136
Mortality in Young Calves in India
no sign of vitamin-A deficiency in the cow calves such as night blindness had been noticed, but such
signs might easily have been overlooked without a special examination. Although the buffalo dry
stock also get no green fodder, deaths in the buffalo calves were mostly due to other causes than
pneumonia. The most likely explanation of the difference is that buffaloes are. able to convert caro-
tene into vitamin-A much more readily than cows and in amounts sufficient at least to prevent pneu-
monia. In the same connection, it may be observed that at the Military Farm at Quetta, where no
green fodder at all was grown, blindness in cow calves was at one time common whereas the buffalo
calves were unaffected.
Seasonal effects. The mortality rates at the two centres have a definite seasonal swing, being
higher in the winter, both in the gross and in the special case of pneumonia at Secunderabad. Although
certain relationships have been established between seasonal mortality rates and weather factors,
it does not of course follow that these factors contribute directly to the deaths. Any direct influence
in fact seems to be unlikely, except just possibly in the case of the minimum air temperature at Air-
field, though even here there was not undue exposure. It might be thought that, since the
number of calves born in the winter is relatively greater than the number born in the summer,
the higher winter death-rate is simply due to crowding. This, however, does not seem to be the case.
since examination of the total births and deaths for the period October to March of different years
shows no significant association between the numbers of births and deaths. With buffalo-calves,
this relationship between births and deaths could not be studied because of the animals born so few
are retained.
This is not the place to attempt a full discussion of the difficult subject of seasonal variation of
disease. A few points were briefly referred to in a former paper on the incidence of equine strangles
[Minett, 1944], and an interesting recent discussion of the subject as a whole is given by Aycock and
others [1945]. Wilson [1930] rightly objects to the use of the word ' seasonal'. unless it is shown that
the changes in question occur with regular sequence in the same direction at corresponding periods of
successive years. Unfortunately, my figures for annual deaths are too small for statistical examination
in the sense of Wilson's definition, but the combined figures for the period do show significantly higher
death-rates in winter. The most likely explanation is a greater susceptibility of the calves in winter,
which may arise through dietary causes or through lowered activity of the tissues physiological in
origin (' fluctuating immunity ' of non-specific kind). The latter may, of course, be dependent on
dietary causes, while'climatic and other agencies may act in a secondary manner. In amplification
of this, the following references may be quoted. Brown and others [Brown, 1929] have shown that
the body undergoes seasonal variations in its physical and chemical constitution, which are related to
(a) variations in functional activity, rendered necessary by a changing environment, and (b) suscepti-
bility to disease, infectious or otherwise. An example of (a) is that the weights of the endocrine
organs are at an overall maximum in summer. As regards a direct dietary causation, Watson
[1937] showed that young mice on a diet containing dried evaporated milk were more resistant to
experimental infection, perhaps due to the extra provision of milk protein. Quite apart from the
specific deficiency in the diet at Secunderabad, it is easily possible that there and also at Airfield the
calves were not getting enough milk for their optimal requirements, at least during winter ; at Air-
field too the winter colostrum may have been qualitatively somewhat deficient in vitamin-A. .It
may be noted in this same connection that Keener and others [1942] have shown that the minimal
carotene requirements of dairy calves may be at least twice as great during severe winter weather as
during warmer weather.
Reduction of calf mortality. The steps that may be taken to reduce mortality in young calves
have often been considered. The importance of good general hygiene in the matter of sanitation and
nousing, and of adequate colostrum, milk and vitamin-A feeding is well established. In spite of
what seems adequate attention to such matters, losses are sometimes unduly high.
One outstanding point which often does not receive due attention is the grouping of calves during
early life. It may be insufficient to form two age groups, viz. calves from birth up to three months,
and calves from three months upwards. Savage and McCay [1942] refer to some observations
by Harrison in the Cornell University herd. From 1932.37, out of 515 calves born, 109 (21.2 per cent)