Recent advances in the use of processed protein products in early nutrition for broiler chickens

Abbreviated Title: Processed protein in broiler nutrition

Summary

Keywords:

Introduction

The poultry industry considers nutrition a vital element in the success of poultry production. Over the years, the nutritional aspect of poultry production has received wide interest from researchers, leading to the development of several concepts and strategies that have contributed immensely to the development of the industry. Concurrent development over the past 7 years has led to the emergence of broiler strains with remarkable genetic potential, such that male meat-type broilers are able to reach 3 kg weight within 40 days of age, and white-egg layers are capable of producing 330 eggs in 52 weeks of lay (Leeson, 2012). As a result, feeding programmes for broiler chickens have continued to evolve, with changes in diet specifications. These changes have been determined by the need to meet the demands of these new strains of birds, and at the same time put into practice recent regulations requiring the reduction of certain additives such as antibiotics, as well as control the impact of poultry production on the environment. While Havenstein (2003a) suggested that there have been great changes in the nutritional requirements of broilers over the years as a result of the improved performance, due to genetic selection by commercial poultry breeders, the attention of researchers has started to turn to the nutrition of newly-hatched and young chicks. This is as also due to evidence that has emerged concerning the physiological processes within the first few days of newly-hatched chicks, and the perceived benefits of maximizing these first few days for a future gain, through early nutrition. For example, the small intestine of a newly-hatched chick grows rapidly (Sklan, 2001; Uni and Ferket, 2003; Yegani and Korver, 2008), and faster than the rest of the body (Uni et al., 1999) within the first few post-hatch days. This development is significantly faster in birds supplied with feed and water immediately at hatch (Dibner et al. 1998), and is further associated with later growth performance (Iji et al., 2001a). It is therefore suggested that feeding newly-hatched chicks would further optimize the development of the digestive organs, leading to better performance (Noy et al., 2001; Potturi et al., 2005). Consequently, Leeson (2012) proposed that if we wish meat birds to achieve an ever-increasing weight-for-age, greater emphasis should be placed on both early and late-phase nutrition. Hence, the search for new strategies to feed young birds.

Early nutrition strategies and chick development

The concept of delayed access to feed and water by newly-hatched chicks is not new, although the impact may have just become a key area of focus for many researchers in recent times. In the commercial hatchery, broiler chicks within a set batch of eggs would hatch within several hours of one another (Bigot et al. 2001) and chicks would need to be sorted before being delivered to various farms. In practice, that could leave some of the earliest hatching chicks without food or water for up to 48 h after hatch (Noy and Sklan 1999a). This results in weight loss of about 4 g for each 24 h spent in the hatcher, partially as a result of moisture loss as well as yolk and pectoral muscle utilisation (Halevy et al. 2003, Careghi et al. 2005), hampers the development of the gastrointestinal tract (GIT) and could have lasting negative impact on the overall performance of the birds (Batal and Parsons, 2002a; Juul-Madsen et al., 2004). The GIT develops most rapidly within the first 4–7 days of life (Uni et al. 1995; Iji et al. 2001b). In order to overcome or mitigate these challenges, an early and continuous feeding process needs to be established to supply nutrients in ovo to the developing embryo, specialized feed and water to the newly hatched chick within the hatchery, and prestarter diet containing highly digestible nutrients at placement on the farm. It is noticeable that the availability of appropriate nutrients before or immediately after hatch may result in a more uniform gut development, a more stable gut microflora and a more mature immune system. Such nutrients should be readily available, to provide the energy and protein for intestinal growth (Noy and Uni 2010). Access to readily digested feed or nutrients within this period would aid the development of the GIT (Bigot et al. 2003; Gonzales et al. 2003). Early nutrition in broiler chickens involves providing newly-hatched chicks with feed and water as early as possible after hatch. Therefore, it seems that these early nutrition strategies would be the most appropriate means to combat the negative impacts of delayed access to feed resulting from present-day conventional hatchery practices. This makes it important to further study how to enhance and maximize early nutrition strategies in poultry production.

In ovo feeding technology

In ovo technology has advanced to include not only prevention of disease through vaccination of avian embryos at transfer, but also the possibility of gender discrimination of avian embryos, through identification of sex-specific hormone levels in allantoic fluid samples withdrawn from broiler embryos at 13-17 d of incubation. Investigators are also exploring the possible use of blastodermal cells, embryonic stem cells, or primordial germ cells as vehicles to improve traditional poultry breeding schemes (Ricks et al., 2003). To date, approximately 95% of broilers are vaccinated by in ovo injection (Zhai et al., 2011a).

