|dc.description.abstract||In general farming practice in New Zealand maiden awes
are not mated at puberty but are carried forward unmated
under conditions more or less favourable to full growth and
development until the second breeding season after birth.
They thus bear their first lamb at an age of 2 years. Puberty
may occur at 9 or 10 months of age and although it is the
experience of many farmers that fertile matings can and do
occur at this age, their occurrence has been found too unreliable,
even if desirable, for adoption into general
practice. These observations result from unintentional
matings often occurring as late as June or July well after
the normal mating period. No accurate data exists in this
country as to the frequency of oestrus, level of fertility
and size and vitality of lambs born to immature sheep or of
their productivity in subsequent years. It is generally
held that the unreliability of conception and the penalty
which early pregnancy places on the growth and development of
the young animal in its first critical winter period make
the practice most unsound. Doubt is also expressed as to
the ability of the immature animal to rear the lamb adequately
and provide the milk necessary for its rapid growth.
Because full growth and development at the hogget
stage is considered necessary to lifetime productivity it was
decided to compare the performance in their first productive
year of normal well grown hoggets with those penalised from
weaning by a poor inadequate level of feeding. These
comparisons were expected to yield information on the following
(1) The effect of nutritional treatment on the
nature and time of onset of the breeding season.
(2) The influence of other environmental factors
common to both groups in determining the
characteristics of the breeding season.
(3) The regularity and pattern of oestrus after
(4) The effects of nutritional regime on stock health
(5) The effects of treatment on the number of viable
lambs born and the incidence of multiple births
within the groups.
Although not specifically designed to study influences other
than nutrition, the data gained has been used to support
considerations of a more fundamental nature in relation to
the initiation of sexual activity in seasonal breeding
Two such important aspects have been given consideration.
It is recognised that without careful design
reliable analyses of environmental conditions are difficult.
Under field conditions they interact freely and it is seldom
easy to gain critical information on one or the other without
creating some degree of artificiality or by imposing extremes
which are seldom found in the natural environment. This
defect can be noted in the nutritional regimes imposed.
Although the well grown hoggets received conditions comparable
with normal good management of the district, the poorly
fed group, were subjected to severe conditions seldom if
ever pertaining on this class of land. This was done to
accentuate the possible results of the treatment and to throw
into greater relief their response to subsequent management
after the conclusion of this part of the investigation.
Studies are being continued by Lincoln College with
these animals on the lifetime productivity of ewes harshly
reared in this apparently critical stage of development
to detect the degree of permanence, if any, of the initial
handicap and the resilience they display in responding to
|dc.publisher||Canterbury Agricultural College, University of New Zealand||en
|dc.title||A study of fertility in two-tooth ewes||en
|thesis.degree.grantor||University of New Zealand||en
|thesis.degree.name||Master of Agricultural Science||en
|lu.thesis.supervisor||Coop, I. E.||
|lu.contributor.unit||Department of Agricultural Sciences||en
|dc.rights.accessRights||Digital thesis can be viewed by current staff and students of Lincoln University only. Print copy available for reading in Lincoln University Library. May be available through inter-library loan.||en
|dc.subject.anzsrc||070206 Animal Reproduction||en