78         THE INDIAN JOURNAL OF VETERINARY SCIENCE AND ANIMAL HUSBANDRY [ I, II

gets older and therefore deteriorates in its nutritive value ; furthermore that this
seasonal variation is much more pronounced in Penrith than in Norfolk because of
the feeding of roots and other succulent foods to Norfolk cows as compared with
Penrith ones during the hot months when pastures parch and dry off and therefore
there is scarcity of succulent food and whatever grass there is, it is very fibrous
and low in nutritive value.

         A consideration of the above results as reported by Sanders together with a
study of the actual conditions under which the animals of our data have made their
records further supports the claim that these differences in milk yield means for
different calving months cannot be very significant, for the system of herd manage-
ment at these Military Dairy Farms is more or less perfect as an attempt is always
made to keep the feeding and management conditions quite uniform throughout
the year by stall feeding. Adequate protection from inclemencies of weather is
always provided by way of proper housing. Supply of succulent fodder is ensured
all the year round, either in the form of green fodder—there being no pastures—or
silage when green fodder is not available, though in the winter months roots, etc.,
are also fed, and during the months roughages are of poor quality they are supple-
mented by a fixed though liberal concentrate allowance. Under such ideal con-
ditions of herd management it is only too natural that there be no very great sea-
sonal variation of milk yield. That such is very probably actually the case is
shown by the results given above, hence no corrections have been applied for this
factor to the data. In this connection it might as well be noted that it is by no
means the intention of the author to imply that the lactation milk yield of a cow
cannot be affected by her month of calving. That such an effect is possible
is fully realized though its presence in the data reported is rather doubtful. This
conclusion, however, requires further investigation.

VARIATION OF LACTATION MILK YIELD AS AFFECTED BY :—B. SERVICE PERIOD.

         The distribution of the S. P. and its relations with the other three factors in
our data have already been discussed. In the present section an attempt has been
made to study the effect of S. P. on total lactation milk yield. To do this a
correlation surface was drawn for these two variables, i.e., milk yield and S. P. and
the mean milk yields worked out for the different service-period intervals, a study
of which showed the variation of milk yield with S. P. to be quite regular and
definite, the means for successive S. Ps. being quite smooth running. The main
statistical constants as derived from the same table are given in Table IX.