A STUDY OF THE DATA OF MILK YIELDS OF VARIOUS TYPES
                          OF CATTLE OBTAINED FROM THE RECORDS OF
                               GOVERNMENT MILITARY DAIRY FARMS.

          I. RATE OF DECLINE IN MILK YIELD WITH ADVANCE IN LACTATION.

                                                       BY

                                        K. P. R. KARTHA, B.A.,

Statistical Assistant, Animal Husbandry Bureau, Imperial Council of Agricultural
                                                  Research.

                 (Received for publication on the 14th December 1933)

                                         (With seven charts)

                                           INTRODUCTION.

It is well known that the rate of milk secretion in dairy animals rises rapidly
during the first few weeks following parturition, reaches a maximum and then de-
clines more or less rapidly until the animal dries off. The length of the milking
period depends largely on the service period, which is the length of the interval that
elapses between calving and the recurrence of conception. If conception takes place
within two to three months, the animal will remain in milk for about ten months
and longer if conception is delayed.* Of this milking period only during the first
month is the yield found to be rising. The maximum is generally reached at the
end of the first month, or in the second month, and the rest of the lactation period
is associated with decline. The period of rise is thus very small compared to the
period of decline ; the yield for the lactation should, therefore, depend to a large ex-
tent on the rate at which the yield falls off. In the following pages it is proposed
to examine this rate of decline in the case of herds of Indian and cross-bred cattle
and buffaloes living under fairly good conditions of feeding and management obtain-
able in the Government Military Dairy Farms in India.

                                                   METHOD.

The rate of decline, or its complement, persistency, has been studied by various
investigators in England and America, and various methods have been employed in

* How far the lactation length depends upon service period will be seen from the correlation between
the two. The coefficient of correlation is about 7. For every month's delay in service the lactation is
prolonged on an average by a little over half a month.

                                                      (36)