The “hatching window” represents the 24-48 hour period during which the eggs hatch. The newly hatched chicks remain in the incubator until all of them have hatched, after which they undergo routine treatments such as selection, vaccination, sexing and grading, before being transported to the farm. Depending on the length of the hatching window, routine procedures and transport to the farm, the chickens can remain under fasting conditions for a period that could reach, according to legislation (EC No 1/2005), up to a maximum of 72 hours.

Chicks need to learn to consume feed as soon as possible to allow their digestive system to undergo a rapid anatomical and physiological transformation, as well as help the development of the immune system. They also need to start consuming water in a short time to compensate for the dehydration they experience from hatching to their arrival at the farm, thus also favoring the consumption and digestibility of the feed. Fasted chicks are more susceptible to pathogens, lose weight easily, critical tissue development and survival can be compromised, and those that survive often exhibit stunted growth, low disease resistance, inefficient feed use and low meat yield. For this reason, it is critical to understand the effects of delayed access to feed and water on chick gastrointestinal development, immune system activity, body weight, and overall short- and long-term development.

Hatching window extension

The length of time that characterizes the hatching window seems to be the cause of the difference in biological age and quality of chicks from the same flock. The biological age of the chick expressed in days indicates the days since hatching, while the chronological age indicates the days since hatching of the entire flock. This means that although the chronological age of the batch is the same, the biological age is not.

Thus, in the same flock, there are chicks with a biological age of two days, and consequently a longer fasting period than those hatched in the last hours of the hatching window, whose biological age is 0 days. The difference becomes evident in practice, especially if the length of the hatching window decreases or increases. Different conditions can affect the length of the hatch window, including incubation temperature, egg weight, storage conditions, gaseous environment, as well as the age of the breeders.


The yolk, rich in lipids, is the main source of energy during the development of the embryo, while the albumen is the main source of protein. Given the low level of carbohydrate in the egg, it is very likely that part of the yolk sac albumen provides gluconeogenesis after absorption from the yolk sac membrane. Therefore, protein metabolism via gluconeogenesis appears to be the source of glucose for glycogen accumulation that subsequently fuels egg hatch. However, after hatching, if the chick does not have access to glucose sources for energy generation, reliance on gluconeogenesis involves the consumption of protein resources that would otherwise be used for development and growth. After hatching, the predominant energy source for a chick shifts from yolk lipids to exogenous carbohydrates introduced through the diet, in order to increase glucose levels in blood and consequently gluconeogenesis activity. However, under fasting conditions, when access to external carbohydrate sources is delayed, the increased reliance on fat for energy increases the likelihood of ketosis and dehydration. Therefore, it is necessary to ensure that the chick has access as soon as possible after hatching to the main source of energy, starchy carbohydrates.

Chicks fasted for prolonged periods show an increase in hematocrit level of up to 24%. It is also observed that hemoglobin is higher with decreasing body weight. One possible explanation for these elevated levels is the use of body fluids to cope with dehydration caused by delayed access to food and water. Furthermore, the high plasma corticosterone levels confirm that delayed feed access is, along with many other factors, a significant stressor for the chick. These stress factors will affect the final performance of the broiler, leading to decreased final body weight, higher feed conversion and, in some cases, higher mortality.

Hormonally, chicks that undergo long hours of fasting have lower than normal plasma T3 levels, indicating a lower overall metabolic rate. Thyroid hormones have also been shown to play a crucial role in thermoregulation. Chicks fasted for more than 16 hours and exposed to cold for a short time have a lower body temperature than chicks fed immediately after hatching, and this temperature seems to be maintained during the first week of life. At the same time, fasting and lower body temperature appear to correspond with lower serum T3 levels and higher serum T4 levels; opposite data were observed in chicks fed before cold exposure. These results suggest that the delay in access to feed and water after hatching impairs the thermoregulatory capacities of chicks, which implies the need to regulate the climatic conditions of the environment to preserve the quality of fasting chicks when they reach the farm.

Growth and development

Delayed access to feed and water after hatching causes significant weight loss during the incubation period, mainly due to dehydration and yolk use, but as soon as the chicks begin to feed, weight body begins to increase. Early access to feed improves growth performance, body weight gain, pectoral muscle size and promotes intestinal development.

A meta-analysis study verified the effects of fasting on the productive performance of broilers. Although the chicks were able to compensate for the growth retardation caused by starvation, this compensation is not sufficient to match the development of chicks fed immediately after hatching. In fact, statistically significant differences in the live weight of the chickens at 42 days of age were highlighted between those fed immediately and those that were late in accessing the feed.

On the other hand, in addition to the need to provide feed and water as soon as possible, it is important that the macronutrients in the diet are perfectly balanced to promote efficient growth. The role of proteins in muscle development is fundamental, for this reason the importance of giving chicks a diet containing highly digestible proteins to promote growth from the first hours of life is emphasized. Feeding chicks immediately after hatching is essential for muscle development as glycogen stores are used immediately after hatching, leaving the chick in a state of energy deficit.

