Abstract:
(1) One hundred and ninety-six merino sheep, maintained under
dry lot conditions, were submitted to artificial insemination with
fresh and stored semen obtained from highly fertile merino rams.
The resulting pregnancies were compared with eighteen control sheep
which were mated normally. Table 16 shows the results in
summarised form.
(2) The technique employed in the operation was satisfactory,
as indicated by the results in groups 2, 3 and 4.
(3) The cause of failure to impregnate by stored semen is due
to deterioration in fertilising capacity. The activity of the spermatozoa
is not always an indication of their capacity to impregnate,
although active motility is necessary for fertilisation.
(4)The number of inseminations required to establish pregnancy,
the gestation periods and the weights of the lambs born do not differ
significantly from normal mating.
(5) There were five cases of dystocia in the groups treated by
artificial insemination as compared with two in the normal service
group. One deformed lamb was born in the inseminated groups.
No importance is attributed to these occurrences.
(6) The lambs born were of normal weight and their post-natal
development was excellent.
(7) A field observation was carried out on 680 Karakul sheep;
378 lambs were born with a mean gestation period of 150.1 days.
These sheep were divided into two groups because of their condition:
482 sheep were suckling lambs; of these 319 became pregnant and
324 lambs were born. The percentage pregnancy was 66.1848. The
other group was not suckling lambs and was fat. There were 198
ewes inseminated of which only 51 became pregnant and gave birth
to 54 lambs. The percentage pregnancy was only 25.7599.
There is an indication that the fat condition of the ewes rendered
conception more difficult.
(8) The artificial insemination of sheep with fresh semen or with
semen stored up to 12 hours will give satisfactory results in sheep
husbandry in South Africa. However, it is suggested that the
employment of artificial insemination has a limited value in
reproduction of sheep when the local conditions are compared with
those in countries where insemination has become a routine measure
in the production of livestock.
(9) No pregnancies followed insemination with semen stored
longer than 72 hours.
(10) Artificial insemination overcomes the difficulty experienced
in mating sheep with extreme tail development. It has proved
satisfactory with the Karakul and Ronderib-Afrikaner.
(11) Dilutor with pH value of 6.9 to 6.99 gave the most satisfactory
results.
