Recent Research Trends in Hatchability—Related Problems of The Domestic Fowl

Acute exposure to hyperthermic oscillating temperatures during pre-incubation influences northern bobwhite development, hatching, and survival

Temperature extremes alter development, growth, hatching, and survival of eggs of ground-nesting birds, particularly during pre-incubation (egg laying) when eggs are left unattended and exposed to the environment for days or weeks before parental incubation begins. The northern bobwhite quail is a ground-nesting bird whose eggs experience high temperatures (≥45° C) during pre-incubation. It is known that chronic high temperatures during pre-incubation alter development and reduce hatching and survival of bobwhite eggs, but it is not known if acute doses of high temperatures during pre-incubation have the same effect. In this study, the 12-d pre-incubation period was divided into thirds. Fresh bobwhite eggs were exposed to either a commercial holding temperature for all 12 d (serving as a control), or a high oscillating temperature regimen for 4 d (one third of pre-incubation) either in the early, middle, or late third of pre-incubation, with a low oscillating temperature regimen during the remaining 8 d. The timing of acute exposure to high oscillating temperatures significantly affected bobwhite development. Eggs exposed in the first 2/3 of pre-incubation developed twice as much as eggs exposed late in pre-incubation, even though all eggs received the same amount of heating degree-hours. Thus, a critical window of thermal susceptibility exists for developing northern bobwhites. Acute exposure to high oscillating temperatures resulted in reduced hatchling mass, hatching success, survival, and compromised hatching synchrony. Thus, acute hyperthermic nest temperatures during pre-incubation could result in the observed reductions in the percentage of juveniles in natural populations during hot and droughty years.

Incubation temperature impacts nestling growth and survival in an open-cup nesting passerine

For oviparous species such as birds, conditions experienced while in the egg can have long-lasting effects on the individual. The impact of subtle changes in incubation temperature on nestling development, however, remains poorly understood, especially for open-cup nesting species with altricial young. To investigate how incubation temperature affects nestling development and survival in such species, we artificially incubated American robin (Turdus migratorius) eggs at 36.1°C ("Low" treatment) and 37.8°C ("High" treatment). Chicks were fostered to same-age nests upon hatching, and we measured mass, tarsus, and wing length of experimental nestlings and one randomly selected, naturally incubated ("Natural"), foster nest-mate on days 7 and 10 posthatch. We found significant effects of incubation temperature on incubation duration, growth, and survival, in which experimentally incubated nestlings had shorter incubation periods (10.22, 11.50, and 11.95 days for High, Low, and Natural eggs, respectively), and nestlings from the Low treatment were smaller and had reduced survival compared to High and Natural nestlings. These results highlight the importance of incubation conditions during embryonic development for incubation duration, somatic development, and survival. Moreover, these findings indicate that differences in incubation temperature within the natural range of variation can have important carryover effects on growth and survival in species with altricial young.

Upper lethal temperatures of Northern Bobwhite embryos and the thermal properties of their eggs

Northern Bobwhite eggs in the southern United States are often exposed to ambient temperatures in excess of their normal incubation temperature when unattended during their typical extended preincubation period. In drought years, typified by high ambient temperatures, Bobwhite eggs are often exposed to temperatures > 45°C, well-above the upper lethal temperature of most other birds. Because the upper lethal temperature of Bobwhite embryos is not currently known, simulated clutches of eggs were exposed to preincubation temperatures ranging from 39 to 52°C for exposure times of 1, 3, or 6 h. The upper lethal temperatures and the temperatures resulting in ≥ 50% death of Northern Bobwhite embryos were recorded in addition to the time to thermal equilibrium of Bobwhite eggs. The upper lethal temperature for 1, 3, and 6 h of preincubation exposure was 51, 49, and 46°C, respectively. The temperatures resulting in ≥ 50% death were 46, 44, and 40°C for eggs exposed to elevated temperatures for 1, 3, and 6 h, respectively. The mean time for the inner-egg temperature to reach the ambient temperature was 38 ± 1 min (± SE). The thermal tolerances of Northern Bobwhite embryos were much higher than expected, and among the highest reported for birds, indicating an adaptation to the naturally occurring temperature extremes that often occur in the Bobwhite's semi-arid southern range. However, as the temperature increased above the incubation temperature, hatching success declined, showing that increased thermal tolerance has a cost. Although Bobwhite producers, managers, and researchers will find this information useful, it seems most interesting that high temperatures could plausibly have contributed to the population decline observed in the Bobwhite's semi-arid range.

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.

Low temperature effects on embryonic development and hatch time

A series of experiments was conducted to estimate phenotypic correlations between incubation characteristics, and to evaluate the effects of cold stress and genotype during incubation on chick weight, egg weight loss, hatching time, and embryonic mortality. Eggs were cooled at 18 or 24 C, for 12, 24, 36, 48, or 72 h beginning on Day 8, 12, 14, 16, or 18 of incubation. Other eggs were cooled intermittently for 6 h every 48 h or 12 h every 96 h. A control group in each experiment was not cold stressed. Results indicated a low and negative correlation between hatching time and chick weight, and a low and positive correlation between hatching time and weight loss from transfer to hatching when variability due to egg weight was removed. Chick weights at hatching were lower in chicks from cooled eggs than those of chicks from eggs incubated under normal temperature. The chicks from cooled eggs were more susceptible to dehydration during holding in the hatcher. Incubation times were delayed approximately as long as the times of embryonic cooling. Embryonic mortality was significantly increased under continuous (single period) cold stress, but not under intermittent cooling (6 h every 48 h). Significant genotype by environment interactions were found in the response of embryos of various strains to cold stress. Exposure for 36 h or longer had detrimental effects on chick weight and embryo viability, but these effects were modified by interactions among the factors involved. The results indicated that embryos from cooled eggs lose more weight during incubation and that the neonatal chicks are more susceptible to dehydration during holding time, and have a longer incubation period, and a greater embryonic mortality.

Short-term changes in incubation temperature: behavioral and physiological effects in the chick embryo from 6 to 20 days

In 3 experiments we have attempted to determine the extent to which the chick embryo is behaviorally and physiologically responsive to short term changes (.5-2 hr) in the normal ambient incubation temperature. Embryos ranging in age from 6-20 days of incubation have been examined after exposure to temperatures ranging from 30.5 degrees to 44.4 degrees C (normal incubator and nesting temperatures are 37-38 degrees C). At 6,9 and 12 days of age the heart rate and the duration of amnion contractions were significantly altered by exposure to temperature either higher or lower than normal although overt neuromuscular activity (motality) remains unchanged. At 15 and 20 days, however, (hatching occurs on Day 21) the rate of neuromusclar activity is altered at both low and high temperatures. At 20 days, beak-clapping, vocalization, and respiration rates also change reliably upon short-term exposure to both high and low temperatures. The possibility is discussed that embryonic responsiveness to temperature changes in the environment during natural incubation may play some role in later behavioral capabilities.