Reproduction in Domestic Animals

142 KM Mortonoocytes derived from adult and prepubertal animals.Alterations in the expression of several developmentallyimportant genes have been observed in embryos derivedfrom prepubertal cattle (Oropeza et al. 2004) and sheep(Leoni et al. 2006a). Gene expression and epigeneticstudies will undoubtedly elucidate differences in oocytesand embryos derived from adult and prepubertalanimals. Furthermore, this technology will be used tore-evaluate hormone stimulation and IVP systems, sothat prepubertal oocytes and embryos may haveimproved competence.Two new techniques have great potential for combinationwith JIVET. Further reductions in the generationinterval on the female side could be achieved by incorporatingfoetal oocytes into IVP systems. Yet, foetal calfoocytes display lower rates of maturation, fertilization,cleavage and embryo development compared with oocytesfrom adult animals (Chohan and Hunter 2004) andfurther research is required. Utilization of gametes fromprepubertal male animals could dramatically reduce thegeneration interval on the male side. Spermatogenesiscan be initiated in prepubertal ram lambs by administeringeCG (Morton et al. 2004c). The injection of gametesfrom prepubertal ram lambs into IVM oocytes fromadult and prepubertal lambs resulted in the production of16–32 cell stage embryos (KM Morton, SL Catt, WMCMaxwell and G Evans, unpublished data). This technologyoffers, for the first time, a chance for producers toreduce the generation interval on the paternal side. Whilethe potential of this method has been demonstrated, thebirth of lambs produced from both prepubertal ram andewe lambs, and further refinement of treatment regimesfor ram lambs are required.In conclusion, oocytes from prepubertal animalsdisplay a reduced developmental competence whencompared with oocytes derived from their adult counterparts,resulting from perturbations to cytoplasmic andnuclear maturation. Despite these perturbations, oocytesfrom prepubertal lambs as young as 3–4 weeks of age arecapable of developing into viable offspring after transferto recipients. Recent advances in JIVET technology,which have significantly improved its efficiency, havebrought its commercialization closer and facilitatedincorporation with other emerging reproductive technologiessuch as sperm sexing. With the developments ingenomic technologies continuing to add to knowledgeregarding the differences between oocytes derived fromadult and prepubertal animals and the improvements inthe efficiency of JIVET this will bring, commercializationof this technology is foreseeable.AcknowledgementsThe Australian Research Council (ARC), XY Inc, Bioniche AnimalHealth Australasia and Sydney IVF for funding and research support.Professor W.M.C. Maxwell is thanked for his invaluable editorialassistance.ReferencesArmstrong DT, 2001: Effects of maternal age on oocytedevelopmental competence. Theriogenology 55, 1303–1322.Armstrong DT, Holm P, Irvine B, Petersen BA, Stubbings RB,McLean D, Stevens R, Seamark RF, 1992: Pregnancies andlive birth from in vitro fertilization of calf oocytes collectedby laparoscopic follicular aspiration. Theriogenology 38,667–678.Armstrong DT, Irvine BJ, Earl CR, 1994: In vitro fertilisationof follicular oocytes from juvenile lambs and their developmentalcompetence in vitro and in vivo. Biol Reprod50(Suppl.), 189.Armstrong DT, Kotaras PJ, Earl CR, 1997: Advances in theproduction of embryos in vitro from juvenile and prepubertaloocytes from the calf and lamb. Reprod Fertil Dev 9,333–339.Chohan KR, Hunter AG, 2004: In vitro maturation, fertilizationand early cleavage rates of bovine fetal oocytes.Theriogenology 61, 373–380.Cognie Y, 1999: State of the art in sheep-goat embryo transfer.Theriogenology 51, 105–116.Dominko T, First NL, 1997: Timing of meiotic progression inbovine oocytes and its effect of early embryonic development.Mol Reprod Dev 47, 456–467.Earl CR, Irvine B, Armstrong DT, 1994: Development oftechniques for the production of viable embryos from sixto seven week old lambs. Proc Aust Soc Anim Prod 20,428.Earl CR, Irvine BJ, Kelly JM, Rowe J, Armstrong DT, 1995a:Ovarian stimulation protocols for oocyte collection andin vitro embryo production from 8 to 9 week old lambs.Theriogenology 43, 203.Earl CR, Kotaras PJ, Rowe J, Kelly JM, DeBarro TM, 1995b:Laparoscopic selection of juvenile donors prior to stimulation.Proc Aust Soc Reprod Biol 26, 2.Howell CY, Bestor TH, Ding F, Latham KE, Mertineit C,Trasler JM, Chaillet JR, 2001: Genomic imprinting disruptedby a maternal effect mutation in the Dnmt1 gene.Cell 104, 829–838.Kelly JM, Kleeman DO, Walker SK, 2005a: The effect ofnutrition during pregnancy on the in vitro production ofembryos from resulting lambs. Theriogenology 63, 2020–2031.Kelly JM, Kleeman DO, Walker SK, 2005b: Enhancedefficiency in the production of offspring from 4- to 8-weekoldlambs. Theriogenology 63, 1876–1890.Kelly JM, Kleeman DO, Maxwell WMC, Walker SK, 2007:Effect of GnRH treatment on the maturation and in vitrodevelopment of oocytes collected from 4- to 6-week-oldMerino lambs. Reprod Fertil Dev 19, 947–953.Kennedy JP, Worthington CA, Cole ER, 1974: The postnataldevelopment of the ovary and uterus in the Merino lamb. JReprod Fertil 36, 275–282.Kochhar HP, Wu B, Morris LH, Buckrell BC, Pollard JW,Basrur PK, King WA, 2002: Maturation status, proteinsynthesis and developmental competence of oocytes derivedfrom lambs and ewes. Reprod Domest Anim 37, 19–25.Ledda S, Bogliolo L, Calvia P, Leoni G, Naitana S, 1996a:Developmental competence of follicular oocytes from juvenilelambs matured in vitro in different conditions. J ReprodFertil Abstr Ser 17, 28.Ledda S, Bogliolo L, Leoni G, Calvia P, Naitana S, 1996b:Influence of vasoactive intestinal peptide (VIP), atrialnatiuretic peptide (ANP) and insulin-like growth factors-I(IGF-I) on in vitro maturation of prepubertal and adultsheep oocytes. Zygote 4, 343–348.Ledda S, Bogliolo L, Calvia P, Leoni G, Naitana S, 1997:Meiotic progression and developmental competence ofoocytes collected from juvenile and adult ewes. J ReprodFertil 109, 73–78.Ledda S, Bogliolo L, Leoni G, Naitana S, 1999: Productionand lambing rate of blastocysts derived from in vitromatured oocytes after gonadotropin treatment of prepubertalewes. J Anim Sci 77, 2234–2239.Ó 2008 The Author. Journal compilation Ó 2008 Blackwell Verlag