MVSc

The present study was undertaken with a VIew of
estimating body weights of crossbred calves in the field conditions
of Kerala at birth, three, six and twelve months of age and to find
association of these body weights with age at first calving and first
lactation milk yield.
The data for the present study were taken from the
records of ICAR Field Progeny Testing Scheme of Centre for
Advanced Studies in Animal Genetics and Breeding, Kerala
Agricultural University. The data were of the 1993-2000 period.
Body weights at birth, 3, 6, 12 months and at calving were predicted
from body measurements using Minnesota formula given by
J ohnson,( 1940).
The data were analyzed using least squares analysis of
variance to study the effects of non-genetic factors on different traits
under study. The data adjusted for significant non-genetic factors
..
were used to study the effect of sire and for estimating heritability
and correlation among body weights and between body weights and

age at first calving and between body weights and first lactation
milk yield.
The overall average body weights of crossbred calves at
birth, 3,6 and 12 months of age were 26.0 ± 0.38 kg, 48.7 ± 1.26 kg,
74.1 ± 2.81 kg and 151.0 ± 7.74 kg, respectively.
Least squares analysis of variance has shown that the
effect of season of birth was significant (P~0.05) only on body
weight at six months of age. The influence of period of birth was
significant for all body weights upto one year age except for body
weight at six months of age. Centre was a significant source of
variation for all body weights upto one year age,
The mean Age at First Insemination, Age at first
calving and Weight at first calving of crossbred cattle were
689.3 ± 22.9 days, 1013.6 ± 21.74 days and 284.9 ± 7.71 kg
respectively.
The season of birth did not affect age at first
insemination, age at first calving and weight at first calving. The
significant (P~0.05) influence of period of birth and centre were
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observed on age at first insemination and age at first calving only
but not on weight at first calving.
The effect of period of calving and centre on first
lactation milk yield was significant whereas the effect of season of
calving and age at first calving did not affect first lactation milk
yield. The average first lactation milk yield of crossbred cows was
1958.5 ± 30.74 litres.
The sire wise means of body weight at six months of
age, weight at first calving and first lactation milk yield did not
differ significantly but sire effect was significant (P~0.05) in all the
other traits.
Heritability estimates were calculated by paternal half
sib method for different traits under study. The low heritability
estimate was obtained for birth weight, body weight at six months of
age, age at first calving and weight at first calving. But the
heritability estimates of body weight at three months of age and
body weight at twelve months of age were high. Age at first
insemination was moderately heritable. The heritability estimate of
first lactation milk yield was -0.069 ± 0.05.
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Association among body weights and that between body
weights and age at first calving followed no definite trend. However,
the genetic correlation (0.46) between body weight at six months
and first lactation milk yield and high, positive (> 1) genetic
correlation between body weight at twelve months and first lactation
milk yield indicates strong genetic association of body weight at six
months and body weight at twelve months with first lactation milk
yield and their relationship can be used advantageously for selection
of heifers for milk production under field conditions.