NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
June, 1958 ] V. N. AMBLE, K. S. KRISHNAN AND J. S. SRIVASTAVA 63
2.5.2—Sire indices
The corrected daughter average sire indices based on first lactation records in
respect of the four characters studied are given along with their standard errors in
Table XX. The indices were worked out on the basis of herd averages of 2,700 lb.
for lactation yield, 270 days for lactation period, 10 lb. for yield per day of lactation
and 7 lb. for yield per day of calving interval.
The following conclusions may be drawn from a perusal of Table XX.
(i) Victory should be considered as the most meritorious bull having an index
of 3,823 lb. for lactation yield, 13.1 lb. per day of lactation and 9.2 lb. per day of
calving interval. These indices were all significantly higher than the herd averages,
the increase being of the order of 42 per cent, 31 per cent and 31 per cent respectively
for the lactation yield, the yield per day of lactation and the yield per day of calving
interval.
(ii) Unique should be considered as the second best with indices of 3,312 lb.,
11.9 lb. and 8.2 lb. respectively for the lactation yield, the yield per day of lactation
and the yield per day of calving interval. The index in respect of the lactation
yield was in excess of the herd average by more than 20 per cent while the indices
for the yield per day of lactation and the yield per day of calving interval were more
than the respective herd averages by 19 per cent and 17 per cent respectively.
(iii) Hosur Raj should be considered as having the lowest transmitting ability
for milk production. Its indices for milk production were 1,797 lb. forlactation yield,
7.5 lb. for yield per day of lactation and 5.1 lb. for yield per day of calving interval
which are about 33 per cent, 25 per cent and 27 per cent lower than the respective
herd averages.
(iv) The sire index for lactation period was the highest for Xavier and lowest
for Hosur Raj. Both these were more than 20 per cent higher and lower respectively
than the herd average of 270 days ; but the differences from the herd average were
not significant.
On the basis of the indices for lactation yield the 12 bulls used can be grouped
as follows:
(1) Highly meritorious (indices 20 per cent or
more above the herd average)
(2) Moderately good (indices between 10 per cent
and 20 per cent above the herd average)
(3) Of average calibre (indices within 10 per cent
on either side of the herd average)
(4) Poor indices between 10 per cent and 20 per
cent (below the herd average)
(5) Very poor (indices 20 per cent or more below
the herd average)
Victory, Unique
Warrior, Tazman, Xavier
Hosur Gulam, Sulaiman
Ziman, Erab, Erio
Sikandar
Hosur Raj
64
STATISTICAL STUDIES ON BREEDING DATA [Vol. XXVIII, Part II,
TABLE XX
Sire indices of Sindhi bulls at Bangalore
Serial
No.
1
1
2
3
4
5
6
7
8
9
10
11
12
Bull's name
2
Victory
Unique
Warrior
Tazman
Xavier
H. Gulam
Sulaiman
Ziman
Erab
Erio
Sikandar
H. Raj
Daughter-
dam pairs
3
6
18
7
10
9
12
10
19
19
13
9
7
Herd average to
which
indices
correspond.
Lactation yield (lb.)
Average
for dams
4
2,679
2,541
3,807
2,898
2,479
2,131
3,282
2,930
3,363
4,117
2,542
2,773
Corrected
daughter average
Index
5
3,823
3,312
3,163
3,160
3,104
2,798
2,735
2,587
2,577
2,519
2,425
1,797
S.E.
6
236
324
462
242
628
362
452
279
302
424
492
525
2,700
Yld./day of lact. (lb.)
Average
for
dams
7
9.67
8.52
12.14
10.51
9.27
8.23
10.64
10.59
11.17
13.10
10.19
9.27
Corrected
daughter average
Index
8
13.14
11.88
10.91
10.51
9.10
9.75
9.60
8.97
9.13
8.57
8.72
7.50
S.E.
9
1.28
0.71
1.19
0.99
1.05
0.91
0.99
0.70
0.71
0.87
1.05
1.19
10
Yld. day of calling interval
(lb.)
Average
for
dams
10
5.56
5.33
9.02
6.79
5.96
4.93
7.30
7.04
7.70
9.29
6.62
5.65
Corrected
daughter average
Index
11
9.17
8.20
7.21
7.84
7.10
6.48
6.74
5.79
6.05
6.10
6.20
5.12
S.E.
