NationalLibraryOfScotland/medical-history-of-british-india huggingface dataset:
38 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ IV, I.
RESULTS : BUFFALOES' WEEKLY YIELDS.
The data for buffaloes were first made use of for testing if the equation accu-
rately represents them. There were 140 lactations obtained for buffaloes from the
records of the Northern Circle. The average weekly yield of each week of lactation
was worked out. These are represented by the dotted line in Figure I. It will be
seen that the yield rises up to the 5th week, remains steady till the seventh and
declines from the 8th. The equation was applied to the decline portion of the curve,
FIG. I.—Lactation curve for buffaloes—weekly yields.
that is, to the data of yields from the 8th week of lactation, and the values of
the constants, maximum and rate of decline were determined. The method of
determining these is by what is known as method of least squares,* the virtue of
which is that the error is the least possible. The smooth curve obtained from the
calculated data is represented by the continuous line in Figure I. From this it will
be seen that the average buffalo starts with a maximum of 142.5 lb. per week in the
7th week of lactation and then declines weekly at the rate of .0265 lb. per lb.
per week (which is about 2.65 per cent.). The observed and calculated values of the
weekly yields are given in Table I. Column 5 of this Table shows by how much the
* The method of calculation is explained in Appendix I.
RATE OF DECLINE IN MILK YIELD OF VARIOUS TYPES OF CATTLE
39
TABLE I.
Average weekly milk yield of buffaloes during weeks following maximum—
All observations. (Maximum:—7th week.)
Weeks after
calving
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
No. of records
averaged
135
136
139
140
139
138
139
138
139
140
139
139
139
139
138
139
138
139
137
136
135
133
131
122
116
109
100
Data of milk yield in lb.
Observed
134.3
131.2
127.9
126.0
123.9
120.8
117.7
115.5
113.4
110.5
108.4
106.2
102.4
100.6
98.8
95.2
92.3
88.0
87.5
85.5
82.8
80.4
76.6
74.5
73.2
69.5
66.6
Calculated
138.8
135.2
131.6
128.1
124.8
121.5
118.4
115.3
112.3
109.3
106.4
103.6
100.9
98.31
95.72
93.24
90.70
88.41
86.10
83.85
81.66
79.50
77.43
75.41
73.43
71.52
69.63
Deviation
—4.5
—4.0
—3.7
—2.1
—0.9
—0.7
—0.7
0.2
1.1
1.2
2.0
2.6
1.5
2.29
3.08
1.96
1.60
—0.41
1.40
1.65
1.14
0.90
—0.83
—0.91
—0.23
—2.02
—3.03
Rate of decline per lb. per week:—.0265.
Ratio of any week's yield to that of preceding week:—.9738.
40 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [IV, I.
calculated values deviate from the observed. The deviation is only about 1.6
per cent. of the average weekly yields. Such an error is not at all large for data
like milk yields, which are in their very nature subject to very large variation,
depending as they do on a large number of factors of heredity and environment.
It will also be noted that the smooth curve cuts through the data admirably well.
To compute yield for any period.
The milk producing capacity of an animal is thus described in terms of the two
characters, the maximum and the rate of decline. The yield for a lactation or for
any stated period can be calculated when these are known. Thus at maximum the
buffalo yields 142.5 lb. a week. In the 8th week its yield would be diminished by
2.65 per cent., that is, the yield would be .9735 × 142.5 lb. In the 9th week the yield
would be 97.35 per cent. of the yield in the 8th, i.e., .9735 ×.9735× 142.5 lb.; in the
10th, .9735 3 × 142.5 lb., and so on. By adding these quantities over the length of
the lactation, or for any other period desired, the total yield is obtained. The
calculation is laborious, no doubt, but with the aid of calculus it is very simple, the
summation being performed by a simple process, namely, integration. Graphically
also the yield for any period can be calculated without much labour. Yield is
represented by area under the curve, and when the lactation curve is drawn, the
yield between any two dates is obtained by erecting ordinates at these two dates and
computing the area enclosed by them, which is done by counting the number of
squares enclosed.
The data were next examined to see how the rate of decline is affected by
pregnancy. For this purpose the lactations were sorted out into groups according
to the lengths of service periods for the lactations. All calculations were made as
before and the figures are given in Tables II to V.
