title: Relationship between in vitro fertilisation of ewe oocytes and the fertility of ewes following cervical artificial insemination with frozen-thawed ram semen.
abstract: No laboratory test exists that can reliably predict differences among rams in field fertility after artificial insemination (AI) with frozen-thawed semen. In vitro fertilisation (IVF) has been proposed as a method of predicting these differences. The objectives of this study were to evaluate whether IVF system could discriminate among rams of different fertility in vivo after AI using frozen-thawed semen. Also, to examine effects of lowering sperm concentration on discrimination power between rams used for IVF. The aim of Experiment 1 was to evaluate the effect of altering the sperm concentration from 2 x 10(6) to 0.03125 x 10(6) spermatozoa/mL on subsequent cleavage rate and blastocyst rate in vitro. In Experiment 2, six rams (three High and three Low in vivo fertility; average pregnancy rates of 37.6% and 21.8%, respectively) were compared for their fertilising ability in IVF. Spermatozoa from each of the six rams were added to ewe oocytes using a concentration of either 2 x 10(6) or 0.0625 x 10(6)/mL. There were six replicates with 25 oocytes per well and two wells per ram per replicate. Cleavage rate was monitored at 48 h post-insemination (p.i.) and blastocyst rate determined on Days 6-8 p.i. In Experiment 1, cleavage rate increased with increasing sperm concentration and blastocyst rate was not affected by sperm concentration on any day. When the six rams were tested using 2 x 10(6) spermatozoa/mL, no significant differences were found between High and Low fertility groups for cleavage rate or blastocyst rate on Days 6, 7, or 8 p.i. (P>0.05). When the experiment was repeated using 0.0625 x 10(6) spermatozoa/mL, no differences were found between High and Low group rams for blastocyst rate on any of Days 6, 7 or 8 p.i. (P>0.05). However, there was a significant difference between High and Low fertility rams for percentage of oocytes cleaved (16.4, S.E. 2.02%; P<0.01) and the correlation between fertility in vivo and cleavage rate in vitro was significant (P=0.013). Replicate of IVF was a source of significant variation for both cleavage rate and blastocyst rate and conditions need to be further controlled. However, we suggest that using a low concentration of spermatozoa (0.0625 x 10(6)/mL) for IVF may be a useful method for predicting field fertility of frozen-thawed ram semen.
authors.affiliation: Department of Animal Science, The Centre for Integrative Biology, Conway Institute of Biomedical Research, University College Dublin, Lyons Research Farm, Newcastle, County Dublin, Ireland.
authors.forename: C M
authors.initials: CM
authors.lastname: O'Meara
authors.forename: J P
authors.initials: JP
authors.lastname: Hanrahan
authors.forename: A
authors.initials: A
authors.lastname: Donovan
authors.forename: S
authors.initials: S
authors.lastname: Fair
authors.forename: D
authors.initials: D
authors.lastname: Rizos
authors.forename: M
authors.initials: M
authors.lastname: Wade
authors.forename: M P
authors.initials: MP
authors.lastname: Boland
authors.forename: A C O
authors.initials: AC
authors.lastname: Evans
authors.forename: P
authors.initials: P
authors.lastname: Lonergan
mesh_terms: D000818:Animals; D002584:Cervix Uteri; D015925:Cryopreservation / Q000662:veterinary*; D005260:Female; D005298:Fertility; D005307:Fertilization in Vitro / Q000662:veterinary*; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D008297:Male; D009865:Oocytes / Q000502:physiology*; D011247:Pregnancy; D012661:Semen / Q000502:physiology*; D012662:Semen Preservation / Q000662:veterinary; D012756:Sheep; D013076:Sperm Count