Does dietary supplementation of pregnant mares with a commercial stud feed balancer improve the transfer of passive immunity in their foals? A controlled field trial.

Overview

• This study investigated whether feeding pregnant mares a commercial stud feed balancer during late pregnancy improves the immune protection passed to their foals through colostrum.
• The research found that mares receiving the feed balancer produced foals with better passive immunity transfer, reducing the likelihood of failure of passive transfer (FPT) in foals.

Background and Purpose

• Passive immunity in foals is crucial because newborn foals rely on antibodies obtained through the mare’s colostrum to protect them from infections during early life.
• The quality of colostrum and the resulting antibody concentration in foals can be influenced by the mare’s nutrition during pregnancy.
• The study aimed to assess whether supplementing pregnant mares’ diets with a commercial stud feed balancer improves the quality of colostrum and enhances transfer of passive immunity to foals.

Study Design and Methodology

• The trial was prospective and controlled, conducted on a single stud farm with 82 pregnant mares eligible to participate.
• Mares were divided into two groups:
  • Intervention group: Received the commercial stud feed balancer as a dietary supplement starting between 64 to 224 days before giving birth.
  • Control group: Received the stud’s home-mix concentrate instead of the commercial balancer.
• Other than the supplementation, all mares were fed the same forage-based diet.
• Data from 68 mare-foal pairs were analyzed using Intention To Treat (ITT) principles to reflect outcomes based on initial group assignment.
• A sensitivity analysis was also conducted on 57 mare-foal pairs who strictly followed the study protocol.

Primary Outcome and Measurements

• The main outcome investigated was failure of passive transfer of immunity (FPT) in foals, defined as an immunoglobulin G (IgG) concentration of less than 8 g/L measured 12-36 hours after the foal’s first suckle.
• Colostral quality was assessed using Brix refractometry, with a value ≥23.0 indicating good colostrum quality.

Key Results

• Foals from mares in the Intervention group were significantly less likely to experience FPT compared to those in the Control group.
• Mares receiving the commercial feed balancer had colostrum with significantly higher quality as measured by Brix values.
• In a multivariable statistical model, both the group assignment (Intervention vs. Control) and the foal’s sex were significantly associated with the likelihood of FPT.
• Other potential risk factors for FPT investigated in the model did not show significant effects.

Interpretation and Significance

• Supplementation of pregnant mares with a commercial stud feed balancer in late pregnancy improved colostrum quality, enhancing transfer of passive immunity to their foals.
• Improved passive immunity transfer reduces neonatal foal susceptibility to infectious diseases during a critical early life period.
• This suggests that appropriate nutritional management of pregnant mares can have a direct beneficial impact on foal health outcomes.
• The identification of foal sex as a factor may indicate physiological or immunological differences affecting antibody uptake or metabolism.
• Results support using feed balancers as part of herd management strategies to reduce the incidence of FPT and improve foal survival and wellbeing.