An adequate supply of colostrum is important for the prevention of hypogammaglobulinaemia in foals. In addition to the quantity of colostrum consumed and the time of consumption, the quality of the colostrum, the immunoglobulin (Ig) G concentration, is crucial. The aim of this study was to determine whether the viscosity of equine colostrum was a suitable estimate of IgG concentration. IgG content of colostrum was measured by ELISA and viscosity directly measured with a cone plate viscometer and indirectly assessed with a funnel. Analysis of 56 colostrum samples obtained from 40 mares at different postpartum time points was conducted to assess colostrum samples with varying levels of quality. The range of IgG concentrations determined by ELISA was 0.83 to 245.5 mg/mL (30.69 ± 41.92 mg/mL). The range of viscosity values determined by the cone plate method was 1.84 to 110.00 cP (7.86 ± 17.48 cP) at a shear rate of 3 rpm. Colostrum drainage from the funnel (drainage time), varied between 7.9 and 30.0 s, with an average of 9.96 ± 4.48 s. As the data were not normally distributed, Spearman's rank correlation analyses were calculated and significant correlation found between viscosity and IgG content (ρ = 0.71, P < .001), as well as between drainage time and IgG content (ρ = 0.75, P < .001). These correlations indicate that determining the viscosity of equine colostrum by cone plate or drainage time, may be an effective proxy measurement of IgG content.