Patterns of plasma prolactin in post-partum suckled cows

Area of Science:

• Veterinary Medicine
• Animal Physiology
• Endocrinology

Background:

• Prolactin is a key hormone regulating lactation and reproduction in mammals.
• Understanding prolactin secretion patterns is crucial for assessing bovine reproductive health and productivity.
• Seasonal variations and sampling techniques can influence hormone level interpretation.

Purpose of the Study:

• To investigate the diurnal patterns of prolactin secretion in lactating cows.
• To compare prolactin concentrations obtained through different blood sampling methods.
• To examine the relationship between prolactin levels, stage of lactation, and photoperiod.

Main Methods:

• Blood samples were collected from 12 suckled cows between days 14 and 48 postpartum.
• Indwelling jugular venous catheters and jugular venepuncture were used for sample collection.
• Continuous sampling over 72-hour periods at 2-hour intervals was performed.
• Plasma prolactin concentrations were analyzed in relation to sampling time and lactation stage.

Main Results:

• Prolactin concentrations were significantly lower when sampled via catheters on alternate days compared to intermediate days via venepuncture.
• A consistent daily biphasic pattern of prolactin secretion was observed, with peaks at 13:00 and 23:00 h.
• A significant negative correlation was found between the stage of lactation and plasma prolactin concentrations.
• Photoperiod (season of calving) did not show a significant direct correlation with prolactin levels in this study.

Conclusions:

• The method of blood sampling significantly affects measured prolactin concentrations in cows.
• Bovine prolactin exhibits a distinct diurnal rhythm with predictable high and low points.
• Prolactin levels naturally decline as lactation progresses, independent of photoperiod in this study.