Factors that influence passive transfer of immunoglobulins in foals
Authors: LeBlanc Michelle M. , Tran Thang , Baldwin Jay L. , Pritchard E. Lane 
Published: December 2023

Effects of farm management, breed, mare age, gestation duration, and climatologic factors on colostral specific gravity, colostral IgG concentration, and foal serum IgG concentration were evaluated. Climatologic variables measured were daily maximal, minimal, and mean air temperature, precipitation, average relative humidity, and total solar radiation. Presuckle, postpartum colostrum samples were collected from 140 Standardbred, 94 Thoroughbred, and 59 Arabian mares from January through June during 1985 and 1986. Thoroughbred (farm A, n = 61; farm B, n = 33) and Arabian (farm C, n = 45; farm D, n = 14) mares were located in Ocala, Fla; Standardbred mares (farm E) were in Montgomery, NY. Mares from farms A, B, D, and E foaled in box stalls, and mares from farm C foaled in sand paddocks. Mares with premature lactation >12 hours were not included in the study. Foals were clinically normal at birth and suckled colostrum without assistance within 2 hours of parturition. Specific gravity of presuckle colostrum samples was measured by use of an equine colostrometer. Blood samples were collected 18 hours after parturition from 253 of the 293 foals (n = 45, 25, 32, 13, 138 on farms A through E, respectively) to determine serum concentration of IgG. The IgG concentrations in colostrum and serum were measured by single radial immunodiffusion. Data were analyzed by multiple regression or Χ2 analysis.

The most important determinants of foal serum IgG concentration were the IgG content and specific gravity of presuckle colostrum samples (P < 0.0001). Colostral IgG concentration was highest in mares 3 to 10 years old, and mean values were higher in Thoroughbred and Arabian mares than in Standardbred mares (P < 0.01). Failure of passive transfer (serum IgG concentration <400 mg/dl) was observed in 13% of the foals, and highest prevalence was in foals that suckled mares >15 years old (P < 0.001). Seventy percent of foals whose dams were <15 years old had serum IgG concentration >800 mg/dl, whereas only 45% of foals whose dams were >15 years old had serum IgG concentration >800 mg/dl. Farm management affected passive transfer of IgG; mares from farm D had the highest mean colostral specific gravity, but their foals had the lowest mean serum IgG concentration (P < 0.01). Arabian foals born between 335 and 345 days of gestation had the highest mean serum IgG concentration; values decreased in bell-shape fashion as gestation duration increased or decreased. Similar pattern was observed for colostral specific gravity and IgG concentration of Arabian and Thoroughbred mares. Total solar radiation was the only climatologic variable that affected IgG concentration in colostrum or foal serum. Only horses on farm E (temperate environment) were affected. As total solar radiation increased, IgG concentration in colostrum and foal serum increased. These results indicate that foals from dams >15 years old, foals whose dams have a colostral specific gravity <1.06, and foals born in cold, wet environments may need supplemental colostrum to prevent failure of passive transfer. Farm management, premature birth, and birth after day 345 of gestation may adversely affect absorption of colostral IgG in foals.