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STATISTICAL STUDIES ON BREEDING DATA [Vol. XXVIII, Part II,
The index for bull No. 255 in the Hosur herd was as low as 2917 lb. even though
its dam's performance, averaged over three lactations, was as high as 9164 lb. Again
amongst the five bulls in the Bangalore herd for which the dams' records were
available, the index for Ziman was the lowest and that for Unique was the highest
even though the average yield of Ziman's dam was higher than that of the dam of
the latter bull.
The above results clearly indicate that selection of bulls from high yielding dams
is not sufficient to ensure their good transmitting ability. Emphasis should also
be laid on the breeding worth of the sires of these young bulls. In other words
the selected bulls should not only be from high yielding dams but should also have
high yielding paternal half or full sisters. A uniform policy of using each bull
in service on a sufficient number of cows to obtain about 15 daughters and of
maintaining all the daughters until they complete one lactation on the farm will be
necessary to assess the prepotency of the different sires used. Exceptions could
be made only in the cases of calves suffering from contagious diseases or sterility.
Retention of all female calves born till the completion of one lactation and
selection of the stock on their milking performance would naturally necessitate the
culling of the bulk of the cows after three or four lactations in the herd except for a
few very high yielders, if the herd strength is to remain nearly constant. This
would incidentally bring down the generation interval between dam and daughter.
It is recognised that the increase in the proportion of first calvers in the herd would
result in the dimunition of the annual herd average initially. Such a temporary
loss is likely to be more than compensated by the accelerated pace of genetic improve-
ment through a sounder selection policy. In so far as the principal object for which
these herds are maintained is the production of superior genetic stock and not solely
economic supply of milk as in the case of commercial dairies, it is of utmost importance
that a scientific breeding programme which ensures most rapid achievement of the
aim is adhered to in spite of any additional outlay necessary for carrying out such
a programme.
It is necessary to point out that the present study, comprehensive as
it was aimed to be, suffered from handicaps owing to gaps in information which it
would be desirable to avoid. For a critical quantitative appraisal of the changes
brought about in a herd in the course of a period of years to be really fruitful, it is
not only necessary that records on various relevant items are maintained carefully
but it is also equally essential to have periodic statements describing specifically and
accurately the breeding policy followed (including criteria for selection and the system
of mating) and also the changes in it and in the feeding schedules and practices of
management as and when introduced. Without these it is difficult to assign con-
cretely the changes observed to different sources of variation and draw conclusions
of practical value for the future. The few gaps in the data such as the maintenance
of records of all the services including infertile ones, the specific reason for culling
of each individual, the separate recording of milk yield at each time in the case of
three times milking, etc. have been already mentioned. Except for this, the data
which were on the whole carefully recorded provided a satisfactory basis for the
present study.