Early Feeding-When should we begin feeding our poultry? Y. Noy Miloubar Feedmill, MP Ashrat Israel

Transcription

1 Early Feeding-When should we begin feeding our poultry? Y. Noy Miloubar Feedmill, MP Ashrat Israel Introduction What are current acceptable commercial hatchery practices? At what point should the poultry industry be considered nutritionally responsible? Must it start with the breeders, during embryonic development, immediately posthatch or when day olds arrive to poultry farms? These are all questions that have been addressed over the past two decades and many theoretical approaches have been developed. In addition, in recent years the industry is marketing broilers at younger ages thus, the 21 d incubation period in relation to the entire grow out is playing a more dominant role and must be addressed. A nutritional link tying the breeders, hatchery processes, day olds and broilers is necessary in order to attain their genetic potential. The present review will examine the advantages and challenges of the early nutrition concept with an emphasis on its applications in the current market. Commercial Hatchery Practice. Eggs hatch over a period of 48 hrs in a Gaussian curve in the hatching trays. Logistics usually determines that chicks are removed from the hatchery trays after a major proportion of the eggs have hatched. At hatch the chick weighs approximately 45 g with a yolk sac of approximately 8 g. This yolk which comprises around 20% of chick body weight, has been internalized into the abdominal cavity during the last days of incubation (Noble and Ogunyemi, 1989) providing a continuous source of energy posthatch (Romanoff, 1960). Thus, early hatched birds remain within the hatchery without food and water for an extended period. Hatchery treatments, such as sex determination, sorting, vaccinations and transport to the farms involve a further holding time, therefore some birds will be held for over 48 hr prior to initial access to feed and water, during which time body weight decreases (Noy and Sklan, 1998, Batal and Parsons,2002 and Tweed, 2005). Holding hatchlings without food and water for more than 24 h can have lasting negative effects on both broilers and turkeys (Tarvid,1992, Knight and Dibner 1998; Batal and Parsons, 2002; Juul- Madsen et al 2004). When delaying access to feed and water hatchlings become more susceptible to pathogens,(dibner et al., 1998) and the development of critical

2 tissues is restricted (Hatevey et al., 2000). Studies have indicated that immediate access to feed improved early growth with effects which were still apparent at marketing (Noy and Sklan, 1999, Henderson et al., 2008). Yolk Utilization Pre and Posthatch During poultry embryonic development yolk is the sole energy source. Lipids from the yolk are transferred during this period from the yolk sac to the embryonic circulation as lipoprotein particles (Lambson, 1970). Close to hatch, remaining yolk is internalized into the abdominal cavity through the yolk stalk and the lipids are transferred to the embryonic liver. Yolk comprises 16-20% fat and 20-25% protein at hatch (Moran and Reinhart, 1980, Reidy et al, 1998). These lipids can be utilized as an energy source for the hatchling, however, the composition of residual yolk lipid suggests that it is more efficient to use these lipids for cell membrane structure and central nervous system development (Noble and Ogunyemi, 1989; Anderson, Connor and Corliss, 1990). Energy available from the yolk lipids is barely sufficient to cover the energy needs of the hatchling for the 48 hours post hatch. During the initial 48 hours post hatch 80% of the yolk lipids are transferred to tissues. At hatch the yolk contains1.6 g protein almost all of which has disappeared by day 4 (Romanoff, 1960, Noy and Sklan, 1998a). Yolk protein may be the source of the amino acids required for the preferential gastro intestinal growth observed in newly hatched chicks (Noy and Sklan, 1999). However, this protein contains substantial amounts of maternal antibodies which may be better utilized for passive immune protection rather than be broken down for use as amino acids (Dibner et al, 1998) Examination of the intestinal contents at hatch reveals yellow pigments identical those of yolk, thus it appears that yolk is transported to the intestine through the yolk stalk. Yolk contents are digested initially by pancreatic and finally by brush bother hydrolases (Geyra, et al. 2001a). The morphology of the yolk stalk through the posthatch phase has been examined and an open passage was observed at hatch which became narrower with age. After 48 h lymphoid cells began to increase in the yolk stalk and the passage was almost completely occluded by 72 h (Olah and Glick, 1984, Noy et al. 1996). In addition to transport of yolk to the GIT, yolk utilization via the circulation also remained functional during the first 48 h after hatch after which transfer began to decrease (Esteban et al. 1991, Noy et al, 1996). In fact the yolk was in equilibrium with body fluids and movement was bidirectional and nonspecific (Noy et al, 1996, Noy and Sklan, 1998a).

