|dc.description.abstract||Two studies using the Booroola Merino crossbred animals were
conducted. In the first, the flock mating performance of Booroola
Merino-Romney crossbred ram lambs mated to Perendale ewes was
examined. The second study comprised observations on the incidence
of foot "conditions" in young Booroola Merino crossbreds and Perendale
sheep grazed on hill country.
Eighteen Booroola Merino x Romney ram lam's (6 control, 12 mating
group) were selected according to weaning weight, fleece characteristics
and general body condition. Nine ram lambs were exposed to
ewes prior to mating for two weeks (trained) and nine kept separate
from any ewes (untrained). The ram lambs of the mating group (6
trained, 6 untrained) were allocated to six groups of ewes which were
"single-sire" mated. Groups 1, 2, 3, 4 comprised 140 ewes each and
Groups 5 and 6 comprised 100 e'\.;res each. The ram lambs were changed
after eight, eight, seven and seven days of mating, Periods P1, P2,
P3 and P4 respectively, and a total of 12 "single-sire" mating groups
generated. All ram lambs produced a satisfactory semen sample before
joining with the flocks. Mating commenced on 30 March 1981.
The flock mating performance of each ram lamb was assessed by
recording the percentage of ewes raddled, percentage of ewes returning
to service, percentage of pregnant ewes, percentage of ewes
lambing, docking rate and weaning rate. Differences among each of
these parameters were attributed to various factors. Trained and untrained ram lambs were similar in most of the observed parameters of
flock mating performance. There were no differences between individual
ram lambs within each sire-group (trained or untrained) in
mating performance. There were differences in the percentage of
ewes raddled between first and second oestrous cycle of mating.
Live weights of the ram lambs were measured from weaning
(December 1980) until the end of the trial (December 1981), at weekly
intervals during the mating periods and at monthly intervals during
the post-mating and post-shearing periods. There was little loss
in the mean live weight of the mating group ram lambs after P1.
Overall the live weights of both groups increased consistently
throughout the trial.
Semen samples (collected by electro-ejaculation) from the ram
lambs of the mating group were microscopically examined for general
motility after each mating period at least for three days. Recovery
from mating exhaustion occurred four and six days after P1 and Pz
respectively, while three and two days were required after P3 and P4
Semen samples were also collected on two occasions from the
rams (only 15) as two-tooths and examined for general motility, sperm
concentration and percentage of live sperm. There were no differences
in semen characteristics between rams of the mated and control groups.
The two-tooth rams were also subjected individually and randomly
on three occasions to pen-libido tests, each with two oestrous ewes.
Mating ability was assessed by recording the number of mounts
attempted on the oestrous ewes, the number of services, the reaction
time to mount (in seconds) and the reaction time to service. There
were no differences between the mating and control groups in the
number of mounts and number of services performed on each occasion
of the libido test. Significant differences were found between both
groups in reaction time to mount and in reaction time to
service but only at the first libido test.
It was concluded that the Booroola Merino x Romney ram lambs
had achieved satisfactory levels of flock mating performance under
the conditions of the trial. No adverse effects of mating on the
post-mating body development of the ram lamb could be detected.
Semen quality from the ram lambs deteriorated during mating but
recovered shortly after mating. The use of ram lambs as sires had
no adverse effects on their semen characteristics and libido performance
at the two-tooth age.
The incidence of abnormal foot shape, foot scald and footrot was
observed in Perendale and Booroola Merino crossbreds. The animals
were generated in 1980 and 1981. Observations on foot "conditions"
were made at the lamb, hogget and two-tooth ages for animals born in
1980, and at the lamb and hogget ages for those born in 1981. A
scoring system was used to rank the various foot "conditions" (shape;
scald; footrot) which were assessed separately. Booroola Merino crossbreds showed significantly a higher incidence of abnormal foot shape, foot scald and footrot than did
Perendale sheep. Significant differences in foot "conditions" were
also found between (Booroola x Romney) x Perendale and Booroola x
Romney sheep. Sires of the progeny generated in 1980 and 1981
provided a major source for the variation in the incidence of these
Estimates of heritability of each of the observed foot
"conditions" were calculated at different ages (lamb, hogget and
Sex of the lamb caused significant effects on the incidence of
abnormal foot shape and foot scald between ram
lambs and ewe lambs, but not on the incidence of footrot.
Differences in the incidence of abnormal foot shape and foot
scald occurred between 1980- and 1981-born sheep. These differences
were attributed partly to the particular climatic conditions in each
year (notably the annual rainfall).
It was concluded that under environmental conditions similar to
that of the present trial, long-term selection programmes could be
applied to enhance the natural resistance of sheep against foot