A comparison of Merino and Dormer rams in terms of mating dexterity and sperm subpopulations characteristics

Thesis (MSc)--Stellenbosch University, 2016.

ENGLISH ABSTRACT: Assisted reproductive techniques (ART’s) play an increasingly important role in sheep farming systems to ensure the viability and cost-efficiency of production. Sperm quality is a major determinant of the successful application of ART’s, and therefore it is important to understand the factors that affect the viability and fertilizing ability of sperm. This study aimed to determine the influence of breed and genetic selection for reproduction potential on mating dexterity, sperm morphometric subpopulation characteristics and fertilizing ability. The technique used to collect semen samples can influence the quality of the sample, with the artificial vagina (AV) method yielding better samples than those collected by means of electro-ejaculation (EE). The use of the AV method requires the prior training of rams, and to date no standard operational procedure (SOP) has been formulated for the training of rams to use the AV. During the training of rams to use the AV, both inexperienced and experienced Dormer rams found mature Dormer ewes more attractive than yearling Dormers ewes, and in the training sessions the Dormer rams did not discriminate between Dormer and Merino ewes (in oestrus), that were used as teaser ewes to stimulate a sexual response in the rams. In contrast, Merino rams in this study were less discriminatory in their choice for either mature or yearling Merino ewes, with experienced Merino rams exhibiting a definite preference for a Merino teaser ewe. There was no conclusive evidence of a breed preference in inexperienced Merino rams. Breed and degree of sexual experience did not influence ease of habituation of a ram to the presence of the semen collector and/or assisting staff. Rams could be habituated within approximately 4 weeks and during a minimum of 8 training sessions when trained by experienced personnel. A higher frequency of training, i.e. 18 training sessions during this 4-week period will result in a more established baseline behaviour that will indicate whether a ram could be successfully trained to use the AV. There was no conclusive evidence that experienced Merino or Dormer rams ejaculated into the AV more readily, when compared to the Dormer and Merino inexperienced rams. It has to be noted that only 50% of the experienced Dormer rams could be successfully trained to use the AV, compared to 90% of the experienced Merino rams. Of the inexperienced rams only 40% of both the Merino and Dormer breeds could be trained to use the AV. Four distinct sperm morphometric subpopulations were identified in semen samples obtained from Dormer and Merino [High reproduction potential line (HL) and Low reproduction potential line (LL)] rams in this study. No significant differences were reported between the breeds in terms of ejaculate sperm subpopulation structure. The sperm subpopulation analysis of the HL and LL ejaculates indicated minor but non-significant differences between certain subpopulations. Breed or genetic selection had no influence on most post-thaw sperm parameters, except for post-thaw sperm viability that differed between HL and LL rams. A significant difference was observed between the sperm binding capacity of Dormer and Merino sperm. Sperm obtained from HL rams tended to have a better binding capacity than sperm obtained from the LL rams. No conclusive evidence of a correlation between sperm binding capacity and any sperm morphometric subpopulation was obtained. In conclusion, the factors contributing to the difficulty of training experienced Dormer rams, as well as inexperienced Dormer and Merino rams, to use the AV warrants further investigation. Future studies should further investigate the influence of breed and genetic selection on sperm subpopulation traits. Additional research to clarify the relationship between sperm subpopulations traits and the potential role of sperm competition in the determining the fertilizing potential of sperm, is warranted.