3 Yolk comprises between 15-25% of BW at hatch and the amount of yolk decreases logarithmically with time. Thus by 4 d approximately 1 g of yolk remained. However, surprisingly, in chicks without access to feed the rate of yolk utilization was slower. Further studies indicated that in poultry without access to feed a greater proportion of the yolk contents were transferred to plasma and only small amounts were transported to the intestine. In addition to its value to the immune system the yolk is utilized for the preferential early growth of the small intestine which occurs both in the presence and in absence of feed, although in the absence of exogenous feed both absolute and relative growth is lower (Noy and Sklan, 1999). In the held bird the substrates for this growth apparently originate from the yolk indicating the high priority for intestinal growth posthatch. Transition Period Energy metabolism which so far has been primarily based on yolk lipid supply must shift to a predominantly exogenous carbohydrate feed basis (Swennen et al, 2009).Providing immediate available energy from a carbohydrate source spares yolk lipids to be used for phospholipid membrane of new cells. Thus optimal chick nutrition during the first week posthatch should spare yolk lipids and proteins for their optimal utilization during the chick's metabolic transition period. It is essential that there be an efficient transition period during which the GIT becomes nutritionally responsible. (Jin et al., 1998; Vieira and Moran, 1999). Throughout the immediate posthatch period intense changes occur in the small intestines of birds. (Bayer et al. 1975; Cook and Bird 1973; Uni et al. 1996)The small intestines increase in weight more rapidly than the whole body mass. This process of rapid relative growth was maximal at 6-10 d in the chick (Akiba and Murakami, 1995, Noy and Sklan, 1999). In contrast other digestive tract organs such as gizzard and pancreas do not show parallel enhanced changes in the relative size (Uni et al. 1998). The temporal increases in intestinal weight and length are not identical in the different segments with the duodenum showing earlier rapid growth then the jejunum and ileum (Uni et al. 1999). At hatch small intestinal enterocytes are round and immature. Immediately posthatch dramatic changes occur commencing with enterocytes rapidly increasing in length and developing a pronounced polarity and defined brush border. Small intestinal villi are undeveloped at hatch and in the intervillus spaces crypts are not

4 detectable. During late embryonic development enterocytes are intended for macromolecular transfer; however, posthatch those arising from the crypts replace embryonic ones and provide the necessary tools for efficient digestion and absorption (Uni et al., 1998, 2003a,Uni et al., b). A combination of both types of enterocytes exists at hatch and therefore several days are needed before effective feed utilization is attained. (Raheja et al., 1977; Sulistiyanto et al., 1999; Batal and. Parsons, 2002 ; Sklan, 2003). Patterns of development differ between intestinal segments with the duodenum and jejunum continuing to develop after the ileum has reached a constant number of crypts per villus. Morphometric measurements of the small intestinal mucosa indicated that villus height increased twofold in the 48 h posthatch and reached a plateau at 6-8 d in the duodenum and after 10 d or more in the jejunum and ileum in chicks. The width of the villi also increased slightly; thus growth in surface area tended to be parallel to changes in villus height. From these data total segment surface area can be estimated and this increased in all segments in parallel until 3 d posthatch after which the jejunal area increased more rapidly than the duodenum and ileum. With the growth of the villus the number of enterocytes per villus also increased (Geyra et al. 2001a). In chicks all small intestinal enterocytes are proliferating at hatch. The proportions of proliferating cells decrease rapidly with age reaching approximately 50% in the crypts after h, and along the villus the proportion of proliferating enterocytes decreases rapidly at first and then more slowly reaching 6-15% by 10 d posthatch (Geyra et al. 2001b). Thus the extensive changes in the morphological development close to hatch include the crypt definition and basic differentiation of enterocytes as well as enlarging the intestinal absorptive surface many-fold. The gastro-intestinal tract makes this transition within approximately a 2 wk period during which time, all vestige embryonic reserves disappear. Depletion of yolk sac, must be in phase with the ability of the gastrointestinal system to recover nutrients from feed. Most starve-outs fail to make the transition and commonly maximize around 3 to 4 d posthatch.(moran, 2007). What effects do the nutrients have immediately posthatch on the transition period? How critical is the nutrient composition during 0-3 days post hatch on marketing parameters? As previously stated yolk consists predominantly of lipids whereas feedstuffs are generally comprised of large proportions of carbohydrates. Thus, the utilization of feed is dependent on development of the required intestinal and metabolic functions. Digestion and absorption of solid feed promotes the necessary morphological and developmental changes of the digestive tract