In ovo injection technology further provides a practical means by which to safely introduce external nutrients into developing embryos. Today, the technology has been adopted for what is termed “in ovo feeding”. The science of early feeding in the poultry industry is still nascent but equipment for the in ovo delivery of nutrients to the developing embryo has been developed by Uni and her research collaborators (Uni and Ferket, 2004). Paralleling the development of appropriate delivery technology is the concerted search for suitable products that can be delivered in ovo, or in a manner that can be ingested by the chick at hatch (Bhuiyan et al., 2011).

Supplements used for in ovo feeding

Amino acids

The use of AA for in ovo feeding has gained prominence as much as carbohydrate products, with several researchers reporting on their use and their potential effects as in ovo feeding nutrients or supplements. Al-Murrani (1982) demonstrated that injecting an AA mixture (identical to the AA profile of egg protein) into growing embryos from broiler breeder eggs, resulted in higher chick BW at hatch and at 56 d of age, compared to chicks from control embryos. This increase in chick BW may be caused by increasing AA yolk content or increasing AA utilization by the embryo, as it has been suggested that in ovo administration of AA may increase AA concentrations in chicken embryos and other egg contents (Ohta et al., 2001). Bhanja and Mandal (2005) were of the opinion that in ovo injection of a combination of different AA (lysine+methionine+cysteine), (threonine+glycine+serine) or (isoleucine+leucine+valine) resulted in a higher immune response to cell mediated and humoral immunity and may act as an immunomodulator. Kadam et al. (2008) injected threonine in ovo to test its effects on early growth, some immunological responses and the activity of digestive enzymes of broiler chicks. They concluded that injections of 20-30 mg threonine into the yolk sac can improve post-hatching growth and humoral responses of broiler chicks. L-arginine injection into eggs of 0-day-old quail embryos, at 2 % and 3 % arginine, resulted in a significant improvement in the productive and physiological performance of the quail, suggesting that L-arginine could be used to enhance the hatchability and productive performance of birds (Al-Daraji et al., 2012). All these studies and many more, show the huge potential of AA as in ovo nutrients in broiler chickens and hence should be explored further.

Beta-hydroxy-beta-methybutyrate

For over a decade, HMB has been used as a dietary supplement for the enhancement of muscle deposition. Beta-hydroxy-beta-methybutyrate is a metabolite of the essential amino acid, leucine. Approximately 5 % of leucine metabolism follows this pathway, thus producing small amounts of HMB. Multiple studies have revealed that when dietary HMB is consumed multiple physiological enhancements occur. Early studies reported by van Koevering et al., (1994) demonstrated that HMB supplementation in steers caused an increase in carcass quality, morbidity was decreased by 40 % and mortality by 50 % in shipping stressed calves fed HMB. Nonspecific early mortality in male broilers was reduced when HMB was supplemented between 0.003 and 0.01 % of the diet (Nissen et al., 1994). A study by Uni and Ferket (2003), revealed about a 40 % increase in liver glycogen of turkey poults fed in ovo HMB (0, 0.1, 1.0, and 10 g) over the injected and non-injected controls, with a quadratic response as the level of HMB injected in ovo increased. Moreover, hatchability rates were found to be positively correlated with liver glycogen content of turkey and chick embryos before hatch (Uni and Ferket, 2003). Foye et al. (2006) went further to confirm that in ovo feeding of HMB may enhance hatch BW and glycogen status of poults during the neonatal period.

L-Carnitine

The physiological roles of L-carnitine include its action as an antioxidant that ultimately results in a decrease in reactive oxygen species by removing excessive levels of intracellular acetyl-CoA, which induces production of mitochondrial reactive oxygen species (Agarwal and Said, 2004; Agarwal et al., 2005). L-carnitine also has the ability to transport long-chain fatty acids across the mitochondrial membrane and to subsequently facilitate β-oxidation of long-chain fatty acids for energy production (Keralapurath et al., 2010a). It is also proven that chicken embryos have a limited capacity to synthesize L-carnitine during incubation due to the lower activity of the enzyme, γ-butyrobetaine hydroxylase, which is essential for L-carnitine biosynthesis (Rebouche, 1992). Keralapurath et al. (2010b) reported that increasing the levels of L-carnitine by adding it to commercial vaccine diluent between 0.5 and 8.0 mg/100 µL for commercial in ovo injection did not significantly influence subsequent broiler performance at market age or slaughter yield. In fact, a dose above the stated quantity may have the potential for significantly increasing incubation length and increasing hatchability of broiler hatching eggs.

