The research involved studies in dry, late-pregnant Ayrshire dairy cows on grass silage (GS) based diets. The principal aim was to investigate the effect of prepartal plasma non-esterified fatty acids (NEFA) level and the effect of prepartal dietary energy intake on the development of insulin resistance (IR) during late pregnancy and changes in insulin resistance in early lactation. Detailed, extensive physiological studies were conducted to understand the mechanisms underlying the development of maternal insulin resistance and to investigate the impact of changes in dietary energy level and subsequent changes in plasma NEFA concentration prepartum. The insulin resistance was assessed by interpretation of data from intravenous glucose tolerance test (IVGTT) with minimal model (MM) approach and by insulin challenge (IC) data. Besides insulin resistance, also the impact of prepartal energy intake on metabolic adaptations, tissue deposition and mobilisation as well as dry matter intake (DMI) and lactational performance were investigated.
The moderate negative effects of gradual restriction of prepartal energy and dilution of energy by mixing GS with wheat straw on early lactation production response demonstrated that these feeding practices were not optimal for transition dairy cows. A moderate or ad libitum overfeeding affected peripheral insulin resistance in the level of prepartal lipid metabolism, while ad libitum overfeeding of GS induced changes in prepartal glucose metabolism as well. Both the difference in energy intake and the composition of the diet contributed to the observed effects on glucose and NEFA dynamics orchestrated via changes in insulin concentration in the transition period. Collectively, the findings of the thesis suggest that peripheral insulin sensitivity of Ayrshire dairy cows is not profoundly affected by prepartal energy level on grass silage-based diets during the transition period.
MSc Siru Salin will defend her doctoral dissertation entitled "Effect of energy allowance during the dry period on insulin resistance and metabolic adaptation in transition dairy cows on grass silage-based diets" in the Faculty of Agriculture and Forestry, University of Helsinki, on 17th December 2020 at 13 o’clock. The public examination will take place at the following address: Auditorio108 (B3), Metsätieteiden talo (Latokartanonkaari 7) Viikki, Helsinki. Professor Geert Opsomer, Ghent University, will serve as the opponent, and Professor Aila Vanhatalo as the custos. The defence can be followed remotely using the following link: https://helsinki.zoom.us/j/63255864721?pwd=amVtajJrNXlzY0VMenloa0R3WFkzZz09
The dissertation is available in electronic form in E-thesis service.
Contact: Siru Salin (siru.salin@helsinki.fi)