Body weight of chicks increases by approximately 50- fold within 40 days of hatch. This includes an adaptation period from utilising embryonic yolk to exogenous carbohydrate rich feed. The newly hatched chick contains about 20% yolk, which provides a continuing source of energy after hatch (Romanoff, 1960).
Chicks are precocial and on hatching will forage for feed and then begin to grow, whereas holding birds without feed results in loss of weight until at least 24 hrs after birds are fed (Noy and Sklan, 1998a). Several authors have suggested that yolk is used for maintenance whereas exogenous energy is utilised for growth (Anthony et al., 1989), however deutectomy (yolk sac removal) studies (Murakami et al., 1992) contradict this theory.
Access to nutrients initiates growth some 24 hrs postingestion and early access to feed resulted in more rapid intestinal development immediately after hatch. This paper will describe some of the dramatic changes occurring during the initial post-hatch period and examine the physical and functional development of the small intestine during this period.
During embryonic development yolk is the sole nutrient source. Lipid yolk contents are transferred during this period from the yolk sac to the embryonic circulation as lipoprotein particles (Lambson, 1970). Close to hatch the intestine contains yellow-green viscous material (Romanoff, 1960) from which yellow pigments identical to those of yolk were found (Noy and Sklan, 1998a).
This represents yolk that has been transported to the intestine through the yolk stalk. Histology of the yolk stalk shows an open pathway at hatch that becomes narrower with age. After 48 hrs lymphoid cells begin to congregate in the yolk stalk, almost occluding the passage by 72 hrs (Noy et al., 1996); thereafter the yolk stalk was converted to lymphopoietic tissue (Olah and Glick, 1984).
In addition to transport of yolk to the GIT, yolk utilisation via the circulation (Romanoff, 1960; Lambson, 1970) also remains functional during the first 48 hrs post-hatch after which transfer begins to decrease (Esteban et al., 1991; Noy et al., 1996). In fact the yolk appears to be permeable in both directions and transfer is nonspecific. (Noy et al., 1996; Noy and Sklan, 1998a).
In the hatching chick yolk comprises approximately 15-20% of body weight, containing 20-40% lipids (mainly triglycerides) and 20-25% protein (Moran and Reinhart, 1980; Reidy et al., 1998). Digestion of the yolk lipids can be clarified by following the changes occurring in intestinal lipid fractions in the early posthatch period. The lipid fraction of yolk consists predominantly of triglycerides and phospholipids with small amounts of cholesterol esters and no free fatty acids (Noble and Ogunyemi, 1989; Noy and Sklan, 1998a).
The lipid composition of the intestinal contents at different times before and after hatch is shown in Figure 1. In the duodenum some free fatty acids are found even before hatch and their proportion increases with age while the percentage of triglycerides decreases.
In the caecum, however the composition of the lipid fractions resembles the yolk composition at hatch and only after four days begins to show increasing free fatty acid levels. Thus it appears that yolk reaching the distal small intestine is probably not utilised and may explain the green sticky viscous excretions observed close to hatch (Noy and Sklan, 1998a).
The sum of both yolk transport and utilisation routes is reflected in the decrease in weight of the yolk. Yolk weight decreased as a logarithmic function with time, thus by day 4 approximately 1 g of yolk remained.
However, surprisingly, in chicks with access to feed the rate of yolk utilisation was faster. This may be due to increased intestinal mechanical (antiperistaltic) activity (Noy et al., 1996). (Figure 2).
Figure 1. Lipid class distribution in the duodenum, ileum and caecum before and after hatch.
Utilisation of yolk in fed and held birds together with body weight gain and intestinal weight changes in the immediate post-hatch period are shown in Figure 3. Chicks with access to feed consumed 6.5 g in the first 48 hrs after hatch and BW increased by 5 g.
During this period yolk size decreased by approximately 60%, transferring close to 1 g fat and protein for utilisation by the bird. Concomitantly the small intestines increased in weight by more than 2-fold. In contrast, birds without access to feed decreased in body weight (BW) by 3.5 g during the 48 hrs after hatch. In these chicks yolk size decreased less than in fed birds, and thus slightly less yolk fat and protein were used.
