Immunoglobulin concentration, specific gravity, and nitrogen fractions of colostrum from Jersey cattle.

Colostrum samples from 88 Jersey cows were analyzed for concentrations of IgG, IgM, IgA, total solids, specific gravity, and N fractions. Colostrum (50 ml) was sampled from each cow as soon as possible after parturition, and specific gravity was determined immediately using a hydrometer. Samples then were frozen prior to analysis of Ig, fat, and N fractions. Mean concentrations of IgG, IgM, and IgA were 65.8, 2.4, and 1.7 g/L, respectively. Concentration of IgG was lower, and IgA was higher, in colostrum from second lactation cows than from first lactation cows or from cows in third or later lactations; IgM increased linearly as lactation number increased. Total N, protein N, noncasein N, and fat contents also were lower in second lactation cows. Regression of total Ig (grams per liter) on specific gravity was -1172 + 1180 x specific gravity (r2 = .38). Relationship of total Ig to specific gravity differed from colostrum of Holstein cattle and may have been related to differences in fat and noncasein N concentrations. Use of specific gravity hydrometer to estimate Ig concentration using equations derived from Holstein cattle appears to underestimate Ig concentration in colostrum from Jersey cattle.