Nutrient needs central to satisfactory egg incubation well-being undergo several major changes from fertilization until the reliance of the chick on feed. Glucose is central, with the initiation of incubation until the chorioallantois accesses O(2) to use for fatty acid oxidation. Nutrient recovery from albumen and yolk is largely commensurate with body assembly through to completion of the embryo by 14 d. Remaining albumen mixes with the amniotic fluid and is orally consumed until initiation of emergence. A portion of the albumen is absorbed by the small intestine to expand body glycogen reserves. The residual not absorbed contains digestive enzyme contributions and enters the yolk sac through its stalk at the jejunum and ileum. Interaction of the albumen-amnion digestive enzyme mixture with yolk sac contents leads to diverse alterations that influence subsequent use of lipids. Rapid removal of very low-density lipoprotein ensues, until pipping with triglycerides, expanding body fat depots while cholesterol deposits in the liver. A concurrent translocation of Ca from shell mineralizes the skeletal system while also crossing yolk sac villi for deposition on phosvitin-based granules accruing in its lumen. Loss of chorioallantois with pipping and the start of pulmonary respiration predispose a dependence on glycolysis to support emergence. Small intestinal villi progressively reorient their enterocytes from macromolecule transfer to competence at digestion and absorption after hatching. Mobilization of body fat complements contributions from the yolk sac to provide fatty acids for generating energy, heat, and water while also combining with hepatic cholesterol for membrane expansion and continued development. Calcified granules evacuate the yolk sac to further skeletal mineralization in the absence of shell contributions. Egg mass, its interior quality, and turning during early incubation directly influence the ability of the embryo to access nutrients and provide resources to support emergence and the transition of the chick to self-sufficiency.

An experiment was carried out to collect data suitable for testing methods used to describe the potential growth and body composition curves of broilers. Males and females of two commercial broiler strain-crosses were grown to 16 wk of age with birds taken at 0, 2, 4, 6, 8, 12, and 16 wk of age for chemical analysis and for the measurement of feather weight and breast meat (Pectoralis major and Pectoralis minor) weight at these ages. The data were used to test the Gompertz growth equation and the assumption of chemical allometry, as well as to estimate the values of the growth parameters for the different genotypes. Feeding and environmental conditions were intended to be such that potential growth and body composition could be attained. The weights of the chemical components for each of the four genotypes were described in terms of the mature weight of these components, their rates of maturing, and the time taken to reach the maximum rate of growth of each component. Allometric relationships between the weights of the chemical components and that of body protein were estimated. The ratio of ash to protein was essentially constant. Water matured more slowly, and lipid faster, than protein. For males, and for females up to 8 wk, the models were satisfactory. For females after this age, lipid growth was faster than expected from the earlier period, probably in preparation for egg production. There were small, but important, differences in the values of some parameters between the strain-crosses. For each of the four genotypes the changes in weight of feathers and breast meat with time were described in terms of the Gompertz growth function, which described the data very well. The parameters of the function for each component and genotype-mature weight, rate of maturing, and the time taken to reach the maximum rate of growth B were evaluated. For the feathers, the value of the rate parameter was higher than that estimated for the body as a whole. For the two breast muscles, and for their total weight, the value of the rate parameter was similar to that for the body as a whole. There was a simple allometric relationship between the weights of the breast muscles and that of the whole body. As a consequence, the development of the yield of breast meat for a given genotype could be described by the values of the two parameters: mature yield and the allometric exponent. A description of each genotype of interest is seen as an essential first step in using a simulation model either to predict requirements, or to predict the effects of different feeding programs, and environmental conditions, on the performance of broilers.

