A mutual anxiety with new nursing mums is milk supply
To preserve a full supply of human milk a mother must empty her breasts often to create a demand. As simple as it sounds, the essential rule of milk production: increased demand = increased supply.
When we decrease the demand from the body for milk production by supplementing over time your body will product less milk.
A supplementing mum who has been told she should only feed her baby every x number of hours, quickly finds that her milk supply dwindles, and she becomes frustrated and/or sad that breastfeeding "just isn't working out" for her and her baby.
Using a breast pump if baby is not available will help keep up the demand, even if you don’t use the milk. Also a good brand of nursing tea my help with mums with low milk supply.
The female body is a powerfully wonderful, working organism - one which overcomes all kinds of obstacles that can happen from time to time. We must provide our bodies with the feedback they need to fulfil what they were designed to do; and in the case of breastfeeding and milk supply, it is all about demand.