incubation day 8 to incubation day 10. A 0.24 g lower residual yolk at the hatch of broiler embryos than for the layer embryos indicated that broiler embryos used more yolk and had a higher energy utilization and energy deposition in yolk-free body mass. Heat production of broiler embryos was higher than that of layer embryos from incubation day 12 to incubation day 18, but efficiency of converting egg energy used by embryos to form yolk-free body mass was similar. In conclusion, broiler and layer embryos have different embryonic development patterns, which affect energy utilization and embryonic heat production. However, the embryos are equal in efficiency of converting the energy used to yolk-free body mass.

Energy utilization and heat production of embryos from eggs originating from young and old broiler breeder flocks

Two experiments were conducted to study the interaction between breeder age and egg size on the energy utilization (experiment 1) and heat production (experiment 2) of broiler embryos. In experiment 1, a total of 4,800 Ross-308 hatching eggs from 2 breeder ages (29 and 53 wk of age, or young and old) and, within each age, 2 egg sizes (57 to 61 g and 66 to 70 g, or small and large) were used. In experiment 2, a total of 240 Ross-308 hatching eggs from 2 breeder flocks at 29 (young) and 53 (old) wk of age, and which were selected from the same egg weight range (58 to 61 g), were tested in 2 replicate chambers. In experiment 1, it was shown that the amount of yolk relative to albumen was higher in the old flock eggs, and this effect was more pronounced in the large eggs. The old flock eggs, especially the larger egg size, contained more energy as a result of a greater yolk size. Energy utilization of the embryos was positively related to yolk size and the amount of energy transferred to yolk-free body (YFB) was largely determined by the available egg energy. The efficiency of converting egg energy into chick body energy (E(YFB)) was equal for both egg sizes and both breeder age groups. Chick YFB weight of young and old flock eggs was equal. However, dry YFB weight of chicks from old flock eggs was higher than in chicks from young flock eggs, which was associated with more protein and fat content and thus more energy accumulated into YFB. As a consequence, embryos derived from old flock eggs produced more heat from d 16 of incubation onward than those of the young flock eggs. In conclusion, the higher energy deposition into chick YFB of old flock eggs, leading to higher embryonic heat production, is the result of a higher amount of available energy in the egg and is not due to changes in E(YFB).

Yolk absorption and embryo development of small and large eggs originating from young and old breeder hens

To evaluate the effect of breeder age and egg size on yolk absorption and embryo development, a total of 4,800 Ross 308 hatching eggs were subjected to 4 treatments arranged in a 2 × 2 factorial randomized complete block design using 2 breeder ages (29 and 53 wk of age, or young and old) and 2 egg sizes (57-61 g and 66-70 g, or small and large). A significant interaction between breeder age and egg size was found for egg composition. Yolk weight increased with flock age, whereas a larger egg size resulted in higher albumen content. A significant interaction between breeder age and egg size was found for yolk-free body (YFB) weight only at d 7. Until the fourteenth day of incubation, eggs from the old flock yielded greater YFB weight than did eggs from the young flock. At hatch, chicks of both age groups had comparable wet YFB weight, chick weight, wet and dry residual yolk weight, and chick length. Dry YFB weight of chicks from the old flock was higher than that of chicks from the young flock. Compared with the small eggs, embryos and chicks of the large eggs had greater YFB weight from d 14 to hatching. At hatch, these chicks were also heavier, longer, and had higher wet and dry YFB and residual yolk weight. Yolk absorption at d 18 and at hatch of embryos and chicks of the old flock was higher than that of the young flock, both in absolute values and percentages. Rates of absolute and percentage yolk absorption through d 18 and percentage yolk absorption at hatch were higher in the small eggs than in the large eggs. It can be concluded that egg size influences chick length at hatch and embryo development when expressed in terms of total and YFB weight. Although yolk availability and rate of absorption may have influenced dry YFB weight, they did not influence hatching chick length or total and YFB weight.

