04-Lancaster Farming, Saturday, September 20, 1997
WHAT ARE THE
EFFECTS OF VARYING
DAY LENGTH ON
GROWTH OF BROILERS?
R. MICHAEL HULET
Associate Prof.
Dept. Poultry Science
Many investigates have
looked at various day lengths to
determine what is optimum foi
broiler growah and meat produc
tion Continuous daylight, in
creasing day lengths, intermittent
lighting, and short and long day
lengths have been compared
The data indicate that the most
rapid growth lot modem broileis
occurs when birds are grown under
continuous 23- or 24-hour day
lengths Continuous daylight al
lows buds access to teed and water
at all times, especially during the
coolest portion of the day during
hot weather Continuous day
length allows broilers to reach
their genetic potential for growth
and meal production
However, genetic selection tor
increased broiler growth has re
sulted in chickens developing
some metabolic lesions it not cor
rectly managed Rapidly growing
birds have a higher incidence of I)
Sudden Death Syndrome (SDS),
2) leg abnormalities such as tibial
dyschondroplasia (TD), rotated and
twisted tibia or femurs, or rickets
type slipped tendons, and 3) asci
lics, which is also called “water
belly" All these lesions have
been linked with the rapid rate of
growth of broilers
Some investigators have advo
cated dilterenl management re
gimes to prevent or reduce the de
velopment ol the symptoms of
metabolic diseases among rapidly
glowing birds Investigators from
Canada (Classen and Riddel, 1989;
Classen ct al, 1991, Blair et al,
1991) have shown that short day
lengths al early ages can decrease
skeletal disorders and incidences of
Egg Age to Haugh Unit Relationship
Haugh
unit
6 10 1C 20 2C 30 3S 40 48
Age (days)
R square = 0 0269, P = 0.001, 0 = 67.5 Haugh units
Egg Age to Weight Relationship
Egg 61
Wt(g)
6 10 18 20 2C 30 , 36 40 48
R square = 0.0124, P = 0.01,0 = 60.3 g
SDS
Alabama rcseaichers (Rendcn et
al, 1991 and 1992) also showed
fewer leg abnormalities and im
proved carcass yield with a light
ing program that provided de
creased day length early in the
production cycle
However, all ol these experi
ments resulted in significantly
lower body weights Most oi the
decreased day-length programs re
duced the day length to 6 hours of
light at 3 to 5 days of age causing
a reduction in feed consumption
and bird growth during this critical
period Other researchers have
merely reduced feed provided to the
birds for an 11 - to 14 day period
early in life to reduce growth and
hopefully reduce the other meta
bolic side effects This strategy
has also been successful in reduc
ing metabolic lesions but still at
the expense of reduced body
weight at market age
In 1997, a study was reported
from Penn State University at
poultry science meetings in Geor
gia, where light was reduced to 16
hours a day from 3 to 28 days of
age and then increased gradually as
the birds approached market age.
This lighting regime was tested
against a conventional 23-hour per
day lighting treatment on three
different strain crosses of birds.
Although there were some
strain differences in body growth,
it was found that the birds on the
experimental lighting treatments
had two percent less mortality at
seven weeks and actually an in
crease in body weight over those
raised on the control (23 hr) light
ing system." The lowered percent
age mortality and enhanced growth
was consistent for the three differ
ent strain crosses of broilers.
Increased activity was noted
for the broilers on the experimen
tal lighting treatment and may
have contributed to the improved
health and growth of the broilers. 1
all eggs (771 doz)
all eggs (771 dozen)
Age (days)
Therefore, reduced lighting treat
ments starting at three days of age
was shown to be an effective
management tool for reducing
metabolic lesions and mortality
while promoting growth of broil
ers.
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