Assessment of day-old chicks

Day-old chicks are the end-product of the hatchery and form the starting material for commercial production of eggs and meat. With regard to economic aspects, the main purpose of a hatchery is to achieve a high percentage of hatchability, while the quality and health of newly hatched birds determine performance outcomes to slaughter. According to Tona et al. (Reference TONA, BRUGGEMAN, ONAGBESAN, BAMELIS, GBEASSOR, MERTENS and DECUYPERE2005) it is generally believed that high hatchability is associated with high quality of chicks, and maximisation of hatching success translates into optimal quality of day-old chicks. The lack of explicit parameters to describe chick quality has led many researchers to create and standardise their own scales (Boerjan, Reference BOERJAN2002; Tona et al., Reference TONA, BAMELIS, DE KETELAERE, BRUGGEMAN, MORAES, BUYSE, ONAGBESAN and DECUYPERE2003). In analogy with the Apgar score for the assessment of newborn infants, the Pasgar score has been developed as an objective measure for day-old chick quality. High-quality chicks receive a maximum score of 10 points. Another quality indicator is the Tona score, which is based on information collected from farms and hatcheries, whereby Belgian researchers defined the criteria for qualitative chick scoring based on parameters such as activity, outward appearance and yolk sac resorption. These characteristics are assessed according to their importance on a scale of 0 to 100. The sum of the scores for all characteristics is used as a tool for assessing the quality of day-old chicks (Tona et al., Reference TONA, BAMELIS, DE KETELAERE, BRUGGEMAN, MORAES, BUYSE, ONAGBESAN and DECUYPERE2003).

Another quality indicator is chick length, which is measured from the tip of the beak to the tip of the middle toe (Mukhtar et al., Reference MUKHTAR, KHAN and ANJUM2013). The authors of numerous publications have observed a positive correlation between the length of newly hatched chicks and final body weight of broilers (Wolanski et al., Reference WOLANSKI, RENEMA, ROBINSON, CARNEY and FANCHER2007; Molenaar et al., Reference MOLENAAR, REIJRINK, MEIJERHOF and VAN DEN BRAND2008; Petek et al., Reference PETEK, ORMAN, DIKMEN and ALPAY2008). Although the weight of newly hatched chicks is often used as a determinant of their quality, authors differ regarding its relationship with final slaughter weight (Vieira and Moran, Reference VIEIRA and MORAN1999; Tona et al., Reference TONA, BAMELIS, DE KETELAERE, BRUGGEMAN, MORAES, BUYSE, ONAGBESAN and DECUYPERE2003; Wolanski et al., Reference WOLANSKI, LUITEN, MEIJERHOF and VEREIJKEN2003). Meijerhof (Reference MEIJERHOF2009) concluded that the weight of day-old chicks is of limited value as a quality indicator, and highlighted a positive correlation between the weight of hen eggs and the weight of chicks. In turn, in newly hatched chicks, body weight has been correlated with the remaining yolk sac. The above information suggested that increased amounts of yolk in the chick's body cavity provide evidence of poor utilisation. In addition, weak embryos, which are deemed to be hatchery waste, do not completely absorb the yolk sac (Özlü et al., Reference ÖZLÜ, SHIRANJANG, ELIBOL and BRAKE2018). It follows that chick body weight is not an optimal indicator for the quality of newly hatched chicks and their slaughter potential. In this situation, measurement of yolk free body mass (YFBM) is seen as a reliable qualitative method. YFBM is calculated by subtracting the residual yolk from the chick body weight. High values of YFBM suggests a better development of the chick. Under hatchery conditions, however, this method has limited practical application because a large number of chicks have to be killed to determine the yolk free body mass. In the case of visual appraisal, an interesting concept has been introduced by Petek et al. (Reference PETEK, ORMAN, DIKMEN and ALPAY2010), who chose chick feather colour as an indicator of quality. Because feather pigmentation comes from the yolk, they concluded that more yellow feathers may be indicative of maximal yolk uptake, which translates into day-old chick quality. However, because the number of studies that test this hypothesis is small, this assertion cannot be conclusively confirmed.

