19 FACTORS AFFECTING PREGNANCY RATE AFTER ARTIFICIAL INSEMINATION WITH EQUINE SEMEN: PRODUCTION OF THE FIRST FOAL USING FROZEN SEMEN IN KOREA

Abstract

Research in the area of equine artificial insemination (AI) has led to its increased application in field trials (Loomis and Graham, 2008). However, procedures for equine semen collection, cooling and freezing of semen and artificial insemination need further improvement. This study examined the effect of semen preparation and ovulation on equine AI success. Stallion semen was collected via artificial vagina, diluted with skim-milk extender, and preserved by either cooling to 4°C or cryopreservation and storage in liquid nitrogen. Mares were examined by ultrasound for follicle development with every 12 h during oestrus. During AI, semen was inserted into uterine horn adjacent to the ovulating follicle sized over 4 cm and irregular shape. In experiment 1, mares were inseminated with either cooled, cooled-transported, or frozen–thawed semen. Cooled semen was used immediately after collection and cooling. Cooled-transported semen was used 4 h after semen collection and dilution. Semen freezing procedure was followed by Moore et al. (2006). In experiment 2, we examined the effect of buffer (skim-milk extender), which was infused into the uterus at the time of AI with frozen–thawed semen. In experiment 3, we compared AI pregnancy rates for mares ovulating spontaneously v. after treatment with hCG. Pregnancy data were analysed Chi square test where P-values < 0.05 were considered significantly different. In experiment 1, the pregnancy rates after AI using cooled, cooled-transported, and frozen–thawed semen were 60 (10/6), 50 (8/4), and 37.5% (8/3), respectively, and similar among treatments. In experiment 2, the pregnancy rate of mares infused with buffer at AI was 37.5% (8/3) which was higher than that with no buffer (0%; 6/0). In experiment 3, the pregnancy rates of mares were similar between ovulated spontaneously (25%; 8/2) and ovulated with hCG (50%; 8/4). The results suggest that equine semen that has been cooled, cooled and transported or frozen can be successfully used to establish AI pregnancy. Also, the pregnancy rates after AI can be increased by infusing buffer into the uterus at AI or by inducing ovulation with hCG. These experiments resulted in the first foal produced in Korea with frozen–thawed equine semen.