Some species nurse very quickly, requiring a higher rate of flow. Others are accustomed to casual nursing at a much slower rate. And after mastering the flow rate for each species, you still have to deal with individual preference. A baby may not like the taste of the new milk or the feel of the new nipple. It may nurse quickly, but requires a thinner stream of milk as it nurses to avoid aspirating the formula.
Making a nipple opening too large could drown (aspirate) a baby. You could literally watch a baby starve to death because of it's frustration or refusal to nurse due to the wrong size nipple opening or flow of milk, etc.
Common methods of making a nipple opening include using heated sewing needles or diaper pins (sterile, of course). The heated needle is usually forced through the tip of the nipple. This is difficult, especially when using smaller, specialized nipples. Time is limited because the needle will cool before proper alignment can be made.
An alternative method is to insert the cold needle or pin through the bottom of the nipple. Once it is directly underneath the top of the nipple it is gently forced through to expose the tip of the needle. This is easiest to accomplish by holding it against a vertical surface (wall, fridge, etc). Heat is applied to the tip of the needle, and the needle is then gently forced through a little more until the desired opening is acheived. (NEVER heat the nipple, it could scorch or catch fire). The nipple flow is then tested, and the process repeated if necessary. Generally, the milk should flow out in a thin, smooth stream with only a moderate amount of pressure. Heavy streams that shoot out at the slightest pressure usually mean that the opening is too large. You should always test using heated formula that has been well mixed. If you test it using water, you will not have the same results later because water does not have the same solids content as the formula. Although you are applying pressure to test the nipple opening, it should not be necessary to apply pressure when the orphan nurses.
Once satisfied with the opening, it is tested on the orphan and adjustments are made to suit it's preference. When in doubt, always make the openings slightly smaller and adjust as necessary. If heavier streams of milk are needed, it is better to make several smaller holes in the tip than one larger one; this will provide for a smoother flow of milk and lower the risk of aspiration.
If the nipple slides off the syringe too easily, you can score or sandpaper the tip of the syringe for better gripping.
Unfortunately, acheiving perfection still does not guarantee that the baby will nurse. If the baby is warm and healthy, it still may need tube feeding by a professional until it is nursing properly.
For larger mammals, turn the nipple inside out, then put a pencil or other hard object inside the nipple, stretching it slightly, then with sharp exacto type blade you can easily nick in an 'X' or 'Y' opening. Turning the nipple inside out serves the same purpose as above, allows the sucking action to more naturally open the nipple.
When the holes are made from the exterior of the nipple the sucking action can at times actually close the opening.Lorinne Anderson
Care Of Nipples
After going to all the trouble of making the perfect nipple, you should take care of it to extend it's usefulness. Rubber (latex) nipples are made from natural rubber (NR) and are biodegradeable. They can become damaged from heat extremes, direct sunlight and contact with petroleum products. They should be cleaned after each use and completely dried before being stored. After cleanings, they should be somewhat "tacky" but never gummy. A light dusting with corn starch will prevent them from sticking during storage. Rinse thoroughly before use.