Background: Overconditioned dairy cows are prone to greater insulin resistance in transition to successfully adapt to negative energy balance. The associations among body condition score (BCS), insulin resistance, lipid metabolism and oxidative stress in cows during late lactation with positive energy balance remain to be elucidated.
Methods: The objectives of this study were to investigate insulin sensitivity and oxidative status in late lactating dairy cows with different BCS but similar milk production, parity and days in milk. Forty-two multiparous Holstein cows were fed the same diet under the same management and divided into three groups based on BCS: low BCS (LBCS; BCS ≤ 2.75; n = 12), medium BCS (MBCS; 3.0 ≤ BCS ≤ 3.5; n = 15) or high BCS (HBCS; BCS ≥ 3.75; n = 15). Blood samples used for analysis of biochemical and hematological parameters were collected from the coccygeal vein at the end of experiment.
Results: The concentrations of insulin and nonesterified fatty acid were higher and the revised quantitative insulin sensitivity check index (RQUICKI) was lower in HBCS cows than in LBCS and MBCS cows. These results suggest that insulin resistance exacerbates lipolysis in HBCS cows. Serum concentrations of very low-density lipoprotein, apolipoprotein A-I, and apolipoprotein B were lower in HBCS cows than in LBCS or MBCS cows. Although LBCS and MBCS cows had higher reactive oxygen species levels than did HBCS cows, the malondialdehyde concentration was not different among cows with different BCS. Ceruloplasmin activity was higher in MBCS and HBCS cows than in LBCS cows, but superoxide dismutase, glutathione peroxidase, and paraoxonase activities were not different among cows with different BCS. Despite the higher percentage of granulocytes in MBCS cows than in HBCS cows, no differences were found in leukocyte counts, red blood cell profiles and platelet profiles among the cows in the three groups.
Conclusions: Results of this study showed that compared with MBCS and LBCS cows, HBCS cows at late lactation stage may have accumulated more hepatic triacylglycerol and lower antioxidant potential due to greater insulin resistance.
Keywords: Body condition score; Hematological parameters; Insulin resistance; Lipolysis; Oxidative stress.