Comparison of hepatic adaptation in extreme metabolic phenotypes observed in early lactation dairy cows on-farm.

The aim was to study the variation in metabolic responses in early-lactating dairy cows ( n = 232) on-farm that were pre-selected for a high milk fat content (>45 g/l) and a high fat/protein ratio in milk (>1.5) in their previous lactation. Blood was assayed for concentrations of metabolites and hormones. Liver was measured for mRNA abundance of 25 candidate genes encoding enzymes and receptors involved in gluconeogenesis (6), fatty acid β-oxidation (6), fatty acid and triglyceride synthesis (5), cholesterol synthesis (4), ketogenesis (2) and the urea cycle (2). Two groups of cows were formed based on the plasma concentrations of glucose, non-esterified fatty acids (NEFA) and β-hydroxybutyric acid (BHBA) (GRP+, high metabolic load; glucose <3.0 m m, NEFA >300 μ m and BHBA >1.0 m m, n = 30; GRP−, low metabolic load; glucose >3.0 m m, NEFA <300 μ m and BHBA <1.0 m m, n = 30). No differences were found between GRP+ and GRP− for the milk yield at 3 weeks post-partum, but milk fat content was higher (p < 0.01) for GRP+ than for GRP-. In week 8 post-partum, milk yield was higher in GRP+ in relation to GRP− (37.5 vs. 32.5 kg/d; p < 0.01). GRP+ in relation to GRP− had higher (p < 0.001) NEFA and BHBA and lower glucose, insulin, IGF-I, T₃, T₄ concentrations (p < 0.01). The mRNA abundance of genes related to gluconeogenesis, fatty acid β-oxidation, fatty acid and triglyceride synthesis, cholesterol synthesis and the urea cycle was different in GRP+ compared to GRP− (p < 0.05), although gene transcripts related to ketogenesis were similar between GRP+ and GRP−. In conclusion, high metabolic load post-partum in dairy cows on-farm corresponds to differences in the liver in relation to dairy cows with low metabolic load, even though all cows were pre-selected for a high milk fat content and fat/protein ratio in milk in their previous lactation. [ABSTRACT FROM AUTHOR]