Buyse et al. (2001) reported that during the later stages of incubation, especially during the pipping process, the embryo expends increased amounts of energy, and therefore, L-carnitine level could be a limiting factor for the β-oxidation of fatty acids during emergence from the eggshell. At such times, exogenous supplementation of L-carnitine could prove to be advantageous. Zhai et al. (2008) conducted a study in which L-carnitine was injected in ovo in a 0.05 to 10 μmol/egg dose range on d 17 or 18 of incubation, and reported the treatment to have no effect on hatchability, yolk sac weight or BW in eggs from single comb White Leghorns. Nevertheless, Zhai et al. (2008) also considered L-carnitine as a potential candidate for improving hatchability and grow-out performance of commercial layers when injected in ovo at concentrations higher than 10 μmol/egg, considering its physiological benefits and the lack of any evidence for its toxicity in poultry when injected in doses up to 10 μmol/egg.

Effects of in ovo feeding on broiler chickens

Previous studies have shown that feeding immediately after hatching accelerates the morphological development of the small intestine (Noy and Sklan, 1998a), while delayed access to external feed arrests the development of the small intestinal mucosa (Geyra et al., 2001a; Uni et al., 1998; Uni et al., 2003b).  Furthermore, day-old chicks denied access to their first feed for 24-48 h have decreased villus length, decreased crypt size and crypts per villus and decreased enterocyte migration rate (Geyra et al., 2001b). In addition, delayed access to feed for 48 h post-hatch resulted in changes in mucin dynamics, which affects the absorptive and protective functions of the small intestine (Uni et al., 2003b). Early feeding has a great effect in triggering gut development in broiler hatchlings. Previous studies by various scientists showed that the nutrient supply to chicks as early as possible, can increase intestinal mechanical activity and accelerate intestinal development, leading to greater assimilation of feed, faster development of immunity and thereby overall growth performance.

Reports have shown that toward the end of incubation, the residual yolk sac is internalized into the abdominal cavity. Yolk provides much of the nutrition for the embryo during incubation directly through the circulatory system, whereas close to hatch and thereafter, the yolk also reaches the GIT (Noy and Sklan, 1998b). It has been shown that during the initial 48 h post-hatch, yolk contributes to small intestinal maintenance and development. During this period, the chick must make the transition from utilizing energy in the form of lipid supplied by the yolk, to utilization of exogenous carbohydrate-rich feed (Noy and Sklan, 1999a). Intake of exogenous feed is accompanied by rapid development of the GIT and associated organs. The timing and form of nutrients available to chicks after hatch is critical for development of the intestines.

Early access to feed has been shown to stimulate growth and development of the intestinal tract and also enhance post-hatch uptake of yolk by the small intestine (Uni, et al., 1998; Geyra et al., 2001a; Noy and Sklan, 2001; Noy et al., 2001; Potturi et al., 2005). It has also been demonstrated that supplying nutrients to the growing embryo through in ovo feeding may enhance the development of the GIT. Administration of exogenous nutrients into the amniotic fluid at 17-18 d of incubation enhanced intestinal development of chicks by increasing the size of the villi and by increasing the intestinal capacity to digest disaccharides. These observations indicate that the small intestine of in ovo-fed chicks is functionally equivalent to conventionally fed 2-d-old chicks. The BW of those chicks was greater than controls (Tako et al., 2004).

In another experiment with turkeys, it was shown that the in ovo-fed poults (injection of arginine and β-hydroxy-β-methyl-butyrate into amnion) hatched with a greater intestinal digestive and absorptive capacity than the conventional poults (Foye et al., 2007). Birds show slower intestinal development and depressed performance when access to feed is delayed (Geyra et al., 2001a; Bigot et al., 2003; Maiorka et al., 2003; Potturi et al., 2005). Usual hatchery practices result in a 24-72 h transition between hatching and placing chicks on the farm (Uni, 1999). The lack of access to feed during this time leads to a depression in intestinal function and bird performance, which may not be overcome at later stages in life (Uni, et al., 1998; Geyra et al., 2001a; Bigot et al., 2003; Potturi et al., 2005).

Processed protein products as supplement for in ovo feeding

At the time of this review, there was no available literature reporting studies where processed plant (soy) protein products or their derivatives, have been used as in ovo feeding supplement. However, the potential benefits of processed protein products in broiler nutrition have been studied (Edwards et al. 2000; Payne et al. 2001; Batal and Parsons, 2003; Kim et al. 2014). Their use as in ovo feeding supplements may further extend the knowledge on usefulness of processed protein in broiler production, especially with the continual search for an in ovo feeding supplement that will confer optimal benefits until market weight in broilers.