Breed

Commercial strains of broilers (two paternal strains and two maternal strains) have been developed to achieve high meat performance These strains must show good muscling and high reproductive parameters. In response to genetic selection, the body weight of current meat breeds has increased over 30 years by 400%, while feed conversion has improved by 50% (Buzala and Janicki, Reference BUZALA and JANICKI2016). At the same time, commonly used breeds exhibit significant productive differences, and commercial strains, which are the basis for production of poultry, are not uniform. Sterling et al. (Reference STERLING, PESTI and BAKALLI2006) showed higher body weight and better feed conversion ratios in Cobb compared to Ross broilers. This difference was supported by Hristakieva et al. (Reference HRISTAKIEVA, MINCHEVA, OBLAKOVA, LALEV and IVANOVA2014), who reported that the body weight of newly hatched chicks was higher for Cobb compared to the Ross line. The data on final body weight of the chickens confirmed a continuing trend. Comparative analyses from commercial strains of broilers are quite common, and, to date, have focussed on production results and meat quality (Farran et al., Reference FARRAN, KHALIL, UWAYJAN and ASHKARIAN2000; Rahimi et al., Reference RAHIMI, ESMAEILZADEH and KARIMI TORSHIZI2006; Kosarachukwu et al., Reference KOSARACHUKWU, IHESHIULOR, OMEDE and OGBUEWU2010; Dozier and Gehring, Reference DOZIER and GEHRING2014), rearing conditions and housing systems (Altan et al., Reference ALTAN, OĞUZ, PABUÇCUOĞLU and KONYALIOĞLU2000; Arruda et al., Reference ARRUDA, MENDES, GUIRRO, SCHNEIDER, SIKORSKI, SAUSEN, DIAS and BONAMIGO2016; Bergmann et al., Reference BERGMANN, SCHWARZER, WILUTZKY, LOUTON, BACHMEIER and SCHMIDT2017), feeding of birds (Heck, et al., 2004; Sterling et al., Reference STERLING, PESTI and BAKALLI2006), incubation and hatchability (Suarez et al., Reference SUAREZ, WILSON, MATHER, WILCOX and MC PHERSON1997; Abudabos, Reference ABUDABOS2010). Publications by Tona et al. (Reference TONA, ONAGBESAN, JEGO, KAMERS, DECUYPERE and BRUGGEMAN2004; Reference TONA, ONAGBESAN, KAMERS, EVERAERT, BRUGGEMAN and DECUYPERE2010) are among the few to provide a comprehensive analysis of embryonic development and to compare physiological parameters of embryos and the quality of chicks from different commercial lines of broilers.

According to Nangsuay et al. (Reference NANGSUAY, MEIJERHOF, VAN DEN ANKER, HEETKAMP, KEMP and VAN DEN BRAND2015), intensive genetic selection in modern broiler lines (Cobb 500 and Ross 308) has influenced the post-hatching development of chicks and stage of incubation. The intense metabolic processes that occur in the avian embryo generate heat. The combination of this heat emission with the temperature of the incubation environment influences the embryo's body heat, which is reflected as eggshell temperature. In turn, this property may affect embryo development, chick quality, as well as future growth performance (Molenaar et al., Reference MOLENAAR, HULET, MEIJERHOF, MAATJENS, KEMP and VAN DEN BRAND2011). During incubation, Ross 308 embryos used 13.9 kJ more energy than Cobb 500, and the efficiency of converting energy to yolk free body mass was approximately 7.6% lower compared to Cobb 500 (Nangsuay et al., Reference NANGSUAY, MEIJERHOF, VAN DEN ANKER, HEETKAMP, KEMP and VAN DEN BRAND2015). The discrepancies observed between these lines were determined by different metabolic strategies during the period of limited gas exchange at incubation.

