ULTRASONOGRAPHIC ANALYSIS OF GESTATION IN MINK (MUSTELA-VISON)

Mink are seasonal breeders that display an obligate delay preceding im plantation and a post implantation gestation of 31 d. The purpose of t his study was to evaluate gestational parameters in mink by ultrasonog raphy. A total of 92 female mink were mated twice during the period fr om March 2 to 20. The mink were scanned once and allowed to whelp (n=5 5); or scanned at 3 to 5-d intervals until parturition (n=13); or imme diately subjected to autopsy (n=24) after scanning. Embryonic age was calculated from the date of parturition or from crown rump length. Ute rine swelling diameter and fetal head size were correlated with embryo nic age. The gestational sec grew rapidly once implantation had occurr ed. Uterine swellings of 4 to 5 mm in diameter were found on Days 2 to 4 Post implantation and increased through Days 18 to 20, at which tim e they began to elongate due to the longitudinal growth of the fetus. Fetal cardiac activity could be detected on Days 10 to 12 post implant ation in live embryos. The heart frequency was 198+/-3.0 beats per min ute and did not vary from Days 12 to 30 post implantation. Fetal head diameter of 5 mm was first detected on Day 19 post implantation and gr ew gradually to 9 to 10 mm at parturition. It was not possible to accu rately assess the number of conceptuses in utero. We conclude that ult rasonography can be employed in mink to diagnose pregnancy, to predict the parturition date and to determine the presence of live fetuses.