12
1.39
0.30
1.27
1.10
1.04
0.94
0.98
0.76
0.71
0.90
1.10
1.27
7
Lactation period (days)
Average
for
dams
13
257
258
299
269
238
226
292
255
295
304
217
281
Corrected
daughter average
Index
14
297
296
291
302
329
282
267
277
276
258
242
203
S.E.
15
8
18
21
21
45
25
32
21
16
30
30
53
270
66
STATISTICAL STUDIES ON BREEDING DATA [Vol. XXVIII, Part II,
TABLE XXI
Repeatability estimates for milk characters for Red Sindhi herds at Hosur and Bangalore
Character
Lactation yield
Yield/day of lactation
Yield/day of calving interval
Lactation period
Calving interval
Sindhi herd at Hosur
Degrees of freedom
Between
animals
304
304
274
304
274
Within
animals
617
617
517
617
517
Repeat-
ability
.61
.60
.47
.33
.21
95 per cent
confidence
limit
.56 to .67
.54 to .66
.39 to .54
.26 to .40
.13 to .28
Sindhi herd at Bangalore
Degrees of freedom
Between
animals
269
269
243
269
243
Within
animals
689
689
609
689
609
Repeat-
ability
.54
.43
.40
.46
.08
95 per cent
confidence
limit
.38 to .67
.36 to .50
.33 to .47
.30 to .61
.00 to .22
June, 1958] V. N. AMBLE, K. S. KRISHNAN AND J. S. SRIVASTAVA 67
TABLE XXII
Heritability estimates for milk characters for Red Sindhi herds at Hosur and Bangalore
Character
Lactation yield
Yield/day of Lactation
Yield/day of calving interval
Lactation period
Calving interval
Age at first calving
Sindhi herd at Hosur
Intrasire
degree of
freedom
182
182
155
182
155
192
Heritability
.34
.20
.20
.04
—.08
—.09
S.E.
.18
.20
.21
.22
.20
.17
Sindhi herd at Bangalore
Intrasire
degree of
freedom
143
143
125
143
125
134
Heritability
.37**
.54**
.38*
.33*
.13
.16
S.E.
.14
.14
.15
.16
.20
.29
The standard errors of the coefficients were generally high indicating that the
extent of data available is not quite adequate to get precise estimates of the herit-
ability coefficients.
For the Hosur herd the heritability was the highest for the total lactation yield,
being 0.34±0.18. The estimate of heritability for this character in the Bangalore
herd was also of the same order (0.37±0.14). The results indicated that about one-
third of the total variation in the lactation yield of different cows is attributable to
differences in their genetic makeup.
The estimates of heritability of the yield per day of lactation and the yield per
day of calving interval for the Hosur herd were lower than that for the lactation
yield ; but the corresponding estimates of these characters for the Bangalore herd
were higher than that for the lactation yield.
Difference between the two herds was also observed in respect of the lactation
period. The component of variation in this character ascribable to genetic causes
was less than 5 per cent for the Hosur herd while it was as high as 33 per cent for
the Bangalore herd.
Of the six characters studied, calving interval and age at first calving were the
least heritable in both the herds. The heritability estimates for both the characters
were not significantly different from zero for the two herds. It would appear that
the variation present among the cows in respect of these two characters was to be
ascribed mostly to environmental and possibly to non-additive genetic causes.
3.3—NON-HERITABLE VARIATIONS
The non-heritable component of the total variation includes the order of lacta-
tion which is a physiological factor and a number of environmental factors connected
with management such as season of calving, service period, dry period preceding
the lactation, number of milkings per day, level and standard of feeding, condition
Plate
I.]
[Indian J. vet. Sci.
HERD AT HOSUR
HERD AT BANGALORE
Performance of Red Sindhi cows in later lactations as percentage of
the first.
June, 1958] V. N. AMBLE, K. S. KRISHNAN AND J. S. SRIVASTAVA 69
TABLE XXIII
Lactation correction factors for Sindhi herds at Hosur and Bangalore
Lactation order
Sindhi herd at Hosur
Pairs of
records
Later record
as per cent of
the first
Factors for
converting
to first
lactation
basis
Sindhi herd at Bangalore
pairs of
records
Later records
as per cent of
the first
Factors for
converting
to first
lactation
basis
Lactation yield
I
II
III
IV
V
VI
VII
VIII
..
206
141
101
75
55
36
21
100.0
105.5
107.6
107.0
104.6
101.0
97.1
91.1
1.000
0.948
0.930
0.935
0.957
0.990
1.030
1.098
..
