Effects of rangeland grazing environment on production traits of domestic sheep / Effekter av utmarksmiljøet på produksjonsegenskaper hos sau
The general aim of this thesis was to investigate how different environmental factors affect production and life-history parameters in domestic sheep and other animals grazing Norwegian rangelands. Relationships between climatic conditions – measured as both global and local indices – were studied, and patterns of between-year weight variation was investigated for sympatric sheep and reindeer. Lastly, the effect of ewe lambs’ first rangeland season on their life-long reproductive output was studied.
There were non-linear and reversible relationships between the global winter climate and autumn body weights in sheep and red deer. As the effect on the sheep, which is kept indoors during winter, and the deer had the same pattern and magnitude, it was concluded that indirect effects, e.g. via spring snow conditions, are important. No relationships were found between lamb weights and local climate measured as monthly means of temperature and precipitation. These results challenge earlier studies that have demonstrated such effects. The explanation for this discrepancy might be that in the present work the statistical method reflects the structure of the data in a superior way, and that model selection was not used. Instead, indices known from the literature were tested.
Juvenile autumn body weights in sympatric reindeer and sheep were studied. The between-years pattern of mean weights was relatively similar for the two species, indicating that a “good” year for sheep was a “good” year for reindeer as well. No difference was found in the relative between-years variation between reindeer and sheep, indicating that the summer environment was of superior importance to both calves and lambs.
The environmental conditions during the first grazing season, measured as lamb autumn weights, affected ewes’ life-long reproduction. Increasing autumn weight was related to heavier lambs throughout the ewe’s life, and to increased litter size at ewe ages one and two years. The results show that the mechanism for the trans-generational effects is at least partly non-genetic.
The large quantity of high quality data steadily accumulating for Norwegian sheep represents a treasure chest for further research. Combined with ecological theory, this will contribute to enhance general ecological theory, as well as animal production science.
Pr. desember 2004: Geir Steinheim, Universitetet for miljø- og biovitenskap, IHA, Postboks 5003, 1432 Ås