TABLE II.
RATE OF DECLINE IN MILK YIELD OF VARIOUS TYPES OF CATTLE
41
TABLE II.
Average weekly milk yield of buffaloes during weeks following maximum—
service period :—2—6 weeks. (Maximum :—5th week.)
Weeks after
calving
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
20
27
28
29
30
31
32
No. of records
averaged
29
28
27
29
30
30
29
29
30
30
30
30
29
30
30
30
30
30
30
29
29
28
27
26
26
23
21
Data of milk yields in lb.
Observed
127.6
124.4
125.6
121.4
117.2
115.8
112.4
111.3
106.9
101.9
99.5
95.5
93.1
92.3
90.1
90.4
86.6
81.6
77.6
77.7
74.5
72.3
71.0
70.2
64.7
62.9
59.2
Calculated
132.6
128.8
125.2
121.6
118.1
114.8
111.5
108.3
105.3
102.3
99.38
96.56
93.8
91.14
88.54
86.02
83.58
81.21
78.89
76.65
74.47
72.36
70.30
68.29
66.36
64.46
62.63
Deviation
—5.0
—4.1
0.3
—0.4
—0.9
1.0
0.9
3.0
1.6
—0.4
0.12
—1.06
—0.70
1.16
1.56
4.38
3.02
0.39
—1.29
1.05
0.03
—0.06
0.70
1.91
—1.66
—1.56
—3.43
Rate of decline per lb. per week :—.02885.
Ratio of any week's yield to that of preceding week :—.9714
42 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ IV, I.
TABLE III.
Average weekly milk yield of buffaloes during weeks following maximum—service
period:—6—10 weeks. (Maximum:—7th week.)
Weeks after
calving
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
No. of records
averaged
43
43
43
43
43
43
43
43
43
43
43
43
43
43
42
43
42
43
42
42
42
41
40
36
32
30
25
Data of milk yields in lb.
Observed
130.6
128.1
124.7
121.7
119.3
115.7
112.1
111.8
110.4
107.8
105.7
103.8
99.3
96.8
97.7
92.7
90.7
84.02
84.2
82.4
80.5
74.5
71.3
69.0
69.95
64.6
59.2
Calculated
135.8
132.0
128.4
124.8
121.4
118.8
114.8
111.6
108.5
105.5
102.7
99.79
97.05
94.36
91.75
89.23
86.76
84.37
82.04
79.77
77.57
75.43
73.35
71.32
69.34
67.44
65.57
Deviation
—5.2
—3.9
—3.7
—3.1
—2.1
—3.7
—2.7
0.2
1.9
2.3
3.0
4.01
2.25
2.44
5.95
3.47
3.94
—0.35
2.16
2.63
2.93
—0.93
—2.05
—2.32
0.61
—2.84
—6.37
Rate of decline per lb. per week:—.02800.
Ratio of any week's yield to that of preceding week:—.9724.
RATE OF DECLINE IN MILK YIELDS OF VARIOUS TYPES OF CATTLE
43
TABLE IV.
Average weekly milk yield of buffaloes during weeks following maximum—Service
period 10—14 weeks (Maximum—7th week).
Weeks after
calving
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
No. of records
averaged
22
22
22
22
22
22
22
22
22
22
22
22
22
22
21
21
21
22
21
21
21
21
20
19
19
19
17
14
13
Data of milk yields in lb.
Observed
136.97
135.9
134.4
132.0
129.5
127.2
122.3
117.1
115.5
112.3
113.3
110.1
105.7
103.8
102.9
101.0
99.1
90.8
93.8
92.3
84.4
87.3
84.9
79.7
78.6
67.6
70.5
71.2
67.5
Calculated
143.1
139.4
135.9
132.5
129.1
125.9
122.7
119.6
116.6
113.6
110.8
108.0
105.2
102.6
100.0
97.47
95.01
92.62
90.31
88.00
85.76
83.60
81.49
79.43
77.43
75.48
73.57
71.71
69.90
Deviation
—6.13
—3.5
—1.5
—0.5
0.4
1.3
—0.4
—2.5
—1.1
—1.3
2.5
2.1
0.5
1.2
2.9
3.53
4.09
—1.82
3.49
4.30
—1.36
3.70
3.41
0.27
1.17
—7.98
—3.07
—0.51
—2.40
Rate of decline per lb. per week—.02558.
