ABSTRACTS
Bull indexing. E. B. RICE and D. J. SHEAHAN (1941). Queensland J. Agri
55, 2, 126.
T HE genealogical history of each breed of dairy animals must be tabulated in Herd
Books. It must then be assumed that milk yield and butter fat contents are factors
which depend upon genes which are transmissible according to established Mendelian
rules of heredity. Milk yields should then be recorded. These premises having been
completed, the fundamental basis for dairy herd improvement is established.
Until the introduction of bull indexing, the milk and butter fat yields could be as-
certained for only the females. The male, however, is more important, economically,
because of its greater number of progeny than that of any one female. Out of the need
to determine the capacity of bulls to sire high producing daughters grew the various
methods of proving bulls. Such systems have been adopted in several countries during
the last two decades.
A bull is ' proved ' by comparing the milk and butter fat records of his daughters
with those of their dams. Yuill, of Victoria, recommends that ' there should be at least
ten daughters from at least five tested dams ', although in practice all daughters' records
should be compared with their dams. The ' proved ' bull sires daughters which definitely
produce more milk and/or more butter fat than their dams. The United States Depart-
ment of Agriculture found that only 52 per cent of 2242 bulls in the United States were
capable of doing this. Of 51 sires in selected herds studied in England, eight were found
to increase the production of their daughters over their dams. Artificial insemination,
it is suggested, would greatly assist the distribution of the germ plasm of such bulls.
Although many systems of comparing records of daughters and their dams have been
developed, the 'Mount Hope Commercial Index ' is used in Queensland. The most
important factors affecting the production of a cow, and therefore the index, are ' age of
the animal, the effect of environment, the length of dry period before commencing lacta-
tion, calving period, feeding, etc. ' Age correction is possible. Furthermore, the greater
the number of comparisons the less will be the effect of the other factors.
The bull index is based on the fact that the average production of, the daughters is
half way between that of their parents. This applies to both milk and butter fat yield.
In the Mount Hope Commercial Index the milk yield is age corrected and the actual test
averaged. The daughters are then placed midway between the dam and their sire giving,
thereby, the index of the sire. For example, if the average age corrected butter fat yield
of all dams is 350 lb. and that of their daughters, from the same bull, is 375 lb., the index
of the bull is 400 lb.
Age correction may be accomplished in many ways. Such correction is based on the
fact that a two-year old cow gives 70 per cent of its mature yield, a three-year old 80 per
cent and a four-year old 90 per cent. Yuill has worked out a table, giving at a glance
the age corrected figure for pounds of fat or gallons of milk, which is included in the
article.
[J. N. W.]
Uniformity through inbreeding. J. E. BALMER (1941). Holstein-Friesian
World 38, 10, 533.
THE theory of inbreeding is based on the fact that ' uniformity will best be achieved
by making the germ cells more uniform '. To accomplish this, animals are mated
to close relatives. Protoplasm is so complex that it cannot be analysed chemically ; it
can only be analysed by different matings. Line-breeding, inbreeding and in-and-in
breeding are each an attempt to concentrate the protoplasm of a particular family ; they
differ only in the degree of concentration they effect. Inbreeding with rigid selection,
it is said, is more useful for protoplasm analysis, or more specifically germplasm
analysis, than outcrossing. Gones may become so dilute and dissipated from outcrossing
that uniformity is almost impossible.
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