Despite the lack of feed intake during this time the small intestine increased in weight by 80%. Since the held birds did not consume any exogenous protein during this period, the protein required for the intestinal growth probably originated in the yolk.
Examination of the changes occurring between 2 and 4 days after hatch when all birds had access to feed showed similar growth increments in both held and fed chicks although intestinal development was less in the held chicks.
Yolk is utilised for 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 post-hatch.
Thus the yolk sac has essentially disappeared by day 5 and further nutrient supply is solely from exogenous feed. We will now examine the gastrointestinal development during this period.
Close to and after hatch dramatic changes occur both in the intestinal size and morphology (Bayer et al., 1975; Cook and Bird, 1973; Uni et al., 1996). In the immediate post-hatch period, the small intestine increases in weight more rapidly than the whole body mass and this process of rapid relative growth was maximal at 6-10 days 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 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 than the jejunum and ileum (Uni et al., 1999). At hatch enterocytes and villi are poorly developed, and few crypts are detected. This picture changes dramatically within hours of hatching.
Figure 2. Effect of feed on chick yolk weight.
Figure 3. Wet weight changes between 0-2 and 2-4 days (B = body weight, P = body protein).
Enterocytes change from round and relatively non-polar to elongated polar cells. Villi height and area increase rapidly but at different rates in the different chick intestinal segments reaching a plateau at 6-8 days in the duodenum and after 10 days in the jejunum and ileum.
Crypts increased in number and size and branched rapidly in the days immediately post-hatch (Geyra et al., 2001a).
Thus, the extensive changes in the morphological development close to hatch include crypt definition and basic differentiation of enterocytes as well as enlargement of the intestinal absorptive surface many fold, but apparently they are sensitive to perturbations in the nutrient supply. We will now examine the gross effects of early feeding and the changes accompanying the intake of exogenous feed.
The effect of early feeding
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 hrs after feeding (Moran, 1990; Pinchasov and Noy, 1993).
In practice eggs within a single tray will hatch over a 24-36 hr window during which time the birds that have pipped are without feed. Hatchery treatments and transport to the farm involve a further holding period.
Thus, as we have previously mentioned, often birds are held for 48 hrs or more before initial access to feed and water (Hill and Green, 1977; Misra and Fanguy, 1978). During this time chicks decrease in weight at an approximate rate of 4 g per 24 hrs due in part to moisture loss as well as yolk utilisation.
We will examine some of the effects of this holding period both on growth close to hatch and later on in their development.
Body weight up to 21 days of age of chicks provided at hatching (within 1 hr of clearing the shell) with either solid feed, semi-solid feed or non-nutritious bulk (sawdust) was compared to that of chicks held for 36 hrs (Figure 4).
Provision of all of these materials resulted in increased BW at day 4 although the effect of sawdust was transient. This suggests that there may be some mechanical stimulation of the GIT close to hatching, but with no nutrient followup this advantage is not maintained. (Noy and Sklan, 1998b). Further studies have addressed the effect on BW through to marketing of the form of feed (solid, liquid nutrient supplement or water) presented to chicks held for 48 hrs (Noy and Sklan, 1998b).
Provision of caloric nutrients in solid or liquid form produced a considerable increase in BW, which was maximal between 4 and 8 days 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 days. This transient response to water intake close to hatch probably represents in part enhanced hydration with no long-term physiological effect.
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 to 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 supplying 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 short-lived response (Moran, 1990; Pinchasov and Noy, 1993; Noy and Sklan, 1997). This may be because glucose is absorbed with no additional enzymatic activity, therefore no stimulation of intestinal processes occurs and a growth advantage due solely to the energy intake was found.
Figure 4. Effect of feed form presented after hatch on body weight in early life.
