
Absorption of antibodies from colostrum decreases rapidly over the first 24 hours of life so it's important calves get close to 10% of body weight as close to within 12 hours of birth as possible.
The quality of colostrum in the cow varies ( heifers are generally poor ). But the longer cows are left post calving the poorer their colostrum becomes.
SO MILK FRESHLY CALVED COWS AS SOON AS THEY GET TO THE SHED.
Milk individually on CLEAN test buckets.
Make sure the colostrum doesn't get contaminated with faeces etc.

Put a drop of milk on the refractometer.

Look into refractometer and you'll see a dark and light section. The line where they join is the reading ( here about 12 ) It needs to read above 22 Brix to be good quality.
A quick way to find cows with good colostrum is to strip 6 plus squirts from each quarter into a cup. Then simply test the cup and decide which ones to milk for collection. Make sure you strip out seal if used first. PLEASE wear gloves unlike this rushed video I built!!!
You can pool good quality colostrum and milk the next cow.
It will store in a fridge for a day or two but preferably use fresh colostrum daily.