Analysis of the antitrypsin activity and immunoglobulin G concentration in equine colostrum and milk.

Overview

• This study measured and analyzed the activity of the enzyme inhibitor antitrypsin and levels of immunoglobulin G (IgG) in horse colostrum and milk.
• The goal was to understand how antitrypsin may protect IgG to ensure effective transfer of immunity to newborn foals.

Background and Importance

• IgG antibodies are crucial for newborn foals as they provide passive immunity from the mother via colostrum.
• These antibodies must remain intact through the foal’s digestive system to be absorbed properly.
• Antitrypsin is an enzyme inhibitor present in equine colostrum thought to protect IgG proteins from breakdown (proteolysis) in the gastrointestinal tract.

Objectives of the Study

• Quantify antitrypsin activity in equine colostrum and milk at different times postpartum (first five days after birth).
• Compare antitrypsin activity levels between the left and right mammary glands.
• Investigate differences in antitrypsin activity between mares giving birth for the first time (nulliparous) and those who have given birth previously (pluriparous).
• Evaluate the correlation between antitrypsin activity and IgG concentration.
• Examine whether the age of the mare affects antitrypsin activity.

Methods

• Samples were collected retrospectively from 67 mares with 73 deliveries, resulting in 145 colostrum and 207 milk samples.
• When possible, samples were taken from both the left and right mammary glands.
• Antitrypsin activity was measured using a colorimetric trypsin inhibition assay — a test to evaluate the ability of colostrum or milk to inhibit trypsin enzyme activity.
• IgG concentrations were quantified using enzyme-linked immunosorbent assay (ELISA), a standard immunoassay technique.
• Data were reported primarily as median values with ranges, and statistical correlations were analyzed.

Key Findings

• Antitrypsin activity levels in colostrum were significantly higher in nulliparous mares (median 1.09) compared to pluriparous mares (median 0.78), with substantial ranges noted.
• Antitrypsin activity declined progressively over the first five days postpartum to a median of 0.49.
• No significant difference in antitrypsin activity was found between the left and right mammary glands, indicating symmetrical production.
• A strong positive correlation (rs = 0.77) was observed between antitrypsin activity and IgG concentration in colostrum, suggesting linked physiological regulation.
• No correlation between antitrypsin activity and IgG concentration was found in regular milk samples (rs = -0.04), indicating the relation is specific to colostrum rather than milk later postpartum.
• Mare age did not have a significant correlation with colostral antitrypsin activity (rs = -0.09), indicating age is likely not an influencing factor.

Conclusions and Implications

• Antitrypsin activity is highest immediately after birth in colostrum and is particularly elevated in mares having their first foal.
• The close association with IgG concentrations suggests that antitrypsin plays an important protective role to preserve these antibodies from degradation in the foal’s digestive system.
• Understanding and measuring antitrypsin activity in colostrum could improve assessment of colostrum quality, helping to ensure effective passive immunity transfer to newborn foals.
• This insight can inform neonatal care strategies to optimize the health and survival of foals by ensuring they receive colostrum that maximally protects vital immune proteins.