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 Beneficial
news and researches
Poultry Research Centre News
Poultry Research Centre News Vol 11 No 2, May 2002
Determining When the Broiler Breeder
Female is Most Sensitive to Overfeeding
F.E. Robinson, R.A. Renema, N. Tremblay, N.C. Theriault
and J.A. Proudman
Research efforts at the University of Alberta have focused
on the "critical period" between photo-stimulation
(the time of increasing day length to stimulate puberty) to
the time of peak egg production (approximately 30-32 weeks
of age). This is one of the most important periods in a pullet's
life since how the ovary develops during puberty can affect
egg production throughout lay.
Bird age and feeding level influence ovary development. It
has been shown that a flock will enter production more quickly
when photo-stimulation is delayed, since a greater proportion
of the flock will be physically capable of responding to a
photo-stimulatory cue. Research has shown that extra feed
will accelerate sexual maturation. However, overfeeding breeder
females can cause abnormal ovary development by as early as
14 weeks of age, when some early follicle development can
occur.
The weeks immediately following photo-stimulation have been
shown to be the most critical period where excess feed has
the greatest impact on ovary development. After peak egg production
near 30-32 weeks of age the ovary of most genetic strains
gradually becomes more immune to the detrimental effects of
overfeeding.
Both the reproductive hormones and the reproductive system
are sensitive to changes in feeding program. Better feeding
management decisions could be made during the critical period
of sexual maturation and early egg production if the sensitivity
of breeders to extra feed were more clearly identified.
This research intended to provide potential answers to the
following specific questions:
1. Does the way a broiler female
partitions dietary nutrients change with minor changes in
nutrient intake?
2. To what extent does nutrient
partitioning vary in females after sexual maturity compared
to before sexual maturity?
3. If we knew how the hen responded
to energy intake (grew bigger or produced eggs) would we know
more about when to photo-stimulate a flock?
How was it done?
400 Shaver Starbro pullets were reared to 17 weeks of age
in a light tight facility. The 252 closest to the target body
weight were then individually caged and assigned to a study
group and feeding treatment. The first of the two-week treatment
periods (A20) started at 18 weeks of age and the last (A32)
started at 30 weeks (36 birds per period for 7 periods). These
study periods were intended to cover the entire interval between
photo-stimulation and peak egg production. At the beginning
of each treatment period, half of the birds remained on the
feed restriction diet (Control) to maintain target body weight,
or were switched to a bonus treatment (Bonus) in which birds
were allocated the control feed volume plus an extra 30g of
fed per bird each day. 36 birds under treatment were dissected
for determination of carcass composition parameters and ovarian
morphology at the end of each study period. All birds were
photo-stimulated at 22 weeks of age.
What was measured
The effects of the Control and Bonus feeding treatment on
the following characteristics were measured. Each carcass
was dissected to record the weight of the breast muscle, abdominal
fatpad (the major fat depot), liver, ovary and oviduct. Fat
was extracted from ground liver, ovary and fatpad samples
to trace changes in fat allocation. The amount of fat and
protein in the whole bird was measured by analyzing homogenized,
freeze dried representative samples of each bird. Weights
of the key reproductive structures, consisting of the oviduct,
ovary and stroma (ovary tissue remaining after removal of
the large (yolky) follicles) were determined. The individual
weights of large yellow follicles (>10 mm in diameter)
were recorded to help investigate treatment effects on the
follicular hierarchy. The stroma was examined for the number
of small yellow follicles (5 to 10 mm), and small white follicles
(2 to 5 mm).
Blood samples taken at the beginning (Day 0) and the end (Day
14) of each treatment period were used to measure the concentration
of 3 reproductive hormones; luteinizing hormone (LH), follicle
stimulating hormone (FSH) and estradiol- 17?. LH and FSH directly
stimulate ovary development while estradiol-17 stimulates
the formation of secondary sexual characteristics and processes
that support egg production.
Effect of Bonus feeding on carcass traits
Exposing broiler breeders to the Bonus feeding regimen increased
body weight, breast muscle weight, keel length, abdominal
fat pad weight, liver weight and fat content. Some of the
differences could be explained simply as additional growth.
Breast muscle, for example, weighed more on the Bonus diet,
but still represented the same proportion of body weight as
with the Control diet.
The most notable result with the carcass traits was that the
effects of feed allocation on these traits varied with time.
The Bonus feeding regimen generated the biggest increase in
carcass measurements during the 24 to 26 week of age study
period, representing 2 to 4 weeks after photo-stimulation.
