Masters Degrees (Animal Sciences)

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Browsing Masters Degrees (Animal Sciences) by browse.metadata.advisor "Coetzer, W. A."

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    The Damara sheep : an appraisal of its reproductive performance and potential
    (Stellenbosch : Stellenbosch University, 1998-03) Schoombee, Cornelius Johan Albertus; Coetzer, W. A.; Barry, Daniel Malan; Stellenbosch University. Faculty of AgriSciences. Dept. of Animal Science.
    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.