Abstract
( 1 ). !n this thesis the relationship between eggshell quality
and bone biology was examined over the laying life of two
strains of hen; a highly selected commercial line and the
relatively unselected J.Line.
(2). The efficiency of using osteocalcin as a marker of osteoid
formation, in collaboration with established markers of bone
mineralisation and bone resorption, during eggshell
calcification was ratified.
(3). It was established that magnesium is actively removed from
bone hydroxyapatite during resorption and transported to
the shell gland pouch for incorporation into the palisade
layer of the eggshell.
(4). A relationship was demonstrated between hatched eggshell
quality and the bone biology of newly hatched chicks.
(5). The association between high egg output and poor bone
structure was evident in the commercial laying strain hen.
No such deficit in skeletal quality occurred in the relatively
unselected J.Line.
(6). The commercial line demonstrated a significantly higher rate
of bone remodelling at late lay concomitant with
osteoporosis.
(7). The unselected J.Line demonstrated significantly higher
rates of bone remodelling throughout lay. It was
hypothesised that this was due to a greater propensity for
bone upkeep during the inter-egg interval.
(8). The provision of a prelay diet influenced neither bone
volume nor mineral composition at the beginning of lay.
(9). The feeding of a prelay diet led to a longer period of
sustained high production and an earlier increase in egg
weight. This was accompanied by a delay in the increase in
osteoid formation and decreased levels of blood ionised
calcium. This led to high “on farm ” seconds at late lay due
to abnormally high fracture toughness and the incidence of
type B’s within the mammillary layer.
(10). The reason for the observed decrease in hatchability
associated with poorly pigmented eggshells in a commercial
guinea fowl flock was related to premature expulsion of the
egg. These thinner shelled eggs may have resulted from the
process of artificial insemination.
