38
CONTROL OF FERTILITY IN FARM ANIMALS [Vol. XXVI, Part I,
examination of pregnant genitalia showed the incidence of embryonic mortality in
9 per cent of the buffalo-cows and 8 per cent of the cows. The dissection of the
after birth showed no signs of embryonic remains in the three classes of animals.
DISCUSSION
In buffalo-cows the breeding efficiency was considerably higher than that reported
by Hafez [1952b] from the breeding records under free mating conditions. The
interval to post partum conception in the present study was shorter than that reported
by Hafez [1954]. The previous records for the breeding efficiency was 85.80 per cent
and the interval to post partum conception 43 days on an average. This shows that
some of the oestrus cycles were either of short duration or of weak symptoms. Such
cycles can be detected by close observation and by continuous association with the
buffalo-bull. This point is of major significance in practical buffalo breeding.
The proximity of the male has an effect on the degree of receptivity of the female
and probably on the duration of oestrus [Hafez, 1954]. Cows which are classified
as shy breeders (showing weak signs of oestrus) must be joined continuoulsy with the
bulls when mating is desired. In general expectancy lists of oestrus must be kept
for all the breeding females (calculating the expected cycle by adding some 21 days
to the previous oestrus) so as to raise the reproductive efficiency. Since the interval
from calving to conception is unduly prolonged, it is advisable to mate the buffalo-
cow some 30 to 40 days after calving instead of the usual practice of 60 days. The
probable decrease in the milk yield due to subsequent pregnancy would be less ex-
pensive than cutting down the reproductive potentiality of the animal which is as
good as risking a whole lactation.
Since the genotype environment may be important in fertility [Hignett, 1950]
breeds or types adapted to particular environments are required to obtain maximum
fertility. The best genetic method for achieving fertility is not by selection but by
crossing. A certain amount of risk is attached to the use of first claves (in sequence
of calving) for breeding unless adequate reproductive records of ancestors and sisters
of the dam are available, as data on the dams' own performance at that time are
insufficient.
The common measure of fertility usually used is the conception rate in various
forms. This is unsatisfactory since it does not take into account those animals which
fail to show reproductive regularity. Calving intervals are also used as a measure
of fertility. They do not include animals which have calved and may be biased by
deliberate extension of their intervals to obtain maximum production from persistent
milkers. Meanwhile little is known about the extent to which dams differ in their
ability to produce offsprings of high or low conception rate. On the other hand, there
is little information on the extent to which the differences between bulls are genetic
and are capable of being transmitted from bull to bull.
The Egyptian fat-tailed ewe lambs showed their first oestrus during the shortest
days of the year (December). This is in agreement with a previous report by Hafez
(1952a). Conception in the Rahmani ewe lambs took place after an average of 1.1 ser-
vices. This shows that the first oestrus was accompanied by ovulation. It is sugges-
ted here that the first observed oestrus was preceded by one or more silent heats
(ovulations without oestrus) as the ewe lambs show in the field some sexual desire