The researchers speculate that prolonged fasting may result in less muscle development due to lower satellite cell activity. Poultry show less mitotic activity of satellite cells when they are deprived of food. Although mitotic activity resumes once feed is given, the response is not sufficient to compensate for that of fed chickens, neither with respect to satellite cell activity nor with respect to muscle growth. This is further confirmed by the increase in Pax7 protein expression in fasted chickens which, after a period of stress, appears to be related to low levels of satellite cell mitotic activity.

The physical, morphological and physiological development of the gastrointestinal tract of birds occurs during the first weeks of life. It has been observed that the yolk favors the initial development of the small intestine during the first 48 hours, but the introduction of an exogenous diet just after hatching favors a more rapid development of the gastrointestinal tract. Therefore, the introduction of feed is essential for intestinal development and can affect the ability to digest and absorb nutrients throughout the life of the chicken. Numerous studies record the negative effects that fasting has on the length of the duodenum, jejunum, and ileum. Furthermore, during the first two weeks of life, intestinal villus height appears to be significantly lower in fasted than in fed chicks, while less crypt depth has been found in the jejunum from the first week of life. Although the effects of prolonged fasting on intestinal morphology do not appear to be long term, the incidence and severity of side effects cannot be excluded.

New feeding strategies

The first days after hatching are critical for growth, activation of the immune system, stimulation of digestive enzymes and the development of the birds’ organs. Therefore, there is a great interest in looking for alternative solutions to be able to feed the chicks right after hatching by providing them with energy sources directly in the hatching trays and during transport.

A new technology to ensure nutrient intake from the first hours of life is the administration of hydrated gels sprayed on the chicks as small drops that the chicks consume quickly thanks to their innate instinct to peck at each other. In this way, the chicks ingest all the nutrients contained in the gel drops without getting wet or cold. LICUICEL COMPLEX is an effective and innovative strategy that is administered directly in the hatchery with a gel and a specialized machine. LICUICEL COMPLEX contains nutrients, vitamins, minerals, highly digestible amino acids, and prebiotics that promote the development and functioning of the gastrointestinal system and help the development of the immune system, improving resistance to infections and positively influencing growth and productive performance, promoting the chick welfare. Supplementation with LICUICEL COMPLEX in newborn chicks provides the benefit of its anti-inflammatory and antioxidant properties, improving yolk absorption into the small intestine.

La suplementación con LICUICEL COMPLEX en los pollitos recién nacidos aporta el beneficio de sus propiedades antiinflamatorias y antioxidantes, mejorando la absorción del vitelo hacia el intestino delgado.

The results obtained through acoustic studies and hematological analyzes suggest that the administration of LICUICEL COMPLEX significantly reduces the level of stress in newly hatched chicks. The hematocrit values of the LICUICEL COMPLEX group indicate less dehydration, therefore, a more efficient maintenance of homeostatic balance. In addition, the monocyte count, lower in the control group than in the LICUICEL COMPLEX group, confirms that prolonged fasting is the cause of severe stress in the animals.

Wellness measurements when applying LICUICEL COMPLEX

The field of bioacoustics allows the study of animal vocalizations through various acoustic descriptors such as the frequency of vocalization and the number of calls per minute. These indicators allow a quantitative value of animal welfare to be obtained.

A high temporal repetition frequency of chick calls can be an indicator of stress when there is a high number of vocalization repetitions. A high vocalization frequency indicates stress, as well as the maximum vocalization frequencies of the entire productive cycle during the first three days of life on the farm, probably due to transport stress.
Obtaining lower values of temporal repetitions and maximum frequency are objective indicators of less stress and consequently improved animal welfare.

CEALVET has analyzed the improvement of applying LICUICEL COMPLEX (Licuicel group) during the first hours of life compared to the Control group to which no product has been administered during prolonged fasting of 48 hours.

Graph 1 shows how the average indicated with a green triangle on the box diagrams is lower in the Licuicel group compared to the control (200 Hz difference), as well as the control group presents many more repetitions of vocalizations than the group treated with Licuicel.

In graph 2, in the zone of more stress (more vocalizations and more frequency of calls), marked in red, there are samples of the control group with respect to the zone of less stress where there are fewer repetitions of calls and a lower frequency of singing, marked in green where most of the Licuicel samples are found.

The use of LICUICEL COMPLEX in the group that has received early feeding presents more well-being and less stress in accordance with the indicators of the vocalizations of the chicks.

Conclusions and prospects

Fasting affects various metabolic parameters, impairs the activation of the immune system and impedes the morphological and physiological development of the gastrointestinal tract. Therefore, the importance of feeding an early diet to the chicks directly in the hatchery is emphasized, in this way the early chicks can withstand the long hours of the hatching window and start their correct development using the nutrients of the yolk and the macronutrients from the exogenous food source.

In our preliminary study, bioacoustic measurements have confirmed that the administration of hydrated gels such as LICUICEL COMPLEX, enriched with nutrients that can help the chick to meet its energy and nutritional needs, is shown to be a valid solution to promote the well-being of chickens from the first hours of life.

The main objective will be to continue with more studies that confirm and deepen these results, demonstrating that access to a diet immediately after hatching can be of vital importance for the well-being and correct physical and physiological development of the chicks.

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