Ratio of any week's yield to that of preceding week—.9748
44 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ IV, I.
TABLE V.
Average weekly milk yield of buffaloes during weeks following maximum—Service
period 14—26 weeks (Maximum—7th week).
Weeks after
calving
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
No. of records
averaged
30
29
30
31
31
31
31
30
31
31
31
31
31
31
31
31
31
31
31
31
31
31
31
30
30
28
27
27
24
21
20
19
18
Data of milk yields in. lb.
Observed
139.7
135.9
133.7
132.3
130.1
128.6
127.8
126.9
123.7
121.5
118.3
114.7
110.4
109.8
106.5
103.5
99.0
96.5
96.0
93.6
91.2
98.0
84.7
83.9
81.2
79.9
79.7
74.3
75.5
74.0
78.0
75.0
71.2
Calculated
143.5
140.3
137.3
134.2
131.2
128.2
125.4
122.7
119.9
117.5
114.7
112.1
109.6
107.3
104.8
102.5
100.0
98.04
95.88
93.76
91.68
89.64
87.66
85.70
83.83
81.96
80.15
78.38
76.63
74.94
73.28
71.66
70.06
Deviation
—3.8
—4.4
—3.5
—1.9
—l.l
0.4
2.4
4.2
3.8
4.2
3.6
2.6
0.8
2.5
1.7
1.0
—1.0
—1.54
0.12
—0.16
—0.48
—1.64
—2.96
—1.80
—2.63
—2.06
—0.45
—4.05
—1.13
—0.94
4.72
3.34
1.14
Rate of decline per lb. per week—.02239.
Ratio of any week's yield to that of preceding week—.9782.
RATE OF DECLINE IN MILK YIELDS OF VARIOUS TYPES OF CATTLE
45
Although the population becomes very small when divided into the various
service period groups, the error is never more than three per cent. of the average
weekly yields. It will be seen that the rate of decline is affected but slightly by
pregnancy. But no conclusion can be drawn from results based on such a small
number. The subject will be examined in greater detail in a separate paper.
RESULTS —ALL BREEDS.
It will be seen from the above that the equation made use of represents the data
fairly accurately as far as the decline portion of the curve is concerned. But by
representing the data by this equation five to seven weeks' yields have to be omitted.
By taking monthly instead of weekly yields the equation may be made to represent
a larger part of the lactation. Further, examination of more data showed that the
variation from week to week is not so regular or marked; and this short-time
variation also could be eliminated by taking monthly yields. The work was done,
therefore, in the case of Indian and cross-bred cows with monthly instead of weekly
yields, and for uniformity the same was repeated with buffaloes. A month was
taken to be of four weeks. The first fortnight was omitted and average monthly
yields were obtained, in the case of Indian and cross-bred cows and buffaloes, for
full months beginning with the third week of lactation. The maximum and the
rate of decline were obtained as before. The data are given in Tables VI to IX
TABLE VI.
Average monthly rate of milk secretion of cross-bred cattle, with advance in lactation.
Month after
calving
1
2
3
4
5
6
7
8
9
No. of records
averaged
157
157
157
167
157
157
157
157
157
Milk yield in lbs.
Observed
946.9
902.9
834.7
754.5
679.9
617.5
565.3
515.0
462.7
Calculated
980.9
894.5
815.8
744.0
678.5
618.9
564.4
514.7
469.5
Deviation
—34.0
8.4
18.9
10.5
1.4
—1.4
.9
.3
—6.8
Rate of decline per lb. per month:—.09215.
Ratio of any month's yield to that of preceding month:—.9121.
46 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ IV, I.
TABLE VII.
Average monthly rate of milk secretion of pedigree Sahiwals with advance in
lactation.
Month after
calving
1
2
3
4
5
6
7
8
No. of records
averaged
112
112
112
112
112
112
102
102
Milk yield in lbs.