Hatchery diet/feeding

Research interest in developing a type of diet that can be readily provided to newly-hatched chicks in the hatchery, while waiting to be processed or during transportation from the hatchery to the farms where the birds would be raised, has continued to grow for obvious reasons in terms of the effects of delayed access to feed on newly-hatched chicks. Currently, there are a few commercially developed products that can serve this purpose. Some examples include EarlyBird^TM (Sigrah-Zellet, LLC, Fayetteville, AR.), Oasis^TM (Novus International, Inc., MO), and Aqua-block (Ashkan Animal Health (Pty) Ltd, South Africa). EarlyBird^TM is an all-natural hydration and nutrition supplement for young birds. One gram of EB contains 64 % of water, 22 % of protein, 10 % of fibre, 20 % carbohydrate, and less than 2 % fat (Biloni et al. 2013), while Oasis^TM is a semi-solid hydrated nutritional supplement that contains 8 % protein, 16 % carbohydrate, 1 % fat, 1 % fibre, 2 % ash, and 70 % water (Dibner et al. 1998; Noy and Sklan, 1999b). The first two products have been tested in various early feeding studies with some level of success (Noy and Sklan, 1999b; Batal and Parsons, 2002a; Jackson, 2005; Biloni et al., 2013). Their success has led to further interest in developing similar products for hatchery feeding.

The need for a hatchery diet/feeding

The need for hatchery feeding is necessitated by the delay in access to feed and water due to conventional hatchery practices, highlighted previously. Providing a hatchery diet to chicks immediately after hatch may help mitigate the contributory effect of a long HW. Transporting chicks from the hatchery to the farm leads to further chick weight loss and dehydration (Noy and Sklan, 1999b, 2002; Hooshmand, 2006; Henderson et al., 2008). During the period between hatch and first feed or water on farm, the residual yolk water and protein can supply nutrients to the hatchling until feed and water become available; however, this would be at the expense of conferment of passive immunity, a function for which the residual yolk nutrients are more valuable, as well as providing support as structural material for the developing bird (Dibner, 2007). Forcing chicks to rely solely on their maternal antibody reserves for energy is highly inefficient and harmful to production because these birds then have increased risk of infectious diseases (Dibner et al., 1998; Batal and Parsons, 2002a).  Some of the lipids used have a specific function in early growth and some fatty acids are important as precursors for secondary messengers. For these reasons, utilization of yolk as the sole source of energy for prolonged time periods before placement is a very damaging and expensive proposition (Biloni et al., 2013). Hence, in order to reduce total dependence on the residual yolk nutrients and thereby predisposing the newly-hatched chicks to reduced immune status, the options are either to supplement the breeder hen’s diet with nutrients that are transferred to the yolk sac, which has been shown to increase the availability of trace minerals to the progeny (Kidd et al., 2000), or by providing newly-hatched chicks with a special and highly soluble feed or nutrient immediately after hatch and during processing and transportation.

Nutritional composition of hatchery diets

There is not much data available on nutritional composition or what the optimum nutrient balance of hatchery diets would be, although early work defining the nutritional profiles for the high moisture supplements, EarlyBird^TM and Oasis^TM, indicate that best intake and performance in newly-hatched chicks could be achieved with a high carbohydrate, high protein supplement containing only a little fat. Sklan and Noy (2003) reported that the nutritional requirements of birds at this initial stage have not been precisely defined. However, there are a few studies where diets were formulated specifically to serve as hatchery diet, or to be fed while transporting chicks to the farm. Inferences can be drawn from these studies to understand what the typical nutrient composition of a hatchery diet should be. Batal and Parsons (2004) investigated the relative use of various carbohydrates in chicks over 0-7 days, by age. In their study, the energy value of the diets ranged from 3000 kcal/kg dry matter (DM) to 3313 kcal/kg DM and they reported a higher apparent metabolizable energy (ME_n) for birds on the diet with 3313 kcal/kg during 0-2 days. Kidd et al. (2007) produced metabolizable energy (ME) values ranging from 3080 to 3175 kcal/kg. With respect to protein content of hatchery diets, Sklan and Noy (2003) and Kidd et al. (2007) suggested diets with as high as 28 and 26 % crude protein levels, respectively. Little work has been done to estimate amino acid requirements of baby chicks. However, the work of Sklan and Noy (2003) estimated that for a 7-day old broiler chick, the lysine requirement was from 1.03 to 1.08 %, whereas for total sulphur AA the requirement was 0.91 %, on a total basis. A higher lysine and total sulphur AA of 1.45 and 0.94 % at maximum levels were reported in a more recent study by Kidd et al. (2007). However, Garcia and Batal (2005) found only minimal changes in the digestible lysine or sulphur AA estimated requirements occurred during the first 21 days of age, suggesting that the recommended digestible lysine and sulphur AA levels determined at 21 days of age, appear to be adequate to meet chick needs for the first week after hatching. More work on specific nutrient requirements in the neonate and their potential to impact on long term health and performance needs to be done. It is crucial that studies include other systems, both support and demand, in addition to performance efficiency in the criteria for determination of requirements.

