A survey of reproductive success in South African Thoroughbred horse breeding from 1975 to 1999.

The data and an analysis of the statistical summaries from the 'Return of Mares' of the General Stud Book of The Jockey Club of Southern Africa from 1975-1999 are presented. The total number of mares covered per season ranged from 7393 (1992) to 5180 (1995). The total living produce in the period surveyed was 95 317 foals. The categories of data examined include: the total number of mares covered per season; the total numbers and percentage of their living produce; the total numbers and percentage dead produce, 'slips' and foals born dead, barren and 'no return' mares; and the total number of live twins reported. The percentage live foals per season increased from 52 to 62% and the percentage barren and 'no return' mares declined from 35.50 to 28.40% over the period surveyed. The number of live twins reported showed a dramatic reduction from 156 to 5. These apparent improvements are ascribed to a combination of factors including advances in veterinary knowledge and technology. The findings are similar to those reported by similar surveys of national Thoroughbred populations from North America and Germany. There is an indication to broaden this annual survey by recording additional parameters more accurately reflecting reproductive efficiency rather than a cumulative annual total of live foals.