72 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ I, II
The D. P. is above the normal for the months June to October—126.81╤ 4.68
and below the normal for the remaining months—mean 111.59 ╤ 2.02. The
difference of 15.22 ╤ 5.09 between these two means, however, is not significant as
it is only 2.99 times P. E. But since the figures for the variation of D. P. with
calving months are very smooth running, more reliance might be placed on the
differences between these monthly means than is indicated by their probable errors.
It will be noticed that this seasonal variation of D. P. coincides with that of S. P.
and since cows with long S. P. tend to have longer D. P. before they calve again
than those with short S. P., the longer D. P. for the cows calving in June to
October may partly be due to their longer S. P. This seasonal variation of D. P.
is different to that in Sanders' data in which the mean D. Ps. are lower than the
normal for the months July to October.
Table V shows the distribution of the milk records included in different calving
months according to the ages at which these records were made.
TABLE V.
Relation of month of calving and age % in lactations.
% Distribution in different ages of total.
|
Calving |
1st lac- |
2nd |
3rd |
4th |
5th |
6th |
7th |
8th |
9th |
10th |
11th |
12th |
Total |
|
January |
33.08 |
22.56 |
10.52 |
14.29 |
8.27 |
6.01 |
1.50 |
2.26 |
1.50 |
.. |
.. |
.. |
99.99 |
|
February |
21.71 |
20.0 |
17.14 |
13.14 |
9.72 |
7.43 |
5.72 |
2.86 |
.. |
1.41 |
0.57 |
0.57 |
100.00 |
|
March |
14.70 |
19.12 |
23.53 |
12.75 |
10.29 |
5.88 |
4.41 |
3.92 |
4.41 |
0.49 |
0.49 |
.. |
99.99 |
|
April |
21.38 |
22.76 |
17.93 |
12.41 |
12.41 |
4.14 |
4.83 |
3.45 |
.. |
0.69 |
.. |
.. |
100.00 |
|
May |
23.25 |
22.48 |
11.63 |
15.50 |
10.08 |
8.52 |
3.88 |
1.55 |
2.23 |
.. |
0.78 |
.. |
100.00 |
|
June |
28.57 |
14.29 |
22.22 |
7.93 |
7.93 |
7.93 |
1.59 |
1.77 |
1.59 |
3.18 |
.. |
.. |
100.00 |
|
July |
17.91 |
19.40 |
19.40 |
14.92 |
5.97 |
10.45 |
5.98 |
1.49 |
1.99 |
1.49 |
.. |
.. |
100.00 |
|
August |
8.93 |
17.86 |
16.07 |
14.29 |
12.50 |
7.15 |
8.93 |
10.72 |
.. |
1.78 |
1.78 |
.. |
100.00 |
|
September |
11.90 |
21.43 |
14.29 |
28.57 |
4.76 |
9.52 |
1.38 |
.. |
1.38 |
1.38 |
1.38 |
.. |
99.99 |
|
October |
12.12 |
16.67 |
24.24 |
19.70 |
9.09 |
6.06 |
9.09 |
1.51 |
1.51 |
.. |
.. |
.. |
99.99 |
|
November |
13.92 |
18.99 |
22.78 |
21.52 |
8.86 |
6.33 |
3.80 |
2.53 |
.. |
1.26 |
.. |
.. |
99.99 |
|
December |
18.26 |
17.39 |
19.13 |
14.78 |
13.04 |
4.35 |
5.22 |
3.48 |
3.48 |
0.87 |
.. |
.. |
100.00 |
|
Average |
19.94 |
19.86 |
18.13 |
14.76 |
9.89 |
6.59 |
4.63 |
3.14 |
1.81 |
0.87 |
0.39 |
0.08 |
99.99 |
The percentage distribution of cows of different ages in different calving
months is far from uniform ; e.g., 1st calvers constitute 33.08 per cent. of the
total of January calvers, whereas in the months of April and September they
constitute only 21.38 and 11.99 per cent. respectively. This goes to show that
there exists in our data a relation between the age of cow and the month of
calving.
The correlation coefficients as derived from the correlation surfaces drawn
separately for the variable age and S. P. and age and D. P. were —.067 ╤ .017 and