Effect of hatchery diet on broiler chickens

In the past years, there have been attempts by different researchers to validate the effect of use of hatchery diets, in response to delayed access to feed and water suffered by newly-hatched chicks. Dibner et al. (1998) compared several aspects of immune tissue development in fasted chicks with chicks fed a specialized hydrated nutritional supplement (Oasis^TM) for the first two days after hatch. In their study, day of hatch was considered to be day 0 and the subsequent days were considered days 1 and 2. Although not always significant, the weight of the bursa was consistently, heavier in the chicks fed Oasis compared with the fasted birds until 10 days of age. From 10 to 15 and 15 to 20 days of age, however, there were considerable increases in bursal weight in both the Oasis and fasted chicks, with a rather blunted response in the fasted chicks. Interestingly, early treatment effects were most clearly expressed at least 10 days post-feeding.

Halevy et al. (2000; 2003) conducted a poults study in which half the birds were fed at hatch and the other group was fasted for 48 hours prior to feeding. The authors concluded that the initial fasting period resulted in a significant reduction in body weight for 41 days. The authors tried to support a hypothesis that early fasting had a profound and prolonged effect on satellite cell proliferation but again, the data did not fully support that hypothesis.

Noy and Sklan (1999a) examined the changes in body weight and composition in broilers that either had immediate access to feed and water, or had not been fed for 48 h post-hatch. In their study, chicks without access to feed decreased in BW by 7.8 % in the 48 h post-hatch, which was equivalent to 5.3 kcal/45 g chick/d. However, during this period the small intestine increased in weight and protein content by at least 80 %. They observed a decrease in yolk fat and protein, accounting for most of the changes in body composition in the feed-deprived chick. In contrast, fed chicks grew by 5 g and used 4.5 kcal/day for maintenance. During this period small intestinal weight increased by 110 %. In another study, Noy and Sklan (1999b) concluded that feeding solid, semi-solid or liquid nutrients post-hatch resulted in increased BW, which was maintained until market weight in both chicks and poults.

Evidently, the use of hatchery diet reveals the potential to mitigate the negative effects of delayed access to feed and water and could be beneficial to the poultry industry. However, there is a need for further studies to identify ingredients and supplements, and also establish a standard for nutrient composition for hatchery diets, for conventional use in hatchery and during transportation of birds, as is found in other stages of growth of broiler chickens.

The Prestarter diet

The use of prestarter diets has been a common practice for a number of years in the pig industry. The aim of this practice is to provide to the weanling pig highly digestible feed ingredients which will enhance the utilization of nutrients, and with a nutrient status close to that of sow’s milk. (van Dijk et al., 2001).

According to Garcia (2006), some of the first published research regarding prestarter diets originated in India. As early as 1974, poultry nutritionists initiated the concept of a prestarter diet for broiler chickens, with the goal of boosting the growth rate of the chicken during the initial phase of its productive life. At that time in India, broiler chickens were raised to 10 weeks of age, and conventionally fed in two feeding phases: starter feed from 0 to 6 weeks, and finisher feed from 6 to 10 weeks.

Sahoo and Rao (1974) reported that feeding diets to broiler chickens with levels of up to 28 % crude protein (CP) during the prestarter period, by definition from 0 to 2 weeks of age, followed by CP levels as high as 26 % during the starter phase, defined from 2 to 4 weeks of age, improved BWG and feed conversion at 4 weeks of age. Mathur et al. (1976) formulated prestarter diets containing from 24 to 26 % crude protein and calorie: protein ratios of 120:1 and 110:1, respectively. The chickens fed the prestarter diets were significantly heavier than birds fed a conventional starter diet at 3 weeks of age. However, the chickens were not able to maintain the initial growth rate, and no differences were observed in performance at 10 weeks of age. The conclusions of the authors were that the use of prestarter diets carried no added value. In a similar study, Saxena and Singh (1976) fed broilers diets containing up to 26 % CP during the prestarter phase, defined from 0 to 3 weeks of age. No differences were found at market age (10 weeks), although it was noticed that feeding higher CP levels during a prestarter period could be more economical than feeding the conventional CP levels throughout the starter period. There could have been many reasons for these results. These may be based on genetic makeup of the birds, total composition of the diets and the ingredients used, as well as the environment in which the birds were reared.

