The Damara sheep : an appraisal of its reproductive performance and potential

Schoombee, Cornelius Johan Albertus (1998-03)

Thesis (M.Sc. in Animal Science) -- University of Stellenbosch, 1998.

Thesis

ENGLISH ABSTRACT: Investigations undertaken in this research program was hampered by mainly two aspects viz. small numbers of animals available for research purposes and that the work was executed, due to circumstances, under intensive conditions, taking into account that the breed is recognized for its ability to survive under extensive and harsh conditions. The results that came forth from this work should therefore rather be regarded and treated as a springboard for further research on aspects investigated and also on additional topics of importance, rather than a set data base representing the Damara breed. Treatment of Damara ewes with different synchronisation procedures gave rise to inconsistent results with regard the interval from cessation of treatment to onset of oestrus. Group Al differed significantly from Groups A2, A3 and A4 ( P < 0.05 ). In most instances the interval under discussion tended to be longer-than findings quoted in the literature. with regard duration of oestrus, all treatment groups showed comparable oestrous durations except the PMSG treated group which showed a markedly longer oestrous period. The 'difference was however not significant ( P > 0.05 ). Breeding techniques (AI vs natural tupping ) had no significant effect on reproductive performance with reference to the two experimental groups ( P > 0.05 ). The average duration of the gestation period was 150 days which \ is in agreement with that recorded for other sheep breeds. The Damara ewe seems to have some resistence towards lower levels ( 5 mg ) of PGF2a during pregnancy but is vulnerable towards higher concentrations ( 10 mg ) during early pregnancy. Plasma progesterone profiles indicated that the Damara ewe has a fairly extensive natural, breeding season lasting from approximately February until August. From the results obtained, a fair assumption can be made that breeding is possible throughout the year with no significant difference between seasons ( P > 0.05 ). There is a certain degree of variation in the literature as to the age at which ewe lambs reach puberty. The Damara ewe fall well inside this range (·290.43 days and 44.95 kg ). , Similar to other breeds, the Damara ram lamb attain puberty at a relatively early age ( anatomical puberty at 16.15 ± 1.52 weeks; physiological puberty at 19.61 ± 2.06 weeks and 39.54 ± 3.50 kg bodyweight ). Macroscopic investigations of the reproductive tract of the Damara ewe led to the same conclusion. No differentiation that distinguishes the Damara breed from any other sheep breed could be revealed. An impression gained from the results which were obtained from specific tests executed during the program, is that the Damara sheep does not react according to expectations which normally result when certain treatments with an intensive, nature are applied. The Damara breed is a member of the sheep family and as such does not differ exceptionally from any other breed of sheep with regard to many aspects investigated in the program. An outstanding feature of the study which relates to the statement made above, was the disappointing results obtained from experimental work done with regard to superovulation and embryo manipulation. Different aspects of environmental influences and combinations thereof could have been the reason for the results obtained. Since this was one of the primary objectives for the initiation of the investigation, this leaves a wide open and interesting field for research on the Damara sheep with regard to these topics.