The weight of hatching eggs can influence broiler live performance regardless of hen age. Egg composition is altered with egg weight, but such alterations do not seem to have major effects on broiler growth and processing yields. The chick hatches with a yolk sac which provides nutrients for the transition to independent feeding. Alterations in egg weight and composition do not affect the proportion of yolk sac to body weight as much as its composition, particularly with eggs from very young hens. The contents of the yolk sac are high in fat and protein but very low in carbohydrate, which could lead to ketosis with prolonged fasting. Enhancing the first feed with either carbohydrate or gluconeogenics such as propionic acid may alleviate this ketosis and help early development. The digestive system of the chick is physically complete at hatching but is not fully competent at nutrient retrieval as many enterocytes are orientated to immunoglobulin uptake. Villi length and enzymatic activity increases with feeding, reaching maturity within a few weeks. Access to food and water after hatching varies, and long delays until placement are common. These delays cause losses in live performance. Loss in body weight due to late placement or undernutrition may also affect early muscle development. These adverse effects extend to marketing age and reduced meat yield. Factors that affect early chick development are gaining interest as the length of time to market progressively decreases and the chick's first days represent an increasing proportion of the total time for production. ReferencesALLBROOK, D.B., HAN, M.F. and HELLMUTH, A.E. (1971) Population of muscle satellite cells in relation to age and mitotic activity. Pathology 3: 233-243 AMBROSEN, T. and ROTENBERG, S. (1981) External and internal quality and chemical composition of hen eggs as related to hen age and selection for production traits. Acta Agricultura Scandinauica AUSTIC, R.E. (1985) Development and adaptation of protein digestion. Journal of Nutrition 115: BAKHUIS, W.L. (1974) Observations on hatching movements in the chick (Gallus domesticus). Journal of Comparative Plzysiology and Psychology 8 7 997-1003 BARANYIOVA, E. (1972) Influence of deutectomy, food intake and fasting on liver glycogen content in chickens after hatching. Actn Veterinaria Brno 41: 149-159 BARANYIOVA, E. and HOLMAN, J. (1976) Morphological changes in the intestinal wall in fed and fasted chickens in the first week after hatching. Acta Veterinaria Brno 45: 151-158 BELLAIRS, R., BACKHOUSE, M. and EVANS, R.J. (1972) A correlated chemical and morphological study of egg yolk and its constituents. Micron 3: 328-346 BEST, E.E. (1966) The changes of some blood constituents during the initial post-hatching period in chickens. 11. Blood total ketone bodies and the reduced glutathione/ketone body relationships. British Poultry Science 7 23-28 BIELORAI, R., TAMIR, M., ALUMOT, E., BAR, A. and HURWITZ, S. (1973) Digestion and absorption of protein along the intestinal tract of chicks fed raw and heated ...

Starch is the main carbohydrate in the food of poultry. Starch granules are digested by pancreatic alpha-amylase in the small intestine. Intestinal villi have enterocytes that project microvilli with a fibrous glycocalyx from the surface. These fine structures are envisaged to entrap water that is mixed with mucin from nearby goblet cells to form the "unstirred water layer." Maltose, maltotriose and alpha-limit dextrins must diffuse across this first barrier to absorption to be hydrolyzed by maltase and sucrase-isomaltase immobilized at the membrane; however, the resultant glucose, once formed, accrues at the surface to provide a concentration advantage. Fowl adjust to changes in dietary starch by altering the amount of amylase released, intestinal surface area and enterocyte carbohydrase concentration. Enterocytes arising during embryonic development have no carbohydrases and are not involved with glucose absorption, but they appear to be specialized for maternal immunoglobin transfer in ovo. Embryonic villi are stimulated by transfer activity, and their growth depends on enterocytes arising from the crypt. Mature crypt cells are capable of digestion-absorptive activities and dominate the villus shortly after the chick hatches when yolk sac reserves are depleted.

Different incubation conditions can cause eggshell temperature (EST) to deviate from optimum. Two experiments were performed to determine the effect of low EST at the start of incubation and high EST at the end of incubation on hatchability, chick quality, 6-wk live performance, and breast meat yield of broiler chickens. In each experiment, 1,800 eggs from a single flock were divided and set into 2 setters. From 0 to 10 d of incubation, one setter was set to attain an EST of 36.6 degrees C (considered low), whereas the other was set to 37.8 degrees C (the control temperature). Using an infrared thermometer, EST was measured daily on a sample of eggs to ensure treatment intentions. On d 11 of incubation, the temperature of the low EST setter was increased to 37.8 degrees C in synchrony with the other setter until transfer. On d 18 of incubation, eggs from both setters were combined into 2 equal groups and transferred to hatchers. The EST in one hatcher was set to 37.8 degrees C (control) and in the other to 39.5 degrees C (considered high) until 21 d of incubation. Hatched males were placed in battery cages (Experiment 1) or floor pens (Experiment 2) and reared on common feeds to 1 or 6 wk of age, respectively. Low EST in the first 10 d of incubation reduced hatchability, increased BW and chick yield, and reduced 1-wk gain compared with the control EST. Throughout rearing, BW was reduced for low EST chicks compared with control EST chicks; consequently, carcass, fillet, and tender weights were also reduced. High EST in the hatcher increased hatchability, and reduced BW, chick yield, and 1-wk gain compared with control EST in the hatcher. By 3 wk of age, there was no difference in BW between chicks in high EST and control EST treatments. Subsequent carcass and processing yields were also similar. Incubation at the control EST of 37.8 degrees C, particularly from 0 to 10 d, resulted in the best performance overall.