On the other hand, the theory of a specific prestarter diet continues to be of interest (Maiorka et al., 2004). Formulating prestarter diets involves the selection of highly digestible feed ingredients, rather than the need for higher nutrient density. Although corn-soybean meal diets are regarded as ideal for poultry, there is evidence that digestibility is below optimum for the young chick (Leeson, 2012).

Therefore, more recent research studies conducted with young poultry have documented physiological changes in the GIT occurring during the first week post-hatch (Noy and Sklan, 1997; Jin et al., 1998). Nutrient uptake (Noy and Sklan, 2001), digestive enzymatic activity (Nitsan et al., 1991), and nutrient utilization in chickens (Batal and Parsons, 2002b) have been found to gradually increase during and after the first week of life. Increased attention is now being given to the nutritional needs of the chicken during the first week post-hatching, not only because this period has become recognized as being ever more critical in the development of modern broilers, but also because broilers are reaching market weight in a shorter period (Lilburn, 1998). As a strategy to compensate for an initially immature digestive system, interest in the use of prestarter diets arose (Rocha et al., 2003, Garcia et al., 2006), with the goal of providing either a higher concentration of nutrients, or more digestible ingredients, so as to facilitate nutrient utilization during the first week of life.

The need for a prestarter diet

The benefits of using a prestarter diet have been well documented. In today’s commercial hatchery practice, it has been proven that a delay in first feeding, as occurs in reality, leads to a reduced performance of the chicks with respect to growth, immune system activation, digestive enzyme stimulation and organ development (Pinchasov and Noy, 1993; Noy and Sklan, 1999a; Bigot et al., 2003; Gonzales et al., 2003; Careghi et al., 2005). The first priority of an early nutrition programme should thus be to better satisfy the specific needs of the newly hatched chicks with a prestarter diet (Lilburn, 1998). Today’s broiler feeding programmes generally provide a starter feed from chick placement to 10 d (Willemsen et al., 2010a) or 15 d (Swennen et al., 2010) of age. However, the chicks’ requirements change quickly during the first week of life and this should be taken into account in the diet composition. After hatch, a major change occurs in the source of available nutrients for the neonatal chick; the hatchling has to make the transition from metabolic dependence on endogenous lipid-rich yolk to utilisation of exogenous carbohydrate- and protein-rich feed (Noy and Sklan, 1995).

During the initial 48 h post-hatch, the yolk contributes to maintenance and small intestinal development (Noy and Sklan, 1999a). Therefore, optimal nutrition in the first week should take into account the contribution of the yolk and the still-developing ability to utilise effectively exogenous feed (Swennen et al., 2010). The use of an appropriate prestarter feed would meet the specific needs of the newly hatched chick more efficiently.

Macronutrient composition of the prestarter diet

The current nutrient composition recommended by the National Research Council (NRC), (1994) for young broiler chicks pertains to 0-21 days, post-hatch.  Changing the concentration of one macronutrient in the diet has an effect on the level of the other macronutrients, which makes it difficult to ascribe the observed effects to one particular macronutrient (Swennen et al. 2010). However, there is evidence that newly hatched chicks are not developmentally able to efficiently digest protein, carbohydrates, and fat during the first 10–14 days of life (Batal and Parsons, 2002b). Because most changes in gut morphology, growth, and digestive enzymes occur during this period, it is important to ensure that the nutrient composition of a prestarter diet support these changes. There are, however, not many studies that focus on describing the nutrient composition of prestarter diets, with these changes in mind, rather than the ingredients used in formulating the diets. Rocha et al. (2003) reported that feeding up to 26 % CP during the first 7 days of age could significantly reduce feed intake, although at this level the digestibility of DM was reduced. The authors did not observe any significant difference in growth performance when energy levels up to 3000 kcal/kg ME were used. Nascimento et al. (2004) evaluated different dietary energy levels and calorie: protein ratios during the first 7 days of age in broiler chicks. Similar to what was reported by Rocha et al. (2003), a reduction in feed intake and feed conversion was observed when the chicks received an energy level of 3150 kcal/kg ME and 25 % CP. However, no significant effect was observed on BWG. In another study, Ullah et al. (2012) fed prestarter diets formulated with different ME levels lower than reported by preceding researchers, varying from 2750 to 2850 kcal/kg, and different lysine levels varying from 1.3 to 1.5 % but with same CP level (21 %). They concluded that a prestarter diet with ME 2850 kcal/kg and 1.4 % total lysine resulted in optimum performance but carcass yield, weights of visceral organs and parameters of digestive tract morphometry did not show any significant difference. This is an indication that nutrient density in prestarter diets for newly-hatched chicks may be influential in determining their growth and performance in later stages.

