Incubation and Brooding Conditions Essential for Optimisation of Neonatal Nutrition

Growth rates of broiler chickens have increased and production cycle times have decreased by 60% in the last 40 years. This is widely agreed to be the direct result of genetic selection and improvements in poultry nutrition (Havenstein et al., 2003a). The incubation and brooding period has become a larger part of the total life span of the broiler chicken. This is expected to increase even more in the future as the slaughter age decreases (Hulet, 2007). To achieve the genetic growth potential of the bird, neonatal nutrition has become increasingly important nowadays (Havenstein et al., 2003b). Understanding and optimization of incubation and brooding conditions is essential to achieve the largest benefit from neonatal nutrition. 

Nutrients stored inside the egg are utilized for growth and development during the 21 day incubation period of the chicken embryo (Wilson, 1997). To start embryo development, temperature is one of the most important environmental conditions (Romanoff, 1936; Decuypere and Michels, 1992; Meijerhof, 2009). The temperature that the embryo experiences during incubation is especially important and has a large effect on pre- and postnatal survival and development (French, 1997; Leksrisompong et al., 2007; Molenaar et al., 2010a). It is important to point out that the embryo temperature differs from the air temperature inside the incubator as well as the temperature displayed on the outside of the incubator (Meijerhof and Van Beek, 1993). Embryo temperature is the result of embryonic heat production and heat transfer between the egg and its surrounding (Meijerhof and Van Beek, 1993). Actual embryo temperature is difficult to measure without killing the developing chicken therefore eggshell temperature is often used as an indicator rarely deviating more than 0.2ºC from the actual embryo temperature (French, 1997). Eggshell temperature needs to be measured at the equator of the eggshell. A simple ear infrared thermometer is sufficient enough to get a good indication of the eggshell temperature. Different studies have shown that an eggshell temperature of 37.8°C during incubation results in the best hatchability, chick quality, and posthatch performance (Lourens et al., 2007; Leksrisompong et al. 2007, Molenaar et al., 2011). Relatively small deviations from the optimal eggshell temperature (37.8 ± 1.5ºC) can easily occur yet have a major impact on survival and (organ) development (Lourens et al., 2005, 2007). This is thought to be the result of changes in nutrient utilisation and physiological processes during incubation (Molenaar et al., 2010a, 2013).  

Although the chicken embryo is fully grown at hatch, further development and maturation of the thermoregulatory, gastro-intestinal and immune system is necessary in the brooding period (Maiorka et al., 2006; Tzschentke, 2007), comprising the first 7 days of the chick’s life. The sensitivity of the brooding period is highlighted by the fact that chicks are unable to regulate their body temperature posthatch; they are completely dependent on environmental temperature to maintain their body temperature (Romanoff, 1941). Ideally, body temperatures of chicks need to range from 40.0 and 41.0°C throughout the brooding period in order to achieve the lowest mortality and finest development. Comparable with the incubation period, temperature is the most important factor that needs to be controlled during the brooding period (Maatjens, 2010).

Secondly, feed intake is essential to stimulate intestinal and immunological development in the brooding period (Noy and Sklan, 1997). Time between hatch and first feed consumption can be up to 72 hours, because of variations in hatch time, chick handling, and transportation time (Dibner et al., 1998; Van den Brand et al., 2010). During this period without feed and water, the chick has to rely on water and nutrients of the residual yolk (Noy and Sklan, 1997). Early feed consumption is important because intestinal development and growth is much larger with feed than without (Geyra et al., 2001). Furthermore, early feed consumption can improve the immune status of the chick as immunoglobulins from the residual yolk can be utilized rather than acting as an energy source (Dibner et al., 1998). 

Difficulties in optimizing brooding conditions and the large benefits of a good start early in life have led to the development of two commercial brooding systems for chicks.

The commercial brooding systems, Patio system (Vencomatic, the Netherlands) and the HatchBrood system (HatchTech B.V., the Netherlands) have been specifically developed to optimize the early life conditions of the chickens. In the Patio system, the hatching and growout phase are combined. Eggs are transported at day 18 of incubation from the hatchery to the Patio system. Chicks hatch within the system and can eat and drink immediately after hatch. The unit contains different rows and levels to grow the chicks until slaughter age (Van de Ven et al., 2009). The Patio system is a replacement for conventional broiler farms. In the HatchBrood system, chickens are placed in cradles inside the unit after normal processing in the hatchery and they are provided with feed and water for 4 days. The HatchBrood system is used as an extension of the hatchery with the chicks delivered as 4-days-old instead of day-old to the broiler farm (Van der Pol et al., 2013). Environmental conditions and early feed can easily be adjusted to the specific requirements of chicks during the brooding period in these brooding systems.

Neonatal nutrition has gained attention recent years because of the significant benefits that can be achieved on final performance. The first application of neonatal nutrition is with the use of in ovo feed. In ovo feed has been developed to supply the chicken embryo already with additional nutrients (Uni and Ferket, 2004), but is not widely adopted in the commercial poultry industry yet (Kadam et al., 2013). An isotonic solution containing carbohydrates, proteins or a mixture of both is injected into the amnion of the embryo at around day 18 of incubation before the embryo pips the internal shell membrane and starts lung ventilation (Uni and Ferket, 2004). The solution is absorbed by the chicken embryo and can improve hatchability and hatchling quality (Uni and Ferket, 2004) This is a result of increased glycogen reserves, improved gut and muscle development, and better skeletal health (Uni and Ferket, 2004, Bello et al., 2013). The long-term effects of in ovo feed are not consistent (Kadam et al., 2012).

Optimal incubation conditions are very important when in ovo feed is applied. In practice, high eggshell temperatures (>39.5ºC) are often found in the second half of incubation as a result of poor air velocity or cooling capacity, or high temperature settings in the incubator (French, 1997; Lourens et al., 2005). High eggshell temperatures (>39.5ºC) during the second half of incubation have been found to influence embryonic nutrient utilization by an increased glucose demand and a lower protein efficiency for growth (Molenaar et al., 2010a, 2013). If in ovo feed is applied when embryos are experiencing high temperatures, the injected nutrients are likely to be used to compensate for nutrients losses due to this high temperature (Molenaar et al., 2010b). To achieve the highest benefits of in ovo feed pre- and postnatal, eggshell temperatures need to be maintained uniformly at 37.8 ± 0.2ºC in the incubator.

In the brooding period, nutrition is generally given more attention and prestarters are often provided to the posthatch chicks. Recent developments at commercial feed producers to optimize prestarters include: use of highly digestible raw materials, smaller pellet sizes (2.0 mm), and high pellet durability (Wijtten, personal communication). However, chicks need to find and start consuming the feed to benefit from early nutrition. The most important factor involved in the start of feed consumption is the body temperature of the chick. The chick needs to have a body temperature between 40.0 and 41.0ºC posthatch to show normal behaviour and start looking for feed (Molenaar, 2012). At commercial broiler farms, it is often found that the body temperature of chicks becomes too low (<40.0°C); this results in a low feed consumption and decreased development and it can lead to high mortality rates (Maatjens, 2010).

 In conclusion, the greatest benefit of neonatal nutrition on chick performance can be achieved when incubation and brooding conditions are optimized. The body temperature of the embryo and chick temperature is the critical factor that needs to be controlled for optimization of neonatal nutrition. 

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