EQUINE FROZEN-SEMEN - FREEZABILITY AND FERTILITY FIELD RESULTS

The freezability of stallion semen defined as the number of selected e jaculates/total number of ejaculates frozen from 161 different stallio ns was analyzed. Of the stallions, 19, 30, 27 and 24% had a freezabili ty of 0%, 0 to 33%, 33 to 66%, over 66%, respectively. In 85 different stallions, the correlation of freezability between first and second y ear was 0.60 (P<0.001). The relationship between fertility with fresh and frozen semen and freezability was analyzed in 40 stallions whose f reezability and fertility information was recorded during 5 years. The re was a strong relationship between fertility of fresh semen and seme n freezability (P<0.001). However, the relationship between fertility of frozen semen and freezability was not as marked (P<0.05). Analysis of the field fertility per cycle results when mares were bred with 300 or 150 x 10(6) total spermatozoa at different frequencies until ovula tion indicated that mares that were inseminated 2 times or more per es trus show an improved fertility in comparison with mares inseminated o nly once (34%, n = 1576 vs 26%, n = 626; P < 0.001). Foaling rate when mares were inseminated with frozen semen (1858 mares during 8 breedin g seasons) was mainly influenced by mare age (<16 years: 54% vs greate r than or equal to 16 years 42% p<0.001). Date of first insemination ( before May 15: 58% vs after May 15: 37%) also had a significant effect on foaling rate (P<0.001). (C) 1997 by Elsevier Science Inc.