High eggshell temperatures during incubation decrease growth performance and increase the incidence of ascites in broiler chickens

High eggshell temperatures (EST; ≥38.9°C) during the second half of incubation are known to decrease the body and organ development of broiler hatchlings. In particular, relative heart weights are decreased by a high EST, and this may increase the incidence of metabolic disorders that are associated with cardiovascular development, such as ascites. The current study investigated the effects of a high EST on chick quality, subsequent performance, and the incidence of ascites later in life. Eggs were incubated at a normal (37.8°C) or high (38.9°C) EST from d 7 of incubation onward. After hatching, the chickens were housed per EST in pens, and a normal or cold temperature schedule was applied during the grow-out period. Hatchability, hatchling quality, BW, feed conversion ratio, total mortality, mortality associated with ascites, slaughter characteristics, and ascites susceptibility at 6 wk of age were evaluated. Except for total ventricle weight, no interaction was found between EST and the grow-out temperature. Hatchability was comparable between the EST treatments, but the percentage of second-grade chickens was 0.7% higher at the high EST. Yolk-free body mass was 3.0 g lower, and heart weights were 26% lower at hatch in the high compared with the normal EST treatment. Body weight continued to be less during the grow-out period after the high EST incubation. However, breast meat yield was 1.0% higher in the high than in the normal EST. Feed conversion ratio did not differ between EST treatments. Total mortality was 4.1% higher and mortality associated with ascites was 3.8% higher in the high compared with the normal EST treatment. The ratio between the right and total ventricle was 1.1% higher in the high compared with the normal EST treatment at slaughter age. In conclusion, a high EST from d 7 of incubation onward decreased hatchling quality and growth performance, but increased breast meat yield. Furthermore, high EST incubation increased the incidence of ascites, which may be related to the reduced heart development at hatch.

Energy partitioning during incubation and consequences for embryo temperature: a theoretical approach

In practice, many hatchability and chick quality problems have been related to the control of embryo temperature (ET) during incubation. Within an incubator, set at a constant machine temperature (MT), ET can vary substantially. Embryo temperature is the result of the balance between heat transfer to and from the embryo and heat production (HP) of the embryo. We investigated which factors theoretically could account for the variation in ET within an incubator. First, the effects egg weight, MT, and oxygen availability on HP of embryos were quantified. Differences in HP could be due only to differences in the amount of energy utilized from the egg or to differences in the efficiency of the conversion of energy in the egg to energy in the chicken, indicated as E(YFB). Results of these analyses showed that differences in HP attributable to egg weight or oxygen availability were mainly a result of the amount of energy used from the egg constituents and not of a change in E(YFB). However, at a given MT, this variation in HP could account for a maximum increase in ET of only 1.21°C, suggesting that other factors played a role because in practice within an incubator, larger differences in ET have been found. The most important factor was probably the difference in air velocity within an incubator, resulting in differences in heat transfer. Because of this variation, ET varied within an incubator and with increasing ET, E(YFB) decreased, resulting in an even higher HP and consequently ET. We concluded that this theoretical approach could explain the wide variation in ET, and consequently could explain the negative effects of high ET on hatchability and chick quality found in the literature. This indicates that, in both practice and in incubation experiments, it is of great importance to realize that any factor affecting HP or heat transfer influences ET. We strongly suggest that ET (or eggshell temperature) be controlled in any incubation experiment involving hatchability or energy utilization.

