cow period diet yield
   1     1     2    25
   1     2     1    38
   1     3     3    15
   2     1     3    86
   2     2     2   109
   2     3     1    39
   3     1     1    72
   3     2     3   124
   3     3     2    27
   4     1     3    76
   4     2     1    86
   4     3     2    46
   5     1     1    35
   5     2     2    75
   5     3     3    34
   6     1     2    63
   6     2     3   101
   6     3     1     1