The developmental patterns of digestive tract grOW[i1 and some digestive
enzymes activity have been studied in two broiler strains at the first day post-hatching,
2, 4 and 6 weeks of age. The strains used were Hubbard (A) and Arbor acres (B).
unsexeo. day-old broiler chicks. Growth performance data and digestive tract length
were recorded. The intestinal contents of proventriculus (P); duodenum (D); jejunum
(J) and ileum (I) were collected. weighed and kept in equal quantities of buffer saline
unitl used in the determination of amylase, lipase, trypsin and chymotrypsin activities
during different growth periods. Some blood plasma enzymes. RBe's count.
haemoglobin concentration and heterophil to tymphocytes ratio were also examined. The results showed significant (P ~ 0.05) strain differences in body weight.
weight gain, feed intake and leed conversion ra\ie. Slarin A surpassed strain B in all
growth performance parameters studied. which reflect their different genetic
background. Moreover. strain A has better feed conversion (2.10) than strain 8 (2.18)
during the whote experimental period. Diges\ive tract length increased rapidly from post-hatcninq to the second
week of age. with the most pronounced increases in duodenum. pancreas. jejunum
and Ileum. In generel. there were significant strain differences in the rate of growth of
different Intesunal segments during the whole experimental period. From the
physiological point of view, these intestinal segments, (D, Panc, J .. and I) are
considered as early mature parts due 10 their importance as sites of digestive
enzymes secretion or nutrients digestion and absorption. Results showed also that amylase actillity was higher in all intestinat
segments studied except in proventriculus contents due to its acidic environment. This
enzyme increased post-hatching till Ihe 4th week of age and then decreased. Lipase
activity increased during the experimental period and reached its maximum level
between 4 and 6 weeks of age. Moreover. lipase acti·,ity was higher (P::; 0.05) in
duodenum. and jejunum than in ileum and proventriculus. A significant (P ~ 0 01)
strain differences in lipase activity were observed which reflect their different obesity
(fatness). Trypsin and chymotrypsin activities were higher at 2 and 4 weeks of age
and then significantly (p~0.05) decreased in both strains, due to the higher rates of
protein turnover (rom digestive tract 10 muscles building during the first period. There were signi(lcant strain and age differences in all blood parameters
studied except the activity of LDH in blood plasma. Howev" .. plasma LDH activity
increased with age and reached its maximum level at 6 week of age. Furthermore,
alkaline phosphatase (AP) activity in blood plasma significanlly (P ~ 0.05) decreased
with age. although higher values were observed during the first growing period (up to
4 wk) , that coincident with the higher osteoblastic activity. Finally, considerable variations in Hb concentration and Rae'S counts were
also observed in bolh strains. and also in HIL ratio which indicates that strain A was
more sensitive to differenl stressors than strain B. It is concluded thaI the developmental growth pattern of the digestive Iracl in
broiler chicks exceeds that of the whole body during early oosr-hatchinc period. Also.