Persistency of milk production during lactation cycle
The 2 major factors determining total lactation yield are peak lactation as well as rate of decline from this peak.
Total milk yield for 300 day lactation can be estimated by multiplying peak yield by 200.
Hence, a cow peaking at 20 litres a day will producing around 4000L per lactation cycle.
On average, cows will produce 7 - 8% less than peak yield from previous month.
However, actual value will depend very much on how the cows are being treated. 3-4% decline per month is possible for fully fed cow while 12% decline is possible for poorly fed cows.
Rate of decline or persistency depends on:
Peak milk yield
Body condition during calving
Generally, the higher the milk yield at peak, the lower its persistency in terms of %.
Negative effects of underfeeding
Underfeeding cows immediately after post-calving will reduce peak yield and have negative effects on persistency and fertility.
Dairy cows have been bred to use body reserves for additional milk production but high rates of live weight loss will delay the onset of oestrus.
Underfeeding cows in early lactation is one of the most common problems faced by smaller farm during humid tropics as they often do not have the necessary feeding system to fully utilise high genetic potential of the cow.
If high genetic quality cows are not fed properly, milk production will reduce and they may not cycle many months post-calving.