During the transition period, dairy cows often experience negative energy balance, which can induce metabolic and immunological disturbances. Previous work has shown that there is a relationship between the dysfunction of immune cells and the increase in blood nonesterified
fatty acid (
NEFA) concentration. Nevertheless, it is difficult to determine the exact effect of
NEFA on the immune system, as other metabolic and hormonal perturbations occur simultaneously during the transition period. In the present study, we have determined the effect of
NEFA on immune functions using an experimental model designed to assess the effects independently of energy balance, as well as hormonal and metabolic changes due to parturition. Six dry and nonpregnant cows were infused with either sterile water (control treatment) or a
lipid emulsion (
Intralipid 20%, Frenesius Kabi,
lipid treatment) at a rate of 1 mL/kg per hour for 6 h according to a crossover design. Blood concentrations of
NEFA, β-hydroxybutyrate (BHB), and
glucose were measured every hour throughout the infusion period, and 1 and 18 h after the end of infusion. Proliferation and
interferon-γ secretion of lymphocytes, phagocytosis, and oxidative burst of neutrophils and blood
insulin concentration were evaluated before, during, and at the end of the infusion. For
NEFA, BHB, and
glucose, treatment × time interactions were present. When compared with the control condition,
NEFA and BHB levels were greater in the plasma of cows infused with
lipids from 1 h after the start of infusion until 1 h after the end of infusion.
Glucose level also increased in response to
lipid infusion from 2 h of infusion until 1 h after the end of treatment. For sterile water and
lipid infusions, respectively, maximal concentrations were 0.06 ± 0.10 mM and 1.39 ± 0.10 mM for
NEFA, 0.70 ± 0.05 mM and 1.06 ± 0.05 mM for BHB, and 4.56 ± 0.27 mM and 6.90 ± 0.27 mM for
glucose. For all blood metabolites, there were no differences between treatments 18 h postinfusion.
Lipid infusion significantly increased blood
insulin concentration at 3 and 6 h of infusion. However, it returned to its basal concentration 18 h after the end of the infusion. Lymphoproliferation declined as early as 3 h after the start of the
lipid infusion. At 3 and 6 h of infusion,
lipid treatment significantly reduced INF-γ concentration in the culture cell supernatant. The
lipid infusion did not affect neutrophil phagocytosis. Nevertheless, the efficacy of the response was affected by a reduction of neutrophils' oxidative burst. These results confirm that
NEFA inhibits immune functions independently of energy balance and other changes that occur during the transition period. They also indicate that high blood
lipid concentration causes
insulin resistance.