Effect of eggshell temperature and oxygen concentration on survival rate and nutrient utilization in chicken embryos

Environmental conditions during incubation such as temperature and O(2) concentration affect embryo development that may be associated with modifications in nutrient partitioning. Additionally, prenatal conditions can affect postnatal nutrient utilization. Using broiler chicken embryos, we studied the effects of eggshell temperature (EST; 37.8 or 38.9 degrees C) and O(2) (17, 21, or 25%) applied from d 7 until 19 of incubation in a 2 x 3 factorial design. Effects of these factors on embryonic survival, development, and nutrient utilization were assessed in the pre- and posthatch period. High EST reduced yolk-free body mass compared with normal EST (36.1 vs. 37.7 g), possibly through reduced incubation duration (479 vs. 487 h) and lower efficiency of protein utilization for growth (83.6 vs. 86.8%). Increasing O(2) increased yolk-free body mass (from 35.7 to 38.3 g) at 12 h after emergence from the eggshell, but differences were larger between the low and normal O(2) than between the normal and high O(2). This might be due to the lower efficiency of nutrient utilization for growth at low O(2). However, the effects of O(2) that were found at 12 h were less pronounced at 48 h posthatch. When O(2) was shifted to 21% for all treatments at d 19 of incubation, embryos incubated at low O(2) used nutrients more efficiently than those incubated at normal or high O(2). An additional negative effect on survival and chick development occurred when embryos were exposed to a combination of high EST and low O(2). Possible explanations include reduced nutrient availability for hatching, decreased body development to fulfill the energy-demanding hatching process, and higher incidence of malpositions. In conclusion, EST and O(2) during incubation affect nutrient utilization for growth, which may explain differences in survival and development. Embryos raised under suboptimal environmental conditions in the prenatal period may develop adaptive mechanisms that still continue in the posthatch period.

Influence of egg storage time and preincubation warming profile on embryonic development, hatchability, and chick quality

When eggs are stored beyond 7 d, hatchability and chick quality decrease. The cause of the negative effects of prolonged egg storage is not clear. The negative effects may be caused by a decrease in embryo viability due to an increase in cell death. The optimal time and curve of preincubation warming (the preincubation warming profile) may be different for eggs stored over short and long periods of time because embryo viability is dependent on egg storage time. The aim of this study was to investigate whether preincubation warming profiles affect embryonic development, hatchability, and chick quality when eggs are stored for a short or prolonged time. Two experiments were conducted. In both experiments, a 2x2 completely randomized design was used with 2 storage times (4 and 14 d at 17 degrees C in experiment I and 4 and 13 d at 19 degrees C in experiment II) and 2 preincubation warming profiles (within 4 or 24 h from storage temperature to 37.8 degrees C). In experiment I, results suggested that the effect of preincubation warming profile on hatchability was dependent on storage time. However, because a low number of eggs were used in this experiment, these differences were not significant. In experiment II, the interaction between storage time and preincubation warming profile was observed for embryonic mortality during the first 2 d of incubation and hatchability (P=0.006 and P=0.01, respectively). When storage time was 13 d, embryonic mortality during the first 2 d of incubation decreased by 4.4% and hatchability increased by 5.7% when the 24-h preincubation warming profile was used instead of the 4-h preincubation warming profile. However, no effect of preincubation warming profile was observed when storage time was 4 d. In both experiments, chick quality decreased when storage time increased but was not affected by preincubation warming profile. We concluded that a slow preincubation warming profile is beneficial for hatchability when storage time is prolonged but does not affect chick quality.

Early feeding affects resistance against cold exposure in young broiler chickens

In field conditions, a fasting period of 24 to 72 h after hatch is common, which is associated with delayed gastrointestinal development and yolk utilization and retarded subsequent performance. Hardly any information is available about the influence of diet composition in the first days on later life and additionally, effects of early feeding on thermoregulatory development are also not known. The aim of this study was to investigate effects of diet composition in early fed broiler chickens on their (thermoregulatory) development. Shortly after hatch, 200 Hybro chickens (initial BW of 43.6 g) were assigned to 1 of 5 feed treatments: control, dextrose, albumen, prestarter, or prestarter plus fat. Water was available ad libitum. Measurements were done in 10 replicates of 4 chickens per treatment. At d 2 or 3, half of the chickens were exposed to 20 degrees C for 30 min to determine resistance against cold exposure and rectal temperature was determined just before, immediately after, and 30 min after the end of this cold exposure. Thereafter, all chickens were killed to investigate body development. Chickens in both prestarter groups developed faster than in the other 3 groups, expressed by a higher BW, yolk-free body mass, heart and liver weight, and higher chick and intestine length. Between d 2 and 3, differences in these variables among chickens from both prestarter groups and other groups increased. Rectal temperature before cold exposure was higher in chickens from both prestarter groups (40.6 and 40.7 degrees C, respectively) and decreased less (0.6 and 0.7 degrees C, respectively) during cold exposure than in chickens from the control (39.5 and 1.2 degrees C, respectively) and albumen group (39.8 and 2.1 degrees C, respectively), whereas chickens from the dextrose group were in between (40.4 and 1.2 degrees C, respectively). We conclude that early fed diet composition in broiler chickens is (besides general development) important for development of both body temperature and resistance against cold exposure, probably as a reflection of a changed metabolic rate.