Broiler breeder nutrition

Rearing broiler parent stock is a key step in production. Good flock management can guarantee a high percentage of fertile eggs for producing healthy and strong day-old chicks. Over the last few decades, a major problem in parent farms has been the decline in the number of fertile eggs, especially during the second laying period (van Emous et al., Reference VAN EMOUS, KWAKKEL, VAN KRIMPEN, VAN DEN BRAND and HENDRIKS2015). According to Yassin et al. (Reference YASSIN, VELTHUIS, BOERJAN, VAN RIEL and HUIRNE2008), this phenomenon may be triggered by poor management of the flock (genetic origin, bird health, egg quality and flock age). Another key factor is to provide animals with sufficient feed nutrients. A well-balanced diet is a major determining factor for rearing efficiency of parent flocks and for shaping production traits during lay and the production of high-quality eggs.

Eggs have a relatively stable composition and contain all the nutrients needed for embryonic development. Unlike vitamins and minerals, the energy and protein composition of eggs does not change due to the nutrition of layers at the parent farm (Whitehead et al., Reference WHITEHEAD, PEARSON and HERRON1985). Moraes et al. (Reference MORAES, PISHNAMAZI, MBA, RENEMA and ZUIDHOF2011) investigated the effect of dietary protein and energy in broiler breeder flocks on dressing percentage in the offspring. They fed three different energy levels (2950, 2800 or 2650 ME kcal/kg) combined with two protein levels (14 or 16%) and found that the low energy to high protein ratio diet increased breast yield of the offspring.

The observations made to date showed that dietary protein concentration in a breeder flock contributes significantly to progeny performance (Chang et al., Reference CHANG, HALLEY and SILVA2016). To determine the effect of protein content in broiler breeder diets on the development of chickens, van Emous et al. (Reference VAN EMOUS, KWAKKEL, VAN KRIMPEN, VAN DEN BRAND and HENDRIKS2015) used an arrangement of treatments with three dietary protein levels (high, medium, and low protein) and two growth strains (fast and slow growing chickens). The offspring of fast-growing breeders had a higher body weight at 34 days of age than those from slow-growing strains. The low protein diet had a positive effect on breast meat yield in male broilers, while that of female broilers was not affected. In referring to Lopez and Leeson (Reference LOPEZ and LEESON1995), the data showed that a very low protein diet for broiler breeders considerably reduced egg weight and the body weight of newly hatched chicks, but had no significant effect on the body weight and carcass quality in broilers.

Normal chick embryo development is determined by the mineral (macro- and microelements) content of the layer diet on the parent farm. According to Chang et al. (Reference CHANG, HALLEY and SILVA2016), development and quality of day-old chicks are affected by vitamins D and E, selenium, zinc and magnesium. The content of cholecalciferol (vitamin D₃) in the layer diet is positively correlated to the levels of vitamin D₃ and 25-OH D₃ in the hen's egg yolk (Mattila et al., Reference MATTILA, LEHIKOINEN, KIISKINEN and PIIRONEN1999). Vitamin D₃ is converted to the active form 25-OH-D₃ and 1,25-OH-D₃ through metabolic pathways in the liver and kidneys, respectively. The optimum deposition of vitamin 25-OH-D₃ in the layer diet may increase Ca absorption from the intestine, thus improving eggshell quality. Furthermore, increased content of this vitamin has a beneficial effect on hatchability and improves chick quality (Saunders-Blades and Korver, Reference SAUNDERS-BLADES and KORVER2015). The findings of Atencio et al. (Reference ATENCIO, EDWARDS and PESTI2005) suggested that supplementation of 2,000 or 4,000 IU vitamin D₃/kg to parent flock diets will increase the final body weight of the offspring in relation to unsupplemented chickens, while the incidence of tibial dyschondroplasia will be lower in the offspring. Saunders-Blades and Korver (Reference SAUNDERS-BLADES and KORVER2015) determined the effect of vitamin D in broiler breeder diets on innate immune resistance in the offspring and concluded that supplementing with 25-OH-D₃ increased hatchability and innate immunity to E. coli in broiler chicks.

