Lymphocyte functions in dairy cows in hot environment

Area of Science:

• Animal Science
• Immunology
• Environmental Physiology

Background:

• High environmental temperatures (HET) pose significant challenges to dairy cow health and productivity.
• Periparturient dairy cows are particularly susceptible to heat stress, impacting their immune status.
• Understanding the effects of HET on lymphocyte function is crucial for dairy herd management.

Purpose of the Study:

• To investigate the impact of intense high environmental temperatures (HET) on lymphocyte functions in periparturient dairy cows.
• To compare immune responses and plasma cortisol concentrations between spring- and summer-calving cows.
• To elucidate the role of neuroendocrine changes in HET-induced immune perturbations.

Main Methods:

• Blood samples were collected from 34 Holstein cows (22 spring-calving, 12 summer-calving) before and after calving.
• Peripheral blood mononuclear cell (PBMC) function was assessed in vitro via DNA synthesis and IgM secretion assays.
• Plasma cortisol concentrations were measured to evaluate stress levels.
• Temperature Humidity Index (THI) was monitored to quantify heat stress exposure, including heat waves.

Main Results:

• Summer-calving (SU) cows experienced significantly higher THI values and heat waves compared to spring-calving (SP) cows.
• SU cows exhibited lower DNA synthesis (P < 0.0001) and higher IgM secretion (P < 0.01) compared to SP cows.
• Pre-calving plasma cortisol concentrations were elevated in SU cows (P < 0.01) versus SP cows.

Conclusions:

• Intense high environmental temperatures significantly alter lymphocyte functions in periparturient dairy cows.
• The immune response to HET is function-specific, affecting DNA synthesis and IgM secretion differently.
• Neuroendocrine alterations, indicated by elevated cortisol, likely contribute to immune dysregulation under heat stress.