A study published in the July Journal of Dairy Science showed large variation in the amount of IgG transferred to colostrum. Penn State researchers (Baumrucker et al) collected 214 colostrum samples from 11 Pennsylvania farms and analyzed their IgG content. In addition to measuring the concentration of IgG, researchers measured the total amount of IgG in colostrum collected at the first milking. Concentration of IgG in colostrum is dependent on the volume of water in colostrum, and water volume begins to increase soon after calving and is affected by the time between calving and the first milking. Comparing cows based on the total amount of IgG they produced allowed the researchers to remove the effects of water volume and focus on the ability of cows to transfer IgG into colostrum.
Concentration of IgG ranged from 9 to 166 mg/mL and averaged 37.5 mg/mL. Total amount of IgG in colostrum collected at the first milking ranged from 14 to 2,223 grams with an average of 291.6 grams. Both measures indicated tremendous variation in colostrum IgG content, but the measurement of total IgG also showed that individual cows varied in their ability to transfer IgG into colostrum. Approximately 10 percent of the cows sampled, including some cows in their first lactation, produced colostrum containing more than 607 grams of IgG (one standard deviation above the mean). Production of IgG also was compared to an estimate of mammary parenchyma tissue, but no relationship was found. In this study, there was no relationship between IgG concentration and colostrum volume.
The researchers suggested that variation in IgG production may be due to hormonal or genetic differences between cows. Further research in this area may provide new ways to increase colostrum IgG concentration and improve passive transfer to calves. These results also provide further evidence that heifers can provide quality colostrum for calves and their colostrum should not be discarded automatically.