STATISTICAL STUDIES, INDIAN DAIRY CATTLE                 97

different lengths of S. P. after calving, 85 days S. P. being chosen as
the standard. These corrections agree very well with those of Sanders
and Hammond [ 1923 ] for Penrith.

4.  S. P. affects the total lactation yield by affecting the length of the lacta-
         tion period.

5.  The curve describing the function of variation of milk yield with age is
         logarithmic in nature, meaning thereby that lactation milk yield at
         first increases at an ever decreasing rate with increase of age till the
         age of maximum production, and from there it decreases at an increas-
         ing rate with advance in age.
6.  The actual age of maximum productivity is roughly 3rd-4th lactation for
         pure-bred Sahiwals as against about the 6th for foreign ones, and
         approximately 8th for Pusa cross-breds. This earlier maturity of
         Indian cows is due to their age at 1st calving being a year higher
         and their lactation period being about two months longer on the
         average as compared with the foreign ones.
7.  Separate correction tables are given for Sahiwals and cross-breds to
         standardize their milk records for age to mature standard basis, and a
         comparison made between these results with those for foreign cows.
         It has been shown that whereas foreign cows and Pusa cross-breds
         increase to the extent of 30 to 40 per cent. of their 1st lactation yield
         till their age of maturity, and then begin to decline, the best average
         pure-bred Indians increase by approximately 10 per cent. only. This
         is very important, for it proves the extremely poor milking qualities
         of Indian cows and the highly efficient nature of cross-breds as milk
         producers. It further emphasises how indispensable cross-breds are
         for the quick solution of the Indian urban milk supply problem.

         Acknowledgments. I am highly thankful to Mr. W. Smith, Imperial Dairy
Expert, Bangalore, who arranged for the supply of all data and gave valuable
guidance throughout the progress of the work. But for the interest he evinced in
this investigation it could never have been so satisfactorily concluded. I am also
very much indebted to Bhai Balmukand, M.A., M.Sc., of the Department of Agri-
culture, Punjab, who gave much help in the mathematical part of the work, and to
S. Labh Singh, B.Sc. (Agri.), L.Ag., and S. Kartar Singh, B.Sc. (Agri.), L.Ag.,
N.D.D., of the Department of Agriculture, Punjab, and Mr. Z. R. Kothawala, B.Ag.,
B.Sc. (Edin.), N.D.D., Assistant to the Imperial Dairy Expert, Bangalore, for much
valuable help and criticism in the preparation of this paper.

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