The greatest challenge for modern hatchery is to achieve uniform, high vitality flocks of day old chicks. Next to incubation technology, good hatchery management can greatly influence this. Uniformity is an important issue for a hatchery, and the use of good hatchery management practices can make a valuable and lasting contribution, from the hatchery right through to farm level.
Uniform incubation conditions support equal, syncronised embryonic development for each individual egg in the incubator, which is fundamental to a narrow spead of hatch.
Traditionally, the emphasis on uniformity of broiler chicks has been dictated by the last part of the production chain. The automated slaughtering process demands uniformity of product entering the processing plant. Often, achieving uniformity is regarded as the broiler farmer’s job and indeed, uniformity of broilers at slaughter weight can be greatly influenced by what happens on the broiler farm. As chick uniformity is unlikely to increase during the production process, a key prerequisite to a uniform end product is uniformity in the day olds. Day-old flocks showing poor uniformity are impossible to manage properly, which will result in lower growth, increased feed conversion and higher mortality during the first week.
Flock uniformity - particularly during the first week - is an important issue for management because at the moment of hatching, a number of physiological systems are still developing in the chick, and this process continues during the first seven to ten days of life. Amongst these systems is the thermoregulatory system. During the first days of their lives, newly hatched chicks have little or no ability to regulate their body temperature. This means that as environmental temperature decreases, the internal temperature of the chick is also reduced - and as small chicks have a higher surface to volume ratio, they lose more heat than large chicks. Consequently, small chicks may benefit from an environmental temperature that is 2°C higher than large chicks. Furthermore, an air temperature that is too cool will prevent chicks from getting adequate feed and water. To conserve warmth, birds respond by huddling together but are then unable to get to feeder lids and drinkers.
Next to the development of thermoregulation, the complete development of the digestive tract and immune system is equally important. Maturation of the digestive and immune systems depend, in the first few days, on the chick getting all the nutrients and antibodies provided by the yolk sac. As the uptake of nutrients from the yolk is stimulated by the intake of feed, the development and growth of the newly hatched chick relies on having almost immediate access to feed and water.
During the brooding period, the chick is highly dependent on its environment. Good management, especially during the first days of a chick’s life, is crucial to maximise performance and liveability. In order to realise optimum environmental conditions and feed/water supply for a maximum number of chicks, uniformity of dayolds is a prerequisite. Next to providing optimum conditions, having chicks separated by size may reduce competition within the flock, decrease mortality, increase growth rate and improve uniformity of marketing weight when the birds enter the processing plant. Uniformity of day olds is therefore highly valued by the farmer-customer.
There appears to be general consensus about the importance of chick uniformity. However, some confusion arises when it comes to the question of measuring uniformity. Poultry growers generally assess the uniformity of a flock ‘by eye’ – though in general terms, information regarding practical standards for measuring the uniformity of day-olds is lacking. In broiler production, uniformity is expressed as the percentage of birds whose weight falls within 10% of the flock’s average weight - and current industry standards dictate that to achieve good uniformity, 80-85% of birds must fall within 10% of the average flock weight. In day-olds, it is possible to achieve 100% uniformity based on this standard; hence this range may reasonably be narrower than 10% for newly hatched chicks (Figure 1).
For the purpose of this article, we will take chick weight as a measure for uniformity and focus on aspects of hatchery management that affect the range of weights in day old chicks.
Spread of hatch
Variation in day old chick body weight at the moment of placement in the farm may be much higher than the variation of newly hatched chicks. The weight of chicks at placement is affected by their weight at hatch and the length of time they are held in the hatcher. Chicks that have to wait in the incubator for prolonged periods dehydrate and lose weight. Spread in chick weights upon placement - and thus uniformity - is consequently influenced by the spread of hatch.
Regarding spread of hatch, numerous studies have investigated the effects of a delayed access to water and feed for day old chicks. Time until first feed/water intake depends on the duration between hatching and placement at the farm. Spread of hatch within a batch of chicks in one hatcher causes variation in the time at which first feeds can be made available. Thus, spread of hatch is likely to have similar effects to variations in the time taken to first feed intake, as measured in the studies shown in Table 1.
The table summarizes recent results from these studies, and clearly demonstrates a negative effect on body weight at eight days of age. The delay in feed/water intake was shown to negatively influence body weight up to slaughter age.
Differences in body weight were significant when the spread in the time of access to feed and water was more than 24 hours.
In multi-stage incubation, the hatching process may take two days, and chicks are removed from the incubator only when a majority have hatched. From the results shown above, we may conclude that chickens hatched early will indeed show different growth rates to late hatches up to slaughter age.
Spread of hatch depends on equal development of the embryos at the start of incubation, combined with uniform rates of development in the eggs within one incubator. A number of factors are summarised below, that are known to affect the spread of hatch.