5 (Pinchasov and Noy, 1993; Noy and Sklan 1999, Diber 1999, Gonzales et al., 2003; Bigot et al, 2003; Uni et al, 2003 Uni, 2006). The shift to external nutrients is complete within 4-6 d posthatch and therefore the overall "well managed" transition period is necessary for achieving the genetic potential and maximizing performance parameters. The multitude of strategies that provide early nutrition to either an embryo or immediately post-hatch provide an advantage to this transition, thereby improving long term performance (Baranyiova, 1987; Noy and Pinchasov, 1993; Ohta et al., 1999; Tako et al., 2004; Foye et al., 2006a,b). Effect of Early Access to Feed on Marketing Parameters When can early feeding begin? Recent studies indicated that chicks are capable of utilizing nutrient solutions prior to hatch. Establishing a stable and sufficient glucose status is critical for the hatching process and post-hatch development of poultry until exogenous feed is consumed. Toward the end of incubation embryos use their energy reserves to meet the high demand for glucose to fuel hatching activities (Christensen et al., 2001). Glucose is primarily generated from protein by gluconeogenesis or by glycolysis of glycogen reserves (John et al., 1987). Poultry store most of their glycogen in the liver and in glycolytic muscles. These glycogen reserves are depleted during the hatching process (Christensen et al., 2001). Gylocgen reserves are replenished when poultry consume exogenous carbohydrate rich feeds. To reduce the use of liver glycogen reserves and the depletion of muscle protein studies have indicated that administering ß-hydroxy- ß-methylbutyrate, a leucine metabolite, along with carbohydrates into the embryonic amnion fluid prior to hatch (IOF (in ovo feed) solution) support the energy status of hatchings and thus improve posthatch performance (Uni et al.2005; Kornasio et al., 2011). Similar results have been obtained in turkeys (Foye et al., 2006,2007) Birds are precocial and will forage for feed immediately and begin to grow, whereas holding them without feed results in body weight loss for some 24 h after poultry are fed (Moran, 1990, Pinchasov and Noy, 1993). In practice eggs within a single tray will hatch over a hr window during which time the birds which have pipped are without feed. Thus, as we have already mentioned that often birds are held for 48 h or more before initial access to feed and water (Misra et al. 1978). During this time both chicks decrease in weight at an approximate rate of 4 g per 24 h, due in part to moisture loss as well as yolk utilization. We will examine some of the

