The influence of lactation on insulin and glucose metabolism, lipid profile, and cytokines in pregnant mares.

Overview

• This study investigated how lactation affects insulin and glucose metabolism, lipid profiles, and cytokine levels throughout pregnancy and early postpartum in mares.
• It compared metabolic and physiological differences between lactating and non-lactating pregnant mares at multiple stages of gestation and after birth.

Background and Purpose

• During pregnancy, glucose metabolism changes to support fetal development, leading to increased insulin resistance and insulin secretion to maintain stable blood glucose.
• These metabolic adjustments can influence mare fertility, maternal health, and neonatal outcomes.
• Prior to this study, the effects of lactation on metabolic parameters during pregnancy in mares had not been compared directly to non-lactating mares.
• The purpose was to analyze differences in body condition, fat distribution, insulin and glucose dynamics, lipid metabolism, and cytokine production between lactating vs. non-lactating mares across pregnancy and postpartum periods.

Study Design and Methods

• Twelve pregnancies were studied involving nine broodmares divided into two groups: five non-lactating (NL) and seven lactating (L) mares.
• Measurements were taken at the day of ovulation (baseline), at several gestational time points (55, 110, 165, 220, 275, 330 days), and 21 days after foaling.
• Key parameters evaluated included:
  • Body condition score (BCS), crest neck score (CNS), and rump fat thickness (RUM) to assess adiposity.
  • Basal and stimulated insulin and glucose; area under the curve measurements for glucose (AUCg) and insulin.
  • Insulin sensitivity and glucose tolerance indices such as RISQI (insulin sensitivity) and MIRG (insulin secretion).
  • Cytokines like resistin, leptin, adiponectin, and tumor necrosis factor alpha (TNFα).
  • Lipid metabolism assessed via non-esterified fatty acids (NEFA).

Key Findings

• Lactating mares (L) exhibited:
  • Lower basal insulin and glucose levels early in pregnancy compared to non-lactating mares (NL).
  • Smaller insulin and glucose responses over time, indicating better insulin sensitivity and glucose tolerance.
  • Lower body fat and condition scores (BCS, CNS, RUM), suggesting less adiposity.
  • Higher insulin sensitivity (RISQI) and adiponectin levels, which help regulate metabolism.
  • Higher tumor necrosis factor alpha (TNFα), a cytokine involved in inflammation.
• Non-lactating mares (NL) showed:
  • Higher basal insulin and glucose areas under the curve, indicating reduced insulin sensitivity.
  • Increasing levels of NEFA (fatty acids) towards late pregnancy (D275), a pattern not seen in lactating mares.
  • Metabolic profiles closer to thresholds associated with metabolic syndrome, a condition linked to insulin resistance and obesity.
• Cytokine fluctuations during pregnancy:
  • Resistin peaked mid-gestation (D110 and D165) and declined later.
  • Leptin was elevated early-mid pregnancy but decreased later and postpartum.
  • The variation in cytokines corresponds with shifts in metabolism and adiposity throughout pregnancy.

Conclusions and Implications

• The study demonstrated that lactation significantly influences metabolic, hormonal, and inflammatory markers during pregnancy in mares.
• Lactating mares maintained better insulin sensitivity and healthier lipid metabolism compared to non-lactating ones, possibly reducing the risk of metabolic syndrome.
• Since many embryo transfer recipient mares are non-lactating, understanding these differences is critical for managing mare health and optimizing offspring development.
• The authors recommend further research to explore how lactation affects metabolic health and reproductive outcomes in mares, contributing to improved management strategies.