Theoretical and empirical studies on temperature and moisture loss of hatching eggs during the pre-incubation period

In the Netherlands, approximately 800 million hatching eggs per year are produced on highly specialized broiler breeder farms. On this farms, the eggs are produced and stored for several days. Normally once or twice a week the eggs are collected from the farms and transported to the hatchery, where they are set and incubated.

Between production of the eggs and setting, a certain amount of mortality occurs in the eggs. As a result of this mortality and because some embryos are not able to complete the pipping process in time, about 10% of the fertile eggs do not hatch. A certain percentage of these eggs are not hatching because the conditions in the period before incubation are not set at a level that is optimal for embryo survival. To minimize the number of non hatching fertile eggs, the conditions during the pre-incubation period must be set at a level that meets the demands of the embryo. In commercial situations, the management decisions concerning the egg handling that have to be taken in the pre-incubation period are mainly influencing the effects of tune, temperature and relative humidity.

The aim of the studies presented in this thesis was (1) to formulate analytical equations to calculate the temperature development and moisture loss of hatching eggs, (2) to determine the climatic conditions in the pre-incubation period that can occur in field situations and (3) to determine the influence of these conditions on hatchability.

In chapter 1 a review of the literature concerning the treatment of eggs in the pre-incubation period is presented. From this review, it can be concluded that the majority of the research on this subject is done in the period before 1970. The availability of experimental results on this subject with eggs produced by the modem type broiler breeder is limited. In chapter 1, some hypothesis are formulated to explain the influence of storage time and storage temperature on hatchability.

With the analytical equations formulated in chapter 2, the effect of climatic conditions on the temperature development and moisture loss of eggs can be calculated. Therefore, climatic conditions that occur in field situations can be evaluated on their influence on the eggs. One of the conclusions from these calculations is that air velocity will have a major influence on internal egg temperature in the second half of the incubation process.

In chapter 3 and 4, the results of the calculations based on the equations are compared with measurements. The results show that temperature development and moisture loss of eggs can be predicted rather accurate when eggs are placed in litter nests and roll away nests. When birds have access to litter nests, eggs are warmed by the birds. Under these conditions, accurate calculation of temperature and moisture loss is not possible. During storage, no accurate calculation of temperature and moisture loss could be made, because of natural convection in hatching egg containers and protection of the storage system against moisture loss.

In chapter 3, the temperature and moisture loss of eggs during their period in the nest boxes is examined. The results indicate that eggs produced in litter nests are warmed by the birds to a temperature above the minimum level for embryo development Eggs produced in roll-away nests are not warmed by the birds and their cooling process starts immediately after production, with the cooling rate and final temperature level depending on the climatic conditions in the house. Moisture loss of eggs in produced in litter nests is higher than in roll-away nests, but relatively low compared to the total moisture loss during incubation.

During storage, temperature and moisture loss characteristics are dependent on the position of the eggs in the containers, the method of storage and the storage conditions (chapter 4). Eggs placed in centre position of containers experience a slow warming and cooling process when compared with eggs in side positions. When eggs are stored on incubator trays, cooling and warming of eggs is more rapidly than when eggs are stored on cardboard trays. The rate of cooling and warming of eggs stored on plastic trays is intermediate. When air velocity is increased, the cooling and warming rate of eggs increases. The use of coverages over containers decreases the rate of temperature change.

Moisture loss of eggs in containers can not be calculated directly from temperature and relative humidity of the air surrounding the container. The containers provide a protection against moisture loss, probably due to the presence of a boundary layer around the eggs, which forces the eggs to loose less water than is expected from the climatic conditions.

The influence of temperature during the pre-incubation period on hatchability is examined in chapter 5. The results indicate that the influence of storage time and pre-incubation temperature on hatchability is related with age of the flock Pre-incubation treatments that can be classified as having a negative influence on hatchability were more detrimental for eggs of older birds than for eggs of younger birds.

The results presented in chapter 5 indicate that hatchability of eggs that has experienced a high temperature during the nesting period is lower than of eggs that has experienced a low temperature in this period. This indicates that eggs produced in litter nests will have a lower hatchability than eggs produced in roll away nests, due to differences in egg temperature. From the results presented in this chapter it can be concluded that eggs of younger birds can be stored for longer periods than eggs of older birds. For both age groups, the combination of longer storage periods and low storage temperature is beneficial for hatchability compared to longer storage periods and high storage temperature. According to the results presented in this chapter, low storage temperatures can also be used when eggs are stored for relatively short periods.

In chapter 7, some possible explanations for the reported relations between storage time, storage temperature and bird age are discussed. It is suggested that the development of albumen pH determines the suitability of eggs for storage of eggs and that storage conditions can be evaluated on their influence on the albumen pH development.

In chapter 6, the influence of moisture loss during storage on moisture loss during incubation and hatchability is reported. The results presented in this chapter indicate that moisture loss during storage influences moisture loss during incubation. As a result relative humidity during storage has a smaller effect on total amount of moisture lost between oviposition and hatching than would be expected from the amount of moisture lost during storage. Moisture loss during storage had no significant effect on hatchability.