All these studies indicate that early access to nutrients produced an initial enhancement in BW which, although decreasing with age, was generally maintained through to marketing. The enhanced BW induced by early feeding was accompanied by an increase in breast meat percentage. 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 and are instrumental in determining later stage muscle development (Halevy et al., 2000; 2003). Early access to feed enhances satellite cell proliferation during the initial post-hatch period and may affect skeletal muscle growth through to market. An additional system that undergoes major structural development during this period is the small intestine.
The effect of holding poultry without feed on the morphological development in the different intestinal segments in the post-hatch chick has been examined (Baranylova and Holman, 1976; Geyra et al., 2001b).
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 days after hatch.
Early crypt development and the number of cells per crypt were also decreased. Electron microscopy 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.
Fasting or feeding influences many aspects of functional poultry development, therefore we will explore some of these effects.
During this early post-hatch period the chick must also undergo significant metabolic adaptations in order to adjust to the different exogenous nutrient sources.
Carbohydrates, lipids and protein reaching the intestine must be hydrolyzed before uptake. During late embryonic development and at hatch, pancreatic enzyme activities are found in the small intestine (Marchaim and Kulka, 1967). Several studies have determined specific activities of pancreatic enzymes with age.
However, since the enzymes must be secreted to the intestine and then activated, this provides little information concerning intestinal enzymatic activities.
It is only possible to determine the net secretion to the duodenum using non-absorbed markers and since these must be in steady state with respect to input-output, quantitative determination of enzymatic secretions are only possible from 3-4 days after hatch.
Determination of total intestinal activities close to hatch indicated increases in total intestinal trypsin, amylase and lipase activities, which were correlated with both intestinal and body weights (Sklan and Noy, 2000).
Determination of activities of some enzyme secretions using a nonabsorbed marker showed an increase from day 4 with age and with feed intake.
It should be noted that rates of increase in secretion differed among these three enzyme activities. However, calculation of secretion per g feed intake indicated no major changes in quantities of trypsin, amylase and lipase activities secreted per g between four and 14 days post hatch (Uni et al., 1999).
In fed birds intestinal pancreatic enzymatic activities were correlated both with BW and intestinal weight (Sklan and Noy, 2000; Sklan, 2001). These findings suggest that feed intake triggers secretion of pancreatic enzymes, which are then secreted at relatively constant amount per feed intake as the chick grows.
In parallel the daily secretion of nitrogen and bile acids to the duodenum were determined using non-absorbed markers. These similarly increased with both BW and intestinal weight when calculated per feed intake as the chick grows (Noy and Sklan, 1995).
SMALL INTESTINAL ABSORPTION
Following hydrolysis, the capacity for uptake must be available for maximal growth. Intestinal uptake capacity has been examined in vitro, and excess absorptive capacity appears to be available at hatch (Shehata et al., 1984; Noy and Sklan, 1996).
In situ studies in posthatch birds with buffered solutions also indicated little change in uptake per g of small intestine with age (Noy and Sklan, 1998b). However, there are distinct differences close to hatch between uptake from buffered solutions in vitro and in situ as compared to yolkcontaining solutions.
Absorption of glucose or methionine from yolk-containing solutions was generally only 20-35% of uptake from buffered medium. We have attributed this in part to the hydrophobic nature of yolk and also to the low luminal concentrations of sodium, which is required for full activity of the sodium-glucose and sodium-amino acid co-transporters (Noy and Sklan, 1999; Stevens et al., 1984).
In vivo, non-absorbed marker determinations close to hatch have also indicated that uptake of glucose and methionine was relatively low, increasing by day 4 posthatch (Noy and Sklan, 1999; Sklan and Noy, 2003).
This low uptake of hydrophilic components has been confirmed by TME measurements, which indicated low availability of carbohydrates and proteins close to hatch.
Availability of both increased with age, reaching adult values by 10 days (Sulistiyanto et al., 1999). Uptake of fat and starch was found to be over 80% at 4 days posthatch whereas absorption of protein increased from day 4 to day 10. However, in the immediate post-hatch period the increase in uptake of hydrophilic compounds was delayed in held chicks and increased only after feeding.
This may cause a lag in nutrient supply as compared to immediately fed birds. Thus, both hydrolytic enzyme secretions and subsequent nutrient absorption are retarded in chicks without access to feed.
