LH and IGF-1 release during oestrus and early luteal phase in lactating and non-lactating horse mares.

The study sought to investigate how lactation affects the basal LH and IGF-1 concentrations and the LH response to a GnRH-analogue during different stages of the oestrous cycle in horse mares. It found that lactation is linked to lower basal and GnRHa-stimulated LH release, mainly during the early luteal phase.

Objective of the Research

• The primary goal of this research was to understand the effects of lactation on the basal concentrations of Luteinizing Hormone (LH) and Insulin-like Growth Factor 1 (IGF-1), and the LH response to a Gonadotropin-Releasing Hormone (GnRH) analogue during various phases of the oestrous cycle in horse mares.

Methodology

• Seventeen cyclic Haflinger mares participated in the study.
• The researchers conducted experiments on lactating mares during the first postpartum oestrus, subsequent early luteal phase, and second postpartum oestrus.
• Non-lactating mares were also included in the study and observed during both oestrus and early luteal phase.
• Every 15 min, blood samples were drawn for one hour. The mares were then given an injection of the GnRH-analogue buserelin (GnRHa), with blood samples taken every 15 min for another two hours.
• The researchers utilized radioimmunoassay (RIA) to determine the LH in all samples and the base IGF-1 concentrations.

Key Findings

• In lactating mares, basal LH concentrations during the early luteal phase tended to be lower, and the LH response to GnRHa was less pronounced compared to non-lactating mares.
• The basal LH concentration between the first early luteal phase and second oestrus in lactating mares differed significantly, with a lower net response to GnRHa between first oestrus, second oestrus, and first early luteal phase. This contrast, however, was not observed between the first and second postpartum oestrus.
• The group of non-lactating mares exhibited a lower LH response to GnRHa during oestrus than during the early luteal phase.
• IGF-1 concentrations showed no significant differences between groups or stages of the cycle within the groups.

Conclusion

• The study concluded that LH release, both basal and GnRHa-stimulated, is lower in lactating mares compared to non-lactating mares, specifically in the early luteal phase.
• However, the LH concentration in lactating mares seems to be sufficient for ovulation to occur.