LACTATION YIELDS AS MEASURES OF A COW'S MILKING CAPACITY.  243

used for this study of the 194 cows, whose milk yield for the first 4 lactations at
least is known, though actually, for a very large number of the cows' included,
the number of records known has been more than 4. Where, therefore, the
number of records known has been larger than 4, the highest of these, though
where only 4 are known, the highest out of the four, has been taken to measure
cows' milk-giving capacity. This procedure is justified in view of the results
already reported regarding the variations of milk yield with age, wherein it was
shown, that Indian cows in general increase in their yield till their 3rd lactation,
maintain it in the 4th, and thence decline at an ever-increasing rate, and there-
fore, where we know the yields for the first four lactations of a cow, as in this case,
we generally know her maximum milk-yielding capacity.

It is recognised that this idea of talcing the corrected maximum lactation
yield, as a measure of a cow's milking capability, might not find favour with
practical breeders, who feel, and rightly so, that in a cow it is not the exceptionally
high yield in any one lactation that counts, but it is the yield over a number of
lactations that really matters, and consequently in selecting cows, we should take
average yield for life, rather than the yield for any one lactation. But as shown
below the mean yield of a cow for several lactations and her maximum lactation
yield are highly correlated, and thus mutually convertable. Besides the maximum
yield is less variable and hence more reliable than the mean yield for several
lactations. This latter point is well-illustrated in Table II which gives the main
analytical constants of the curves for the generally accepted measures of a cow's
milking capability, e.g., mean corrected yield for first three or four lactations, and
the measure used in this study " corrected " maximum lactation yield.

                                        TABLE II.

Analytical constants of the curves for the mean " corrected" yields for the first 3 or 4
              lactations and " corrected " maximum lactation yields.