Photoperiodic effects on dairy cattle: a review

Area of Science:

• Animal Science
• Endocrinology
• Dairy Production

Background:

• Long-day photoperiods (16L:8D) have been shown to increase milk yield in dairy cows since 1978.
• The specific endocrine factors mediating this galactopoietic response remain largely unidentified.
• Recent research suggests insulin-like growth factor-I (IGF-I) may play a key role.

Purpose of the Study:

• To investigate the role of IGF-I in mediating the galactopoietic effects of long-day photoperiods.
• To explore the practical applications of photoperiod management in dairy production throughout the lactation cycle.
• To assess the impact of photoperiod management during the dry period on subsequent milk yield.

Main Methods:

• Studies involved monitoring IGF-I levels in heifers and lactating cows under different photoperiods.
• Melatonin administration was used to mimic short-day conditions.
• Effects of photoperiod management were evaluated in conjunction with bovine somatotropin (bST) and during the dry period.

Main Results:

• Long days increased IGF-I levels in heifers and lactating cows, independent of growth hormone.
• The increase in IGF-I preceded the rise in milk yield in lactating cows.
• Melatonin suppressed IGF-I increases in heifers but did not affect milk yield in cows.
• Long-day photoperiod responses persisted throughout lactation and were additive with bST.
• Short-day photoperiods during the dry period resulted in the greatest subsequent milk yield increase.

Conclusions:

• IGF-I is a likely mediator of increased milk yield under long-day photoperiods.
• Photoperiod management offers a viable strategy to enhance milk production, particularly when combined with other practices like bST.
• Strategic photoperiod management during the dry period is essential for optimizing milk yield in the following lactation.