152 EFFECT OF EMBRYO TRANSFER AFTER ARTIFICIAL INSEMINATION ON THE CONCEPTION RATE IN DAIRY COWS UNDER HEAT STRESS IN SOUTHERN JAPAN

Abstract

A serious decline in the reproductive performance of dairy cows occurs in southern Japan in the summer period, when the total number of hot days ≥35°C numbers more than 20 days annually. Previous reports have mentioned the effectiveness of embryo transfer (ET) at 7 days after AI (AI/ET) under heat-stressed conditions. In the present study, we investigated the effect of AI/ET on conception rate (CR) under heat-stressed conditions in the summer period. Artificial insemination was performed at 13 commercial dairies in this study from August through September in 2007 and 2008. Seven days after AI, a single embryo was transferred into the uterine horn contralateral to the ovary with a corpus luteum (AI/ET, n = 82). Artificial insemination at oestrus without further treatment was assigned as the control group (AI, n = 367). In 2007, frozen–thawed embryos of Japanese Black cattle were transferred, and the same cattle were used for ET of fresh embryos in 2008. The temperature-humidity index [0.8 × temperature + 0.01 ×relative humidity (temperature –14.4) + 46.4], rectal temperature, and diurnal highest or lowest and average ambient temperatures were measured at the time of AI and ET. Cows were diagnosed for pregnancy at 42 days after AI by palpation per rectum and were reexamined by transrectal ultrasonography at 60 days after AI. The CR was calculated as the number of cows diagnosed as pregnant 60 days after AI divided by the number of cows inseminated. Fetal loss was calculated as the number of cows that did not deliver calves after term divided by the number of cows diagnosed as pregnant. The CR, number of AI, fetal loss, and type of newborn (Holsteins, AI origin; Japanese Black, ET origin) were confirmed retrospectively. For statistical analysis, Fisher’s exact test and Student’s t-test were used for comparison of the CR, fetal loss, and body temperature by using a statistical software program for PC (Excel Statistics 2006). The CR for AI/ET was 30.4% and for AI was 13.8% in 2007 (P < 0.01), and the CR for AI/ET was 30.8% and for AI was 21.5% in 2008 (P = 0.294). The average diurnal temperature was 31.1°C in 2007 and 30.1°C in 2008, and the temperature-humidity index was 81.8 and 80.8, respectively. On Day 8, the pregnant cows had a lower rectal temperature than the open cows in 2007, but not in 2008 (38.9 v. 39.4°C in 2007; P < 0.05; and 39.1 v. 38.9°C in 2008; P > 0.05). The fetal loss was 38.1% in AI/ET v. 7.4% in AI in 2007 (P < 0.05) and 12.5% v. 0% in 2008 (P < 0.05), respectively. The AI/ET procedure could improve CR in dairy cows during the summer period in southern Japan. However, other problems may accompany AI/ET, such as higher fetal losses.