AFRIKAANSE OPSOMMING: Ondersoeke watgedurende die projek uitgevoer is, is hoofsaaklik deur twee faktore beinvloed nl. klein getalle diere wat vir navorsingsdoeleindes beskikbaar is en die feit dat 'n groot gedeelte van die werk vanwee omstandighede onder intensiewe toestande uitgevoer is, in ag genome die bekende gegewe dat die Damaraskaap erken word vir sy vermoe om in moeilike en ekstensiewe toestande te oorleef. Die resultate wat hieruit voortgespruit het, moet dus eerder beskou word as 'n wegspringplek vir verdere navorsing rakende aspekte wat ondersoek is asook bykomende onderwerpe wat belangrik geag mag word, eerder as 'n vaste stel gegewens wat verteenwoordigend is van die Damararas. Onder optimale toestande gedy die Damaraskaap ten opsigte van die neerlegging van energiereserwes, veral in die stert, rug en liesareas soos vasgestel met behulp van karkasse van geslagde proefdiere. Vanuit 'n ander oogpunt beskou, kan dit eweneens een van die aanleidende oorsake wees van die onverwagte swak resultate wat tydens superovulasie verkry is. Dit vestig weereens die aandag op die moontlike uitwerking wat verskillende aspekte van omgewingsinvloede , en/of kombinasies daarvan op navorsingsresultate kan he. Toepassing van verskillende sinchronisasie prosedures het afwykende resultate opgelewer ten opsigte van die interval vanaf einde van behandeling tot aanvang van oestrus by die Damara-ooi. Die tydsduur van Groep Al was betekenisvol langer as die van Groepe A2, A3 en A4 ( P < 0.05 ). Die duur van die periode onder bespreking was langer in vergelyking met beskikbare data uit die literatuur. Met verwysing na die duur van oestrus, het drie groepe oestrusperiodes van vergelykbare lengte vertoon terwyl die PMSG-behandelde groep se oestrusperiode opmerklik langer was as ooreenstemmende data uit die literatuur. Die verskil was egter nie betekenisvol nie ( P > 0.05 ). Teeltegniek ( KI vs natuurlike dekking ) het nie 'n betekenisvolle invloed op reproduksierespons tussen die twee eksperimentele groepe getoon nie ( P > 0.05 ). Die gemiddelde duur van dragtigheid ( 150 dae ) stem egter ooreen met die van ander skaaprasse. Die Damara-ooi het oenskynlik 'n mate van weerstandbiedendheid teen laer vlakke ( 5 mg ) PGF2a gedurende dragtigheid, maar is gevoelig vir hoer konsentrasies ( 10 mg ) veral gedurende vroee dragtigheid. Plasmaprogesteroonpeile het aangetoon dat die Damara-ooi oor 'n redelik uitgebreide natuurlike teelseisoen beskik wat van ongeveer Februarie tot Augustus duur. Eksperimentele data wat verkry is, dui egter daarop dat die Damaraskaap nie noodwendig 'nseisoensgebonde teler is nie. Siklisiteit het nie betekenisvol tussen seisoene verskil nie ( P > 0.05 ). Puberteitsondersoeke het getoon dat die gemiddelde ouderdom waarteen Damara-ooilammers geslagsrypheid bereik, 290.43 dae teen 44.95 kg is. Ramlammers bereik puberteit teen 'n relatiewe vroee ouderdom wat 'n algemene verskynsel by skape blyk te weeSe Die gemiddelde ouderdom vir Damararamlammers was 16.15 ± 1.52 weke ( anatomiese puberteit ) en 19.61 ± 2.06 weke fisiologiese puberteit ) teen 39.54 ± 3.50 kg liggaamsmassa. Makroskopiese ondersoeke van die geslagskanaal van jong Damara ooie het geen ooglopende verskille aandie lig gebring nie. In hierdie opsig verskil die Damaraskaap ook dus nie van ander skaaprasse nie. Vanuit bepaalde resultate wat uit die ondersoek na vore gekom het, is die indruk gewek dat die Damaraskaap nie op spesifieke behandelings reageer soos algemeen verwag word wanneer sodanige behandelings toegepas word nie. Vanuit 'n breer perspektief beskou, verskil die Damaraskaap as lid van die skaapfamilie nie buitensporig van enige ander skaapras ten opsigte van meeste aspekte wat in die projek ondersoek is nie. Met verwysing na bostaande was veral opvallend die teleurstellende resultate wat verkry is van die eksperimentele werk wat gedoen is met betrekking tot superovulasie en embriomanipulasie. Die moontlike uitwerking wat verskillende aspekte van omgewingsinvloede en/of kombinasies daarvan op navorsingsresultate kan he, kom weer hier onder die soeklig. Aangesien dit een van die motiverende oorsake vir die inisiering van die ondersoek was, bied dit 'n wye en interessante veld vir verdere navorsing op die Damaraskaap.

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