Observed
779.5
750.0
692.0
628.5
585.0
521.0
518.5
473.5
Calculated
791.1
734.1
681.6
632.5
587.2
545.0
505.9
469.6
Deviation
—11.6
15.9
10.4
—4.0
—2.2
—24.0
12.6
3.9
Rate of decline per lb. per month : —.0745.
Ratio of any month's yield to that of preceding month :—.9277.
TABLE VIII.
Average monthly rate of milk secretion of ordinary Sahiwal cows, with advance in
lactation.
Month after
calving
1
2
3
4
5
6
7
8
No. of records
averaged
89
89
89
89
89
89
89
89
Milk yield in lbs.
Observed
495.7
443.2
390.4
351.2
314.7
287.7
253.9
230.2
Calculated
492.0
440.8
394.9
353.7
316.8
283.8
254.2
227.7
Deviation
3.7
2.4
—4.5
—2.5
—2.1
3.9
—0.3
—2.5
Rate of decline per lb. per month :—.1101.
Ratio of any month's yield to that of preceding month:—.8968.
RATE OF DECLINE IN MILK YIELDS OF VARIOUS TYPES OF CATTLE
47
TABLE IX.
Average monthly rate of milk secretion of Indian buffaloes, with advance in lactation.
Month after
calving
1
2
3
4
5
6
7
8
No. of records
averaged
140
137
139
139
139
138
134
112
Milk yield in lbs.
Observed
531.0
528.7
488.4
447.4
408.0
363.0
325.3
283.8
Calculated
570.9
520.2
474.2
432.1
393.9
358.9
327.1
298.2
Deviation
—39.9
8.5
14.2
15.3
14.1
4.1
—1.8
—14.4
Rate of decline per lb. per month :—.09281
Ratio of any month's yield to that of preceding month :—.9112
TABLE X.
Yield per month at maximum and the rate of decline per lb. per month for various
breeds of animals.
Breed
Cross-bred cows
.
.
.
.
.
Pedigree Sahiwal
.
.
.
.
.
Ordinary Sahiwal
.
.
.
.
.
Buffaloes
.
.
.
.
.
.
.
Yield per
month at
maximum
980.9
791.1
492.0
570.9
Rate of decline
per lb. per
month
.09215
.0745
.1101
.09281
Ratio of any
month's yield to
that of preceding
month
.9121
.9277
.8958
.9112
E
48
FIG.
2.—Lactation curves.
RATE OF DECLINE IN MILK YIELDS OF VARIOUS TYPES OF CATTLE
49
and the constants are tabulated in Table X. The curves for each breed are shown
in Fig. 2. From these it will be seen that the smooth curve fits the data very
well.
Table X shows that the ordinary Sahiwal cow is the least persistent (i.e.,
declines most), while the specially bred Sahiwal cows at Ferozepore are most
persistent. The buffaloes and the cross-bred are more or less on the same level and
are between the other two. (The Ferozepore Pedigree Sahiwals are known to almost
equal the cross-bred in milk production. From Table X it will be seen that their
maximum is much lower and persistency is much higher than that of the cross-bred.
Although these two samples of the two breeds may not be equal exactly, it is still
clear that the pedigree animals are able to make up in the course of a lactation a
good portion of the difference in their starting yield by virtue of their higher
persistency. This shows how important persistency is as a factor in the economical
production of milk.)
Two facts might be noticed in the tables that account for a portion of the dis¬
crepency between the actual and the theoretical values of the yields. It will be
seen that the larger deviations are in the early part of the lactation, which is parti-
cularly marked in the case of the buffalo and the cross-bred. This is due to the
tendency in many individuals to maintain the rate of yield they attain in the maxi-
mum month instead of declining continuously as shown by the theoretical equa-
tion. The lactation curve for buffaloes given in Fig. 1 shows this to be the case :
here the yield is found to remain steady between the 5th and the 7th week of lacta-
tion. Further, the yields as recorded in the tables are from the third week onwards,
while the maximum actually occurs a little later in the lactation. The whole of the
first month is not, therefore, on the decline portion of the curve, and the theore-
tical maximum is in excess of the actually realised maximum on account of this as
well.
