Laws relating to breastfeeding and breast milk on Shabbos:
It is permitted without restriction for a woman to breast-feed a child on Shabbos, even if the child does not need to breast-feed such as if he is already satiated, or has formula or other foods available. Thus, a woman may nurse her child on Shabbos even if her child is already satiated and is doing so simply to release breast pain or due to feeling engorged. The following will discuss various regulations relating to releasing the breastmilk not in the form of nursing:
Squeezing the milk into a cup and the like: It is Biblically forbidden for a woman to squeeze breast milk into a cup or other vessel in order to feed it to her child [or for any other purpose], unless it is a case of Pikuach Nefesh.
Trickling the milk in order to stimulate the child to nurse: However, it is permitted for a woman to squeeze out some milk [and have it trickle down her skin onto the ground] having it go to waste, in order to stimulate the child to nurse. [However, she may not squeeze the milk directly into his mouth even in order to stimulate him to nurse.]
Squeezing out the milk to relieve breast pain? It is for permitted a mother to squeeze out breast milk with her hands in order to relieve breast pain [that is caused by the engorged breast]. However, this allowance only applies if the milk will be going to waste [however, to pump into a vessel is Biblically forbidden, as explained above]. [See Q&A regarding using a pump]
Squeezing out breast milk for other reasons: Based on the above, it is understood that it is forbidden to squeeze breastmilk on Shabbos even if the milk will be going to waste, unless it is being done for the sake of the nursing child or to relieve breast pain. Thus, she may not squeeze out the milk simply to look at its color, or to see how much she has, and the like.
Is forbidden for a woman to squeeze breast milk into a vessel due to the Biblical detaching prohibition. However, it is permitted for a woman to squeeze out some milk and have it trickle down her skin in order to stimulate her child to nurse. As well, it is permitted for her to squeeze milk onto the ground in order to relieve breast pain caused by the milk. It is forbidden to squeeze breastmilk on Shabbos for other purposes.
Q&A-Coming up in Part 2
1. During nursing, may woman press on her breasts in order to help more milk come out into the baby’s mouth?
2. May a woman pump out milk to bottle feed her baby if he refuses to nurse?
3. May one squeeze the milk directly into the baby’s mouth in order to stimulate it to eat?
4. May a woman use a pump to release milk in order to relieve breast pain?
5. Is breastmilk Muktzah on Shabbos?
6. May a woman wear nursing pads on Shabbos?
7. May a woman wear a milk collector cup on Shabbos?
 See Admur 328:41; Michaber 328:34-35; Piskeiy Teshuvos 330:10-12
Muktzah of Nolad: See Admur 305:31 regarding milk of an animal that it is forbidden on Shabbos due to Nolad/Muktzah Vetzaruch Iyun why no mention of this is recorded here!
 Why is there no prohibition of Mifarek involved in breast feeding a child on Shabbos and may one breast feed even if the child can eat other foods? The allowance is based on the fact that it is considered Derech Achila, and hence one may breastfeed even if other foods are available, and even if the child is full. [See Shulchan Shlomo 328:56 in name of Rav SZ”A; Piskeiy Teshuvos 330:10]
 Admur ibid; Michaber 328:34; Shibulei Haleket 123; Tosefta 10:14
 The reason: The reason for this is because one who milks into a vessel is completely detaching [the milk from its source] and is liable for the threshing prohibition. It was only permitted to do a Biblical prohibition in a case of life-threatening danger [and not simply to feed a child]. [Admur ibid; Beis Yosef 330; Mordechai Remez 371]
 Admur ibid; Michaber 328:35; Shibulei Haleket 123
 Implication of Admur ibid who in his reasoning writes that the milk is going to waste; P”M 328 A”A 41; Ketzos Hashulchan 138 footnote 30;
Other opinions: Some Poskim rule that it is better to squeeze the milk into the baby’s mouth then to squeeze it onto the floor, as squeezing it onto the floor is not allowed according to some opinions. [Kaf Hachaim 328:206]; See
 The reason: The reason for this is because this milk [that is squeezed] is going to waste and therefore it does not contain a Biblical “detaching” prohibition, but rather a Rabbinical prohibition as explained above, and for the need of a child [the Sages] did not apply their decree. [Admur ibid; Olas Shabbos 328:35; Kaf Hachaim 328:205; See Admur 320:21; 330:9; Or Zarua 2:58]
 Ketzos Hashulchan 138 footnote 30; P”M 328 A”A 41, as understood by Shaar Hatziyon 328:81; Tehila Ledavid 328:59; See Tosefes Shabbos 328:59 who questions the allowance of Shibulei Haleket; See Shaar Hatziyon 328:81 who also questions the allowance of Shibulei Haleket and leaves this matter with a Tzaruch Iyun; See Kaf Hachaim 328:206 that so is implied from Admur ibid and Olas Shabbos ibid, however, he understands their ruling to simply permitting even squeezing onto the ground and not excluding squirting into the mouth; See Piskeiy Teshuvos 330:10
Other opinions: Some Poskim rule that she may even squirt the milk directly into the baby’s mouth. [Chayeh Adam 69:10; Shibulei Haleket 123; Mishneh Berurah 328:112 (However, see Shaar HaTziyon ibid in which he questions as to why this is allowed.); See Kaf Hachaim 328:206 that in his understanding this applies according to all opinions, even Admur ibid, and the dispute is on the contrary if it may be squirted onto the ground; Thus, he concludes that it is better to squirt it into the mouth and not onto the floor unless it is a time of need; See Or Sameiach on Rambam Shabbos 8:10; Migdanos Eliyahu 3:53; Chayeh Halevi 5:35; Megilas Sefer 7:5 in name of Rav SZ”A; Piskeiy Teshuvos 330:10 footnote 80]
 Admur 330:9; Michaber 330:8; Shabbos 135a; Rosh Shabbos 19:5; Tosafus Shabbos ibid
 The reason: The reason for this allowance is as since this milk is going to waste it does not contain the [Biblical] detaching prohibition but rather [only] the Rabbinical prohibition, and due to her pain, they did not decree [against removing it]. [Admur ibid; Rosh ibid; Tosafus ibid; Olas Shabbos 330:8; M”B 330:32; Kaf Hachaim 330:49]
 Admur ibid; Rosh ibid; Tosafus ibid; Beis Yosef 330 in name of Mordechai; Olas Shabbos 328:38; Kaf Hachaim 328:203
 Piskeiy Teshuvos 330:8
The issue of Muktzah: Vetzaruch Iyun as to why none of the Poskim who deal with this question touch upon the idea that squeezing into a vessel transgresses the laws of Muktzah due to it being Mivatel Keli Meiheichano.