Throughout this early post-hatch period there are constant dramatic developments occurring both in structure and function of the small intestine and these impinge on performance both during this period and throughout development.
Early availability of feed thus results in the following:
1. Yolk is used for initial GIT growth, which is augmented by exogenous feed.
2. Crypt formation, villus growth and enterocyte maturation are enhanced, whereas lack of nutrients retards GIT development and has an impact on further growth.
3. Exogenous feed enhances yolk utilisation, stimulates intestinal peristalsis and triggers secretion of pancreatic enzymes enabling efficient digestion of nutrients after 4 days post-access to feed.
4. Glucose and methionine, hydrophilic compounds, are better absorbed from sodium-containing aqueous solutions than in the presence of yolk whereas oleic acid is well absorbed at hatch.
5. Birds that eat grow. These findings indicated that appropriate nutrition and access to feed close to hatch can accelerate GIT development, increase absorptive surface area and thus enhance nutrient assimilation, contribute to muscle growth and finally result in increased marketing performance.
Early nutrition research was done jointly with Professor David Sklan, who passed away on Sept. 1, 2004. His contribution to the scientific community was cherished and his absence is and will be greatly felt.
Author: YAEL NOY
Akiba, Y. and H. Murakami. 1995. Partitioning of energy and protein during early growth of broiler chicks and contribution of vitteline residue. In: Proceedings of the World Poultry Science Conference.
Antalia, Turkey. Anthony, N.B., E.A. Dunnington and P.B. Siegel. 1989. Embryo growth of normal and dwarf chickens from lines selected for high and low body weight. Archives fur Geflugelkunde 53:116-122.
Baranylova, E. and J. Holman. 1976. Morphological changes in the intestinal wall in fed and fasted chickens in the first week after hatching. Acta Vet. Brno 45:151- 158.
Bayer, R.R., C.B. Chawan, F.H. Bird and S.D. Musgrave. 1975. Characteristics of the absorptive surface of the small intestine of the chicken from 1 day to 14 weeks of age. Poult. Sci. 54:155-169.
Cook, R. and F. Bird. 1973. Duodenal villus area and epithelial cellular migration in conventional and germ free chicks. Poult. Sci. 52:2276-2280.
Esteban, S., J.M. Rayo, M. Moreno, M. Sastre, R. Rial and J. Tur. 1991. A role played by the vitelline diverticulum in the yolk sac resorption in young posthatched chickens. J. Comp. Physiol. (B) 160:645-648.
Geyra, A., Z. Uni and D. Sklan. 2001a. Enterocyte dynamics and mucosal development in the post-hatch chick. Poult. Sci. 80:776-782.
Geyra, A. Z. Uni and D. Sklan. 2001b. The effect of fasting at different ages on growth and tissue dynamics in the small intestine of the young chick. Br. J. Nutr. 86:53-61.
Halevy, O., A. Geyra, M. Barak, Z. Uni and D. Sklan. 2000. Early starvation affects satellite cell proliferation and muscle growth in the chick. J. Nutr. 130:858- 864.
Halevy, O., Y. Nadel, M. Barak, I. Rozenboim and D. Sklan. 2003. Early post-hatch feeding feeding stimulates satellite cell proliferation and skeletal muscle growth in turkey poults. J. Nutr. 133:1376- 1382.
Hill, A.T. and R. Green. 1977. Effect upon subsequent broiler growth of delaying the removal of chicks from the hatchery. In: British Columbia Research Review, Agassiz Research Station Report. Agassiz, BC, Canada, pp. 3-4.
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. 129:1- 20.
Marchaim, U. and R.G. Kulka. 1967. The non-parallel increase of amylase chymotrypsinogen and procarboxypeptidase in the developing chick pancreas. Biochimica et Biophysica Acta 146:553-559.
Misra, L.K. and R.C. Fanguy. 1978. Effect of delayed chick placement on subsequent growth and mortality of commercial broiler chicks. Poult. Sci. 57:1158.
