Photoperiodic effects on endocrine and immune function in cattle

Area of Science:

• Animal physiology
• Endocrinology
• Environmental biology

Background:

• Photoperiod is a key environmental cue for animal physiology, influencing reproduction, growth, and immunity.
• Cattle, unlike strict seasonal breeders, offer a unique model to study photoperiod's effects beyond reproduction.
• Light exposure alters melatonin secretion, impacting various physiological processes.

Purpose of the Study:

• To investigate the effects of photoperiod on cattle growth, lactation, and immune function.
• To understand the endocrine mechanisms, including melatonin, prolactin, and IGF-I, mediating photoperiodic responses in cattle.
• To explore receptor-mediated pathways involved in photoneuroendocrine responses in cattle.

Main Methods:

• Manipulating light exposure to create long-day and short-day photoperiods.
• Measuring circulating hormone concentrations (melatonin, prolactin, IGF-I).
• Assessing physiological responses to immune challenge (lipopolysaccharide) under different photoperiods.
• Investigating photoperiod-induced shifts in receptor expression in target tissues.

Main Results:

• Long-day photoperiod reduced melatonin secretion duration.
• Increased prolactin and IGF-I concentrations were observed under long-day conditions.
• Long-day photoperiod mitigated metabolic disruptions following lipopolysaccharide challenge.
• Evidence suggests both hormonal and receptor-mediated mechanisms are involved.

Conclusions:

• Photoperiod significantly influences cattle physiology, impacting growth, lactation, and immune function.
• Endocrine shifts, particularly involving melatonin, prolactin, and IGF-I, are key mediators of these effects.
• Receptor-mediated responses in tissues like the mammary gland, liver, and leucocytes are crucial for photoneuroendocrine signaling in cattle.