| dc.description.abstract | Records of the Kenya Sahiwal Stud were analysed
with regard to factors affecting reproductive traits
and milk yield in temales born in the period 1963
through 1983. Genetic parameters and the relationship
among the traits were studied.
Two data sets were analysed: one with 2238 heifer
records, and the other with 3518 heifer and cow
records. The overall means and standard deviations
were 881.1~107.7 days for age at first service,
930.3~130.5 days for age at conception, 1218.0~130.7
days tor age at first calving, 2.7~1.7 number of
services per conception, 49.6~85.0 days for
insemination period, 287.6~7.5 days for gestation
length, 1145~523 kg for 305-day milk yield. For the
combined data set, corresponding values were 2.1~1.6
for number of services per conception, 50.2~89.7 days
for insemination period 287.7~7.7 days for gestation
length, and 1287.8~565.9 kg for 305-day milk yield.
Heritability estimates were O.25~O.06 for age at
tirst service, O.15~O.05 for age at conception and
O.29~O.06 for age at calving, O.08~O.05 tor number of
services per conception, O.12~O.05 for insemination
period, O.08~O.05 for gestation length, and O.35~O.07
tor milk yield in the heiter data set. The
corresponding values for the combined data set were
O.02~O.03 for number of services per conception,
O.05~O.03 for insemination period, O.07~O.03 for
gestation length and 0.36~0.06 for 305-day milk yield.
Genetic correlations among the reproductive
characters examined ranged from -0.1 to 0.9, with the
high values among the ages at first service, at
conception and at calving. Corresponding phenotypic
and environmental correlations were also high, ranging
from 0.7 to 0.9 among the ages at first service, at
conception and at calving, but relatively low
(within a range of -0.03 to 0.6) among the other
traits. Favourable, negative genetic correlations were
reported between 305-day milk yield and reproductive
performance characters (-0.12 to -0.02) except
gestation length which had positive genetic correlation
with milk yield. The phenotypic and environmental
relationship between milk production and reproductive
traits were low but positive in the two data sets.
It was concluded from this study that the
reproductive characters could be improved by
environmental improvement as selection for such traits
would be unrealistic due to their low heritability
estimates. However, selection for milk yield should be
continued at the stud since no antagonism was observed
in the relationship between milk yield and the
reproductive traits. | en |
