There has been development of an antiretrograde flow device (DARIO), for sheep cervical artificial insemination (CAI). There, however, needs to be optimization of sperm volume and concentration of insemination doses when the DARIO is used for CAI. Objectives were to compare fertility rates (proportion of ewes lambing as a result of CAI) when there was use of the DARIO for CAI: two sperm volumes containing equal numbers of spermatozoa: 0.25 mL of 1,600 × 10 spermatozoa/mL and 0.50 mL of 800 × 10 spermatozoa/mL (Test 1 group), and two sperm volumes with a different number of spermatozoa/AI dose: 0.25 mL and 0.50 mL of 1,600 × 10 spermatozoa/mL (Test 2 group). There were 335 ewes from seven farms assigned to 60 batches (equally divided into a Control and Test 1 group). For the Test 2 group, 462 ewes from nine farms were assigned to 88 batches (equally proportioned into Control group and Test 2 groups). For the Test 1 group, proportion of ewes lambing as a result of CAI were 0.701 ± 0.2679 and 0.595 ± 0.2393 for the Control and Test 1 groups, respectively (P = 0.163). For the Test 2 group, proportions of ewes lambing were 0.550 ± 0.2598 and 0.658 ± 0.2412 for the Control and Test 2 group, respectively (P = 0.041). An inclusion of a larger number of spermatozoa per insemination in a 0.50 mL dose volume resulted improved proportion of ewes lambing as a result of CAI when there was used of the DARIO.
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