278 THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [VI, III

of the experimental work that we are conducting with dairy cattle and pigs at
the experimental farms of the Institute of Animal Genetics. The method adopted
is to do our utmost to secure a uniform system of management and nutrition over
a long period of years. There is no ' deliberate' experimentation. Results are
being measured continuously. So far as I am aware, nowhere else is this principle
of holding environment, etc., reasonably constant being employed for dairy cattle.
Yet it is precisely the same principle as that employed, though not for genetic
purposes, by the most venerable of all agricultural research institutes. The
' classical ' fields at Rothamsted, where certain plots have been under the same
treatment for ninety years, form an excellent example of this method of passive
research.

Already, and without the results of this planned and yet passive research,
there is information of undoubted value, of which perhaps the most important
is that quantity of milk is transmitted to a great extent independently of quality
as measured by fat-yield. But many of the other results are still open to question.
The problems that are now being tackled are not so much the determination of the
number of genetic factors concerned in the transmission of total yield as the analysis
of particular aspects of total yield, e.g., persistency of lactation. The various
characteristics of the lactation must be considered in relation to each other.

In other words, we are not so much concerned with determining the number
of genetic factors involved, as with analysing the lactation curve of individual
animals under a standard environment. (To ensure this, the greater number of
the calvings occur in two months of the year.) Two cows may give the same
yield of milk, but the one may give that yield in 200 days whereas the other takes
300: or the two cows may give the same yields in the same time but yet have
widely different lactation-curves. These, therefore, must be studied with refer-
ence to the various qualities of the milk, amount of fat, sugar, protein, and natural
minerals, as well as the colour, and size of fat-globule, etc., nor must the question
of the relative weights of the cows be ignored both before and after the lactation.
And all these are peculiarities concerning which we can already trace the workings
of heredity. It is of fundamental importance to understand the action of these
characteristics and their reaction on one another.

Thus it is small wonder that simple selection by the mating of the best to the
best gives a large proportion of disappointing results. One cow may yield 2,000
gallons for one set of genetic reasons, whereas another cow will accomplish the
same yield while possessing a very different constitution. There is, therefore,
need for analysis.

Moreover, research of this nature will certainly discover whether abnormal
modes of inheritance are operating, or whether quantity is simply a matter of
multiple factors. These abnormal modes include such things as sex-linked