Effects of eggshell temperature and oxygen concentration on embryo growth and metabolism during incubation

Embryo development and heat production (HP) were studied in eggs of similar size (60 to 65 g) that were incubated at normal (37.8 degrees C) or high (38.9 degrees C) eggshell temperature (EST) and exposed to low (17%), normal (21%), or high (25%) O(2) concentration from d 9 through 19. High EST initially increased HP, but gradually O(2) became more important for HP than EST. Finally,HP was highest for the combination of high EST with high O(2) and lowest for the combination of high EST with low O(2). High EST decreased hatch time, BW, yolk free BW, and relative heart weight. The EST had no effect on residual yolk weight, chick length, or relative liver weight. Increased O(2) increased yolk free BW and chick length and decreased residual yolk weight at hatch. No interactions between EST and O(2) were observed with regard to embryo development and hatchling characteristics. If embryo development is reflected by HP, it can be concluded that high EST primarily increased embryonic development until the second week of incubation. During the third week of incubation, O(2) had a greater effect in determining embryo development than EST.

Influence of Egg Shell Embryonic Incubation Temperature and Broiler Breeder Flock Age on Posthatch Growth Performance and Carcass Characteristics

A study was conducted to examine the posthatch growth performance of high-yielding broilers when eggs were incubated at 3 different embryo temperatures from 2 flocks of breeders at different ages (different egg size). Two thousand, four hundred eggs from 2 broiler breeder flocks (29 and 57 wk of age) of the same high-yielding strain (Cobb x Cobb) were incubated in the same incubator for 16 d at 37.5 degrees C. Following candling, the eggs from the 2 flocks were transferred into 3 hatcher cabinets at starting temperatures of 36.5 degrees C (low, L), 37.6 degrees C (middle, M), and 38.7 degrees C (high, H) and adjusted to achieve a shell temperature of 37.5 degrees C (L), 38.6 degrees C (M), and 39.7 degrees C (H) using an infrared thermometer. All chicks were taken off at 21 d of incubation, randomized into floor pens, and reared for 44 d. Body weights, feed intake, and feed conversion were determined at 21, 35, and 44 d of age. Body weight of birds from the H treatment was significantly less at 21, 35, and 44 d compared with the M birds. Birds in the L group weighed significantly less at 35 and 44 d compared with the M birds. Progeny from the older breeder flock had significantly greater BW at 1, 21, and 35 d of age, but had only numerically greater BW at 44 d when compared with birds from the younger flock. Feed conversion for the H birds was significantly higher from 0 to 21 d of age compared with the M and L birds. Broilers from the 29-wk-old breeder flock had lower cumulative feed conversion values than the birds from the 57-wk-old flock. No significant differences in mortality were observed. Posthatch performance appears to be affected by hatcher environment as determined by embryo shell temperature.