214
179
135
92
61
42
28
100.0
107.0
110.7
111.2
108.5
102.6
93.5
81.2
1.000
0.935
0.903
0.899
0.922
0.975
1.070
1.231
Yield/day of lactation
I
II
III
IV
V
VI
VII
VIII
..
206
141
101
75
55
36
21
100.0
111.0
115.5
115.1
111.7
106.7
102.0
99.1
1.000
0.901
0.866
0.868
0.895
0.936
1.020
1.009
..
214
179
135
92
61
42
28
100.0
108.5
114.2
117.2
117.5
114.9
109.8
101.8
1.000
0.922
0.876
0.853
0.851
0.869
0.911
0.982
Yield/day of calving interval
I
II
III
IV
V
VI
VII
VIII
..
173
122
85
61
45
28
15
100.0
115.5
121.6
120.9
115.7
108.6
02.1
98.6
1.000
0.866
0.822
0.828
0.864
0.921
0.980
1.015
..
196
155
119
82
53
35
28
100.0
110.3
116.3
118.2
115.8
109.3
98.5
83.5
1.000
0.907
0.860
0.846
0.863
0.915
1.015
1.197
70
STATISTICAL STUDIES ON BREEDING DATA [Vol. XXVIII, Part II,
TABLE XXIII—contd.
Lactation correction factors for Sindhi herds at Hosur and Bangalore
Lactation order
Sindhi herd at Hosur
Pairs of
records
Later record
as per cent of
the first
Factors for
converting
to first
lactation
basis
Sindhi herd at Bangalore
Pairs of
records
Later records
as per cent of
the first
Factors for
converting
to first
lactation
basis
Lactation period
I
II
III
IV
V
VI
VII
VIII
..
206
141
101
75
55
36
21
100.0
98.0
96.0
93.9
91.9
89.9
87.9
85.9
1.000
1.020
1.042
1.064
1.088
1.112
1.137
1.164
..
214
179
135
92
61
42
28
100.0
99.5
98.3
96.7
94.6
91.9
88.8
85.1
1.000
1.006
1.017
1.034
1.057
1.088
1.126
1.175
Calving interval
I
II
III
IV
V
VI
VII
VIII
..
173
122
85
61
45
28
15
100.0
96.9
97.4
100.8
103.9
107.7
110.1
109.8
1.000
1.032
1.027
0.992
0.962
0.928
0.908
0.911
..
196
155
119
82
53
35
28
100.0
98.4
100.6
102.3
101.3
98.0
94.3
94.8
1.000
1.018
0.996
0.979
0.988
1.022
1.063
1.057
of lactation and the yield per day of calving interval were respectively 11 per cent,
18 per cent and 18 per cent above the performance in the first lactation. The
performance in the eighth lactation was less than that of the first lactation by about
19 per cent for lactation yield and 16 per cent for the yield per day of calving in-
terval. Yield per day of lactation in the eighth lactation was more than that in the
first lactation by 2 per cent.
June, 1958] V. N. AMBLE, K. S. KRISHNAN AND J. S. SRIVASTAVA 71
The average lactation period for both herds continuously decreased from the
first to the eighth lactation. The average lactation period for the eighth lactation
was less than that in the first lactation by about 14 per cent and 15 per cent for the
Hosur and the Bangalore herds respectively.
The calving interval for the Hosur herd decreased by about 3 per cent from the
first to the second lactation, remained almost stationary from the second to the
third and then continuously increased up to the seventh lactation. The average
calving interval for the seventh lactation was about 10 per cent longer than that for
the first. The average calving interval for the eighth lactation was almost of the
same order as for the seventh.
The calving interval for the Bangalore herd showed very little variation from
the first to the fifth lactation, the peak in the fourth lactation being only two per
cent higher than that in the first. From the fourth lactation there was a steady
decrease, the calving interval in the eighth lactation being about 5 per cent below
the interval between the first and second calving.
Lactation correction factors for converting later records up to the eighth to the
first lactation basis were also worked out for all the characters and these are given
in Table XXIII. The record for any later lactation may be converted to the first lac-
tation basis on multiplying it by the correction factor corresponding to that lactation.
Correction factors for ninth and later records could not be worked out as the number
of such records was small. Conversion to the first lactation basis was preferred to
any other since the number of first records is likely to be larger and such records
are influenced to the least extent by selection.