6 effects of this holding period both on growth close to hatch and later on in its development. Providing chicks at hatching (within one h of clearing the shell) with either solid feed, semi-solid feed or non-nutritious bulk (sawdust) on BW until 21 d was compared to chicks held for 36 h. Provision of all of these materials resulted in increased BW at 4 d although the effect of sawdust was transient. This suggests that there may be some mechanical stimulation of the GIT close to hatching (Noy and Sklan, 1998b). Further studies have addressed the effect of the form of the feed presented comparing solid feed, a liquid nutrient supplement or water to birds held for 48 h on BW of chicks through marketing (Noy and Sklan, 1997). Provision of caloric nutrients in solid or liquid form produced a considerable increase in BW which was maximal between 4-8 d and then decreased. Supplying water alone also resulted in an increase in BW, but this effect was smaller than that of feed and was no longer apparent after 8 d. At marketing, all birds with early access to nutrient or nutrient solutions were 8-10% heavier then held or watered birds. The cumulative feed efficiency through marketing was not changed by early nutrition, whereas the percentage of breast meat was increased by 7-9% in all fed birds (Noy and Sklan, 1998b). Since provision of nutrients enhanced growth, the effect of applying specific materials by gavaging birds at hatch was examined using glucose, starch, protein, fat or mixtures of the above close to hatch and then returning the birds to the incubation trays. Gavaging with all nutrients enhanced BW close to hatch, although glucose produced the lowest and most transient response (Moran, 1990, Pinchasov and Noy, 1993, Noy and Sklan, 1997). In an additional trial the effect of administering a single immediate posthatch intubation of nutrients to offspring of either mature (65 wks) breeder flock or young maternal flock (28 wk) was compared to held birds. Intubation significantly improved BW performance especially in offspring from young maternal flocks. (Noy and Pinchasov, 1993). This may be due to differential development of the skeleton and muscles or to long term effects initiated by the early feeding. One possibility is influencing satellite cells, myogenic precursor cells, which proliferate rapidly only close to hatch before becoming quiescent, but are instrumental in determining later stage muscle development (Halevy et al, 2000). Early access to feed enhances satellite cell proliferation during the initial posthatch period and may affect skeletal muscle growth through marketing. An additional system that undergoes major structural development is the small intestine. The effect of holding poultry without feed on the morphological development in the different intestinal

7 segments in the posthatch chick has been examined (Baranylova and Holman, 1976; Geyra et al. 2001a). Effects of holding on villus surface area were region dependent, but generally decreased both villus height and width. Both the number of cells per crypt and the number of crypts per villus were initially decreased by lack of access to feed, and access to feed reversed this by 8 d post hatch. Electron microsopy indicated that held birds had changes in the structure of the microvilli (Uni et al. 1998). Thus early access to feed alters both morphological development and enterocyte maturation, indicating a sensitivity to nutrient supply. All these studies confirmed that early access to nutrients produced an initial enhancement in BW which, although decreased with age, was generally maintained through marketing. The enhanced BW induced by early feeding was accompanied by an increase in breast meat percentage. Available Nutritional Solutions Practical nutrional solutions to reduce the adverse effects of delayed feeding have recently been researched. These include the usage of supplements(oasis-novus International, Galito-Vitamex and Gro-Gel-Dawe's Laboratories) known as "early feeding supplements" whose aim is to provide neonate with additional nutrient sources prior to full access to feed and water. These supplements can be provided at the hatchery and/or at placement at the farm. Various commercial methods of immediate feeding have been investigated. Using Earlybird showed that significant increases in body weight (2.7%) can be seen at 21 and 42 d of age (Henderson et. al. 2008). "Chick-aide" contains a high energy content with high percentage of medium chain triglycerides.mct is readily digestible energy source for neonates and is easily utilized by animals compared to long chain triglyceride even if secretion of pancreatic lipase and bile is limited (Greenberger and Skillman, 1969; Odle, 1997). Oasis (Novus International), a semi solid hydrated nutritional supplement with 70% moisture, 10% protein, 20% carbohydrate and less than 1% fat (Batal and Parson, 2002) decreased body weight loss in the 48 h post hatch period and treated chicks maintained this advantage through 21 d and 39 d of age with a higher breast yield (Noy and Sklan, Batal and Parson, 2002). Additional research involved usage of Oasis on female broiler breeders and indicated increased initial body weight growth (Boersma et al. 2003)