Again, to a certain extent the data are vitiated by the occasional sickness of
animals. Such data could be eliminated only when the records contain the remark
" sick ". Often this is not noted in the records, and if noted, the duration of sick-
ness is seldom mentioned. It is not, therefore, possible to know when such animals
have returned to normal health, except by the indication afforded by the restora-
tion of normal milk flow. In certain cases a heavy drop is noticed when an animal
falls sick, and this is not made up during the rest of the lactation.
PRACTICAL APPLICATIONS.
A knowledge of the properties of the lactation curve helps the solution of many
problems that are met with in the course of dairy routine and practice. Only one
E 2
50 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ IV, I.
application is considered here, namely, how it may be tested whether normal condi-
tions of feeding and management exist in a herd and whether the herd has produced
the best that it is capable of under such conditions. The other applications will be
dealt with separately in a later section.
It has been shown that the yield for a lactation or for a given period may be
expressed as a function of the initial maximum rate of secretion and the rate of
decline. Two animals may differ with respect to either or both of these characters.
For purposes of illustration, Tables XI & XII are given. Table XI shows the
monthly yields and total yield for 11 months of animals that have the same maxi-
mum but different rates of decline, and Table XII shows animals with the same rate
TABLE XI.
Monthly rate of yield of four typical animals having the same initial rate of yield but
different persistencies.
Time after calving in
months.
1. . . .
2. . . .
3. . . .
4. . . .
5. . . .
6. . . .
7. . . .
8. . . .
9. . . .
10. . . .
11. . . .
Total for 11 months
Rate of decline per
lb. per month.
Ratio of any month's
yield to that of
preceding month.
YIELD PER MONTH IN LBS.
Type 1.
1000.0
980.2
960.8
941.8
923.1
904.8
886.9
869.4
852.1
835.3
818.7
9973.1
.02
.9802
Type 2.
1000.0
941.8
886.9
835.3
786.6
740.8
697.7
657.0
618.8
582.7
548.8
8296.4
.06
.0418
Type 3.
1000.0
904.8
818.7
740.8
670.3
606.5
548.8
496.6
449.3
406.6
367.9
7010.3
.10
.9048
Type 4.
1000.0
869.4
755.8
657.0
571.2
496.6
431.7
375.3
326.3
283.7
246.6
6013.6
.14
.8693
RATE OF DECLINE IN MILK YIELD OF VARIOUS TYPES OF CATTLE
51
TABLE XII.
Monthly rate of milk yield of four typical animals having different initial rate of yield
but the same persistency.
Time after calving in
months.
1
.
.
.
.
2
.
.
.
.
3
.
.
.
.
4
.
.
.
.
5
.
.
.
.
6
.
.
.
.
7
.
.
.
.
8
.
.
.
.
9
.
.
.
.
10
.
.
.
.
11
.
.
.
.
Total for 11 months .
Rate of decline per lb. per
month.
Ratio of any month to that
of preceding month.
Yield per month in lbs.
Type 1.
400.0
361.9
327.5
296.3
268.1
242.6
219.5
198.6
179.7
162.6
147.2
2,804.0
.1
.9048
Type 2.
600.0
542.8
491.3
444.5
402.2
363.9
329.3
297.9
269.5
243.9
220.8
4,206.1
.1
.9048
Type 3.
800.0
723.8
655.0
592.6
536.2
485.2
439.0
397.2
359.4
325.2
294.4
5,608.0
.1
.9048
Type 4.
1,000.0
904.8
818.7
740.8
670.3
606.5
548.8
496.6
449.3
406.6
367.9
7,010.3
.1
.9048
52
FIG.
3.—Curves for animals with same initial rates of yield but different persistencies.
53
FIG.
4.—Animals with same persistency but different initial rates of yield.
54
FIG.
3a.— Showing Fig. 3 on Logarithmic scale.
55
FIG.
4a.—Fig. 4 on the Logarithmic scale.
56 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ IV. 1.
of decline but different maximum yields. Table XII shows that, if the rate of decline
is the same, the total yields are proportional to the maximum yields. On the other
hand, Table XI shows that with the same maximum the total yield decreases with
increase in the rate of decline. When the decline increases from 2 to 13 per cent.
or which is the same thing, when the persistency decreases from .98 to .87, that is, by
11 per cent. the yield for 11 months decreases by 40 per cent. This shows, by the
way, how important persistency is as a factor in the economical production of milk.