In poultry production, vitamin E is added to the diet in a natural or synthetic form, mainly as α-tocopherol, and, along with selenium, represents an important antioxidant. According to Driver et al. (Reference DRIVER, ATENCIO, PESTI, EDWARDS and BAKALLI2006), chickens may synthesise inadequate vitamin E levels and its concentration in the body depends on the diet. By modifying the composition of the broiler breeder hen diets, it is possible to increase the amounts of both vitamin E and selenium in eggs (Payne, et al., 2005; Mohiti-Asli et al., Reference MOHITI-ASLI, SHARIATMADARI, LOTFOLLAHIAN and MAZUJI2008). Day-old chicks from hens supplemented with vitamin E at 60 IU/kg feed, were characterised by considerably higher antibody titre compared to the control group and the group fed at 20 IU (Andi et al., Reference ANDI, SHIVAZAD, POURBAKSH, AFSHAR, ROKNI, SHIRI, MOHAMMADI and SALAHI2006) According to the same authors, increased transfer of maternal antibodies to progeny translates into a stronger humoral response of day-old chicks and greater immunity to disease. Urso et al. (Reference URSO, DAHLKE, MAIORKA, BUENO, SCHNEIDER, SUREK and ROCHA2015) used a broiler breeder flock to determine the effect of vitamin E and selenium in the diet of hens on the quality of hatched chicks. Hens aged 47 weeks old fed L-selenomethionine (0.4 mg/kg) and 120 mg vitamin E/kg feed produced heavier eggs than the less supplemented groups. The applied rations had no statistically significant effect on the body weight of newly hatched chicks. In the case of selenium, Pappas et al. (Reference PAPPAS, ACAMOVIC, SURAI and MCDEVITT2006) observed that chicks hatched from hens fed diets with 0.5 mg/kg of organic Se, showed a higher tissue Se concentration compared to the unsupplemented group.

Flock age

Egg quality changes with the age of the hens, which may result in lower hatchability and poorer quality chicks. Chang et al. (Reference CHANG, HALLEY and SILVA2016) stated that egg composition might be affected by age of hen, as is the yolk to eggshell ratio. Chicks hatched from older flocks are characterised by higher body weight compared to chicks from younger flocks. This correlation applied to the entire broiler rearing period (Tona et al., Reference TONA, ONAGBESAN, JEGO, KAMERS, DECUYPERE and BRUGGEMAN2004). Yolk sac nutrient reserves were higher in chicks hatched from the older flock. This relationship was confirmed by Ulmer-Franco et al. (Reference ULMER-FRANCO, FASENKO and O'DEA CHRISTOPHER2010), who reported that Cobb 500 hatching eggs from a flock aged 59 weeks had a higher yolk percentage compared to the eggs from a 29-week-old flock. Polish researchers observed that hatching parameters varied according to parent flock age (Nowaczewski et al., Reference NOWACZEWSKI, BABUSZKIEWICZ and KACZMAREK2016). When analysing egg weight changes with regard to hen age, these authors observed the weight of hatching eggs to differ between flocks aged 26-30 and 46-64 weeks. Older hens laid 11.3 g heavier eggs than youngest hens. In view of the above experiments, another important study by Ramaphala and Mbajiorgu (Reference RAMAPHALA and MBAJIORGU2013) demonstrated that the coefficient of correlation between the weight of hatching eggs and the weight of chicks was positive (r=0.995).

Flock age determines traits related to egg content and eggshell quality. Hatching eggs from young flocks are characterised by better albumen quality and stronger eggshells (İpek and Sözcü, 2013). In turn, stronger eggshell reduces oxygen transfer to the developing embryo, which may slower embryo growth and metabolism (Lourens et al., Reference LOURENS, MOLENAAR, VAN DEN BRAND, HEETKAMP, MEIJERHOF and KEMP2006). Older flocks exhibited a higher percentage of abnormalities in newly hatched chicks (Boerjan, Reference BOERJAN2002). Layer age determines egg hatchability, and the results of Abudabos (Reference ABUDABOS2010) suggested that eggs from older Ross hens are characterised by lower hatchability compared to eggs from young hens. The lowest hatchability (70.4%) was obtained from eggs laid by the oldest hens. The average hatchability increased to 85.2% for the younger group of the same strain. It follows from the studies cited above that hatching value of eggs is determined by hen age, which determines egg weight and embryo development.