One shortcoming of the lactation correction factors worked out above is that
a series of extrapolations are involved in their calculations. Hence the precision of
the factors decreases with the advancing order of lactation because of the dependence
of the later factors upon the earlier ones. The precision of the correction factors for
the later records also decreases due to smaller numbers of successive records. It
is, therefore, advisable to avoid the use of these correction factors as far as possible
by making comparisons on like lactations, notwithstanding the small loss of informa
tion involved. Two situations in which this may not be possible and lactation
correction factors are of value are : (i) comparisons involving foundation cows whose
early records are not available and (ii) estimation of repeatability of the different
characters. Lactation correction factors were made use of in both these situations
dealt with in earlier sections. Use of lactation correction factors is also necessary
in cases where the exclusion of later records would introduce bias in the estimates,
as for example the estimation of genetic advance.
72
STATISTICAL STUDIES ON BREEDING DATA [Vol. XXVIII, Part II,
3.3.2—Preceding dry period
Two way frequency distributions of the second lactation yield and the preced-
ing dry period were prepared (Table XXIV) in order to study the influence of the
length of the dry period on the milk yield in the subsequent lactation. These did not
show any material association between the two characters in either of the herds.
3.3.3-—Service period
Service period was yet another factor whose influence on the milk production
was studied. For this purpose the records having lactation period shorter than
service period were omitted as services after the completion of a lactation could
not influence the yield in that lactation. The number of such records omitted was
only 10 per cent for the Hosur herd while it was as high as 29 per cent for the Banga-
lore herd. The higher percentage of omissions in the latter case was on account
of the larger number of cows with short lactation lengths and could not be ascribed
to delayed services since the calving interval in the latter herd was actually smaller
than that in the former.
From Table XXV it may be seen that the influence of service period on lacta-
tion yield is not substantial, except for the fact that the service periods of the low
yielders, i.e., those giving less than 1,600 lb. of milk in their first lactation were in-
variably under seven months. A possible explanation for this feature is the removal
from the herd of low yielders which did not come into heat early.
3.3.4—Age at first calving
The frequency distribution of first lactation records according to age at first
calving was obtained for each herd separately and is given in Table XXVI along
with the average lactation yield for each age group.
Analysis of the yields into between and within age groups (Table XXVII) indi-
cated significant effect of the age at first calving on first lactation in the case of the
Hosur herd, but no material effect was noticed in the case of Bangalore herd. An
examination of the average yields for the different age groups for the Hosur herd
indicated that the average yields were lower for the groups of cows whose age at
first calving was lower than 32 months or higher than 52 months.
3.3.5—Season of calving
Season of calving is one of the possible non-heritable causes influencing milk pro-
duction. It would, therefore, be of interest to examine whether there was a change
in the distribution of calvings in the different months of the year from generation
to generation, and to what extent calvings in different months of the year affected
milk production. For this purpose frequency distributions of calvings in different
calendar months of the year were obtained from the 1,294 calvings of cows belonging
to the six farm-bred generations in the Hosur herd and the 961 calvings of cows
belonging to the four farm-bred generations in the Bangalore herd (Table XXVIII).
Analysis of data from these distributions indicated that the proportion of calvings
in different months was of the same order for all the generations in either herd
June, 1958] V. N. AMBLE, K. S. KRISHNAN AND J. S. SRIVASTAVA 73
TABLE XXIV
Distribution of second lactation yield and preceding dry period for Red Sindhi herds at Hosur and Bangalore
Lactation yield (lb.)
