Vie CONG. INTERN. REPROD. ANIM. INSEM. ARTIF,, PARIS, 1968, VOL. Il

BREEDING EFFICIENCY OF BULL SEMEN
‘FROZEN IN STRAWS AND IN PELLETS

H.C. ADLER, C. JESPERSEN, J.H. MEDING and N.O. RASBECH
Royal Veterinary and Agricultural College, Copenhagen V, Denmark

During recent years much attention has been paid to the freezing
of bovine semen by two different techniques, the method of pelleting
(1) and the straw method (2,3). In Denmark the use of frozen semen is
increasing; so far no A.I. centre has entered upon a loo per cent fro-
zen semen programme, but at present some centres are considering to
do se. In this connection information on the two methods is of inter-
est, and a number of irials in the field under Danish conditions are
therefore being made. The present paper reports one of these trials
by which the breeding efficiency of the two methods was directly com-
pared. As far as known to the writers no such comparison has been re-
ported previously.

MATERIAL AND METHODS. At an A.I. centre semen from 6 bulls collected
during a period of 6 weekg wag used for freezing provided the concen-
tration was at least lxlo /mm and the initial motility was 70% or
more. Semen with a motility of less than 40% immediately after free-
zing was discarded.

Thirty-four ejaculates were accepted for use in the trial. Eight
ejaculates were split in 2 and used for both pellets and straws.
Twelwe ejaculates were used exclusively for pellets and 14 for straws
only. For each bull it was attempted to produce equal numbers of pel-
lets and straws.

Straw semen was diluted 1:9 with Laiciphos (10% egg-yolk) at
35 C and cooled to 4 C in 90 min., then further diluted 1l:1 by
3-fractioned addition of the same diluent containing lo% glycerol so
that the final dilution rate was 1:18 and the final concentration of
glycerol was 5%. The equilibration time was 5 hrs. The semen was
filled into medium straws (0.5 ml) which were sealed, and the free-
zing took place in the horizontal position 4 cm above the surface of
liquid N, in a Linde LR 250. After 7 min. the straws were immersed in
the N2 for storage.

Pellet semen was diluted 1:3 at 35 C with 75.3 ml 117 lactose
to which was added 20 ml egg-yolk and 4.7 ml glycerol and cooled to
4 C in 1 hr. After additional 3 hrs. droplets of 0.l ml were placed
on solid CO, for freezing. After lo min. the pellets produced were
transferred to liquid N, for storage.

Fourteen technicians used the frozen semen for 1. inseminations
during 6 weeks following the period of freezing. For each technician
| and bull every second insemination was made with a pellet and every
| second with a sjraw. Thawing took place in water at 350 C immediately
| before insemination. The pellets were diluted to 1 ml with homoge-
nized sterile milk. The straws were completely emptied at insemina-

| tion by means of Cassous pistolette, whilst 15% of the pellet was
i lost in the vial and the plastic insemination pipette; the dilution

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