An investigation of factors influencing rate of lay, egg weight and embryonic growth in broiler breeder hens.
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Date
1998
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Abstract
The laying performance of broiler breeder hens is characteristically poor. Of
the eggs that are produced, a large proportion are rejected before setting because they
are either too small or excessively big, and of the eggs that are set, hatchability rates
are often low, depending on the age of the hen. Since so much is still unknown about
broiler breeders, many avenues of research would be fruitful. In this study, four
disparate aspects were investigated as a means of improving the number of hatchable
eggs per hen.
The effect of linoleic acid intake on egg weight of broiler breeders and laying
hens was compared. Analysis of both published and experimental data revealed that
egg weight was influenced significantly by this fatty acid. Breeder egg production was
affected concomitantly. Increasing linoleic acid intake of young hens would increase
early egg size and the number of eggs set, while decreasing the linoleic acid intake of
ageing breeders would decrease egg size and production.
The influence of 20 week body weight and nutrient intake on early laying
performance of 360 broiler breeders was determined. The excellent performance
achieved was independent of 20 week body weight. Laying performance and weight
gain increased as food allocation and nutrient density increased. A comparison of
theoretical and recommended nutrient intakes revealed that hens are overfed pre-peak
and that energy intakes should not decline post-peak as is recommended.
The investigation into the effect of breeder age (egg size) on embryonic and
chick growth revealed that exponential embryonic growth was restricted within small
eggs due to a lower yolk supply, rate of yolk absorption, and water loss. Chicks from
small eggs were light, and grew relatively slowly. However, during times of chick
shortage, small eggs could be used successfully if managed correctly.
In the fourth experiment in this series, the response of laying hens to dietary
tryptophan was measured successfully, but the objective of comparing this response
with that of broiler breeders failed. As a result of overestimating the tryptophan
requirement of breeders, the coefficients of response could not be estimated. It was
concluded that an additional breeder tryptophan trial should be conducted.
Description
Thesis (M.Sc.Agric.)-University of Natal, Pietermaritzburg, 1998.
Keywords
Broilers (Chickens)--Nutrition., Poultry--Feeding and feeds., Linoleic acid., Tryptophan., Eggs--Hatchability., Theses--Animal and poultry science.