Again, it will be noted that the yield for any month bears a constant ratio to
that of the preceding month. In actually observed data the ratios will not be so
exactly equal, but they generally tend to equality as has already been observed in
Tables I to IX, where the departures from the calculated values were found to be
very small indeed, a herd as small as 22 (Vide Table IV) giving very satisfactory
results. The constancy of this relation makes it possible to test if normal conditions
of environment exist in a herd. If Y 1, Y 2, Y 3, etc., represent yields for the first
second, third, etc., month of lactation beginning with the first full calendar
month, the following relation will hold good :—
Y 2 /Y 1 = Y 3 /Y 2 = Y 4 /Y 3, etc.
The value of this ratio will be, as will be seen from Table X, .8958 for the
Indian cow, .9121 for the cross-bred and .9112 for the buffaloes. A serious depar-
ture from this value indicates the absence of average conditions, and serves as a
useful pointer to the dairyman to look more minutely into the feeding and manage-
ment of his stock.
Figures 3 and 4 show how this can be verified graphically. They represent
Tables XI and XII, respectively. It will be seen that the slope of the curve
is greater the greater the rate of decline, and they are more or less parallel when the
rates of decline are identical. The slope*, therefore, is a measure of persistency, and
by drawing a curve for the herd to be tested by the side of the curve for the herd
under average conditions it is possible to see if normal conditions existed.
More accurate results are obtained by drawing the curves on a logarithmic
scale. This consists in plotting the logarithms of the yields instead of the yields
themselves, or which is the same thing, by plotting them on semi-logarithmic paper
instead of on ordinary cross section paper. Figures 3a and 4a are reproduc-
tions of Figures 3 and 4 on a logarithmic scale. Here the curves appear as
straight lines, and in the case of straight lines the differences in slopes can be more
readily appreciated, and exactly measured. If two animals are equally persistent,
parallel lines will be obtained. It may be noted in passing that the slopes of
these lines divided by .4343 directly give the rate of decline per pound per month.
The method of calculation is explained in detail in the Appendix.
*The term slope is used here in a loose, and not in its true mathematical, sense.
RATE OF DECLINE IN MILK YIELD OF VARIOUS TYPES OF CATTLE
57
The method explained above is particularly useful when reviewing the results
of, say, a year's production. Thus if two farms show two different figures of
production for herds of the same breed it is conceivable to suppose that the
yields have been affected through their constituent, persistency, and if feeding,
management and care of the animals had been the same in both the farms the
yields would not have been different. Faults in management can thus be easily
checked by means of the lactation curve.
In making comparisons like the above, however, due regard should be paid
to the economy of feeding. It is possible to show higher persistency by forced
feeding and making the animals yield milk beyond the point of greatest efficiency.
When this point is passed the food required per lb. of milk is higher than that
required on a lighter ration. In this connection the following table may be of
interest—it is quoted by Ross, Hall and Rhodes in their study of the feed cost
of milk and fat production as related to yields, and it refers to Holtsmark's work
based on 846 dairy herds in Norway, owned by practical farmers with the idea
of producing milk for profit.
TABLE XIII.
Relation between the amount of feed consumed and the milk produced by 846 dairy herds
in Norway according to Holtsmark.
Number of feed units consumed.
1,500
2,000
2,600
3,000
3,500
4,000
4,500
.......
........
......
.......
.......
........
.......
Yield of milk per cow.
Kilograms.
923
1,424
1,813
2,131
2,399
2,632
2,837
Yield of
milk per 100 lb,
feed units.
Kilograms.
61.5
71.2
72.5
71.0
68.5
65.8
63.1
The point of greatest efficiency is reached in the third group. Groups of cows
fed more than this amount show decreasing yields per unit of feed.
SUMMARY AND CONCLUSION.
498 Milk Records of cross-bred cows, pedigree Sahiwal cows, ordinary Sahi-
wal cows and buffaloes were analysed for examining at what rate milk yield falls
off as lactation advances. It is found that the rate of decline is the lowest in
pedigree Sahiwal and highest in the ordinary Sahiwal; the buffalo and the cross-
bred are more or less on the same level and come between the two. The maximum
rate of secretion is attained at different stages of lactation in different indivi¬