Importance of protein level of prestarter diet

Research on early nutrition indicated that proteins are the most important macronutrient present in the prestarter diet. As reported by Noy and Sklan (2002), once limiting AA and energy are provided at a sufficient level, the influence of dietary composition on immediate post-hatch growth becomes limited. However, as seen in the study by Swennen et al. (2010), caution is necessary as it cannot be guaranteed that low protein diets deliver the necessary amount of nitrogen for the synthesis of non-essential AA, leading to a reduced protein synthesis (Sklan and Plavnik, 2002). These results are similar to those obtained in older broiler chickens, where dietary protein content also had a larger impact on growth, energy and protein metabolism and on intermediary metabolites compared to the carbohydrate and fat fraction in iso-energetically formulated diets (Swennen et al., 2008).

Feed formulations are often based on average requirements for a longer period and therefore not necessarily optimal for the first days, post-hatch (Garcia, 2006). Specific optimal feed formulations for the first post-hatch days of broiler chickens are less known. Understanding the importance of protein level in prestarter diets, is relevant when we take into account that the physiological conditions of post-hatch chicks are different from those of older chicks and this might contribute to a difference in nutritional requirements.

Processed soy protein supplements in prestarter diet

Soybean meal (SBM) is the most widely used protein source for poultry diets, and in a broiler starter diet it usually accounts for approximately 35 % of the feed. However, the presence of antinutritional factors (ANF), such as oligosaccharides and non-starch polysaccharides can adversely affect performance (Kocher et al., 2002), particularly in young chicks. There have been a few attempts to evaluate alternative or processed protein sources, whereby SBM is pre-treated with enzymes and/or microorganisms in order to eliminate the concentration of ANF to produce soybean protein concentrate (SPC), or soybean protein isolate (SPI), with potentially greater nutrient availability, for inclusion in prestarter diets. Prestarter diets of high digestibility and high protein content can be used to meet the requirements of chicks in the first days of life and are considered an investment, not a cost, in poultry production (Lilburn, 1998). Batal and Parsons (2003) studied the utilization of SPI and SPC by chicks during the first week post-hatch. They showed that growth performance was significantly lower in birds fed a conventional corn-soybean meal diet. The poor growth performance is due to an AA imbalance, since the concentrations of sulphur AAs and threonine are low in soybean products (Batal and Parsons, 2003), and hence concluded that there may be some potential benefits of feeding SPC or SPI during the first 1 to 3 weeks, post-hatch. However, the apparent digestibility of lysine in soy protein isolates was higher than that in soybean meal during the first week of age. Again, Shelton et al. (2005), testing SPI as a protein source reported increased average daily gain, average feed intake and feed conversion, but only when the feed was provided in pelleted forms. Jankowski et al. (2009) in a study on turkeys, reported that partial or almost complete substitution of SBM with SPC suppressed the fermentation processes in the ceca but enhanced the growth rate, while substitution of SBM with SPI significantly improved feed utilization, but decreased the BW of 4-week-old turkeys with no effect on growth rate of older 8-week old birds.

There are also some studies that have tested processed animal protein sources in prestarter diets. Longo et al. (2005) evaluated the addition of spray-dried eggs (8 %), blood plasma (5.6 %), SPI (5.35 %), corn gluten meal (7.3 %) and dried sugar cane yeast (13.65 %), in substitution for soybean meal as a protein source, for broiler pre-starter diets between 4 to 7 days. The results did not indicate any significant effects on BWG. However, there was a significant improvement in feed conversion, in the chickens fed SPI and blood plasma.

