Metabolic and productive characterisation of multiparous cows grouped for fat-corrected milk yield and milk protein concentration

Objective of this study was to determine health and productivity of cows grouped for fat corrected milk yield and protein concentration. Therefore 23 cows (6 cows with high FCM and high protein content, 5 with low FCM and low protein, 7 with high FCM and low protein and 5 cows with low FCM and high protein concentration) were examined from two weeks before parturition throughout the first 22 weeks of lactation. Regularly, milk and blood samples were collected and body condition observed. Cows were subjected to 30% feed restriction in early (d 26 to 28 pp) and mid-lactation (d 141 to 143 pp) to evaluate metabolic reaction. Three intravenous glucose tolerance tests (ivGTT; d -14, 20 and 127 pp) were conducted to assess differences in insulin response. Furthermore hepatic gene expression profiles were examined at day of parturition, d 15, 57 and 155 pp as well as at the last day of both feed restriction periods. Measured target genes (20) play key roles in glucose transport, lipid, protein and carbohydrate metabolism as well as in ketogenesis. Milk, blood serum and body condition parameters revealed highest risk for metabolic imbalances of high yielding dairy cows during early lactation. Gene expression profiles indicated that high yielding and especially cows with high FCM and low protein concentration had higher risk for fatty liver development and diminished gluconeogenesis potential. Also, during feed restriction in early lactation, these cows seemed to have reduced physiological adaptation capacities to the exacerbated energetic imbalance. Nevertheless, results of ivGTTs suggest that high yielding cows show gluconeogenesis activity meeting demands of milk synthesis in early lactation and cows with high FCM and protein concentration even seemed to exceed the needs of mammary gland. Insulin sensitivity was reduced in high yielding dairy cows prior to parturition. Furthermore only cows with low FCM and high protein content were able to restore body reserves in mid-lactation. Regarding results of hepatic mRNA abundance and ivGTTs, those cows seemed to be in an improved energetic situation compared to other cows. Moreover, high protein cows showed highest insulin resistance in early lactation. Property of cows with low FCM and low protein concentration was a difference in metabolism due to seemingly enhanced protein catabolism instead of lipolysis. Additionally, protein composition of milk was analysed throughout experimental period with capillary electrophoresis on a chip (Agilent Protein 80 Chip for Bioanalyzer). Cows grouped for FCM yield and protein concentration showed differences in concentrations of major milk proteins α-lactalbumin, β-lactoglobulin, α-, β- and κ-casein, which could be explained by their different genotypes of β-LG and κ-CN: high yielding cows showed lower casein concentrations compared to low yielding cows. Furthermore, low yielding cows had lower contents of α-CN. Composition of milk protein was almost not altered by restricted feeding. Solely restricted feeding in mid-lactation resulted in decreased mean contents of κ-CN and therefore potentially diminished processing quality of milk for cheese making.