How Accurately Does Colostrum Volume Predict Quality?
In a study involving 507 Holstein cows the study team collected colostrum measuring both the volume at first milking and the antibody concentration.
There was a very wide variation in antibody (IgG) concentration at every interval of colostrum volume. For example, at the 4-quart volume the lowest IgG concentration was approximately 15 mg/mL and the highest was 200 mg/mL. Or, at the 12-quart (3 gallons) volume the lowest value was about 40 mg/mL and highest value was 220 mg/mL.
There was a measurable decrease in IgG concentration as volume increased only among cows 3rd lactation and greater. However, this relationship between volume and IgG level was dwarfed by the variation among mature cows at every level of colostrum yield.
No connection was found between volume and concentration among 1st and 2nd lactation samples. Since in the US on average dairy herds are composed of 50 percent in lactations 1 and 2 there are a lot of dams where there is little or no connection between volume and quality
In my opinion, knowing the volume is an unreliable guide to sorting out the lowest quality colostrum. Better to measure than guess.
References: Kehoe, S. I., A.J. Heinrichs, M.L. Moody, C.M. Jones, and M.R. Long, “Comparison of immunoglobulin G concentrations in primiparous and multiparous bovine colostrum.” Professional Animal Scientist 27 (2011): 176-180. E. Hare and Others, "Survival rates and productive life of dairy cattle in US." Journal of Dairy Science 89:3713-3720.