June, 1958] V. N. AMBLE, K. S. KRISENAN AND J. S. SRIVASTAVA 39
compares favourably with those reported for other herds in the country [42.4 months
for the Sindhi herd at Allahabad Agricultural Institute reported by Stonaker and
others 1953, 58.8±0.2 months for Hariana cattle at Hissar Farm reported by
Kohli and Suri 1957 and 47.4 months for Kankrej herd (I.C.A.R. unpublished
report)] though it is high when compared to herds in temperate regions or which
it varies from 27 to 30 months. [Turner 1932, Dickerson and Chapman 1940 and
Johansson and Hansson 1941.]
The interval between the first two calvings based on 261 cows varied from 317
days to 1,568 days with an average of 546±10 days. The average calving interval
over 794 records based on the first seven calvings worked out to 521±6 days. This
was of the same order for the Hariana cattle of Punjab, viz., 531 ±5 days reported
by Sharma and others 1951 but much longer than that for the Kankrej herd at
Anand which was 492 days.
The average age of the parents when the progeny is born is termed the generation
interval. The interval is obtained by first working out the average age of cows
separately when daughters are born and when sons are born. The average ages of
bulls for the progeny of the two sexes are worked out similarly and the mean of the
four average ages gives the average generation interval for the herd. The four
averages were of the same order and the mean generation interval worked out to six
years and two months.
The service conception ratio either for the cows or for the bulls could not be
worked out in the absence of data on infertile services. For the same reason the
number of services per year performed by the bulls also could not be worked out.
The average number of successful services worked out to eleven per bull per year.
This number is, however, likely to be an underestimate since these bulls were also
used to some extent on the other herds in the farm and on outside cows, details of
which are not available.
1.4—GENERATIONWISE COMPARISONS
The overall success of the policy relating to breeding and management can be
studied best by comparing the performance of cows belonging to successive genera-
tions. Such comparisons were made for the six main characters of interest, viz.,
the lactation yield, the yield per day of lactation, the yield per day of calving interval,
the lactation period, the calving interval and the age at first calving. Both overall
and daughter-dam comparisons were made for this purpose.
4.1—Overall comparisons
In order to minimise the influence of culling after successive lactations on the
comparisons and with a view to utilising the largest possible number of records, data
pertaining to the first lactation were taken for analysis for the farm-bred cows.
For the foundation cows, for most of which such records were not available, the
first complete lactation records made on the farm were taken and converted to the
first lactation basis using correction factors obtained by Sander's method
[Section 3.3.1]. The order of lactation was determined approximately on the basis
of age. Records of lactations known to be abnormal due to specific causes such as
stillbirth, etc. numbering 15 in all, were excluded from the analysis.