Storage of eggs

Storage of hatching eggs is a common practice in poultry production, especially in large commercial flocks. However, stored eggs are exposed to many factors affecting the quality of chicks (Goliomytis et al., Reference GOLIOMYTIS, TSIPOUZIAN and HAGER-THEODORIDES2015). During storage, hatching eggs undergo changes in the form of water and carbon dioxide losses as well as an increase in albumen pH (Decuypere et al., Reference DECUYPERE, TONA, GRUGGEMAN and BAMELIS2001; Silversides and Scott, Reference SILVERSIDES and SCOTT2001). Prolonged egg storage periods extend the time for incubation and chick hatching. This situation increases the time newly hatched chicks remain in the incubator and delays their access to water and feed (Tona et al., Reference TONA, BAMELIS, DE KETELAERE, BRUGGEMAN, MORAES, BUYSE, ONAGBESAN and DECUYPERE2003). According to Khan et al. (Reference KHAN, KHAN, BUKHSH and AMIN2014), storage of hatching eggs prior to incubation has no significant effect on hatchability if this period does not exceed eight days. Nevertheless, extending this period beyond seven days after fertilisation reduces hatchability parameters (Fasenko et al., Reference FASENKO, ROBINSON, WHELAN, KREMENIUK and WALKER2001). Goliomytis et al. (Reference GOLIOMYTIS, TSIPOUZIAN and HAGER-THEODORIDES2015) observed that, after four-day storage of eggs, hatchability was around 85%. When this period was extended to 16 days, hatchability decreased to 80%. In the context of prolonged egg storage, an increased percentage of early dead embryos was observed. For eggs from Rhode Island Red hens (RIR), nine days storage of hatching eggs was found to be associated with increased embryonic mortality between one and seven days of incubation (48.3%; Khan et al., Reference KHAN, KHAN, BUKHSH and AMIN2014). A similar phenomenon was reported by Petek and Dikmen (Reference PETEK and DIKMEN2006) for broilers. Higher mortality was characteristic for embryos from eggs stored for 15 days (12.3%) compared to eggs stored for five days, for which early embryonic mortality was 5.1%. These authors stated that development of embryos from eggs stored for a prolonged time (over five days) may not start immediately after placement of the eggs in the incubator or the development stage is slower in the initial incubation period. Prolonged storage of eggs is detrimental to the incubation process and hatchability, and according to Reijrink et al. (Reference REIJRINK, BERGHMANS, MEIJERHOF, KEMP and VAN DEN BRAND2010), early use of ‘fresh’ eggs for incubation (less than four days) increases mortality in chicks.

Incubation and post-hatching period

Technological advances over several decades have improved avian egg incubation techniques. Modern, fully automatic incubators permit precise setting of hatching parameters for different poultry species. According to Udawaththa et al. (Reference UDAWATHTHA, ADIKARI and GAMLATH2018), whether the embryo develops normally or not depends on incubation conditions. Heat produced during incubation is a critical element in initiating the embryonic development of the bird. Small changes in artificial incubation temperature may have a significant impact on embryo development, and later on chick quality and carcass dressing percentage (Lourens and Van Middelkoop, Reference LOURENS and VAN MIDDELKOOP2000). The optimum temperature in the setter should range from 37.6 to 38.0°C (Molenaar et al., Reference MOLENAAR, HULET, MEIJERHOF, MAATJENS, KEMP and VAN DEN BRAND2011). It can be concluded from the results of many studies that fluctuations in incubation temperature affect the development of muscles (Clark et al., Reference CLARK, WALTER and VELLEMAN2017), internal organs (Leksrisompong et al., Reference LEKSRISOMPONG, ROMERO-SANCHEZ, PLUMSTEAD, BRANNAN and BRAKE2007), skeletal bones (Shim and Pesti, Reference SHIM and PESTI2011), and the quality of day-old chicks (Molenaar et al., Reference MOLENAAR, HULET, MEIJERHOF, MAATJENS, KEMP and VAN DEN BRAND2011).

