Factors influencing breast meat yield in broilers.
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Date
2012
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Abstract
The increased demand for breast meat of broiler chickens has challenged researchers to
investigate management techniques that could be used to increase the production of this
valuable commodity. Two experiments were conducted in this study; the first investigated the
effect of early feeding of newly hatched broilers on breast meat yield (BMY) at market
weight, and the second focused on improving BMY of broilers exposed to short daylengths
by feeding higher than conventional levels of dietary protein. In the first experiment, of the
528 eggs set in the incubator, half were placed, at day 18, in hatching trays containing a
commercial broiler starter feed whilst the others (the held group) were hatched
conventionally. Six chicks from both fed and held groups were sampled at nine-hour intervals
from the time that the first chicks hatched for a subsequent period of 36 h. After measuring
their body weight these chicks were euthanised and dissected in order to measure their breast
and yolk weights. Body protein, lipid and water contents were measured on each chick. At
day 21, six birds from the fed and held groups were sampled, and body weight, breast weight
and body protein content were measured. The yolk sac weight for fed birds was significantly
reduced compared to that of held birds (P < 0.001). Both fed and held birds had the same
breast weight at hatch, but at day 21 the mean breast weight of the fed birds was significantly
heavier than of held birds (P < 0.05). The birds that were removed first from the hatcher had a
reduced breast muscle weight compared to those that were removed last. In the second
experiment, a total of 3200 day-old broiler chicks were reared in eight light-tight rooms. Four
lighting regimens (12L: 12D, 16L: 8D, 20L: 4D and 24L: 0D) were randomised between
rooms, with each light treatment being replicated twice. Each room was divided into four
pens and 100 chicks in each pen received one of four dietary protein treatments. At day 35,
three birds from each pen were sacrificed so that measurements could be made of breast,
thigh, drum and wing weight, and carcass chemical composition. Breast weight increased as
daylengths increased except in birds that were fed low protein diet (143 g protein/kg feed).
High levels of dietary protein increased breast weight in birds on all other daylengths except
for those on 12 h which showed a reduced breast muscle weight when dietary protein content
was increased. The results of the first trial suggests that breast meat yield could be improved
if newly hatched chicks are offered feed immediately after hatch, however the hypothesis that
this increment was due to an overall increase in body protein content in the first few days
after hatching could not be corroborated. The results further showed that held birds do not
withdraw nutrients from breast muscle to maintain growth at hatch, this is because birds that
stayed longer in the hatchery without feed showed increased breast muscle weight compared
to those that were removed first. The second trial could not identify a suitable feeding
programme to overcome the problem of a lower breast muscle weight that results from the
use of 12 h of lighting compared to that when long daylengths are used. Highest breast
weight was obtained when birds were fed high protein diet at 20 h. More research is required to further investigate the combined effect of early feeding and daylength on breast meat yield in broiler chickens.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2012.
Keywords
Broilers (Chickens)--Feeding and feeds., Broilers (Chickens)--Growth., Poultry--Feeding and feeds., Poultry--Feed utilization efficiency., Poultry products., Poultry--Growth., Proteins in animal nutrition., Theses--Animal and poultry science.