Metabolic responses of chick embryos to short-term temperature fluctuations

Two experiments were carried out to study embryonic metabolic responses to short-term temperature fluctuations in order to explore the possibilities of using embryonic metabolic responses as a tool to control the incubation process. In the first experiment, eggshell temperature (ET) in the control group was kept constant at 37.8 degrees C, and embryos in the experimental group were exposed to varying ET within the range of 36.8 to 38.8 degrees C using ET steps of 0.2 degrees C and time steps of 3 h. This was repeated in 3 periods between 6.5 and 9.5 d, 10.5 and 13.5 d, and 14.5 and 17.5 d. In the studied ET range, heat production (HP) increased linearly at 4.9% per 1 degrees C ET. In the second experiment, a standard machine temperature (MT) was used for the control group, and eggs in the experimental group were exposed to low (MT - 0.3 degrees C) or high (MT + 0.3 degrees C) temperatures for 1 h of time at d 8, 9, and 11 to 16. When MT was decreased, CO2 production initially increased at 0.5% and decreased thereafter. When MT was increased, CO2 production initially decreased at 0.4% and increased thereafter. It was concluded that embryonic HP responded linearly with short-term ET changes in the studied ET range of 36.8 to 38.8 degrees C. Changes in CO2 concentration due to short-term MT changes could not be explained by embryonic HP only. It can be speculated that blood flow through the chorio-allantoic membrane changes with MT, affecting heat transfer and diffusion of CO2. A second, delayed response to MT changes was in accordance with the findings in Experiment 1. Within the studied temperature range it will be difficult to use embryonic metabolic responses as a tool to control the incubation process. Because HP is linearly related to ET as in the studied temperature range, other factors such as O2 availability or CO2 release may limit embryo development at higher ET. At this moment, research on the effects of gas exchange at different temperatures on embryo development and survival is lacking.

Effect of egg size on heat production and the transition of energy from egg to hatchling

An experiment was conducted to study the effect of egg size on embryo development, heat production, and energy partitioning between egg and hatchling. Small (56.1 +/- 0.12 g SEM) and large (70.0 +/- 0.11 g SEM) hatching eggs were incubated in climate respiration chambers, and eggshell temperature was maintained constant at 37.8 degrees C in both egg weight classes by adjusting machine temperature. Dry matter, ash, protein, and fat contents were determined in albumen, yolk, yolk-free body (YFB), and residual yolk (RY), and carbohydrate contents and caloric values were calculated. To achieve a constant eggshell temperature, machine temperature needed to be set lower from d 15 onward, coinciding with increased heat production in large eggs compared with small eggs. Selective nutrient uptake resulted in higher fat content and lower protein content in RY in chicks that hatched from small eggs compared with large eggs. The respiration quotient in small and large eggs was the same, and embryos in small and large eggs were equally efficient in the transfer of energy from egg to YFB. The surplus availability of nutrients in large eggs was therefore held responsible for the absolute and relative higher weight of RY in chicks that hatched from large eggs compared with small eggs.

Effect of eggshell temperature during incubation on embryo development, hatchability, and posthatch development

An experiment was conducted to study the effects of different eggshell temperature (EST) profiles during incubation on embryo mortality, hatchability, and embryo development. Furthermore, chicks from different EST profiles were reared under low and high housing temperatures to investigate subsequent posthatch growth and rectal temperature. Two batches of eggs were used in this experiment. Hatching eggs were subjected to 36.7 or 37.8 degrees C EST during the first week, to 37.8 degrees C EST during the second week, and to 37.8 or 38.9 degrees C EST during the third week of incubation. Posthatch housing temperature decreased from 35 degrees C at d 1 to 30 degrees C at d 7 (high) or decreased from 30 degrees C at d 1 to 25 degrees C at d 7 (low). The difference between machine temperature and EST (DT) was used to illustrate the effect of EST on heat production during incubation. DT differed per batch, and was smallest when eggs were incubated at 36.7 degrees C instead of 37.8 degrees C during wk 1. High EST during wk 3 of incubation (38.9 degrees C instead of 37.8 degrees C) reduced DT only in batch 2. Embryo development was most retarded in eggs incubated at 36.7 degrees C EST compared with at 37.8 degrees C during the first week of incubation. However, highest hatchability and embryo development were always found when EST was maintained at 37.8 degrees C constantly throughout incubation. Chicks that hatched from eggs incubated at low EST during wk 1 of incubation had lower rectal temperature after hatching, especially under low housing temperatures, and this effect lasted until 7 d posthatch in batch 1. The highest rectal temperatures were always found in chicks incubated at 37.8 degrees C EST constantly throughout incubation. Eggs and chicks from different batches require different environmental conditions for optimal embryo development, hatchability, and posthatch growth. Rearing temperature and incubation conditions affect the ability of young chicks to maintain their rectal temperature during the first week posthatch.