Hulet et al. (Reference HULET, GLADYS, HILL, MEIJERHOF and EL-SHIEKH2007) studied the effect of low (37.5°C), moderate (38.6°C) and high (39.7°C) temperatures on body weight of chicks. Chicks from the group exposed to high temperatures exhibited higher body weight (43.1 g) compared to the middle (42.2 g) and low temperature (41.1 g) groups. A reverse trend was noted towards the end of rearing. The highest body weight was observed in broilers from the group exposed to moderate temperatures, and lowest in the high temperature group (2.263 kg vs. 2.166 kg). An interesting concept was introduced by Tzschentke (Reference TZSCHENTKE2008), who concluded that chicks exposed to high temperature towards the end of incubation can be better adapted to unfavourable environments (e.g. high temperatures) later in the fattening period.

It is common in hatcheries to hold early hatchlings until all chicks in the baskets have emerged. This practice causes the earliest hatched chicks have no access to feed and water for a relatively long time. This situation may be prolonged by other organisational activities, such as sexing, vaccination or transport to the farm. It is known that long-term feed withdrawal may suppress the digestive tract from developing, which impairs the absorption of nutrients and translates directly into weight gains of the chickens (Uni et al., Reference UNI, FERKET, TAKO and KEDAR2005). Delayed post-hatch feeding was the subject of a study by Shinde Tamboli et al. (Reference SHINDE TAMBOLI, AKSHAT GOEL, MANISH MEHRA, ROKADE, PRAGYA BHADAURIA, YADAV, MAJUMDAR and BHANJA2017), in which one-day-old chicks had access to feed within 6, 12, 24 and 36 h of hatching. The authors concluded that post-hatch feed deprivation for the first 24 h did not affect growth performance but improved immune response in slow growing broiler females. However, these parameters were adversely affected when chicks were feed-deprived for more than 36 h.

In ovo feeding

Chick quality can be influenced by using in ovo feeding to embryos (Pawłowska, Reference PAWŁOWSKA2015). This method is described within the US Patent (6.592.878) of Uni and Ferket (Reference UNI and FERKET2003). In ovo feeding involves the administration of nutritive supplements into the embryonic amnion at 17-18 days of incubation. Supplementation at this stage of development allows the chick to ingest the amniotic fluid together with the solution and to absorb it in the intestines. This manipulation has proved effective in several studies which used in ovo injection of carbohydrates (Tako et al., Reference TAKO, FERKET and UNI2004; Uni et al., Reference UNI, FERKET, TAKO and KEDAR2005; Bhanja et al., Reference BHANJA, MANDAL, AGARWAL and MAJUMDAR2008; Zhai et al., Reference ZHAI, ROWE and PEEBLES2011), amino acids (Bhanja et al., 2005; Kadam et al., Reference KADAM, BHANJA, MANDAL, THAKUR, VASAN and BHATTACHARYYA2008; Shafey et al., Reference SHAFEY, MAHMOUD, ALSOBAYEL and ABOUHEIF2014) and vitamins (Nowaczewski et al., Reference NOWACZEWSKI, KONTECKA and KRYSTYNIAK2012; Gonzales et al., Reference GONZALES, CRUZ, LEANDRO, STRINGHINI and BRITO2013; Salary et al., Reference SALARY, SAHEBI-ALA, KALANTAR, REZA and MATIN2014; Gholami et al., Reference GHOLAMI, QOTBI, SEIDAVI, MELUZZI, TAVANIELLO and MAIORANO2015). The studies cited above indicated that the injection of active substances into the egg has a beneficial effect on biochemical processes and the development of the chick embryo, hatchability and quality of newly hatched chicks.