AFRIKAANSE OPSOMMING: Ondersteunende reproduksietegnieke (ORT) speel 'n toenemend belangrike rol in skaapboerdery stelsels om die lewensvatbare en kostedoeltreffende produksie te verseker. Sperm gehalte is 'n belangrike bepalende faktor vir die suksesvolle toepassing van ORT en daarom is dit belangrik om die faktore wat die lewensvatbaarheid en bevrugtingsvermoë van sperme beïnvloed, te verstaan. Die studie was daarop gemik om die invloed van ras en genetiese seleksie vir reproduksiepotensiaal op dekbehendigheid, sperm morfometriese subpopulasie eienskappe en bevrugtingsvermoë te bepaal. Die tegniek wat gebruik word om semen monsters in te samel kan die kwaliteit van die monster beïnvloed, met die kunsvagina (KV) metode wat beter monsters lewer wanneer dit met die elektro-ejakulasie (EE) metode vergelyk word. Die gebruik van die KV metode vereis dat ramme vooraf opgelei moet word en tans is daar geen standaard operasionele prosedure (SOP) geformuleer vir die opleiding van ramme om die KV te gebruik nie. Tydens die opleiding van ramme om die KV te gebruik, is gevind dat beide onervare en ervare Dormer ramme volwasse Dormer ooie meer aantreklik gevind het as jaaroud Dormer ooie. Die Dormer ramme het ook nie tussen Dormer en Merino koggelooie (in estrus) tydens die opleidingsessies gediskrimineer nie. In teenstelling hiermee het die Merino ramme nie tussen óf volwasse of jaaroud en Merino ooie gediskrimineer nie. Ervare Merino ramme het ʼn duidelike voorkeur vir Merino koggelooie gehad, in teenstelling met die onervare Merino ramme wat nie ʼn voorkeur vir onervare of ervare Merino ooie getoon het nie. Seleksie en mate van seksuele ervaring het geen invloed gehad op die gewoondmaak van die ram aan die teenwoordigheid van die semenkollekteerder en/of ondersteuningpersoneel nie. Ramme kan binne ongeveer 4 weke gewoond gemaak word aan die teenwoordigheid van die semenkollekteerder, wanneer opgelei deur ervare personeel, met 'n minimum van 8 opleidingsessies. 'n Hoër frekwensie van blootstelling, d.i. 18 opleidingsessies gedurende hierdie 4-week periode, sal lei tot 'n meer gevestigde basislyn gedrag wat sal aandui of 'n ram suksesvol opgelei kan word om die KV gebruik. Daar was geen afdoende bewys dat ervare Merino of Dormer ramme meer geredelik in die KV ejakuleer het nie, in vergelyking met die onervare Dormer- en Merino ramme. Dit moet genoem word dat slegs 50% van die ervare Dormer ramme suksesvol opgelei kon word om die KV te gebruik, in vergelyking met 90% van die ervare Merino ramme. Wat die onervare ramme betref, kon slegs 40% van beide die Merino en Dormer rasse opgelei word om die KV te gebruik. Vier afsonderlike sperm subpopulasies is geïdentifiseer in Dormer en Merino semen monsters versamel in hierdie studie. Geen beduidende verskille is aangemeld tussen die rasse in terme van die struktuur van die sperm subpopulasies nie. Die ontleding van die sperm subpopulasies in die semen monsters versamel van die HL en LL Merino ramme het klein maar nie-beduidende verskille tussen sekere subpopulasies uitgewys. Ras of genetiese seleksie het geen invloed op die meeste na-ontdooiing sperm parameters gehad nie. Die uitsondering was na-ontdooiing sperm lewensvatbaarheid, wat betekenisvol tussen HL en LL ramme verskil het. ‘n Beduidende verskil is waargeneem tussen die bindingsvermoë van Dormer- en Merino sperme, in vergelyking met sperme van die HL ramme wat geneig het om ‘n beter bindingsvermoë as dié van die LL ramme te hê. Geen afdoende bewys van 'n korrelasie tussen die bindingsvermoë en sperm morfometriese subpopulasies is gevind nie. Ten slotte, die faktore wat bydra tot die probleme wat met die opleiding van die Dormer ramme asook onervare Merino ramme om die KV te gebruik, ondervind is, benodig verdere ondersoek. Toekomstige studies behoort verdere ondersoek in te stel na die invloed van ras en genetiese seleksie op sperm subpopulasie eienskappe. Bykomende navorsing om die verhouding tussen die sperm sub-jpopulasie eienskappe en die potensiële rol van sperm kompetisie in die bepaling van die bevrugtingspotensiaal van sperme, word ook benodig