Harmon et al. (2001) proposed the inclusion of spray-dried eggs, a by-product of hatcheries, from post-candled eggs, in diets for nursery pigs and young chicks. Spray-dried eggs containing 46 % crude protein, contain 37 % more energy than corn (4700 kcal/kg ME, as-fed basis), and 3.72 % lysine (Harmon et al., 2001). Junqueira et al. (2001) reported the inclusion of 0, 5, 10, 15 and 20 % spray-dried eggs in diets for chickens during the pre-starter (1 to 7 days of age) and starter periods (8 to 21 days of age). The use of spray-dried eggs led to a 20 % decreased weight gain during the first seven days of age, and no significant benefits were observed at the other levels of inclusion. In a recent study, Beski et al. (2015a) studied subsequent growth performance and digestive physiology of broilers fed on starter diets containing spray-dried porcine plasma (SDPP) as a substitute for meat meal. Their findings showed that with inclusion of SDPP in the starter diets from 0 to 10 days, feed per gain and BW increased with increasing concentrations of SDPP, irrespective of the type of grain used during the 35-day study. It was noted that increasing concentrations of SDPP in the starter diet improved the activities of maltase, sucrase and alkaline phosphatase at 24 days of age.

The cited studies confirm that these protein products have the potential to improve broiler performance when fed to birds at early age. Their ability to improve performance has been associated with their high nutritional value and minimal or absence of ANFs, factors which may impair intestinal development and have adverse effect on the productivity of birds (Beski et al., 2015b). However, there are still research gaps as to the influence of feed forms, duration of feeding and whether these can be administered through another route, in order to fully maximize their benefits.

Recently, there has been studies with involving a novel soya protein concentrate with a low content of ANFs, additionally containing approximately 10 % yeast, specifically produced for prestarter diets. The addition of yeast to the substrate releases mannan sugars and ß-glucans from the yeast cell walls (Pedersen, 2013), especially developed for poultry prestarter diets (van der Eijk, 2013b). In a bioconversion process, all ANF are reduced to a safe level for young animals – without compromising the protein quality (Beski and Iji, 2015). Similarly, an enzymatically treated soy product that has reduced amounts of oligosaccharides and some ANF components, was used to study the effect of stachyose on growth performance, nutrient digestibility and caecal fermentation characteristics in broilers (Jiang et al., 2006). The study showed that the product improved BW and restricted the effect of stachyose in diets up to 12 g/kg. With the same product replacing fish meal in diets for weaned pigs, BW was improved by 18.4 % compared to the control group (Šiugždaité et al., 2008). There are several other unpublished studies presenting data claiming the potential of an enzymatically treated soy product to improve digestive system development, nutrient digestibility and growth performance when provided in prestarter diets to newly-hatched chicks. One of the most recently published studies on this product was conducted by Beski and Iji (2015), in which they included an enzymatically treated soy protein product at 0, 25, 50 or 100 g/kg in either corn or wheat-based diets provided to chicks aged from 1 to 10 days. They reported improved BW and feed conversion ratio (FCR) for birds receiving a high level of soy protein product in wheat-based diets, a significantly heavier visceral organ at early age, and a higher villus area in birds that received medium level in corn-based diets, suggesting that the soy protein product can be included at between 50 and 100 g/kg in starter diets, depending on the basal diet.

Conclusion

In the conventional hatchery practices, chicks do not hatch at the same time. The biological and chronological ages of chicks vary across the HW. Prevailing hatchery management practices may mean that chicks that hatched earlier could wait as long as 48-72 hours, without access to their initial feed and water. The consequences of such practices have been proven to negatively affect the potential of these birds to perform optimally. Even, when these birds are provided with their first diets at arrival on the farm, these diets are not normally formulated with the aim to meet the physiological and nutritional requirements of newly-hatched and stressed chicks. Thus recently, researchers have been focusing on how to mitigate these challenges, leading poultry nutritionists to develop specific strategies for early nutrition. These strategies are in ovo feeding, formulation of hatchery diet and prestarter diets. One of the areas that has been totally neglected in the development of in ovo feeding technique is the interaction between the physico-chemical properties of the injected solutions, the amniotic fluid and the developing embryo. To date, there is no evidence of a study that has examined this. Some attempts have been made by researchers and commercial poultry industries to develop diets that can be used in the hatchery or provided to chicks during transportation. At this time, no standard product has been developed. And in most cases, these products differ from what is provided as prestarter diets, and mean transiting the newly-hatched chicks from one type of diet to another within a very short time. It may be possible to develop a hatchery diet from the same product that could be used in formulating prestarter diets for broiler chicks. It seems that the scarcest resource in formulating prestarter diet is the protein. It is important that the appropriate protein supplement is used as it is clear that protein supply at the early age of broiler chicks plays an important role in overall development. Hence, there is a need to supplement prestarter diets with a feed ingredient that is high in protein content and also high in digestibility of both protein and amino acids. Again, the form and duration of supplementation of any of these processed soy protein sources needs further elucidation.