Negative energy balance has been implicated in the development of
fatty liver,
insulin resistance, and impaired health in dairy cows. A 4-d fasting model previously was reported to increase liver
triglycerides more than 2.5-fold. The purpose of the present study was to evaluate
insulin response in this fasting model. Nonlactating, nonpregnant Holstein cows were fasted for 4 d (6 cows) or fed continuously as control cows (4 cows). Samples were collected 5 d before fasting, during fasting, and immediately after the 4-d fast, 8 d after the fast, and 16 d after the fast. Fasted cows had greater liver
triglyceride content (49.4 vs. 16.2 mg/g, wet-weight basis) at the end of the fasting period compared with control cows. Fasted cows also had increased plasma nonesterified
fatty acid (
NEFA) concentrations (1.24 vs. 0.21 mmol/L) and increased plasma
beta-hydroxybutyrate (BHBA) concentrations at the end of the fasting period. Liver
triglyceride, plasma
NEFA, and plasma BHBA in fasted cows returned to prefasting concentrations by the end of the experiment. Plasma
glucose concentrations were not affected by fasting. Plasma
insulin concentrations were decreased (6.3 vs. 14.1 microU/mL) and
insulin-stimulated
blood glucose reduction was decreased (24.9 vs. 48.6%) in the fasted cows compared with control cows at the end of the fast, indicating reduced
insulin response.
Insulin response was negatively correlated with plasma
NEFA and liver
triglycerides. Decreased
insulin response may be an important complication of negative energy balance and hepatic
lipidosis.