It was observed that glycerol concentrations above
4% had a toxic effect on spermatozoa, altering their
morphology to give many "bent tail" forms. It was
also noted that complex media gave poorer results
than simplified ones. It was concluded that the
most ideal process would be one fulfilling the
following requirements:

(
(

(
(

Freezing by the pelleting method (Nagase and
Niwa, 1963) was clearly indicated and all subsegquent
freezing work was done by this method using a medium
consisting of 25% egg yolk, 71.5% lactose (11%
solution) and %.5% glycerol, The equilibration
period was two hours. _Pellets were thawed rapidly
in a temperature of 45°C.

) A low rate of dilution.

) A final concentration of glycerol
less than 4%.

A rapid rate of freezing.

A simplified medium,

o' ©

Qo0
NN

With this method adopted as a standard one for
freezing, further studies have been directed at the
suitability otf raw ejaculates, the improvement of
AI instruments and handling methods for ewes and the
optimum time for insemination.

(b) Semen collection and insemination.

It has been found that freezing results are
poorer when the ejaculate is unduly admixed with
accessory fluids as may occur in electro-ejaculation.

A disposable plastic insemination rod with a
beaded tip and angled neck has been found the most
suitable instrument for effecting deep intra-cervical
inseminations. The experiment summarised in table 1
indicates the desirability of a deep deposition of
semen.

The reduction of stress in the handling of the

ewe has been found important and an improved
restraining crate has been found helpful.

1034