Mare colostrum quality and relationship with foal serum immunoglobulin G concentrations and average daily weight gains

Background: Foals suffer from total failure to transfer passive immunity (TFTPI) when serum immunoglobulin (IgG) is <4 g/L, and partial failure to transfer passive immunity (PFTPI) when serum IgG is 4-8 g/L. Objectives: To explore risk factors for poor serum IgG concentration. Study design: Retrospective observational study. Methods: Data from 535 Thoroughbred foals born to 177 mares were analysed and included foal sex, birthweight, month and year of birth and colostrum Brix %. Associations between dam age and colostrum Brix (%); and between foal serum IgG and liveweight gains were also measured. Pre-suckle colostrum samples and foal blood samples were collected (by jugular venipuncture within 12-24 h of birth). IgG was estimated in mare colostrum and foal serum using Brix refractometry and turbidimetric immunoassay, respectively. Foals were weighed within 20 h of birth; daily until 7 days of age and weekly until 130 days of age. Results: Mean foal serum IgG was 10.78 g/L (SD = 3.26) and mean mare colostrum Brix was 27.32% (SD = 5.96). A number of colostrum samples (20.9%, n = 112/535) measured <20% Brix and 20.4% of foals (n = 109/535) had serum IgG concentrations <= 8 g/L, 2.2% of foals (n = 12/535) had serum IgG less than or equal to 4 g/L and 18.1% (n = 97/535) had serum IgG between 4.1 g/L and 8 g/L. Foals had an average daily gain (ADG, kg) of 1.26 kg (SD = 0.14). Serum IgG (g/L) was associated with year of birth, birthweight (kg) and colostrum Brix (%). For every unit increase in foal birthweight (kg), there were small, significant increases in foal serum IgG (0.04 g/L, p = 0.04). Similarly, for every unit increased in mare colostrum Brix (%) there were small, significant increases in foal serum IgG (0.25 g/L, p < 0.001). Month of birth was significantly associated with colostrum Brix (%) and with average daily gains; with lower values for both outcome parameters with increasing calendar month. Increasing dam age at foaling was associated with lower colostrum Brix (%). Main limitations: Retrospective design with missing data, small convenience sample. Conclusions: Several risk factors were significantly associated with foal serum IgG and mare colostrum Brix (%) in the current work.