Check the packet for the milk you are using. Some are up to 1L a day, some up to 1.5L a day.
By five weeks, 2x 500ml should be fine for a Texel type lamb. I’m usually cutting them down from three to two bottles a day during week four.
Milk
must not get into the rumen. Grass and creep
must only get into the rumen. In general, people prefer to keep milk and grass feeds apart, just in case, but actually unless your feeding technique is really bad, or the lamb is so full of grass there is no physical room for the milk stomach to take the whole milk feed, you can’t cause a problem.
But if you’re not sure, keep them in overnight. Bottle in the morning, out to grass afterwards. Fetch in at tea time, feed bottle an hour or so later. Simples
.
Your lamb is probably just being a bit gutsy and inhaling some as well as drinking. Ideally, you don’t want milk in the lungs :/. You could try a smaller hole in the teat.
It might also be worth looking at your feeding position. You don’t want the lamb’s head to be much above the horizontal, and the bottle only tilted as much as required to stop air entering the teat. The milk needs to flow down the oesophageal groove in the front of the gullet, from whence it will be delivered correctly into the abomasum, and this position encourages that.
Sometimes, if a lamb has been bottle fed from the get-go, with poor technique, it may not have developed the reflex which closes the oesophageal groove, and then if it guzzles too fast, milk can get into places it shouldn’t.