Moran, E.T. and B.S. Reinhart. 1980. Poult yolk sac amount and composition on placement: effect of breeder age, egg weight, sex and subsequent changes with feeding or fasting. Poult. Sci. 59:1521-1528.
Moran, E.T. 1990. Effects of egg weight, glucose administration at hatch, and delayed access to feed and water on the poult at 2 weeks of age. Poult. Sci. 69:1718-1723.
Murakami, H., Y. Akiba and M. Horiguchi. 1992. Growth and utilisation of nutrients in newly hatched chicks with or without removal of residual yolk. Growth Development and Aging 56:75-84.
Noble, R.C. and D. Ogunyemi. 1989. Lipid changes in the residual yolk and liver of the chick immediately after hatching. Biology Neonate 56:228-236.
Noy, Y. and D. Sklan. 1995. Digestion and absorption in the young chick. Poult. Sci. 74:366-373.
Noy, Y. and D. Sklan. 1996. Uptake capacity in vitro for glucose, methionine and in situ for oleic acid in the proximal small intestine of post-hatch chicks. Poult. Sci. 75:998-1002.
Noy, Y and D. Sklan. 1997. Posthatch development in poultry. J. Appl. Poult. Res. 6:344-354.
Noy, Y. and D. Sklan. 1998a. Yolk utilisation in the newly hatched poult. Br. Poult. Sci. 39:446-451.
Noy, Y. and D. Sklan. 1998b. Are metabolic responses affected by early nutrition? J. Appl. Res. 7:437-451.
Noy, Y. and D. Sklan. 1999. Energy utilisation in newly hatched chicks. Poult. Sci. 78:1750-1756.
Noy, Y., D. Sklan and Z. Uni. 1996. Utilisation of yolk in the newly hatched chick. Br. Poult. Sci. 37:987- 995.
Olah, I. and B. Glick. 1984. Meckels diverticulum. 1. Intramedullary myelopoiesis in the yolk sac of hatched chickens (Gallus domesticus). Anatomy Records 208:243-252.
Pinchasov, J. and Y. Noy. 1993. Comparison of posthatch holding time and subsequent early performance of broiler chicks and turkey poults. Br. Poult. Sci. 34:111-120.
Reidy, T.R., J.L. Atkinson and S. Leeson. 1998. Size and components of poult yolk sacs. Poult. Sci. 77:639- 643.
Romanoff, A.L. 1960. The Avian Embryo. Macmillan, New York, NY.
Shehata, A., J. Lerner and D. Miller. 1984. Development of brush border membrane hexose transport system in chick jejunum. Am. J. Physiol. 240: G102-108.
Sklan, D. 2001. Development of the digestive tract of poultry. World Poult. Sci. 57:415-28.
Sklan, D. and Y. Noy. 2000. Hydrolysis and absorption in the small intestines of post-hatch chicks. Poult. Sci. 79:1306-1310.
Sklan, D. and Y. Noy. 2003. Functional development and intestinal absorption in the young poult. Br. Poult. Sci. 44: 6511-658.
Stevens, B.R., J.D. Kaunitz and E.M. Wright. 1984. Intestinal transport of amino acids and sugars; advances using membrane vesicles. Ann. Rev. Physiol. 46:417-433.
Sulistiyanto, B., Y. Akiba and K. Sato. 1999. Energy utilisation of carbohydrate, fat and protein sources in newly hatched broiler chicks. Br. Poult. Sci. 40:653- 659.
Uni, Z. Y. Noy and D. Sklan. 1996. Developmental parameters of the small intestines in heavy and light strain chicks pre- and post-hatch. Br. Poult. Sci. 36:63- 71.
Uni, Z., S. Ganot and D. Sklan. 1998. Post-hatch development of mucosal function in the broiler small intestine. Poult. Sci. 77:75-82.
Uni, Z., Y. Noy and D. Sklan. 1999. Post-hatch development of small intestinal function in the poult. Poult. Sci. 78:215-222.
Hebrew University, Faculty of Agriculture, Rehovot, Israel