8 Thus providing an early feeding supplement may help decrease negative effect of delayed feeding. The beneficial effects of the hatching supplements are the access of nutrients in whatever form for the newly hatched chick or poult. Nutritional composition might not be as critical (though this points needs further research) as the stimulatory effect of caloric nutrients on GIT secretions, growth factors or neuronal factors that initiate further GIT development and maintain these advantages through marketing. (Noy and Sklan, 1999b Williamsen et al, 2010). Technology The major question remains how to apply the early nutrition concept. New technologies are being developed to provide feed during transition period. Careghi et al (2005) suggested providing an energy source in the hatching basket and during transport. Hatchery management experts have devised an alternative housing system in which pre hatched eggs (18 d) are placed and at hatch immediately fall on a litter belt where food and water is available. They remain in this housing system till 7-10 days post-hatch. This technique according to Horrox(2006) reduces grow out by one day. However, it requires heavy investment in new equipment (de Oliveira, 2007). A recently developed unique approach is a system that controls the crucial variables during the brooding period. After hatch day old chicks are placed in this system. Chicks have access to fresh water, air and feed. The system, according to the company, guarantees air temperature and controlled air velocity, which assures optimum chick body temperatures throughout the complete system. The chicks will start eating and drinking directly after placement. After 4 days they are transported to the farm for the remaining of their production cycle. A simpler patented technique provides a compartment within the incubator allowing the chick to feed during the hatching process without reducing hatchability or livability with improved developmental parameters. Nowadays, early nutrition is an acceptable concept, the advantages are clearly recognized, nevertheless, a barrier exists in the application of the model in current industry procedures.

9 References: Akiba, Y. and H. Murakami, Partitioning of energy and protein during early growth of broiler chicks and contribution of vitteline residue. World Poultry Science Conference, Antalia, Turkey. Anderson, G.J., Connor, W.E. and Corliss, J.D. (1990). Docosahexanoic acid is the preferred dietary n-3 fatty acid for development of the brain and retina. Pediatric Research 27: Baranyiova, E Effect of intraperitoneal administration of amino acids on the food intake of chickens in the first month after hatching. Acta Vet. Brno 56: Batal, A.B. and C.M. Parsons, Effect of fasting versus feeding oasis after hatching on nutrient utilization in chicks. Poult Sci., 81: Bayer, R.R., C.B. Chawan, F.H. Bird and S.D. Musgrave, Characteristics of the absorptive surface of the small intestine of the chicken from 1 day to 14 weeks of age. Poult. Sci. 54: Bigot, K., Mignon, Grasteau, S., Picard, M. and Tesseraud, S. (2003) Effects of delayed feed intake on body, intestine and muscle development in neonate broilers. Poultry Science 82: Boersma, S.T., Robinson, F.E., Renema, A. and Fasenka, G.M. (2003) Administering Oasis hatching supplement prior to chick placement increases initial growth with no effect on body weight uniformity of female broiler breeders after 3 weeks of age. Journal of Applied Research 12: Careghi, C., Tona, K. Onagbesan, O., Buyse, J., Decuypere, E. and Bruggeman, V. (2005). The effects of the spread of hatch and interaction with delayed feed access after hatch on broiler performance until seven days of age. Poult Sci.84: Christensen, V.L., M.J. Wineland G. M. Fasenko, and W.E. Donaldson Egg storage effects on plasma glucose and supply and demand tissue glycogen concentrations of broiler embryos. Poultry Sci. 80: Cook, R.H. and F.H. Bird, Duodenal villus area and epithelial cellular migration in conventional and germ-free chicks. Poult. Sci. 52: De Oliveira, J. (2007) Effects of In ovo feeding on turkey embryos development, energy status, intestinal maturation, gene expression and post hatch development. Ph.D. Thesis North Carolina State University. Dibner, J. (1999), Avoid any delay. Feed International December Dibner, J.J. C.D. Knight, M.L.Kitchell, C.A. Atwell, A.C. Downs and F.J. Ivey, Early feeding and development of the immune system in neonatal poultry. J. Appl. Poult. Res. 7:425-43