Maternal age influences day old chick weight through its effect on egg weight. On average, day old chicks weigh 67-76% of the initial egg weight. This is a considerable range, and although the influence of egg weight on chick weight is obvious, there are other important, influential factors that must be taken into consideration.
Maternal age also directly affects the rate of embryonic development. It seems that at the moment of oviposition, the eggs of ‘mature’ flocks (>32 weeks) contain embryos in a more advanced state that develop at a higher rate than embryos in eggs from ‘pubescent’ flocks. Consequently, embryos in eggs from the latter group require longer incubation periods. Some studies even report a decrease in incubation time of up to 10 hours between 28 and 32 weeks of maternal age! (Figure 2).
Storage time prior to incubation is known to influence the rate of embryonic development. In stored eggs, the initiation of embryonic development is delayed, and the rate of development is also lower. Recently, a study from the University of Leuven (2003) confirmed the hatchery man’s rule, that “one day storage adds one hour to incubation time”, and indeed, embryos from Cobb eggs stored for 18 days required an additional 16 hours of incubation time, compared to embryos from eggs stored for three days. Incubating fresh and stored eggs in one incubator thus increases spread of hatch by one hour per additional storage day!
It is important to realise that storage conditions also have an impact on the rate of embryonic development during incubation. After oviposition, the temperature inside the egg falls rapidly below the physiological zero: the minimum temperature above which embryonic development occurs. However, temperatures below this point influence other egg characteristics too, thereby affecting egg quality - depending on the duration of storage. Ruiz and Lunam (2002) demonstrated a retardation in embryonic development measured in incubation time in eggs that were stored at 10°C for 9-11 days, compared to eggs that were stored at 16.5°C: chicks that hatched from the ‘cold’ stored eggs, required significantly more incubation time.
Storage begins at the moment of laying. Especially during the summer or in hot climates, the time that eggs are held in the breeder house should be minimised. In order to maximise uniformity of embryonic development, frequent collection of hatching eggs is recommended.
Naturally, a homogenous incubation temperature during the entire incubation cycle is fundamental to equal embryonic development, as temperature directly affects the rate of development in the embryo. Normal embryonic development occurs between 37°C (98.6°F) and 38°C (100.4°F), but the rate of development differs within this range. Turkey embryos have been shown to hatch approximately four hours earlier when incubated at 37.5°C compared to 37°C (Christensen, 2001).
Of particular concern for a small spread of hatch, is an even start of embryonic development. A homogenous temperature for all eggs within one incubator at the start of incubation is fundamental to uniform development for the batch. In this respect, it is important to realise that batches of eggs may require different heat-up times to reach incubation temperature: for example, because of different storage or transport temperatures, or differences in egg size. Consequently, incubating eggs of different backgrounds may cause differences in incubation times.
uniformity Uniformity of day old chicks is a priority for both hatcheries and their customers, because improved chick management will not only improve growth rates, but also decrease losses from natural mortality or culling.
The following is a useful summary of key aspects of hatchery management that will promote optimum chick uniformity:
1. Sort eggs. First, take flock age into account. The age of the mother flock affects egg size and furthermore, maternal age influences the development rate of the embryos (Figure 3). Eggs of young mother flocks (<32 weeks of age) require longer incubation time.
Secondly, consider storage time. Eggs in one incubator should be of approximately the same age (storage time), since storage also retards embryonic development. For every storage day after three days, increase incubation time by ± 1 hour.
2. Pre-heating. Accurately sorting eggs prior to incubation enhances uniformity of embryonic development at the start of incubation. A uniform start may be further improved by pre-heating treatments prior to incubation. Eggs of various backgrounds may require different times to reach incubation temperature. Heating the eggs for several hours to 21- 25°C reduces the variation of temperatures inside the eggs at the start of incubation (Figure 4). This will promote better uniformity of development in eggs within one machine and further reduce spread of hatch.
3. Homogeneous incubation temperature. Incubation temperature influences the rate of embryonic development - and crucially, homogeneous incubator temperature is required to achieve the narrowest spread of hatch. This means that incubators must be designed such that they provide uniform incubation conditions to support equal, synchronised embryonic development for each individual egg within the machine. The incubator should be divided into small, separate units, each with its own climate control. Supporting the natural pattern of the embryo and eggshell temperature during each phase of embryonic development means that optimum conditions vary during the incubation process. Consequently, optimum conditions for uniform incubation can only be achieved in single stage incubation.
A large spread in hatching time, and consequently in the duration to first feed/water intake, causes poor uniformity of day olds, which complicates farm management and undermines performance and results. Minimising spread of hatch is crucial for optimum results. There are two criteria that must be met for a uniform hatch:
- The hatching eggs entering the incubator must be uniform.
- During both the setting and the hatching period, the rate of development of each egg in the batch must be synchronised by a homogeneous incubation temperature.
The hatchery management methods summarised here can greatly improve day old chick uniformity. Application in hatchery practice requires good planning and the use of highly evolved incubation technology, to assist and maximise uniform embryonic development.