The most common cause of low butterfat is a shortage of roughage leading to acidic conditions in the rumen. Roughage keeps the cow chewing her cud and in doing so she id producing copious quantities of saliva containing bicarbonate which buffers the rumen. The amount of bicarb you can add in the feed can be 10% of what she produces in the day! So it is best to optimise what the cow can produce.
The bicarb produced by the cow usually keeps the rumen pH above 5.5 and leads to normal butterfat levels.
In a typical day’s grazing the rumen pH goes up and down but, if there are regular periods during the day when the pH drops below 5.5, this can lead to chronic low butterfat.
To identify the cause, record where your cows are grazing and your daily butterfat levels and see if you can see a correlation. Butterfat responds quickly to diet changes.
A typical scenario is cows consume feed in the bales then head out to lush short ryegrass pasture. The rumen pH will crash and you may get a lower butterfat test. This can often be corrected by offering palatable hay just before or after milking. Often just a hay rack in the laneway can be sufficient or you can increase the buffer level in your bail feed.
Your Riverina nutritionist can help too, they will want to know your cow’s daily routine including any TMR mixes fed during the day.