The amount of fat present in blood plasma was one of the traits
most affected by feeding regimen during the 24 to 26 week
period. Blood fat concentration was rising to supply the ovary
with yolk material, but the process was accelerated by the
Bonus diet.
Monitoring the fat content of the liver, ovary and fatpad
was a more accurate and responsive indicator of nutritional
effects on sexual maturation than looking at the general fatness
of a bird. The specificity of some of these tissues for support
of reproductive function was suitable indicators of gross
changes in patterns of nutrient allocation.
An increase in ovary weight was due to the formation of more
large yellow follicles during the 24 to 26 week period. Furthermore,
once the ovary was developed enough to have large yellow follicles,
the Bonus feeding regimen consistently caused multiple follicle
sets to occur.
Liver fat content was influenced by feed regimen in all study
periods after photo- stimulation, making it one of the most
responsive indicators of changes in fat allocation due to
increased nutrient availability. Not only does the liver supply
fat and specific proteins for egg formation, but it also generates
fats destined for deposition in storage sites and for use
in metabolic processes.
Reproductive hormone response
Allocating the Bonus diet to breeder pullets prior to photo-stimulation
(18 to 22 weeks of age) caused the concentrations of LH, FSH
and estradiol-17 to increase compared to Control fed hens.
The most dramatic change in the concentration of these hormones
was observed during the 14 days of the 22 to 24 week study
period, which immediately followed photo-stimulation. This
response preceded the most sensitive study period for most
other parameters measured for both carcass and reproductive
parameters. The reproductive hormone concentrations peaked
during the 24 to 26 week period.
During the later study periods the use of Bonus feeding appeared
to have a negative effect on the plasma estradiol-17 concentration.
Once ovary formation was actively underway or completed, the
extra feed may have inadvertently increased the clearance
of steroids like estradiol-17 from the blood by stimulating
liver activity.
Peak sensitivity to overfeeding
Most of the traits examined in this study showed the greatest
change in response to the Bonus feeding regimen during the
24 to 26 week period. This coincides with the peak of reproductive
hormones during the same period. Once hormone levels decreased
to their mature concentrations, a bird's response to the Bonus
feeding treatment was less dramatic. In other words, the impact
of excess feed on the relationship between nutrition and reproduction
was less of a problem once a normal, mature feedback relationship
among the reproductive hormones and other messengers was established.
The most critical period of broiler breeder female management
appears to be 2 to 4 weeks following photo-stimulation. Overfeeding
birds immediately following photo-stimulation may have longer
term effects that were not identified within the 14 day treatments
of this research.
What does it all mean?
1. Feeding level can alter the
partitioning of nutrients between growth and reproductive
processes.
2. There are three distinct
phases in the reproductive life of the broiler breeder that
were relevant in this trial. First was the pre-photo-stimulation
phase, when the Bonus diet increased reproductive hormone
concentrations. This was followed by the sexual maturation
phase, which was characterized by a heightened sensitivity
to overfeeding. The final phase was the mature phase, when
most of the flock was in production and the Bonus feeding
did not alter reproductive development.
3. The broiler breeder female
is most sensitive to overfeeding 2 to 4 weeks following photo-stimulation.
Reproductive and metabolic pathways lack the maturity to withstand
the challenge of a sudden increase in nutrient intake.
Patent Title: A Novel Avian Astrovirus
Newly Discovered and Sequenced
Disease-Causing Virus of Turkeys
Technology Description:
Researchers have identified a never before described virus
that infects young turkeys, which has been causing problems
to Southeastern poult producers since the early 1990s. The
virus is associated with Poult Enteritis Mortality Syndrome
(PEMS), a highly infectious, transmissible disease of young
turkeys that causes severe diarrhea, stunted growth, and high
death rates in young flocks. PEMS is also associated with
lifelong changes to the turkey immune system leaving the birds
highly susceptible to other infectious agents. PEMS outbreaks
have cost the turkey industry millions of dollars in losses
annually. The researchers isolated this avian astrovirus?a
small RNA virus also associated with diarrhea outbreaks in
humans and other animals?from turkey poults infected with
PEMS. This information could be used to develop diagnostic
tests and vaccines for the emerging disease. This astrovirus
is very stable and resistant to disinfection, so this information
could also be used to develop kits to test for viral presence
in poultry houses that have been cleaned. Diagnostic and vaccine
companies could use this technology. The animal health industry
will also benefit from this information, as well as turkey
producers.
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