Scimulation der inaktiven Ovarien anöstrischer Schafe und praepuberaler Jungschafe durch niedrig dosiertes Östradiol

49 anoestrous ewes (German Blackface) were treated with 0,1 mg oestradiolvalerianate (OT) during 3 successive days. Intensive follicular development could be observed 24–48 brs. later and 6.5, % of the animals ovulated. HCG (500–700 IU) did not improve the effect on ovulations. Better results were obtained near the end of the anoestrous season. In spite of distinct heat symptoms sexual behaviour was not intact, most of the treated ewes refused the ram. From 84 anoestrous ewes treated by the same method during April, May und July ca. 80 % accepted the ram, 40 % lambed, 20 % conceived during the first heat, 10 % during the second oestrous, 10 % 4–9 weeks after treatment. Only 20 % of the 48 control animals lambed. In maiden-ewes, 6–7 months of age, ovulations without heat could be stimulated by psychological factors (mounting by rams, driving, transport etc.) within 24 hrs. During August 66 % of the immature animals ovulated after treatment with 3 × 0,05 mg OV, but refused the ram. During October all immature animals ovulated following a single injection of 0,05 mg OV and all were mated. The fertilization rate of the eggs was low.     

An assessment of genetical methods in the control of scrapieUne contribution de méthodes génétiques dans la lutte contre la tremblanteEinschätzung genetischer Methoden bei der Bekämpfung der Traberkrankheit der Schafe

Scrapie is caused by a virus-like agent which is transmitted to sheep by both maternal and horizontal routes of infection. The disease can be controlled by selective culling of bloodline relatives of scrapie cases. However, this depends on accurate breeding records which are often not available. Two major studies, with Cheviot and with Herdwick sheep, have shown that ‘susceptibility’ to experimental infection with one source of agent is controlled mainly by a single gene and that the dominant allele confers ‘susceptibility’. There is evidence that scrapie agent may still replicate in some ‘resistant’ sheep, but only after a long delay. For this reason, ‘resistance’ is best regarded in terms of an extended incubation period. Also, ‘resistance’ to one strain of agent does not mean ‘resistance’ to all strains. A ‘resistant’ flock of Swaledale sheep is being developed by experimentally infecting all animals and breeding from the survivors. There have been extensive outbreaks of natural scrapie in the ‘susceptible’ flocks of Cheviot and Herdwick sheep. Investigations of these outbreaks might be able to show whether or not sheep selected for ‘resistance’ could be used to limit the spread of infection in flocks with a serious scrapie problem.