Effects of cervical insemination with frozen semen on fertility and litter size of Norwegian sheep

This paper presents data on fertility and litter size obtained with artificial insemination with frozen semen in five breeds of Norwegian sheep. The study is based on cervical inseminations reported by the technicians/veterinarians for the period 1984–1988. During this period 3000–3600 elite ewes were inseminated each year with semen from genetically superior rams. In addition, lambing data from sheep recording was used in this study. The non-return rate (NR%), defined as percent ewes not returned to service within minimum 20 days, was estimated to be about 60%. This variate was affected significantly by technician/veterinarian, flock-year, ram, age of ewe, number of inseminations per heat, date and time of insemination. The analysis indicates a reduction in litter size at birth of about 0.2–0.4 lambs when elite ewes were artificially inseminated rather than naturally mated. The optimal insemination time was found to be 15–20 hours from heat detection. It is also shown that technicians obtaining high NR% also obtain lower reductions in litter size from AI.