At a recent dairy meeting, I was asked if the time after calving when a cow is milked for the first time makes a difference on colostrum quality. The answer is “Yes” and “No”. It depends on how you measure it and how long it is between calving and first milking.

A study recently reported in the Journal of the American Veterinary Medical Association showed that the concentration of IgG (immunoglobulins) in Holstein cow colostrum decreased 3.7% for each hour after calving (the time after calving to milking ranged from 0.3 to 23.8 hours). Although statistically significant, the time after calving could only account for 18% of the variability in colostrums IgG concentration amongst the cows tested. Other studies have shown that the concentration of IgG is NOT different if the colostrum is harvested within 8 or 9 hours after calving. In the new study, the total mass of IgG found in the colostrum did not change by time after calving. So, what’s happening? It’s obvious that more milk is being secreted the longer the time after calving but no additional IgG is being secreted – and, there are other things that can affect the IgG concentration in the cow’s colostrum.

What can affect the variability of IgG concentration in colostrum? The IgG concentration in the recent study ranged from 9 to 121 g/L (average of 41 g/L) and the IgG mass ranged from 11 to 702 grams – quite a spread in these cows. High quality colostrum should have at least 50 g/L of IgG. The IgG and other proteins accumulate in the mammary gland starting about five weeks before calving and ceases at the time of calving. Therefore, a short dry period will likely reduce the IgG concentration in the colostrum. Although a few studies have shown greater IgG concentration in cow vs heifer colostrum, heifer colostrum is often greater than 50 g/L and should not be summarily discarded. Other factors that will reduce IgG concentration in colostrum include high ambient temperatures, or heat stress, and breed – Holsteins appear to have the lowest concentration of immunoglobulins, on average, followed by Guernsey, Brown Swiss, Ayrshire, and Jersey - having the highest IgG concentration, on average.

How do I know if the colostrum from any particular cow is of high enoughquality to feed to calves? Many dairy producers require that the colostrumbe tested using a colostrometer. The colostrometer measures the specificgravity (a surrogate for the concentration of a fluid). The only problem withthe colostrometer is that it should be read at room temperature (about 72 degrees F) to give an accurate reading. A newer, temperature-independent method, the Brix refractometer, can be used to evaluate colostrum quality (see next article). Probably the easiest way to ensure that adequate IgG gets into calves is to feed 4 quarts (for Holsteins) of colostrum right afterbirth. Even if the quality was 25 g/L, you could get the needed 100 g ofIgG into the calf. And – harvesting the colostrum closer to calving time isstill the best idea, but recognize that there are many other factors that canaffect colostrum quality.

Godden S. Colostrum management for dairy calves. Veterinary Clinics of North America: Food Animal Practice. 2008;24:19-39.

Morin DE, et al. Effect of colostral volume, interval between calving and first milking, and photoperiod on colostral IgG concentrations in dairy cattle. Journal of the American Veterinary Medical Association. 2010;237(4):420-428.