Fertility and fecundity in the Australian sheep flock

Abstract After decades of decline, the Australian sheep flock aspires to rebuild its population of breeding ewes. A successful, rapid rebuild will rely on high pregnancy rates and number of lambs born and reared. To examine this potential, historical pregnancy scanning records were collated from two experienced sheep pregnancy scanning businesses (years 2006 to 2019) from 15,397 mobs of ewes, totalling 7,443,314 ewes. Client details were de-identified and excluded from analyses, but when available details describing the mobs were retained, such as season of mating, production zone, ewe age, and breed. The key finding was a mean pregnancy rate (ewes pregnant per ewe scanned) of 0.76 ± 0.24, with a median of 0.83. Mobs scanned for litter size had a higher mean (0.84 ± 0.15) and median (0.89) pregnancy rate. The mean reproduction rate (fetuses per ewe scanned) was 1.21 ± 0.27 and the median was 1.25. None of the factors including age, breed, season, year or production zone explained the low overall mean pregnancy rate. The unexpected findings imply a problem exists with the fertility of many Australian sheep flocks and that pregnancy rate is a clear constraint on flock rebuilding aspirations.