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lies in the neighbourhood of four and a half years. This average applies to the country as a whole. In those districts where disease is rife, the average life is likely to be less. Thus, the actual milking life of a dairy cow is on the average only half that which might be expected under ideal circumstances.
13. We estimate that this curtailment of productive life is responsible for an annual monetary loss of over £3,000,000, of which £2,500,000 is due to the increased costs of maintaining herds at their full strength; and the remainder to losses of meat condemned on account of disease.* In making this estimate we have not taken into account any increase in the annual productivity of the cow during life, which might follow from the elimination of disease. This loss cannot be estimated, but must be large. We do not suggest that, as a result of the complete disappearance of disease from among dairy cattle any particular class of the community, for example farmers, would benefit to the extent of £3,000,000 annually. The benefit would presumably be diffused throughout the community as a whole.
14. A number of investigations have been made into the causes which are responsible for these heavy losses among dairy cattle. The method of these investigations has been to obtain from farmers! notice of each cow drafted out of his herd and the cause of disposal. Unfortunately the cause which is present in the mind of the farmer is not that which is of interest for our purpose. Broadly speaking, a farmer parts with a cow either because she fails to produce milk economically, or because she is surplus to his requirements. Cows parted with on the first ground may be further sub-divided, from the farmer's point of view, into cows which die, cows which are barren, cows which are unthrifty, and cows which have a low milk yield either naturally or as a result of disease. A further cause of disposal of importance among the producers of tubercle-free milk, is reaction to the tuberculin test. The classification of the causes of disposal of a large number of dairy cows which is given in the table in the following paragraph is evidently influenced by considerations such as these.
In fact, however, this classification throws little or no light on the extent to which infection with any one of the main diseases of cattle is a cause of wastage. For each of the symptoms which leads the farmer to dispose of a cow is compatible with several diseases.
15. The most extensive of the investigations to which we have referred were undertaken by the Hannah Dairy Research Institute, by the National Institute for Research in Dairying at Reading, and
* The grounds upon which this estimate is based are considered in appendix 3.
†These farmers belong to milk recording societies, and may therefore not be representative of farmers as a whole.
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by the School of Agriculture at Cambridge, with the co-operation of the milk recording societies in the counties covered by the inquiries. The total number of disposals recorded in these investi- gations exceeded 17,000. The results are summarised in the following table (table 1) :—
TABLE 1.
Causes of the disposal of dairy cows.
Summary of
all investi-
gations.
Investigation.
Hannah National
Insti- Institute, Reading. tutė.
School of Agriculture, Cambridge.
1930.
466
322
19,263
470 9,478 12,348
2,830
3,620
2,136 3,013 2,461
3,059 2,958 17,247
Number of herds Number of cows in herds Number of disposals re-
corded
Percentage of these dis- posals recorded as being on account of—
1. Diseases of the re- productive organs-
(a) Sterility (b) Abortion
1929-30. 1930-31. 1928-29. 1929-30, 1930-31.
547 13,465 12,984 | 11,36778,905
537
488
17-2 2.1
26.2 3.1
25.6
2-8
23.7 3-6
26.7 26.2 23.8 3.8 2.7 3.0
Total reproductive dis-
ease
19-3
29.3
28.4 27.3
30.5 28.9 26.8
2. Udder disease
15.0
6.4
6.6
7.1
4-8
4.2 7-7
3. Tuberculosis, Johne's disease and wasting
5.4
12.3
12.3
10.4
9.6
10.0
9.7
4. Death and miscel- laneous diseases
15-1
8.8
9.8
9.3
7.9
9.6 10.4
5. Tuberculin test
2-8
5.5
5.5
2.4
1.8
4.1 3.6
57.6
62.3
62.6
66.5 54.6
56.8 58.2
4-9
4.4
3.4
5.3
4.0
3.8
4.3
1.5
1.9
1.7
1.2
1.4
1.0 1.5
16.6 19-4
16.0 19.6
19.1
16.5 17.7
19.4 12.0
16.3 17.4
20-9
21.9 18.3
100.0
100-0 100.0 100-0 100-0
100-0 100.0
Total from disease
6. Old age 7. Accident 8. Low yield 9. Trade
Total
16. The striking feature of this table is the importance of sterility as a cause of disposal. This condition is due to a number of causes, of which infection with contagious abortion is one of the most frequent. Second in importance as a cause of disposal from individual herds is sale to the trade. This is not a source of numerical loss to the herds of the country as a whole, and need not detain us.
A large percentage of cows are disposed of on account
of their low milk yield, which is the third cause of disposal in order of importance. In part these disposals reflect the effort of the farmer
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