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Immunoglobulin G1 concentration was measured in 919 first milking colostrums from Holstein cows during a 4-yr period on a commercial dairy farm. Sources of variation analyzed for effect on colostral IgG1 concentration were season of calving, lactation number, dry period length, intercalving interval, complete lactation milk and fat production, weight of first milking colostrum, and time from calving to first milking. Weight of first milking colostrum was the variable most highly correlated (negatively) with colostral IgG1 concentration (r = -.29). Weight of first milking colostrum and lactation number of the cow were the most significant discriminators between colostrum of low and high IgG1 concentration. The implications of these results for colostrum feeding management are discussed.
Pritchett et al. (Mon,) studied this question.