10 Foye, O.T., P.R. Ferket and Z. Uni The effects of in ovo feeding arginine, beta-hydroxy-beta-methyl-butyrate and protein on jejunal digestive and absorptive activity in embryonic and neonatal turkey poults. Poult Sci 86: Foye, O. T., Z. Uni, and P. R. Ferket Effect of in ovo feeding egg white protein, β-hydroxy-β-methylbutyrate, and carbohydrates on glycogen status and neonatal growth of turkeys. Poult. Sci. 85: Foye, O. T., Z. Uni, J. P. McMurtry, and P. R. Ferket. 2006b. The effects of amniotic nutrient administration, in ovo feeding of arginine and/or β-hydroxy-β-methyl butyrate (HMB) on insulin-like growth factors, energy metabolism and growth in turkey poults. Int. J. Poult. Sci. 5: Geyra, A. Z. Uni, and D. Sklan, 2001a. Enterocyte dynamics and mucosal development in the posthatch chick. Poultry Sci. 80: Geyra, A., Z. Uni and D. Sklan, The effect of fasting at different ages on growth and tissue dynamics in the small intestine of the young chick. Br. J. Nutr. 86: Gonzales, E., Kondo, N., Saldanha, E., Loddy, E. Careghi, C. and Decuypere, E. (2003). Performance and physiological parameters of broilers chickens subjected to fasting on the neonatal period. Poultry Science 82: Greenberger, N.J. and Skillman, T.G. (1969). Medium-chain triglycerides physiologic considerations and clinical implications. The New England Journal of Medicine 280: Halevy, O., A. Geyra, M. Barak, Z. Uni and D. Sklan, Early posthatch starvation decreases satellite cell proliferation and skeletal muscle growth in chicks. J. Nutr. 130: Henderson, S.N., J.L. Vincente, C.M. Pixley, B.M. Hargis and G. Tellez, Effect of an early nutritional supplement on broiler performance. Intl J. of Poult. Sci. 7: Horrox, N. (2006) World focus: a good start, time for a rethink? International Poultry Production 14:5. Jin, S.-H., A. Corless, and J. L. Sell Digestive system development in posthatch poultry. World s Poult. Sci. J. 54: John, T.M., J.C. George, and E.T. Moran, Jr Pre-and post hatch ultrastructural and metabolic changes in the hatching muscle of turkey embryos from antibiotic and glucose treated eggs. Cytobios 49: Juul-Madsen, H.R., G.Su, and P. Sorensen, Influence of early or late start of first feeding on growth and immune phenotrype of broilers. Br. Poult. Sci. 45:

11 Knight, C.D. land J.J. Dibner Nutritional programming in hatchling poultry. Why a good start is important. Poult. Dig. Aug/Sept. pp: Kornasio, R., O. Halevy, O.Kedar and Z. Uni Effect of in ovo feeding and its interaction with timing of first feed on glycogen reserves, muscle growth and body weight. Pout. Sci. 90: Lambson, R.O.,1970. An electron microscope study of the entodermal cells of the yolk sac of the chick during incubation and after hatching. Am. J. Anat. 129: Misra, L.K,. and R.C. Fanguy, Effect of delayed chick placement on subsequent growth and mortality of commercial broiler chicks. Poultry Sci., 57: Moran, E.T. and B.S. Reinhart, Poult yolk sac amount and composition on placement: effect of breeder age, egg weight, sex and subsequent changes with feeding or fasting. Poultry Sci. 59: Moran, E.T. Jr., Nutrition of the developing embryo and hatchling. Poult. Sci. 86: Moran, E.T., Effects of egg weight, glucose administration at hatch, and delayed access to feed and water on poult at 2 weeks of age. Poultry Sci. 69: Noble, R.C. and D. Ogunyemi Lipid changes in the residual yolk and liver of the chick immediately after hatching. Biology Neonate 56: Noy, Y., and Y. Pinchasov Effect of a single intubation of nutrients on subsequent early performance of broiler chicks and turkey poults. Poult. Sci. 72: Noy, Y., and D. Sklan Digestion and absorption in the chick. Poult. Sci. 74: Noy, Y. and D. Sklan, Uptake capacity in vitro for glucose, methionine and in situ for oleic acid in the proximal small intestine of posthatch chicks. Poultry Sci. 75: Noy, Y and D. Sklan, Posthatch development in poultry. J. Appl. Poult. Res., 6: Noy, Y. and D. Sklan, 1998a. Metabolic responses to early nlutrition. J. Appl. Poult. Res., 7: Noy, Y. and D. Sklan, 1998b. Yolk utilisation in the newly hatched poult. Br. Poult. Sci. 39: Noy, Y., and D. Sklan, Energy utilization in newly hatched chicks. Poultry Sci. 78:

12 Odle, J. (1997) New insights into the utilization of medium-chain triglycerides by the neonate. Observations from a piglet model. The Journal of Nutrition 127: Ohta, Y., N. Tsushima, K. Koide, M. T. Kidd, and T. Ishibashi Effect of amino acid injection in broiler breeder eggs on embryonic growth and hatchability of chicks. Poult. Sci. 78: Olah, I. and B. Glick, Meckels diverticulum. 1. Intramedullary myelopoiesis in the yolk sac of hatched chickens (Gallus domesticus). Anat. Rec. 208: Pinchasov, J, and Y. Noy, Comparison of posthatch holding time and subsequent early performance of broiler chicks and turkey poults. Br. Poult. Sci. 34: Raheja, K. L., J. Tepperman, and H. M. Tepperman The effect of age on intestinal glucose transport in the chick (Gallus domesticus). Comp. Biochem. Physiol. A 58: Reidy, T.R., J.L. Atkinson, and S. Leeson, Size and components of poult yolk sacs. Poult. Sci. 77: Romanoff, A.L The Avian Embryo. Macmillan, New York, NY. Sklan, D Fat and carbohydrate use in posthatch chicks. Poult. Sci.82: Sulistiyanto, B., Y. Akiba, and K. Sato Energy utilization of carbohydrate, fat and protein sources in newly hatched broiler chicks. Br. Poult. Sci. 40: Swennen, Q., Everaert, N., Debonne, M., Verbaeys, I., Careghi,C., Tona, K. Janssens,G.P.J., Decuypere, E., Bruggemen, V. and Buyse, J. (2009). Effect of macronutrient ratio of the pre-starter diet on broiler performance and intermediary metabolism. Journal of animal physiology and animal nutrition epub ahead of print (PMID ). Tako, P., P. R. Ferket, and Z. Uni Effects of in ovo feeding of carbohydrates and β-hydroxy-β-methylbutyrate on the development of chicken intestine. Poult. Sci. 83: Tarvid, I Effect of early postnatal long-term fasting on the development of peptide hydrolysis in chicks. Comp. Biochem. Physiol., 101: Tweed, S The Hatch Window. (Cobb-Vantress Technical Focus. Vol. 2. Siloam, Springs, AR. Uni, Z (2006). Early development of small intestinal function. Avian Gut Function in Health and Disease CAB International. p

13 Uni, Z., Y. Noy and D. Sklan, Developmental parameters of the small intestines in heavy and light strain chicks pre and post-hatch. Br. Poult Sci. 36: Uni, Z., Y. Noy and D. Sklan, Posthatch development of small intestinal function in the poult. Poultry Sci. 78: Uni, Z., R. Platin, and D. Sklan Cell proliferation in chicken intestinal epithelium occurs both in the crypt and along the villus. J. Comp. Physiol. B168: Uni, Z., A. Smirnov, and D. Sklan Pre- and post-hatch development of goblet cells in the broiler small intestine: Effect of delayed access to feed.poult. Sci. 82: Uni, Z., E. Tako, O. Gal-Garber, and D. Sklan. 2003b. Morphological, molecular, and functional changes in the chicken small intestine of the late-term embryo. Poult. Sci. 82: Vieira, S. L., and E. T. Moran Jr Effects of egg of origin and chick post-hatch nutrition on broiler live performance and meat yields. World s Poult. Sci. J. 55: Willemsen, H., Debonne, M. Swennen, Q., Everaert, N. Careghi, C. Han, H. Bruggeman, V., Tona, K. and Decuypere, E. (2010). Delay in feed access and spread of hatch: importance of early nutrition. World Poultry Science Journal 66: