VIe CONG. INTERN. REPROD. ANIM. INSEM. ARTIF., PARIS, 1968, VOL. I

Thereafter the quick method of glycerolisation and equi™i-
bration was adopted as routine and 69,240 firstshave shown a
30/60 day non-return rate of 77.3%.

Further study showed that results obtained from six bulls
had a high rejection rate after freezing. Immediately experi-
ments were initiated with the height of the racks above the
liquid nitrogen level, but these had no beneficial effect. There
followed experimentation with the levels of glycerol and length
of equilibration times and it was found that four bulls respon-
ded well to a shorter equilibration period, two bulls to four
hours, one to three and a half hours and one to two hours.
Another bull reacted well to a reduction of glycerol to 5%.

With the sixth bull we have had little success, occasionally

we obtain good frozen semen from different techniques but never
consistently on any single technique. We postulate that there
is a variable factor present in this bull's semen which reacts
against our techniques for freezing, as the bull produces semen
of a high quality and his non-return rate on liquid semen is
excellent.

Finally an experiment was carried out using split samples
of the ejaculates of four bulls of high fertility for a period
of one month in which one half of the sample was diluted to a
dose rate of 20,000,000 total spermatozoa and the other half
to 10,000,000.

The results are shown in fig. c, although as demonstrated
in the table there were very big differences between inseminators.
Those who had enjoyed a high non-return rate prior to the ex-
periment showed little significant difference whilst those insem-
inators normally on the lower plane showed a marked drop on the
lower dose rate.

 

In conclusion, we are of the opinion that the quick method
of glycerolising and short equilibration period described, using
standard 0.5 c.c. straws and vapour freezing, afford a technique
which will give satisfactory results with the great ma jority of
bulls and lastly, but not least, is a technique which fits into
a normal working day.

With the methods described a small laboratory team of one
technician and two female assistants can easily prepare, process
and distribute 20,000 straws per normal working week and within
the compass of a normal day.

The author hastens to acknowledge the publications of
R. Cassou and R. Jondet and co-operation and personal communica-
tions with R. Cassou, R. Jondet, R.J. Cooper and R. W. Hutchinson,

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