The effect of level of feeding in early gestation on reproductive success in young rabbit does

An experiment examined the effect of restricted feeding during early gestation on later feed intake and on kindling performance in young rabbit does. Nulliparous rabbit does (n=94) were inseminated at 14.5 weeks of age. During the first 10 days of gestation, does were fed individually either to appetite (AL) or 1.35 times maintenance requirement (R). After 10 days of gestation, all animals were fed to appetite. Does were weighed at insemination and after kindling. Feed intake was recorded during the first 10 days of gestation and weekly, thereafter. The number of does that kindled, number of live and stillborn kits and litter weight was recorded. The experiment ended after kindling. During feed restriction, AL does consumed 70 g/day more on an average than R does (209 and 139+/-4 g for AL and R, respectively; P<0.001). In the first and second week after feed restriction, compensatory feed intake occurred. Restrictive fed does ate more than AL does (+34+/-5 g/day from days 11 to 17 of gestation; P<0.001; +17+/-6g/day from days 18 to 24 of gestation; P<0.05). In the last week of gestation, feed intake of AL and R was comparable (89 and 100+/-5 g, respectively). At kindling, AL does had consumed 8+/-3g/day more feed over the total gestation period than R does (P<0.04). Feeding level during early gestation neither affected the kindling rate (83%), total litter size (7.9+/-0.4) nor the number of does with stillborn kits (10 versus 9 for AL and R, respectively). Regardless of treatment, in the last week of gestation (days 25-32) the number of does with stillbirth was lower and average birth weight was higher (P<0.01) in does eating more than the average daily feed intake compared to does eating below average. Based on the results of this study it was concluded that feed restriction for 10 days in early gestation does not affect kindling performance of young does, but feed intake in the last week of gestation affects kit survival and birth weight.

The effect of litter size before weaning on subsequent body development, feed intake, and reproductive performance of young rabbit does

An experiment was performed to study the effect of litter size before weaning on subsequent body development and composition, feed intake, and reproductive performance of young rabbit does with the objective to improve reproductive performance. Litter size (LS) before weaning (treatment) was 6, 9, or 12 kits. After weaning (30 d), 58 female kits per treatment (in two successive replicates) were reared and fed for ad libitum intake to 14.5 wk of age (end of rearing). At 14.5 wk of age, receptive does were inseminated. Nonreceptive and nonpregnant does were inseminated at 17.5 wk of age. The experiment ended when the second litter was weaned. Part of the animals was slaughtered to determine body composition at the end of the experiment (replicate one) and at the end of rearing (replicate two). At weaning, BW differed among treatments (P < 0.05; 855, 773, and 664 +/- 15 g for LS6, 9, and 12, respectively). Compensatory growth was observed. At the end of rearing, LS12 does were smaller (P < 0.05) than LS9 and LS6 does (3,524, 3,778, and 3,850 +/- 48 g, respectively). After first lactation, no difference in BW among treatments was found. Compared with LS6, empty body weight (BW minus gut, bladder, and uterus content) of LS12 contained more (P < 0.05) nitrogen (32.5 vs 31.1 +/- 0.3 g/kg), more (P < 0.05) ash (30.7 vs 28.3 +/- 0.6 g/kg), and less (P < 0.05) fat (168.6 vs 200.2 +/- 8.6 g/kg). No differences in body composition among treatments were found at the end of the experiment. During rearing, LS12 had the lowest (P < 0.05) daily feed intake (152, 164, and 169 +/- 2 g/d for LS12, 9, and 6, respectively). During the reproductive period, no differences in feed intake among treatments were found. Kindling rate (the number of kindlings per number of inseminations) was not influenced by treatment. In the first parity, total litter size (number of alive and stillborn kits) was lower (P < 0.10) for LS12 than for LS9 (6.4 vs 8.6 +/- 0.5, respectively). When first mating was delayed by 3 wk, an increased (P < 0.05) total litter size was found regardless of treatment (7.5 and 9.4 +/- 0.3 for 14.5, and 17.5 wk, respectively). Decreasing litter size before weaning from nine to six kits did not alter future reproductive performance. Based on results of this study, it seems advisable to perform a limited standardization level (at nine kits) after kindling and postpone first mating to an older age (17.5 wk) to improve reproductive performance.

