The influence of passage time of the transfer gun through the uterine cervix and body to the embryo insertion site on pregnancy rate was analysed in 248 recipient heifers (mean age: 15–17 months). Embryos (90 fresh and/or 88 and 70 frozen in glycerol and ethylene glycol, respectively, grades 4 and 5, stage 1 or 2) were transferred to the ipsilateral uterine horn on day 7. Two different transfer guns were used in this experiment: a sterilisable steel transfer instrument to be used without sheaths with a removable tip made of gold-plated stainless steel (Wörrlein Minitüb) or a transfer stylet with sheaths with a metal tip and a side opening (Cassou gun, IMV Technologies). The time of passage of the instruments through the uterine cervix and body to the site of embryo deposition in the uterine horn was measured in the study. In order to randomise the risk of errors, all manipulations were carried out by the same experienced operator. The average time needed for the insertion of embryos into the uterus was 50.6 seconds (s) and it was longer for the transfer gun with sheaths than for the metal-tipped transfer gun (60.1 and 40.8 s, respectively) (P < 0.001). The average conception rate was 45.6%. If the time needed to insert embryos into the uterus was 10-60 s, the conception rate was 53.4% (up to 20, 21–30, 31–40, 41–50 and 51–60 s − 57.7, 52.5, 50, 51.5 and 50%, respectively). In contrast, if the time needed to insert the embryo in the uterine horn was longer than 60 s, the conception rate was 20.4% (61–80, 80.1–120 and > 120 s − 28.0, 6.0 and 24.9%, respectively). Thus, it cannot be excluded that the type of the applied transfer gun may influence pregnancy rate in recipient cows due to its effect on cervical passage time.
