Endocrine profiles of periparturient mares and their foals.

The research explores the hormonal changes in mares and their newborn foals around the time of birth, with a focus on leptin, IGF-I, and thyroid stimulating hormone (TSH). It found variations over time in these hormones both in the blood and milk of the mares and in the blood of the foals.

Objective and Methodology

• The study aimed to track the levels of three hormones – leptin, IGF-I, and TSH – in the blood serum of mares before and after giving birth, in postpartum milk from the mares, and in the blood serum of their foals.
• The study utilized nine pregnant Quarter Horse mares and their offspring. All mares were subject to weekly checks starting two weeks prior to their due birth date, which included weight measurements, body condition score (BCS) assignments, and blood samples.
• After birthing and before the foals fed, blood samples were taken from both mares and foals, and a milk sample was also taken from the mares.

Further Observations

• Additional samples of blood from foals and blood and milk from mares were collected at various intervals up to 61 days postpartum. Mares and foals were also weighed and assigned a BCS on certain days.
• An ultrasound was used on the foals on three occasions to measure fat depth and the size of the Longissimus Muscle (LM) to track changes over time.

Key Findings

• There were no significant changes in TSH levels in the blood of both mares and foals.
• There were significant changes in the levels of IGF-I and leptin in the mares’ blood over time. Leptin initially decreased then stabilized after day 5, whereas IGF-I showed a tendency to change over time.
• The study also found that newborn foals experienced an initial increase in IGF-I concentration in their blood, which peaked at day 19 and then stabilized.
• In milk, concentrations of leptin and TSH were highest immediately after parturition and decreased over time, bottoming out at 61 days postpartum. IGF-I levels in the milk also followed this pattern but were no longer detectable by day 12.
• The study revealed that the body weight of mares changed significantly pre- and post-birth, but didn’t along with their BCS over time. However, as the foals aged, they showed a significant increase in body weight, BCS, ultrasonic fat depth, and LM area.

Implications of the Study

• The findings of this study highlight the changes in metabolic hormones during the period surrounding the birth, in mares and their foals.
• This research provides a basis for further investigation into the role these hormones might play in the health and development of the foals, and how they are affected by factors such as the hormones present in the mother’s milk.