6,401 and above
6,001—6,400
5,601—6,000
5,201—5,600
4,801—5,200
4,401—4,800
4,001—4,400
3,601—4,000
3,201—3,600
2,801—3,200
2,401—2,800
2,001—2,400
1,601—2,000
1,201—1,600
801—1,200
401— 800
400 and under
TOTAL
SINDHI HERD AT HOSUR
Preceding dry period (months)
Upto 1
1
1
1
3
Over Upto
1 — 2
2
1
3
2
1
2
11
2 — 3
1
1
1
1
2
2
3
3
2
16
3 — 4
2
1
1
2
1
2
1
2
4
16
4 — 5
2
1
1
2
8
2
1
1
5
1
1
25
5 — 6
2
1
1
1
3
2
3
3
1
1
18
6 — 7
2
1
5
2
2
2
2
2
1
1
1
21
7 — 8
1
1
4
3
1
2
1
13
8 — 9
1
2
2
1
2
1
3
1
1
14
9 — 10
1
1
1
1
2
1
2
3
2
1
15
Above 10
3
3
4
4
5
4
3
4
11
5
3
1
2
1
1
1
35
Total
15
4
9
10
13
29
19
16
23
23
17
15
4
5
1
3
1
207
SINDHI HERD AT BANGALORE
Preceding dry period (months)
Upto 1
1
1
3
2
8
Over Upto
1 —
1
3
3
1
3
3
2
16
2 — 3
1
1
3
1
1
5
3
6
3
3
1
1
29
3 — 4
2
2
1
1
3
3
2
1
8
1
4
1
1
1
31
4 — 5
1
1
3
5
6
3
3
3
2
2
3
32
5 — 6
1
1
1
3
3
4
1
3
2
1
20
6 — 7
1
1
2
1
1
2
2
2
2
14
7 — 8
2
2
1
3
2
2
4
1
1
2
20
8 — 9
1
1
1
1
1
2
1
1
3
1
13
9 — 10
1
1
2
2
2
3
1
1
2
1
16
Above 10
1
1
2
2
3
4
6
4
2
4
1
5
2
37
Total
3
1
7
5
6
10
15
26
22
36
26
27
19
7
12
10
4
236
1 AR/58
6
74
STATISTICAL STUDIES ON BREEDING DATA [Vol. XXVIII, Part II,
TABLE XXV
Distribution of first lactation yield and service period for Red Sindhi herd at Hosur and Bangalore
Lactation yield (lb.)
6,401 and above
6,001—6,400
5,601—6,000
5,201—5,000
4,801—5,200
4,401—4,800
4,001—4,400
3,601—4,000
3,201—3,600
2,801—3,200
2,401—2,800
2,001—2,400
1,601—2,000
1,201—1,600
801—1,200
401— 800
400 and under
Total
SINDHI HERD AT HOSUR
Service period (months)
Upto 1
Over Upto
1 — 2
1
1
2
4
2 — 3
1
3
1
3
2
3
2
1
2
1
19
3 — 4
1
2
2
3
2
1
4
3
1
1
20
4 — 5
1
1
1
1
1
5
2
2
2
1
2
19
5 — 6
1
3
3
1
5
3
2
5
2
2
1
1
29
6 — 7
1
1
2
1
3
2
4
3
1
1
1
20
7 — 8
1
1
1
4
3
3
4
6
2
3
2
30
8 —9
1
1
4
2
1
2
3
2
1
17
9 — 10
3
1
1
2
3
3
1
1
2
17
Above 10
5
2
1
3
11
7
16
14
9
6
8
3
85
Total
11
4
8
10
21
21
36
28
28
35
24
13
4
3
3
5
6
260
SINDHI HERD AT BANGALORE
Service period (months)
Upto 1
1
1
Over
Upto
1—2
1
2
3
4
3
2
2
2
3
22
2 — 3
1
1
1
5
5
2
4
5
2
5
31
3 — 4
1
1
4
6
4
3
2
7
1
2
4
1
36
4 — 5
1
2
1
2
2
3
3
2
1
1
1
19
5 — 6
1
1
1
1
2
2
2
4
4
2
3
4
1
28
6 — 7
2
1
2
1
2
3
1
1
1
1
1
16
7 — 8
2
1
5
2
1
11
8 — 9
1
1
2
2
2
8
9 — 10
1
2
1
4
Above 10
1
1
1
1
1
1
6
Total
1
1
2
5
4
14
15
21
20
22
22
13
9
12
10
11
182
June, 1958] V. N. AMBLE, K. S. KRISHNAN AND J. S. SRIVASTAVA 75
(X 2 =52.2 on 44 d.f for the Hosur herd and X 2 =21.0 on 33 d.f for the Bangalore
herd.) Examination of the overall distributions for different months indicated that
calvings were well distributed throughout the year but for a slight concentration
in the months of September, October and November for the Hosur herd and in
the months of January and February for the Bangalore herd. (X 2 =18.8 on 11 d.f
for the Hosur herd and X 2 =30.5 on 11 d.f for the Bangalore herd.)
TABLE XXVI
Distribution of age at first calving with average first lactation yield in the Red Sindhi
herds at Hosur and Bangalore
Age in months
28—32
33—36
37—40
41—44
45—48
49—52
53—60
Above 60
SINDHI HERD AT HOSUR
Frequency
12
26
99
73
43
20
13
4
Average first
lactation
yield (lb.)
