The present study was carried out to investigate the possibility of alleviating
the adverse effects of heat stress to which broiler chicks are exposed during the
summer season by means of early-age feed restriction (EFR) and/or dietary
supplementation with potassium chloride (KCI). Three hundred and sixty, one-day-old,
broiler-type Hubbard chicks were randomly divided into two halves, each of which was
assigned to four treatments (T), and given starter diets from 1 to 21 days of age, then,
the birds were switched to grower diets from 22 to 42 days of age. Two feeding
regimens were imposed on these birds. Chicks of the first half (T1, T2, T3 and T 4)
were full-fed (FF), during the entire experimental period from 0 to 6 weeks of age,
while birds of the other half (T5, T6, T7 and T8) were subjected to feed restriction;
only during the first week of life. Each of the starter and grower diets were isocaloric
and isonitrogenous, and originally contained about 0.8% K. Diets of T1 and T5 were
unsupplemented with KCI and served as controls, while diets for chicks of T2 and T6,
T3 and T7 or T4 and T8, were supplemented with KCI at levels of 0.75, 1.5 and
2.25%, respectively. Thus, in these diets supplemental KCI plus basal K provided
dietary K levels of 0.8, 1.2, 1.6 or 2.0%, respectively. The criteria of response were some physiological changes, levels of some
blood constituents and nutrients digestibility. The obtained results can be summarized
as follows: Early-age feed restriction (during the first week) of broiler chicks decreased
significantly (P::;0.01) body temperature, panting rate, blood pH and sedimentation
rate, and plasma corticosterone (P::;0.05), but increased (P::;0.01) the activity of
alkaline phosphatase and plasma concentrations of k and T3. However, blood
hemoglobin, concentrations of plasma total protein, total lipids, glucose, cholesterol,
Na, CI, and T4 were not affected. Supplemental KCI decreased significantly (P::;0.01)
body temperature, panting rate, and blood pH and sedimentation rate, but increased
(P::;0.01) the activity of alkaline phosphatase, and the concentrations of plasma total
protein, Na, K, T3 and T4. However, blood hemoglobin, and plasma concentrations of
total lipids, glucose, cholesterol, CI and corticosterone were not affected. Early-age
feed restriction did not affect digestibility of crude fiber (CF), organic matter (OM),
ether extract (EE), nitrogen free extract (NFE), nitrogen retention, ash retention, or k
retention, but decreased dry matter (OM) and crude protein (CP) digestibility.
Supplemental KCI did not affect nitrogen retention and the digestibility of CF or NFE,
but the high level (2.25%) improved the digestibility of OM, OM, EE, and CP and ash
and K retention. The use of early-age feed restriction with 2.25% dietary KCI level for
broiler chicks in hot climate during the summer season was recommended.