Effect of insemination with doses of 2 or 15 million frozen-thawed spermatozoa and semen deposition site on pregnancy rate in dairy cows

The effects of low-dose artificial insemination (AI) on pregnancy rates have seldom been studied in lactating dairy cows. We evaluated the pregnancy results after AI with doses of 2 and 15 million frozen-thawed spermatozoa and the effect of semen deposition in lactating dairy cows. A total of 284 first inseminations with 2 million spermatozoa and 312 first inseminations with 15 million spermatozoa were performed on 480 dairy farms. Low-dose inseminations (2 million spermatozoa) under field conditions in commercial dairy herds, without estrus synchronization, generally resulted in significantly reduced pregnancy rates compared with normal doses (15 million spermatozoa). The bull x technician effect on fertility was statistically significant. This finding indicates that there is a high variability in fertility among bulls using 2 million spermatozoa per dose. The semen deposition site did not influence pregnancy rates. It is concluded that a dose of 2 million frozen-thawed spermatozoa is probably too low for most bulls to achieve acceptable pregnancy rates in dairy cows. (C) 2003 Elsevier Inc. All rights reserved.