3,056
3,711
3,609
3,776
3,856
4,332
2,922
1,654
SINDHI HERD AT BANGALORE
Frequency
3
37
67
68
32
15
15
3
Average first
lactation
yield (lb.)
2,966
2,788
2,399
2,803
2,750
3,384
3,313
2,976
TABLE XXVII
Analysis of variance of first lactation yield of Red Sindhi cows at Hosur and Bangalore
(units of 10 lb.)
Source of variation
Between age groups
Within age groups
SINDHI HERD AT HOSUR
D.F.
7
282
M.S.
56,478
21,012
V. R.
2.69**
SINDHI HERD AT BANGALORE
D.F.
7
232
M.S.
27,964
21,282
V. R.
1.31
76
STATISTICAL STUDIES ON BREEDING DATA [Vol. XXVIII, Part II,
TABLE XXVIII
Distribution of calvings in different months for Red Sindhi herds at Hosur and Bangalore
Months
January
February
March
April
May
June
July
August
September
October
November
December
TOTAL
SINDHI HERD AT HOSUR
F1
17
19
20
17
20
15
24
17
33
24
35
28
259
F 3
18
19
22
24
34
30
32
19
27
27
29
27
308
F 3
20
34
28
26
27
32
32
24
27
40
30
28
348
F 4
19
24
23
28
27
19
14
31
22
24
23
19
273
F 5 & F 6
2
10
8
7
11
4
10
17
9
11
7
10
106
Over all
generations
76
106
101
102
119
100
112
108
118
126
124
102
1,294
Per cent.
5.9
8.2
7.8
7.9
9.2
7.7
8.7
8.3
9.1
9.7
9.6
7.9
SINDHI HERD AT BANGALORE
F 1
33
44
30
21
27
25
26
30
29
36
41
24
366
F 2
41
42
27
19
30
19
30
26
32
25
22
23
336
F 3
21
19
20
15
16
20
12
6
18
23
14
18
202
F 4
10
3
6
4
7
4
2
4
6
3
1
7
57
Over all
generations
105
108
83
59
80
68
70
66
85
87
78
72
961
Per cent.
10.9
11.2
8.6
6.2
8.3
7.1
7.3
6.9
8.8
9.1
8.1
7.5
June, 1958] V. N. AMBLE, K. S. KRISHNAN AND J. S. SRIVASTAVA 77
Analysis of first lactation records grouped according to calendar months of
freshening did not reveal any marked influence of season on milk yield [Table
XXIX]. This result is in agreement with those of Carneiro and Lush [1948],
Berge [1949] and Ragab [1950] on dairy cattle and with that of Ragab et al., [1954]
on Egyptian buffaloes.
TABLE XXIX
Analysis of first lactation yield according to the season of calving (10 lb. unit)
Source of variation
Between months
Within months
SINDHI HERD AT HOSUR
D.F.
11
278
M.S.
30,096
21,545
V. R.
1.40
SINDHI HERD AT BANGALORE
D.F.
11
244
M. S.
33,706
19,843
V. R.
1.70
DISCUSSION
The overall success of past breeding policy in a dairy herd is indicated best by
the comparison of the performance of cows belonging to different generations after
making allowance for the variation due to environmental causes such as feeding
and management. A complete elimination of such variation from the generation
comparisons is not possible. Owing to the fact, however, that the period in which
records of cows belonging to the same generation are made is spread over a number
of years and the periods for the different generations overlap it is possible to make
some adjustment in the generation comparisons for the period to period variations
due to environmental causes by the use of appropriate analysis of variance. Detail-
ed knowledge of the feeding schedules adopted in different years and full information
on the changes introduced in the management practices from time to time would
provide a basis for the grouping of the years under study into suitable periods
such that the conditions of feeding and management can be considered as relatively
uniform within each such period. In the absence of such detailed information for
either herd the years under study had to be grouped arbitrarily into periods of five
years for the purpose of such analysis. That the grouping was fairly effective could
be concluded from the fact that the variation between periods in both the cases was
large as compared with that within the periods. The results of the analysis
indicated that while there was little overall improvement through breeding in
the Hosur herd, a progressive improvement in lactation yield of about 170 lb. per
generation was recorded in the Bangalore herd.
The high heritability coefficients of 0.34 and 0.37 for lactation yield in the two
herds indicated scope for genetic improvement in this character through selection.
The repeatability estimates for lactation yield were also high (0.61 and 0.54). On
the other hand, calving interval and age at first calving had low, non-significant
values of heritability which showed that there was very little genetic variation in