GENETIC STUDIES ON REPLACEMENT RATE AND FIRST LACTATION TRAITS IN HOLSTEIN FRIESIAN CATTLE AT HOLETA BULL DAM STATION, ETHIOPIA
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Date
2014-03
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Abstract
The study was conducted on 901 Holstein Friesian cows maintained at Holeta Bull Dam Station from
1976 to 2003 with the objectives of estimating demographic parameters, genetic of replacement rates
and first lactation traits. The lactation specific parameters viz. loss rate, survival rate, stayability,
expected herd life, female calf births and reproductive value at first lactation were estimated at
0.2619, 0.7381, 0.7373, 2.4573, 0.4808 and 1.0488, respectively. Overall lifetime parameter values
for mean lactations of cows present, mean lactations of cows lost, mean rate of loss per cow per
lactation, average life expectancy at birth, net reproductive rate and generation interval were
computed as 3.4949 lactations, 4.3548 lactations, 0.3204, 1.2825 lactations, 1.4984 female calves per
cow and 3.5451 years, respectively. The overall averages for abnormal and normal births, malefemale
sex ratios, mortality and culling rate in females up to age at first calving and female
replacement rates based on female births and total pregnancies were 12% and 88%, 52.5% and 47.5%,
23% and 7% and 70% and 29%, respectively. The effects of parity and year of calving on above traits
were found to be significant, except parity effects on culling rate and replacement rate based on total
pregnancies, which were non-significant. The season effects for all traits were non-significant. Sire
affected significantly the type of birth, calf loss, replacement rate and coefficient of gene replication.
About 1/3rd of cows calved only once and similar proportion of the cows experienced abnormal
calving during first lactation. The overall means for longevity, productive herd life, total calves,
female calves, selective values and coefficient of gene replication were 2864±63 days, 1638±58 days,
3.55±0.12, 1.68±0.07, 1.12±0.06 and 0.56±0.03. Cows calved at early age and low producers had
short herd life, less number of total and female calves. Heritability for abnormal birth, sex ratio,
mortality, culling, and replacement rate from total calves produced and total pregnancy were
0.16±0.009, 0.10±0.019, 0.18±0.029, 0.71±0.029, 0.00±00 and 0.66±0.029, respectively. The
repeatability for the above traits were 0.964±0.012, 0.038±0.017, 0.060±0.028, 0.0895±0.029,
0.780±0.019 and -0.2403±0.022, respectively. The heritability estimates for longevity, productive
herd life, total calves born, total normal calves born, total female calves born, coefficient of gene
replication and selective value were 0.31±0.085, 0.32±0.088, 0.11±0.018, 0.12±0.018, 0.10±0.019, -
0.08±0.029 and 0.66±0.029, respectively. The heritability for age at first calving (AFC), first service
period (FSP), first dry period (FDP), fist lactation period (FLP), 305 day milk (305DMY), first
lactation milk yield (FLMY) and first calving interval (FCI) were 0.53±0.116, 0.26±0.113,
0.24±0.1170, 0.23±0.102, 0.23±0.106, 0.28±0.124 and 0.28±0.141, respectively. The phenotypic
correlations of AFC with FLMY, 305DMY, FLP, FSP and FCL were very small. High phenotypic,
genetic and environmental correlations existed between FLMY and 305DMY. All correlations among
FSP, FDP and FCL were high and positive. Sire affected the additive genetic variances for abnormal
birth, mortality, culling and replacement rate and their frequency can be changed through selection of
the sire. Moreover, information on the genotype of semen must be available along with production.
Age at first calving had high heritability value and it can be included in the selection index. Further
research is required on identification of genetic abnormalities at embryonic and progeny level and the
effect of storage and deposition of semen on sex ratio.
Description
A Dissertation Submitted to the College of Veterinary Medicine and Agriculture of Addis
Ababa University in Fulfillment of the Requirements for the Degree of Doctor of
Philosophy in Animal Production
Keywords
Demography, first lactation traits, Holstein Friesian, replacement rate