Your baby willingly sucks the bottle, while at breast he struggles and cries, or completely refuses to suck.
It is often said that a baby given a bottle forgets how to suck the breast correctly. Truly, easy suckling of milk from the bottle makes the baby lazy, and when we give the breast and the bottle alternately, the baby will protest seeing the breast, demanding the "easier" source of milk. This happens, however, the situation is often opposite. Suckling the breast is pure pleasure. When the baby grasps and sucks the breast correctly, and thus eats his fill, he will not forgo that pleasure easily. Breastfed babies usually do not want to switch to the bottle.
So what causes problems with breast suckling in babies supplemented with a bottle or given a pacifier? Of course, the reasons can be numerous but usually these babies sucked the breast incorrectly earlier, e.g., grasping too shallowly and not getting enough milk. Maybe this is why the help in form of a milk bottle was provided?
Thus, at the beginning it is good to think why the baby prefers the bottle and does not want to suck the breast. Maybe the milk flow is too fast or too slow? Or maybe the milk supply is insufficient because you rarely latch the baby on? If this is the case, then consider the reasons for this situation. Do you refuse to breastfeed the baby because of pain caused by milk stasis, mastitis or raw nipples? Or maybe you feed rarely because your baby sleeps a lot and for a long time? You can find answers to these questions in the chapters: Incorrect way of breast grasping and suckling by the baby, Milk stasis, Mastitis, Bleeding nipples, Milk flowing too fast, Insufficient milk supply, Flat nipples.
What you can do
When your baby's aversion to breast is caused by closer acquaintance with a bottle, but you really want the baby to suck the breast, stop using the bottle and consistently encourage the baby to suck the breast. First, make sure you latch the baby on to your breast correctly, and that he grasps it correctly (the nipple and a large part of the areola should be in his mouth). Correct and effective suckling is a key to success. When you know why your baby is unwilling to suck the breast, try to change it. Maybe you just need to correct the latching on and breastfeeding technique, and to provide more frequent and patient feeding in a calm atmosphere, for the baby to like suckling of breasts? Moreover:
Try to eliminate all other causes that could interfere with natural feeding (read about them in the chapter Baby refuses to suck breast).
Until the baby does not learn to stimulate and empty breasts effectively, you can extract milk with a pump and give it to the baby, possibly in a way not disturbing a natural rhythm of suckling.
When you have to feed in a mixed way (e.g., when the baby does not gain weight correctly) and you decided to feed him using a bottle, select a teat that forces the baby to place his lips and tongue, and to make such movements as during breast suckling. Of course, nothing can replace the breast. However, you should choose the best option possible. Silicone teats of a shape mimicking woman's breast, which are harder and more dynamic (force the baby to work intensively during suckling) are a good solution. Select the teat with a flow rate appropriate for the baby's age (the younger the baby, the slower the flow).