September, 1952] P. BHATTACHARYA AND S. S. PRABHU 173
to the centres from long distances and as such in a large number of cases, the insemi-
nations took place during the later phase of oestrus. According to Hammond [1927]
ovulation takes place 12 to 17 hours post oestrum. The sperm takes on an average
5½ hours (lesser in heifers) to travel to the place of fertilization [Brester et al.,
1940]. They survive for about thirty hours in the female tract [Trimberger and
Davies 1943; Laing, 1945], so that, if insemination is carried out towards the end
of oestrum, there is a greater chance of fertilisation taking place than if insemination
is performed during early oestrum. Laing [1945 b, c] observed consistently better
service rate among the free service group, i.e., where the bull was allowed to run
with the herd, than in the hand service group, except during the winter months,
when the duration of heat is short. He comes to the conclusion that the better
conception rate in the free service group is due to the service synchronising with
the end of oestrum, and thus close to ovulation. This conclusion is supported by
much higher fertility in herds where the bulls always run with the herd, than in
these where 'hand service' is practised, and the improved conception rates observed
by the Russian workers using double spaced inseminations [Andreev, 1937 ; Kurillov,
1937]. In this connection, the possibility of a certain percentage of the cows brought
to the centre receiving stray natural service either before, or after artificial service
due to the carelessness of the owners, has also to be borne in mind.
Among foreign countries, the most successful results with artificial insemination
are reported from Russia and Denmark. Smirnov-Ugrjumov [1945], reporting
the work of an artificial insemination centre serving several collective farms in
Russia, gives the percentage conceiving with fresh and stored (upto 24 hours) semen
at 96.6 per cent. Sorensen [1938] reports a percentage of 87.6 with 1.68 inseminations
per conception among 1,070 cows inseminated by him in Denmark. Holm [1945]
gives a range of 58—96 per cent for 78 co-operative cattle breeding associations in
Denmark, using artificial insemination and above 85 per cent in 60 out of these
78 associations. The high percentage of fertility observed in Russia might be
in large measure due to the techniques employed (Double-spaced in inseminations
and paper capsule methods of insemination). Twinch [1946] believes that the high
fertility rates achieved in Denmark are due to the Sorensen insemination instrument
and technique [Sorensen, 1946] i.e., use of fresh semen, the sterility service which is
allied with artificial insemination, and the prevalence of self-contained herds.
In the United States, Burch [1939] found among 439 dairy cows in the New York
Dairy herds bred during the five months period from 15 November, 1938 to 15 April,
1939 with semen from seven bulls, an average service rate of 1.99. Henderson
[1939] gives a service rate of 1.9 for 1,089 cows served by eight bulls. Bartlett and
Perry [1939] discussing the five co-operative artificial insemination units including
about 55,000 cows in New Jersey State, observed an average service rate of 2.0
for all inseminations performed. Davis and Williams [1940] found a variation of
1 to 4 inseminations per conception for different bulls with an average rate of 1.3.
Perry and Bartlett [1945] mention a service rate of 1.7 for cows selected at random
from a single artificial insemination association. Synder and Baltzer [1945] reporting
the work of Michigan Artificial Breeders Co-operative Inc. with eighteen bulls
supplying semen for 8,900 cows in eighteen local associations, found a fertility of
47 per cent at first insemination and a further 42 per cent at the second insemination.
In England, the service rate for the Reading centre is given as 1.7 by Bartlett [1944]