42
Paratuberculosis of Cattle in Assam
by sand, clay and gravels arising from large areas of savannahs interspersed
here and there by homesteads. The soils of old alluvial deposits and most
of the hills and the highlands show distinct acid reactions. The most import-
ant characteristic of Assam soils is their acidity which does not usually favour
the growth of some of the crops and the best types of nutritious grasses. In
Assam Valley, soil acidity increases with the rainfall and the heaviness of the
soil.
As stated above, the most important feature of the Assam climate is
its heavy rainfall during the monsoon which breaks in as early as the latter
part of April and continues till September. There is a short winter and
hardly any period of dry summer. Severe dewfall is another important
feature during the non-monsoon period, which at certain places could be
compared to a mild shower of rain. These climatic factors, which are res-
ponsible for the perpetual humidity, exert a deleterious effect on the animal
economy in general, and along with the soil factors account for the degenerate
type of cattle and their poor size and vigour. Thus, on the one hand, the
coarse fodder growing on a poor soil rarely supplies all the essentials of a
balanced diet and, on the other, the heavy rainfall and resultant humidity turn
the pastures and the farm-lands into suitable breeding grounds for parasites
to which the bovine species are particularly susceptible.
In the present section the climatic and the soil factors have been consi-
dered in the light of their bearing on the normal health of cattle, and the
manner in which these factors can possibly influence the course of the disease
under reference are given in some detail in the section dealing with the epi¬
zootology of the disease.
METHODS AND SCOPE OF INVESTIGATION
Though, as already stated, the data collected as a result of the present
survey do not provide an index to the incidence of the disease amongst the
cattle population of this country as a whole, they have, however, as far as
they are concerned, formed the basis for devising the methods of control of this
disease in Assam. This survey has been carried out mainly by the applica-
tion of the double intra-dermal test in all the farm animals over six months
old using avian tuberculin supplied by the Imperial Veterinary Research
Institute, Mukteswar, and in certain number of animals by simultaneous adop-
tion of the bowel-washing method advocated by Krishnamurti Ayyar [ 1929 ].
It has been considered desirable to avoid any reference in this paper relating
to the relative value of avian tuberculin in the detection of Johne's infec-
tion, but it must be observed that an absolutely reliable agent capable of pro-
ducing an allergic response in every positive case of this disease is still not
available. Considering the fact that avian tuberculin fails at times to register
the characteristic response indicative of Johne's infection, positive reactors
at the Government farms and certain jail dairies were frequently subjected
to two or three tests with a view to confirming the positive diagnosis. By
this procedure, animals showing positive reaction at least in two tests were
placed in the category of diseased animals. On different occasions and on
more than a thousand animals, these tests were performed by the writer
himself, so that the variation in human factor, so often stated to influence