One problem encountered in the widespread application of sheep artificial insemination (AI) is the rapid decline in fertility of fresh or liquid chilled ram semen. An effective deep-freezing procedure would enable semen to be collected and stored from selected rams throughout the year for subsequent use in controlled breeding programmes, as well as facilitating the import and export of semen.Following some encouraging results from the use of pooled semen frozen by an Australian pellet method (Maxwell et al 1980), further field trials were conducted to investigate fertility of semen frozen from individual rams as well as pooled semen. The effects of season of freezing and number of inseminations on fertility were also investigated.

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The field application of a laparoscopic technique to permit intra-uterine insemination of ewes with frozen-thawed semen was examined in two trials, conducted over successive years, to (i) determine the optimum time of insemination relative to sponge removal/pregnant mares's serum gonadotropin (PMSG) injection and (ii) establish the relationship between semen dose and conception rate. Pooled semen was used in both trials, and each involved > 900 ewes in a number of commercial flocks. Maximum conception rates were achieved when insemination was conducted between 54 h and 60 h after sponge removal/ PMSG injection. However, there was no significant difference in conception rate when motile sperm numbers were reduced from 52-2 X 10 6 to 13-0 X 10 6 motile sperm per uterine horn. The overall conception rates (pooled over flocks and treatment groups) were 56% and 58% for the two trials, with a wide degree of variation between flocks in both cases (45% to 79% for trial 1 and 45% to 69% for trial 2). However, there was evidence for consistent differences in conception rates between the six flocks involved in both years of the trials.

One of the major limitations to the widespread use of artificial insemination (AI) in the United Kingdom (UK) sheep industry is that with frozen-thawed semen current insemination techniques result in lowered fertility. Consequently, only fresh or liquid-chilled ram semen can be used if commercially acceptable conception rates are to be achieved.

The widespread use of artificial insemination (AI) in the United Kingdom sheep industry has been limited by the poor conception rates obtained after cervical insemination of frozen-thawed semen. The major problem in this respect is the impairment of sperm transport through the cervix, particularly when AI is used in conjunction with oestrus synchronisation.Previous studies (Killeen and Caffery, 1982; Maxwell, 1984) have indicated that a laparo-scopic technique for intrauterine insemination in ewes may overcome such limitations. At the moment, however, sufficient data on the optimum time of insemination and sperm doses required to maximise fertility in British breeds are not available. The present study was conducted to establish the optimum time of intrauterine insemination using frozen-thawed semen.