Egg handling and storage

The temperature and relative humidity of storage, as well as the gaseous environment, interact with the fertile egg over time during storage in such a way as to affect the success of incubation either negatively or positively. This interaction occurs both above and below the "physiological zero", at which embryonic metabolism is minimal. This interaction below physiological zero implies that certain physical aspects of the egg must be affected by the environmental conditions. As the eggshell is a relatively fixed component, changes in albumen, shell membranes, cuticle, yolk, or embryo proper must account for these time- and environment-related effects. It is concluded that the major contributor is the albumen, as it is obviously the most dynamic component below physiological zero and is strategically positioned.

Influence of pre-incubation treatment on hatching results of broiler breeder eggs produced at 37 and 59 weeks of age

1. The influence of temperature in the nest box, temperature during storage, storage time and pre-setting temperature on the hatchability of broiler breeder eggs produced by birds of 37 and 59 weeks of age was examined. 2. All treatments that can be characterised as being less optimal for embryo survival than the control treatment affected the hatchability of fertile eggs more in the case of eggs produced by older birds. 3. A higher temperature in the nest box, longer storage periods, higher storage temperature, especially at longer storage periods, and higher pre-setting temperature significantly reduced the hatchability of fertile eggs from the older birds. 4. For the younger birds, a significant reduction of hatchability was found only for the longest storage period.

The effect of different levels of relative humidity and air movement on litter conditions, ammonia levels, growth, and carcass quality for broiler chickens

An experiment using 4,800 commercial broiler males (Ross x Ross) was conducted in 12 climatic chambers. Three levels of relative humidity (RH) (45, 40, to 80, and 75%) and two levels of internal air circulation (7.7 to 9.9 and 17.8 to 24.5 cm/s), with each level replicated and, therefore, forming a 3 x 2 x 2 factorial arrangement of treatments, arrangement of treatments, were imposed as the main effects. Broilers were group weighed and feed efficiencies calculated at 14, 28, and 42 days of age. Percentage dry matter of the litter and a subjective evaluation of general litter conditions (moisture and caking) were scored weekly, with the percentage nitrogen and total quality of litter produced in each chamber measured at the conclusion of the study. Ammonia levels were measured in each chamber every second day. A sample of birds (36) from each chamber was processed at 42 days and scored for litter spots and ammonia burns on the breast and for the incidence and severity of twisted legs, crooked toes, and infected and calloused hocks and foot pads. Mean body weight was significantly greater (32 g) at 42 days of age in birds exposed to 45% RH compared with the two higher regimens of RH. Both the incidence and severity of ammonia burns on the breast and infected foot pads were significantly higher with 75 versus 45% RH. Increases in RH significantly increased caking and litter moisture and reduced the percentage of dry matter and the percentage of nitrogen found in the litter. Ammonia levels were more variable but generally increased with increases in RH. The two levels of air movement within the chambers produced less influence on the environment than RH, although the scores for both litter moisture and caking were significantly lower with increased levels of internal air circulation.