Insemination time and dilution rate of cooled and chilled ram semen affects fertility.
Adult Merino ewes (n=448) were apportioned into two groups and inseminated with: extended at 30 degrees C with skim milk and stored for 6h at 15 degrees C (cooled semen) or extended with skim milk-citrate trisodium with egg yolk and stored for 24h at 5 degrees C (chilled semen). Each group was further subdivided according to the time of cervical insemination at 42, 46 and 50h after pessary (MAP-60 mg) removal and according to the dilution of the semen (120 x 10(6) spermatozoa in 0.05, 0.1 and 0.2 ml). The pregnancy rate after insemination with cooled semen was 50% better than that after chilled semen (56.7 vs. 37.5%; P<0.001). Pregnancy rate was not affected by the volume of insemination; however, there was a tendency of increased lambing rate with an insemination dose of 0.1 cc (1:2, dilution), especially when the ewes were inseminated with cooled semen. The effect of time on insemination was significant only in ewes inseminated with chilled semen at 5 degrees C (P<0.01). Insemination carried out 46 h after pessary removal resulted in higher pregnancy and lambing rate (36.5, 31.1; 52.0, 45.3; and 24.0, 20.0 at 42, 46 and 50h, respectively). Pregnancy of ewes inseminated with chilled semen at 46 h after pessary removal was similar to that obtained using cooled semen (52.0 vs. 56.7%). From this study, it is concluded that advancing the time of insemination with chilled semen at 5 degrees C improves pregnancy and that the lambing obtained under these conditions is similar to the one obtained with cooled semen.
Fernandez-Abella
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Department of Animal Production, Faculty of Agronomy, Universidad de la Republica, CC, Salto 68136, Uruguay. ferabe@montevideo.com.uy
Preve
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MO
Villegas
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D000818:Animals; D003080:Cold Temperature; D004973:Estrus Synchronization / Q000379:methods; D005260:Female; D005298:Fertility / Q000502:physiology*; D007315:Insemination, Artificial / Q000662:veterinary*; D008297:Male; D008892:Milk / Q000502:physiology; D011247:Pregnancy; D018873:Pregnancy Rate; D011897:Random Allocation; D012661:Semen / Q000502:physiology*; D012662:Semen Preservation / Q000379:methods / Q000662:veterinary*; D012756:Sheep / Q000502:physiology*; D013076:Sperm Count / Q000662:veterinary; D013081:Sperm Motility; D013997:Time Factors