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- ItemEvaluation of microbial ingredients as alternative, sustainable protein sources for fish meal replacement in rainbow trout feed(Department of Applied Animal Science and Welfare, Swedish University of Agricultural Sciences, 2026) Gaudhaman, AshwathThe growing demand for sustainable aquaculture has intensified the need for alternative protein sources that can consistently replace fish meal in salmonid diets. Many current alternatives, particularly plant-based proteins, compete directly with human food resources. Microbial ingredients present a promising solution because they can valorize low-value substrates while providing high-quality nutrients. Although bacterial meals and single-cell fungi have been studied extensively, the use of filamentous fungi as feed ingredients for salmonids remains comparatively underexplored.This licentiate thesis investigates the potential of several filamentous fungi, cultivated on industrial and forestry by-products, as feed ingredients for rainbow trout. Key nutritional and functional aspects were evaluated, including digestibility, effects on growth performance and gut health, and physical pellet quality. In Paper 1, four filamentous fungi namely, Aspergillus oryzae, Rhizopus oligosporus, Rhizopus delemar, and Paecilomyces variotii, were assessed for their chemical composition, amino acid indices, and digestibility. Their influence on pellet quality was also examined. Among these, P. variotii showed the most favourable characteristics and was selected for further evaluation in a growth trial using graded inclusion levels.In Paper 2, a nine-week growth trial was conducted with diets containing 0% (control), 5%, 10%, 20%, and 30% P. variotii. Growth performance, feed utilization, gut health parameters, and technical feed quality were assessed. The results showed no reduction in growth performance compared with the control up to a 20% inclusion level, while performance declined at 30%. Notably, villus length was significantly higher in fish fed the 30% inclusion diet.In conclusion, P. variotii was found to be the most suitable microbial ingredient among the tested ingredients and hence was chosen for further analysis. P. variotii up to 20% inclusion levels did not have any effects on the growth. Further studies with longer feeding periods are required to further judge the efficacy of P. variotii as a suitable microbial ingredient for rainbow trout.
- ItemExtended lactations in multiparous dairy cows(Department of Applied Animal Science and Welfare, Swedish University of Agricultural Sciences, 2025) Hansson, AnnicaThe substantial increase in milk yield capacity in modern dairy herds has generated interest in extending voluntary waiting period (VWP) as a strategy to prolong the calving interval (CInt). This Licentiate thesis investigated the effects of extended VWP on fertility, milk production, and culling in second-parity cows, as well as associations between CInt, milk yield in second parity and mortality during the first month after the third calving. In a randomized controlled study of 819 second-parity cows from 12 high-yielding commercial herds, cows were allocated to either a conventional (50-day) or extended (140-day) VWP. The VWP treatments resulted in calving intervals of 12.5 and 14.0 months, respectively, but had no effect on daily milk yield per calving interval day, milk yield per lactating day, or dry period length. Fertility improved in the extended VWP group, as indicated by a higher pregnancy proportion in the first service, fewer inseminations per calf and a shorter insemination period. No effect on culling rate was observed. In a retrospective cohort study, data from the Swedish Official Milk Recording Scheme was analyzed to evaluate associations between CInt and on-farm mortality after the third calving. An increased risk of mortality was detected in cows with CInt longer than 13 months. Mortality risk was also associated with high milk yield, both as a 305-day yield and as the yield at the last insemination relative to the herd average at the third test milking. In the subset of the most high-yielding herds, this difference was not statistically significant. Together, these findings indicate that an extended VWP can improve fertility in second-parity cows without compromising milk production or affecting culling rates. However, long CInt were associated with an increased risk of on-farm mortality within 30 days after the subsequent calving.